Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jaymz77 on December 17, 2013, 02:03:06 pm
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I thought i would start a new thread about this since it is not longer a build, its trouble shooting.
For some weird reason, the amp works fine, until you crank the clean gain, then it gets a fuzzy type distortion (almost like your radio sounds when its not quite on the right frequency) and loses volume. The volume part even comes and goes to an extent.
It was suggested that i might have a bad solder joint and to go through and check them, which i have done and the problem is still there.
All this started 1 week ago when i accidentally unplugged the cabinet with the head still on, it may have had some signal go through it but only at low volume and only for 5 seconds. After that the amp was humming badly, so i turned it off and let it cool. It then came good.
The next night the problem was back.
I managed to trace the hum to a weak earth connection so that is now solved but this crapping out with the clean gain cranked is still there.
If i leave the gain at 9 o'clock like i usually do the amp is fine, it is also fine on the lead channel where there is MUCH more gain on tap.
Im really at a loss with this and desperately need some assistance.
Cheers
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Hey jaymz,
Good luck with this.....we all know how frustrating troubleshooting can be
There's a couple things that you should do to speed up the process.....
- Bring over the schematic from the other thread
- Show us the actual layout you wound up using
Most important:
- Get us some close up, in focus, hi resolution pics,,,,especially in the area around your input circuit (jacks, preamp volume pot, etc. etc)
Anyone who stops by to help will want this stuff.....I just stopped by first
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Did you check output tubes ?
Transformer ?
These are the first ( and only? ) damaged with no speaker.
If good , check Phase Inverter circuit .
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I'll have to post pics and schem tonight. Can't do it from work.
I thought power tubes, but would it present itself on the lead channel as well? Lead channel has heaps more gain and it's fine. Tranny must be fine too
Everything works fine EXCEPT when on clean with the gain cranked.
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I thought power tubes, but would it present itself on the lead channel as well? Lead channel has heaps more gain and it's fine. Tranny must be fine too.
You are thinking correctly......if the problem was further "downstream" (PI, power tubes, OT), then yes (based off of the 2550x schem. that was posted),,,,it would/should affect the lead channel also....
The fact that it doesn't,,, helps narrow your focus through the first stages.....start there, triple check everything and post the pics
These guys can fix anything.......don't start overthinking and looking at parts of the circuit that aren't directly connected/related to that specific area.....the fix is usually a lot easier than we make it out to be.......finding it is the tricky part
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Bad res. or cap. on the clean side maybe?Or maybe that tube is going out that runs there.
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Thanks guys.
I've had everything from bad solder joint, to bad cap/ res, to tubes, to ot.
That is a big range.
I'm a bit frustrated that I don't know enough to diagnose myself without help.
From what I can work out, I have contradicting symptoms.
This only happened after hot plugging the cab, yet that would suggest the problem is in the output which would mean that it's there regardless of channel or eq settings. But it's not.
Another symptom I didn't mention is that when the amp is on and you switch to standby it kills the sound, as it's supposed to, but then when you turn the power off it hums through the speaker. With standby off! Weird.
This is all made harder by the fact that's it a matter of days before everything is closed. I'm thinking I might just grab some power tubes and if it's not them I have a spare set. At this time of year I would rather not spend any unnecessary money, but I want to be able to play it while I'm off work!
AAARRRGGGHHH!
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1)I'm a bit frustrated that I don't know enough to diagnose myself without help.
2) From what I can work out, I have contradicting symptoms.
This only happened after hot plugging the cab, yet that would suggest the problem is in the output which would mean that it's there regardless of channel or eq settings. But it's not.
3) Another symptom I didn't mention is that when the amp is on and you switch to standby it kills the sound, as it's supposed to, but then when you turn the power off it hums through the speaker. With standby off! Weird.
4)This is all made harder by the fact that's it a matter of days before everything is closed. I'm thinking I might just grab some power tubes and if it's not them I have a spare set. At this time of year I would rather not spend any unnecessary money, but I want to be able to play it while I'm off work!
AAARRRGGGHHH!
I numbered your issues so it would be easier to address:
1) EVERYONE needs help with this stuff.....there are regularly posted troubleshooting questions from guys who have many amp builds under their belt.........you picked a mid-complicated circuit to build, so unfortunately your learning curve is gonna be a big one
2) Yup, but you'll have to diagnose and fix them one at a time,,,by dividing and conquering the schematic
3) It's VERY important to mention everything........there could be a big clue in the smallest detail
4) Stay patient and let us help you fix one thing at a time until it's done.......don't freak out and just start tearing it apart (we've seen that before, and it won't solve anything)
From here out just make concise accurate reports and directly answer the questions that are going to be thrown at you.....pictures will tell us a lot....don't be embarrassed....don't try to fix it by yourself....
If the amp hums continually after you turn the power switch off,,,,then you possibly have that switch miswired,,,,and I would start there
If it only hums for a short period of time after you switch it off,,,,,that might be the length of time it takes for the caps to discharge
Troubleshooting 101:
-The amp cant hum indefinitely without power being applied to it = power switch wired incorrectly OR power cord wires are shorted to something they shouldn't be
When troubleshooting off of a schematic, it makes sense to separate sections of the circuit to isolate issues.....
Start here and figure this part out, confirm all connections, and ask any questions you might have.
Good luck and BE SAFE
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Great response, thanks heaps.
The supply side of things is fine ( however I will double check) I am actually an electrician.
That being said I am an electrician, not an electronics tech so my Achilles heel is my component level knowledge. And I don't pretend to know much in that department, just the basics really.
What I find I struggle with is knowing which components do what job in an electronic circuit like an amp. That kind of knowledge is what would make trouble shooting easier.
As for the bit about the hum on power off, it's a couple of seconds worth. But I don't recall it happening before this issue.
Do you think it's worth me grabbing some tubes before the shops close for Christmas, or is the tubes being the problem a low likelyhood?
I will post some pics and schem when I get home. Damn work computer.
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I'm new at this so keep that in mind.
Save the money on the Power tubes. If it works fine on one channel then I don't see how it could be the final output. Do you? That's like replacing the differential when there's no power in reverse but the forward gears work.
Where is there a negative feedback connection from the output back to the phase inverter connected.
JMZ77 Don't do this until someone with more experience confirms it is a good idea. What does the Forum think of this idea: Lift the 100K resistor in the feedback circuit and see what happens.
I did a search of your symptoms and came up with someone else that built perhaps the same amp you have and from the same information. The schematic looks the same as the one you posted in your prior topic. Check this page for similar problem and the ultimate solution.
http://forum.metroamp.com/viewtopic.php?f=7&t=23389 (http://forum.metroamp.com/viewtopic.php?f=7&t=23389)
Silverfox.
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Thanks mate.
I wish I could tell you where the nf is but I don't have a clue!
I kind of liken myself to a pianola. Just feed the paper in and music comes out. Ie, give me a plan and I'll build anything, just don't ask me to explain how it works!
I'll have a read of that link.
Cheers
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1) The supply side of things is fine ( however I will double check) I am actually an electrician.
That being said I am an electrician, not an electronics tech so my Achilles heel is my component level knowledge.
2)As for the bit about the hum on power off, it's a couple of seconds worth. But I don't recall it happening before this issue.
OK...good
1) As you continue to rule out sections of the circuit that ARE wired correctly,,,,use the schematic as a guide,,,and highlight the parts that you check and confirm......move through the circuit from the supply, through the power transformer, rectifier, and highlight everything as you go until you work your way to the root of the problem............don't guess and don't believe in magic :icon_biggrin:
2) Your filter capacitors store power while the power and standby switches are on.......when you turn the standby switch to the standby position, you are interrupting the B+ supply, and the caps will slowly drain that stored power to ground
If you wait a minute after putting the amp in standby,,,and then switch the main supply power switch off,,,you might not hear the hum because the caps will have already discharged,,,,BUT if you hit the standby and then immediately hit the power switch,,,you could be hearing the hum for the duration of the time it takes for the caps to discharge......that might explain why you didn't hear it before :dontknow:
Sorry I don't have much time to go further,,but there are guys here who know much more than I do.........someone will step up...
It is my humble opinion that anyone who builds an amp has a responsibility to understand a schematic of that amp, and be able to service it,,,,,so this is not a bad thing,,,just a necessary learning experience.
:thumbsup:
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The 100K resistor is the one connected to the Presence Pot at one end, and the 4 ohm tap on the output transformer at the other end of the resistor. I used a layout from the WEB for your amp. It looked like the one you posted here the other day.
Disconnecting this circuit may make the amp sound slightly different so don't be surprised if that is the case. Again, the reason for doing this is to see if the problem is related to that part of the circuit. Just lift the 100K resistor at one end and that will disconnect the circuit.
If you have read the page listed, there are some wiring errors mentioned in the layout and construction. That may be what the problem is.
Does the problem described on the referred page above sound like your problem also??
Silverfox.
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Yeah i read that thread and it does kind of describe my issue in the sense that it sounds like a dying battery.
OT primary wiring is ok. 150 odd ohms pin 3 to pin 3, 88 odd ohms centre tap to each pin 3.
I tried lifting the 100k resistor and it made zero noticeable difference to the tone/ sound of the amp and the problem is still there.
Here are the drawings i used.
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Hey James, I can confirm that the schem is good and that I used it as well
http://www.el34world.com/charts/Schematics/files/marshall/25aniv_silverjubilee_25_50w_2550.pdf (http://www.el34world.com/charts/Schematics/files/marshall/25aniv_silverjubilee_25_50w_2550.pdf)
It matches the marshall one as well.
The only changes is the extra gain pot and the preceding coupling cap is changed from .022 to .033.
I just talked to the guy that has mine and has it set at "10" cause that's where it sounds best, sorry :BangHead:
I would be unusual for a pot to be bad so if you can swap the wiper connection from the clean to the lead just to rule out the pot being funkie
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Will do.
Im off to my lesson now so ill try later.
I just swapped a few of the HT wires to some of a bigger gauge. not so much for the gauge of the wire but for the fact the insulation has a higher rating.
Nothing.
Im starting to think its a tube because it only happens after a minute or two, i.e. warm up time.
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Everything works fine EXCEPT when on clean with the gain cranked.
I did not read that before .
If lead clean work , it is not the tube or OT
If it is an hand made amplifier there is a good chance that several errors are present due to lack of experience.
A revision in detail of all solders and wiring for breakage is required.
The problem in Standby and overdrive seems to have no relationship together
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Hey James, I can confirm that the schem is good and that I used it as well
That's extremely important, because without a confirmed schematic you have no solid basis for your troubleshooting
I tried lifting the 100k resistor and it made zero noticeable difference to the tone/ sound of the amp and the problem is still there.
OK, good....that means you have eliminated the NFB circuit and you can highlight it and move on
Here are the drawings i used.
Are these an exact representation of YOUR amp?.....if you've made any changes we will need to know in order to amend the schematic
Try to get those pics up, and hopefully we'll be able to see where the problem is :huh:
Another step that you could take would be to post short videos of the problems as they occur.....that'll get us as close to working side by side with you as possible....
Here's something for you to try: (all I am doing is giving you a visual confirmation of the caps discharging, in relation to the hum)
- WITH THE AMP OFF AND YOUR SAFETY GLASSE ON, Take your multi meter set to DC volts and connect the black lead to ground (clip it on so you don't have to hold it) , and clip the red to the area circled on the attached pic of your layout......you will be monitoring the B+ voltage we were talking about earlier
- With those 2 leads clipped in place (no hands), switch on the power, wait, then switch the amp out of standby-----mark down that voltage (you should be seeing your full B+ voltage)
- Then after the amp warms up a bit,,,,switch the amp into standby and then immediately switch the power off----while watching the meter
- Does the hum you hear after the power switch is off seem to match the voltage dropping as you see it on the meter??....and does the hum lessen and slowly subside as the voltage drops towards zero?.........get it?
RIGHT NOW WE ARE ONLY TROUBLESHOOTING THE PROBLEM YOU STATED ABOUT THE HUM WITH THE POWER OFF......without a solid, properly functioning power supply it won't make sense to try to solve the clean gain problem.
Divide and conquer Mate :thumbsup:
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Thanks again for a great reply.
I will get pics up ASAP, video too if I can. I have my bum hanging out as most of us do at this time of the year (Aussie slang for busy busy busy)
The drawing are a complete representation of my amp, I have even kept the layout as depicted.
The only changes are that I uses desperate switches instead of push pull pots, I have added a foot switch jack in parallel to the rhythm clip switch to make it foot switchable and I think I reversed the contacts on the relay so that the indicator led on the panel is ON when in lead mode. (Or it might have been that I connected them back the front to begin with and then corrected it, can't remember how it's supposed to operate). I don't believe these changes would affect the amps tone etc.
Otherwise it's as drawn.
I will try your suggestion tonight. However, last night when I upgraded the wires for the HT part of the circuit and tried it, I didn't hear the hum on shutdown. I will confirm tonight because i was on my way out at the time.
Cheers for your help.
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Well...
Im home early today and i thought i would try what Timbo suggested and swap the wipes for the gain pots to see if the clean gain pot was dodgy.
It SEEMS to be ok like that. I don't want to speak too soon (knock on wood, rub a Buddah's belly) but that MIGHT be the problem.
That being said, the problem didn't reappear on the lead channel as you would expect when i swapped the wiper leads.
All i can think of is that maybe that channel is so distorted that its harder to hear. Not sure. But even the volume dropping thing didn't seem to happen. Weird.
Anyway i will keep you all posted and report back when i have worked it for a bit longer. The issue would normally present itself within a minute or 2, i just played for 10 and it seemed ok. I mean, there was a bit of crunch there but I'm pretty sure it was within the normal range considering the gain was cranked. Im sure if i plugged my Les Paul in there would be more crunch.
Anyway, fingers crossed.
Ill chuck some pics up anyway in case we have to revisit this.
Don't pick on my work too much, this is my first amp :icon_biggrin:
Oh, and that last post should read "separate switches", not desperate switches, damn auto correct.
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The forum won't let me upload anything over 1600kb.
I haven't had such low res pics for 10 years. They would be too small to see anything on
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Hey James , you need to compress your pictures down to under 600KB per picture. I have Microsoft picture manager that can do it, do you have anything like that.
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Here we go. but aren't they a bit small to see much?
Anyway your gain pot wiper suggestion seems to have worked Timbo... Fingers crossed
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more
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more
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Don't pick on my newly work too much! :icon_biggrin:
Most of the untidiness is due to me scratching around looking for this problem.
But fingers crossed it seems ok
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James, Those pics are great.
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Cheers.
The board came out pretty good except for the bit around the bias pot. The pot i used was a different shape to the one in the layout and i had already drilled the holes for the turrets, so i kind of had to modify it on the run.
I was going to route the wires all nicely etc, but thought i might get crosstalk. The twisted wires you can see are the heater wires, relay coil wires and led wires. Everything else is loose. Makes working on it easier too.
I made a cabinet, got some tolex to match my Mesa cabinet and it looks good.
Just have to get the Mesa leather corners and the faceplates made. Going for laser engraved stainless faceplates.
As a bit of a joke, i called it the JRM2550x (JRM is my initials) and put my signature where Jim Marshall's would normally be!
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but aren't they a bit small to see much?
Heck no!
Hover over the picture and click they will open up very large. Or click on the title under the picture and it will open up full without having to slide the picture around to see everything.
Brad :icon_biggrin:
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You did a great job with the pictures Jaymz.....
Don't worry too much about how it looks, especially if it's just for you,,,the most important thing is that it works properly and sounds like you want it to sound.
Let us know if there is still a specific problem(s) to be solved.....if there's something still not right,,,only you will know
But other than that, just CRANK IT, and be proud of what you made
:occasion14:
Make sure to post some pics of the completed cabinet when it's ready
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Don't pick on my work too much, this is my first amp :icon_biggrin:
Pick on what? It looks real good and for a 1st amp it's great!
I think it's safe to say that most guys build a Champ or tweed Deluxe for a 1st build, I did, 5E3. You chose a pretty big amp for a 1st 1 to build.
You have nice evenly twisted pairs of wires and your R's/C's look good on the board.
There's some wires that look like they could be shortened up a little and some of your solder joints are a little messy but those things come with more experience. As you build more you'll get better at those things.
Brad :bravo1:
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Thanks for those kind words guys.
Ill post pics of the finished product.
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Right, this is really starting to shit me.
Amp has worked fine since last post. I ran my tv through it for a few days to burn everything in, but it made no real difference to the sound.
So then i decided to try a few of the mods i have seen to see how they effected the tone.
1). When i built it i could not get Malory's in a couple of values so i used what i think was a Malory copy. I have since tracked down a couple of these values so i replaced the caps in question. I was not expecting to hear a difference, i just wanted it to be all Malory's.
I know when you make changes you should only change 1 thing at a time, but since this Malory cap change was planned regardless i decided to remove the bright cap while i was at it to see how it sounded.
All i can say is WOW, what a difference. The clean channel was always WAY WAY WAY too bright, now it is fantastic. Interestingly, the 2550x schematic uses a 1000pf cap for the bright cap. Most forums i have read say that Marshalls use 470-500pf bright caps. Wonder why the 2550x is double the value? One planned mod is to try a 470pf cap there to see how it sounds.
Anyway, i class this mod 1 as successful.
2). With all the talk going on about different circuit revisions in the Jubilee, i decided my next mod would be to convert to the new revision.
The only differences seem to be slightly different values in some locations (people with much more experience than me seem to think these won't make any audible changes), slight differences in the bias circuit (which should have no effect on sound) and the newest version does not have the 47pf cap across V1.
So with the removal of the V1 cap being the only difference that should have an effect on sound i decided to try it.
I have to say my initial impressions are that it doesnt sound quite as good without the cap, but i don't have enough time on the amp in this state to make a firm judgement.
The main reason i don't have enough time on it is because THE PROBLEM THAT STARTED THIS THREAD IS BACK!!!!! Bloody Hell...
Its doing that thing again where if the clean gain is wound up past 3 o'clock the signal deteriorates over the course of a few minutes to become very grainy and harsh (almost like a pedal battery is dying, as someone else described) it also loses volume.
I tried swapping the wiper wires on the 2 gain pots as Timbo suggested before and it made no difference (when previously this solved the problem)
I poked around with a few solder joints that didn't look as nice as some of the others AND THIS MADE IT WORSE!!!!
This is really getting disheartening as i am in love with this amp when its working right.
If anyone can assist with this i would greatly appreciate it.
I thought i had left this issue in 2013...
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I tried swapping the wiper wires on the 2 gain pots as Timbo suggested before and it made no difference (when previously this solved the problem)
I poked around with a few solder joints that didn't look as nice as some of the others AND THIS MADE IT WORSE!!!!
Sounds like bad solder joints.
Brad :think1:
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Are you using shielded wire?
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Bad solder joint seems the obvious but i have checked and rechecked them, so i don't know...
Shielded wire? Yes, but for the signal path to and from the preamp tubes only, not to and from the pots.
But you know the ridiculous thing? Its gone this morning...
I fired it up to play around with it and it was not doing it. The only thing i did differently this morning was that i slowly wound the gain up (searching for a particular tone) until i ended up finding my tone with the gain on max and still no issue.
Its weird. Unless it was too late last night and i was hearing things. Otherwise there is some sort of intermittent issue there.
Any suggestions?
Has anyone ever noticed how, besides almost taking your head off with its brightness, the removal of the bright cap changes the gain levels/ performance? With the cap i had to have the gain around 3 other wise it started to break up too much, now i can have the gain cranked (when the issue is not present) and it just gives that beautiful warm, glowing, ever so slightly breaking up, mid rangey, gainey Frusciante-ness. It did take a little bit of balancing to get the warmth and glow without too much punch on the bass strings when you strike them a bit harder.
Anyway i seem to be closer than i ever have been before (which is more or less spot on) to what has always been my hardest tone to nail to my satisfaction.
Some people seem to be able to just fall into that tone. For me it was always a struggle.
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Yep max or close to it is the sweet spot for the dirty gainy stuff.Don't you just love tube amps?
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Hi James, I ended up putting a 390p in that bright cap position. Just a thought on your problem it may be a resistor that once warmed up breaks down and for that to happen it could be a larger wattage power resistor :dontknow:
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Thanks Timbo, ill keep it in mind if the issue returns.
Im liking the amp with no bright cap at all. I still have the treble on about 4.
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Well its back... Again...
I spent a few hours playing the other day and it was ok. Having said that, i kept thinking i was hearing the issue come and go but could never confirm it. I thought i may have been imagining it on this occasion.
Now, tonight i fired it up and the problem was back within a few mins.
This is killing me.
Is there some way i can post a sound clip on here? That might make it easier to pinpoint
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Is there some way i can post a sound clip on here? That might make it easier to pinpoint
Most guys here get an account on a music hosting site like soundclick or soundcloud and then upload sound clips there and just put links to the clips here....
It might work well in your case so that we can here what you're hearing
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I tried to record a clip tonight, but do you think the silly thing would play up? NOOOOO!
Stay tuned, i post something when i can...
Cheers
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Im still working on getting a sound clip of this issue...
But i have some new information that might help someone smarter than me figure this out.
I have recently been experimenting with my signal chain and setting the amp up for my different guitars. I had been running my Boss ME-50 through the effects loop since my last post and apart from sounding friggin amazing, the issue with the amp had mysteriously vanished.
Today i was experimenting with having the ME-50 up front to see which way i preferred (i had notice the tuner function wasn't liking a bit of noise). When i tried it this way the amp was noticeably louder and within a few minutes the issue had returned.
I then removed the ME-50 all together and went straight in, problem still there and volume still louder. I have now gone back to having the ME-50 through the loop.
For some reason it seems as though something in the amp is crapping out with too much signal. When the signal is cut a little bit, like when i have the ME-50 running through the loop with a bit of compression (even with a bone dry signal) it seems as though the signal is cut just enough for the amp not to crap out.
The amp does seem warmer with the ME-50 through the loop too. Even with nothing on.
I guess i am happy that i can use the amp and get the sound i want in a way that doesn't make it shit itself, but i really want to know what this damn problem is!!!
I should be running the ME-50 up front but i can't and it really bothers me knowing there is a problem there.
Oh and its started making a POP after a minute or so of turning the standby on. Only does it once each time....
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Hi James, I'm no real expert on this and I don't know the function of ME-50, but most of the guys use TIME based FXs in the FX loop. Also the FX loop in the Jubilee although appears PASSIVE could actually be an ACTIVE type as it is jammed between the two triodes of the TS driver.
In most builds the FX loop is just before the PI. So your FX may be increasing the signal too much :dontknow:
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Timbo, the ME-50 is a multi effects unit.
The funny thing is, the ME-50 seems to CUT the signal when connected through the effects loop.
When connected up front, or when not connected at all, is when the problem appears.
So there seems to be too much signal in its normal state.
This is real weird.
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OK...
Here is a link to a video i recorded today.
1) ignore my lame ass playing, it was just for the recording.
2) if anyone cannot understand me, let me know
3) the problem seemed to appear a touch quicker than normal... <1min - 1min
4) in the second part (with the effects in the loop) notice how much warmer and smoother it sounds, as well as quieter. Only a bit of compressor and a touch of reverb used.
If i think of any other points i will add later.
Here is the link...
http://youtu.be/9hQg6eYq93U (http://youtu.be/9hQg6eYq93U)
I really hope someone can assist with this...
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Bump...
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Hey Jaymz, I listened to your clip and nothing stands out to me as "that's it for sure"
If it were in front of me, I would take an oscilloscope and probe it in the signal chain in different spots....watching the wave form....even use a dummy load instead of your speaker, so you don't get a headache
It would be very helpful to have a signal generator, so that you wont have to play and you could just concentrate on finding the issue...
They make simple apps that you can use on your smartphone that will just generate a simple sine wave that you should try to get matched to the amplitude of your guitar signal...
It's the best not-too-technical approach to getting to the bottom of your problem.
Only problem is, you need a scope....they do have apps for those as well (I have no experience with using them).....so with 2 phones you "might" be able to see what's happening :dontknow:
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Thanks for the reply.
Can you actually hear what I'm talking about tho?
I wasn't sure how clear it came through in the video. After all it was recorded on my phone...
It's starting to look like I might have to take it somewhere. I have access, through my teacher, to a guy named Pete Reynolds, who builds the "Reynolds Valveart" boutique amps here in Sydney. He is a bit of a guru who should be able to sort it if he is willing to have a look.
I would really like to solve the issue myself to save money and learn something at the same time but it's looking like I might have to submit.
Cheers again.
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Can you actually hear what I'm talking about tho?
I wasn't sure how clear it came through in the video. After all it was recorded on my phone...
It's starting to look like I might have to take it somewhere. I have access, through my teacher, to a guy named Pete Reynolds, who builds the "Reynolds Valveart" boutique amps here in Sydney. He is a bit of a guru who should be able to sort it if he is willing to have a look.
I would really like to solve the issue myself to save money and learn something at the same time but it's looking like I might have to submit.
Yes, I can hear enough to know that you do have a problem...
Look at it this way,,,if you're going to want to do this more in the future then I would highly suggest that you take the money that you're going to pay someone else to fix your amp,,,,and buy a scope off of ebay, and learn how to use it....(it's not that tough)
If you need a quick fix, then pay a pro....if he's reasonable, he might be able to look at it and tell you how to fix it :dontknow:
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I can borrow an oscilloscope from work, but I would need lessons in how to use it!
Even if I could use it, I wouldn't know how to interpret the results!
Might see if one of the guys who knows how to use it can help me...
I guess I'm glad someone else recognises I have an issue and I'm not just losing the plot!
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Hey James stick with it, The circuit works well so it must be something simple. Have you tried a patch lead or an FX pedal in the FX loop, just to rule out a JACK that's not switching right. Also check your wiring/components around this area.
The guys here http://www.guitargear.net.au/discussion/index.php (http://www.guitargear.net.au/discussion/index.php) are great might be able to point you in the right direction.
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Patch lead or no patch lead makes no difference.
Should the loop jacks be snitching jacks? I don't think the ones i used are
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Hey Jaymz,
I'm not suggesting that a scope is the only way to fix your amp, but it is a great tool to actually see what the wave looks like as it passes through the different stages of your amp....That can be very helpful in narrowing down your problem......
-I would make sure that none of your capacitors are allowing DC to pass....you have to make sure that none of the coupling caps are allowing DC to get onto the grid of the next stage....
-If it were me,,,,I'd assume that I got something wrong in the LED, diode clipping area of the circuit, and I'd probably check over that about 20 times :wink:
- Have you given us voltage measurements from each pin on each socket yet?
-There are so many possibilities for failure in an amp, that it is crazy to guess......voltages and scope traces don't lie
Check out this free book to learn more about troubleshooting with a scope....there is no better way to see inside your sound:
http://www.tubebooks.org/Books/intro_Middleton_troubleshooting.pdf (http://www.tubebooks.org/Books/intro_Middleton_troubleshooting.pdf)
EDITED- The first link I gave you only contained a preview of the book....here's the full book:
http://www.tubebooks.org/Books/Middleton_troubleshooting.pdf (http://www.tubebooks.org/Books/Middleton_troubleshooting.pdf)
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Thanks heaps for that mate!
Ill check over the things you suggested this weekend. Might have to wait another week before i can get the scope, ill check today.
What makes you say the LED/ clipping circuit?
Cheers
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What makes you say the LED/ clipping circuit?
Just the fact that there is a lot going on there....the schematic looks great until I look at that area and then,,,ehhh :huh:
Not really what I want to see in a tube amp.....
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Reading back over your thread now, it seems that I would be incorrect in looking at the clipping circuit, because it gets switched out when you are in the clean channel....
- Are you only experiencing this problem on the clean channel OR is it just easier to hear it without distortion?....I was unclear about this because we have shifted our focus a few times.....
I would strongly suggest to eliminate the ME-50 from the equation because it is adding a variable that we don't need.....the idea that it seems to help, is probably a result of the decreased signal strength
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I will try to confirm this over the weekend but I'm pretty sure it's a clean only issue. I will double check because there IS a shitload of distortion available in the lead channel that makes it hard to hear.
EXACTLY! That's what it sounds like: too much signal but with the ME-50 in the loop the signal is cut. The thing is, the 50 is supposed to be used up front, not through the loop. When it's through the loop the distortions are crap (too noisy) and the tuner function is all over the place due to the harmonics in the signal going through it.
The problem exists with no effects and with the effects up front. The only time it's fine is with the effects through the loop, but then the effects aren't great.
Thanks again
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Try to forget about the ME-50 for now.....go right after the problem without the effects unit in there...
Also confirm/deny:
-Does it happen with the clean gain push/pull pot switched in one direction and not the other?
The area I have circled in this pic probably took a lot of heat to get soldered properly....heat could have damaged one/both of those diodes :dontknow:
They appear to get switched in and out of the circuit by your clean gain pot/switch.
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Fair point.
There is another section near the LEDs that I was always concerned copped too much heat as well. I have some spare diodes so I might try replacing them one at a time and see how it goes.
The area I'm talking about is a junction of a white cap (the value I can't remember), the 2 LEDs and about 3 diodes.
Would I be able to put another diode in parallel to the existing ones (one at a time) to test? Or would I need to pull the existing ones?
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There is another section near the LEDs that I was always concerned copped too much heat as well. I have some spare diodes so I might try replacing them one at a time and see how it goes.
The area I'm talking about is a junction of a white cap (the value I can't remember), the 2 LEDs and about 3 diodes.
That area is in the Distortion channel path, so if you're not having the problem on the Dist. channel (which we need to confirm/deny) then it wont help you
Would I be able to put another diode in parallel to the existing ones (one at a time) to test? Or would I need to pull the existing ones?
I would pull the existing ones...but only do the one's I circled first........try attaching the wire to the turret first by wrapping it around, solder that, and get all of that heat out of the way,,,then you'll only have to heat the cap and 2 diode leads to finish the joint
Definitely check if it is happening with the clean gain pot pulled AND pushed,,,or one or the other......first
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Sweet thanks mate.
I will try and report back
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Just a thought...
Are those diodes you circled only in the circuit when the rhythm clip mode is on, or are they there all the time in the clean channel regardless?
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Hey James, Both of the clipping circuits are separate to the CLEAN path. The rhythm switch adds the (two diodes and .002) clipping to the clean path when the switch is on.
This rhythm sw. is a bit miss leading as it is a type of distortion so it may drop a bit of volume as well distort the playing.
BUT this does not explain why after playing a minute or so it kicks in other than a loose wire is shorting it into the circuit :dontknow:
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I don't think it is cutting in.
Both the clipping circuits seem to be working fine (lead and clipped rhythm).
It's a different sound.
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It's a different sound.
You're probably hearing the sound of a component failing....only problem is that some components don't just die, and that's it...they die slowly, or just live in an undead (but sick) state for awhile.
Diodes can fail in a couple different ways....short, open, leak, and these can be intermittent (which might explain why it comes and goes, or seems to happen intermittently)....that's why we want to rule out the diodes,,,especially because we already know that they took some heat.
Once we rule them out, we check them off our list and move forward...... a wise man once said "divide and conquer"
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Ok no worries.
I'll report back.
Thanks.
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Well the answer to the first question is no, it doesn't seem to be doing it on the lead channel.
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That diode bit of the circuit can't be the problem.
That is the rhythm clip diodes and the issue is there with them switched off.
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the issue is there with them switched off.
Is it there with them switched on AND when they are switched off?....just curious
Are you working on getting us tube pin voltages?
You can try this and report back....
Take your guitar and plug it straight into your ME-50, and then plug the output of the ME-50 into the effects RETURN jack...
You will just be bypassing the preamp section of your amp, up to that point, and then if it doesn't act up, you'll know that your problem is probably before that point in the schematic (I'm guessing it is)
Until we get actual diagnostic tools involved, this is the only way to find a problem (divide and conquer)....poke around and hope to get lucky
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It's hard to tell, but I would say no. When you engage the rhythm clipping the volume drops a bit. With the clipping off, the problem exists with no volume drop.
I'll get pin voltages today
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Actually, I would say yes.
When the signal decays away, engaging the rhythm clipping makes the signal sound worse. So whatever the issue is it doesn't sound like it has anything to do with the clipping circuit.
It sounds to my uneducated ears like something is crapping out from too much signal. With the me50 in the loop, this cuts the signal a bit, cuts it just enough for the problem to go away.
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It's hard to tell, but I would say no. When you engage the rhythm clipping the volume drops a bit. With the clipping off, the problem exists with no volume drop.
OK, I'm confused....let's get this straightnend out and then move forward :icon_biggrin:
When the signal decays away, engaging the rhythm clipping makes the signal sound worse. So whatever the issue is it doesn't sound like it has anything to do with the clipping circuit.
That statement kinda contradicts itself....this is how is sounds to me:
When I switch in the rhythm clipping, it makes it worse,,,,,but I don't think it has anything to do with the clipping circuit :dontknow:
I'm not saying that you're problem is definitely in the clipping circuit, I'm just saying that we have to keep our answers very clear, so we're not on a wild goose chase.....I'll look harder at the schematic
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OK, it appears to me that this small clean/rhythm clipping circuit consisting of 2 diodes and an .002 cap(whatever it does) IS in the circuit regardless of the switch being engaged or not....
The switch just re-routes the path and that affects the input signal strength into V2B grid
-With the switch open, the signal passes through the 10K and then the 100K (110K series resistance), and then the 47K and diodes/cap are the "grid leak path"
-With the switch closed, the signal sees the diodes/cap first as the "grid leak" and then the total series resistance of the grid stopper is reduced to approx. 33K due to the 47K being placed in parallel with the 110K series resistance.
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Sorry.
What I'm saying is that what you engage the clipping it sounds worse because the diodes are clipping a signal that is already damaged/ affected in some way, hence I don't think the diodes are the problem. It's like have 2 distortion pedals in series. The second one would be working with an already distorted signal. In this case the diodes are clipping a signal that already has issues.
Looking at my amp, those diodes and cap are connected to signal ground at one end and the other goes back through the switch. So with that switch open, only the ground end is connected to anything
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I can see what you mean in the drawings, I better make sure I'm wired that way
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HOLD THE PHONE!!!!
Ive just noticed i have a resistor missing!!!! What an idiot.
That 47k resistor from the diodes back to V2.
Geez, how did i miss that? Ill chuck one in and report back!
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Hi guys, SG your doing a great job. I am sure it is something simple. :BangHead:
There is not a lot of components in the CLEAN signal path and some can be removed as they are a tone/fizz control.
I marked a couple of bits that can be removed/changed that I think could be a problem......
Remove 1 - .047 cap
Remove 2 - 47p cap
Change 3 - .033 to .022 cap
Remove 4 - 470p cap
Remove 5 - .001 cap
If this problem DOES NOT present itself when in LEAD mode, the components marked :-
A - 220k
B - .022
C - 220k
D - 110K (220k II)
E - 47k
F - 1M
Are in the clean signal path and need to be checked for value and connection
Hope this helps.
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What program do i need to open that Timbo?
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Hi guys, SG your doing a great job. I am sure it is something simple.
Thanks TIMBO :thumbsup:
What program do i need to open that Timbo?
Express SCH...it comes bundled with Express PCB
http://www.expresspcb.com/ (http://www.expresspcb.com/)
BUT, WAIT!
Did you put the 47K in there?....and then double check that you've got the signal path wired correctly coming off of the pot/switch?
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I just put the missing resistor in.
Im double checking the wiring of the switch now. (i keep saying switch because i didn't use pull pots, i used regular pots with separate switches)
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Any chance someone could pdf that for me?
Well i don't think the resistor is the answer, i think the problem is still there.
Im just letting the tubes cool now, then ill confirm
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:icon_biggrin:
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I'm not gonna have easy access to the forum for a while tonight....
Good luck Jaymz,,,,and at least we fixed one problem
TIMBO....TAG---you're it :icon_biggrin:
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Thanks Timbo. I had E missing!
Well, i have been playing through the amp for a while now and my observations are...
* Amp seems more consistent. IE things seem to be behaving a little more predictably, with and without effects.
* The tone seems more consistent across different volume:gain ratios
* Things don't seem to be intermittent anymore (to be confirmed) i seem to have control over everything.
* That buzzy sort of distortion seems to be still there but it seems to be controllable. If i dial the gain right up it is very buzzy like before, but if i wind the gain back to 8 or 9 it seems to tame it substantially. However if i run my ME-50 through it (up front like its supposed to be used) using only compressor and a touch of reverb, this also seems to tidy the buzziness up a fair bit too.
* Buzziness seems to go away with rhythm clipping engaged.
* Amp seems to have less noise
* This time the ME-50 sounds much closer when its plugged up front or in the loop. Through the loop still sounds a bit warmer, but this time instead of being much quieter it is actually a bit louder. Running through the loop also means certain thing on the ME-50 work a bit better (compressor, delay, chorus) but the fact that the compressor has more effect means that i have to wind the level up to match the dry signal level and this induces more noise.
I think this time around i prefer the ME-50 up front. I just can't quite get the same warmth from the compressor with it up front, less noise though.
Given this new found controllability (using the amp controls alone as well as in conjunction with the ME-50) and the fact that the buzziness seems to go away with the rhythm clipping engaged, I'm starting to wonder if that is how it is supposed to be. Not having a real Jubilee to compare to to makes it hard.
Obviously there was SOME issue going on there (besides idiot me forgetting a resistor) but whether or not that is completely solved or not remains to be seen.
The next thing i will do is try another guitar. All this so far has been with my 62 reissue Strat with Seymour Duncan SSL-1 pickups. Ill try my Les Paul standard and see how that goes.
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AND THANKS HEAPS FOR ALL YOUR HELP SO FAR SILVERGUN!!!!!
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Ok.
I just tried my Les Paul through it and its buzzy as all hell. It fact it is hard to get a clean clean at all. I had to have the gain down below 9 o'clock to get a clean tone.
Again, i don't know if this would be deemed as normal or what, but the type of buzziness I'm getting just doesn't sound right to me. It doesn't sound like typical marshall overdrive to me. It sounds buzzy/ fuzzy.
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Well after poking around a little i can tell you that removing the 47pf at V1 (number 1 in Timbos drawing) makes the buzzy/ fuzzy/ fizziness worse.
Ill be putting that back in...
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*CORRECTION* - Number 2 on Timbos drawing
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That 47pf could be increased up to about 250Pf.
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I was wondering if increasing that value would change anything given removing it makes it worse.
Funny though, when people talk about upgrading their jubilee to the newer revision of the circuit, that cap is removed.
Would you describe the overdrive as fuzzy, TIMBO? I'm mean on the rhythm channel with the clipping off and with the gain above 3 o'clock.
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Even though you found the missing resistor and replaced it, did you ever replace the diodes that we talked about earlier?
They "could" still be contributing to the fizziness if they are failing....
AND THANKS HEAPS FOR ALL YOUR HELP SO FAR SILVERGUN!!!!!
You're very welcome Jaymz...it can be difficult to keep communication clear, and that is my main goal when trying to help someone...
There is a very systematic approach to troubleshooting that involves eliminating all potential problems until you have zero problems to eliminate.
Your problem stood out to me as a signal loss issue, and I chose to focus on an area of the schematic that "might" have something to do with that,,,,and combined with your pictures, I think we are onto something.....
The fact that we got lucky and you found a missing resistor is one victory,,,,but if you missed a resistor,,,there could be more..
You definitely "could have" overheated those diodes while soldering.....it could save you some time "guessing" if you just go in and replace them,,,,and in turn, rule them in OR out.
Good luck mate,
It can be very frustrating to try,,, but very rewarding to succeed....
:thumbsup:
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Will do.
I'll get those pin voltages too.
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Hey James, This is a clip http://www.el34world.com/Forum/index.php?topic=15881.0 (http://www.el34world.com/Forum/index.php?topic=15881.0) with a PL with P90s. This is the clean gain at about 8 and the rhythm switch on.
It could be a bit fuzzy and buzzy with humbuckers, so knock the volume back on your guitar till it cleans up and see how that goes.
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Thanks for that Timbo, nice amp.
I can definitely report though that there is something else going on with mine and its not those diodes Silvergun.
I just changed the diodes, making sure not to put too much heat into them, and it still has that buzzy/ fuzziness that I'm sure is not supposed to be there, least of all with a Strat. The signal gradually decays away into buzziness.
While i was in there i changed the diodes in the bias circuit, Not for any other reason but peace of mind, now i know they are ok too.
The amp does sound a little different (i don't think I'm imagining it) since the diode change, but it has done nothing for the problem. I guess there is a possibility that they might have been contributing because until the signal decays into buzziness it sounds damn good.
The other thing i noticed is that the point on the gain pot where the buzziness starts seems to be a bit higher... maybe an increment or so. Again, i don think I'm imagining it.
So, why do those more knowledgeable than me think i should look at next?
(and i haven't forgotten those pin voltages)
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Pin voltages to ground are as follows (amp idle no input)
V1 V2 V3 V4 V5
p1 237 222 249 0 0
p2 0 0 0 0 0
p3 2 1 44 438 442
p4 0 0 0 433 433
p5 0 0 0 -36 -36
p6 215 159 235 0 0
p7 0 0 28 0 0
p8 1 0 44 0 0
p9 0 0 0
Let me know if you need more info.
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Hey James , Those voltage are a close match to mine so there is nothing that the voltages are causing
Can you try a lower gain tube in V1 like a 12AT7 or AY7???
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Unfortunately I don't have spare tubes of any kind.
It just seems so weird that it happens over time.
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It just seems so weird that it happens over time.
time = heat up = component failure
count how many components are in your amp - subtract from that the number of components that you have ruled out = the amount of components you still have to rule out :wink:
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When you list pin 8 on V2 as having 0 volts, does that mean ZERO?....or is it more like 0.7-0.9 Vdc?
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The path of the clean signal through that area is just as important as the 47K resistor being there, and just as important as the diodes being OK
Use this diagram to double check that your paths match the paths from the layout....take a close look at the area circled in pink and see how the switching works.....if your path doesn't match this path 100%, then there is a problem
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Yes thats zero volts to ground
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Ill go over that tonight.
Im leaning towards something failing tho...
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Yes thats zero volts to ground
If there is no voltage (0.0vdc) on that pin, then the triode is not working and there is your signal loss
The path there is simple....
Pin 8 should go to a 470 ohm resistor to ground....if that is happening, you'll see some Vdc on that pin and the triode will work as intended...
If there is any reason that there is not a good solid path to ground through that resistor, that would explain your problem.
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Hmm ok.
I am at work today (public holiday yesterday) so I will have to check tonight.
If everything is wired up correctly, can you think of any reason why that would be? Or just a bad tube?
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Just reading your post again... Could it be caused by that 470ohm resistor failing if the wrong is correct?
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Could it be caused by that 470ohm resistor failing if the wiring is correct?
Yes, if the resistor is open (or opening after heating up) then there is no path to ground for the cathode.....in a new amp build, it would be more likely that there is a problem with wiring or solder connections...
Check wiring, solder joints, etc....
With no power, you should read 470ohms from pin 8 to ground....
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Ok I'll check all that out tonight.
Thanks.
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Thinking more about this Jaymz,,,,
If you had no path to ground for that cathode, the signal would just die there, and you wouldn't get any sound.....I have a feeling you're gonna see approx. 0.7 Vdc on Pin 8.....unless there is some intermittent issue
Looking closer at that stage you've got a 220K plate resistor, with a 470ohm cathode resistor, and you could be pushing that stage through saturation, with too hot of a signal hitting the grid....(that's what it sounds like)
And that would make more sense, based on your results with the ME-50 in the loop.....it was dropping the signal enough to not push that stage as hard as when it wasn't in the loop...
If all goes well with your tests, I would raise the value of your cathode resistor (on that stage) up to 1K and see if that makes a difference in the fizz
It looks to me like they designed that stage to clip as a result of saturation,,,but if the input signal is too big, it could be pushing straight through to cutoff
There are guys here who can get more in depth about this.....consider me troubleshooting 101,,, and read this (to get really confused):
http://www.valvewizard.co.uk/Common_Gain_Stage.pdf (http://www.valvewizard.co.uk/Common_Gain_Stage.pdf)
This might help:
http://vimeo.com/33244955 (http://vimeo.com/33244955)
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Thanks for that.
I have no idea which is the more likely situation, and I have next to no idea what each parts job in the circuit is.
But based on SOUND alone, that seems to describe what I'm hearing.
The fact that I can now control the buzz with the gain pot kind of makes me wonder if the amp Sounds as it was intended, just the overdrive is not to my ears. Having said that, I find it hard to believe that a real jubilee would buzz like this.
Cheers
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I have no idea which is the more likely situation, and I have next to no idea what each parts job in the circuit is.
But based on SOUND alone, that seems to describe what I'm hearing.
The fact that I can now control the buzz with the gain pot kind of makes me wonder if the amp Sounds as it was intended, just the overdrive is not to my ears. Having said that, I find it hard to believe that a real jubilee would buzz like this.
I am starting to think that I am definitely onto something with your specific issue....If you find that changing the 470ohm resistor to a 1K helps, then you can try a couple of different values there to get it where YOU want it......higher values should get you further away from saturation clipping, but also further away from the intended design..
...we can also consider dropping a little signal by lowering the value of the 1M grid leak resistor that feeds that stage, or installing a pot in it's place to make it adjustable (like an effects return pot)...(the 1M that's shown on the effects return jack in the layout)
From what I've read,,,Frusciante uses his Jubilee for 1 specific sound, so maybe he just doesn't push the gain controls as far as you are :dontknow:....and maybe there is a good sound to be had there...
And I remember reading where guys would remove the diode clipping part of the circuit because it sounded too much like artificial distortion.......add that to the saturation clipping stage and maybe you have a buzz machine?
WE can alter the circuit to fit your tastes, but for now we should stick to getting your issues figured out, and make sure you have a healthy amp to start with.
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Given my new found controllability since installing the missing resistor I would say you are right re frusciante. He uses his jubilee for crunch only, the major is for cleans. I have a couple of pics of his amp settings and if I match those setting the amp sounds damn like his UNTIL it starts fizzing out. With that in mind I'm leaning towards a bad component.
Like Timbo, I have a switch to bypass the rhythm clipping giving me clean clean, clipped clean and lead. I actually like the diode clipping unlike a lot of people. All of this has been with the rhythm clipping off, so it should not be so buzzy.
I might look at tweaking to taste at some stage but for now I just want to have the amp working as it should without buzzing.
I will try replacing the resistors with same values first to see if that fixes the buzzing. The. I might change some values.
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I just re checked the voltage on p8 V2.
It started at 0.17 volts, i then watched it slowly rise to 0.19 volts before i stopped measuring.
Is this right?
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I just left the amp on for about 10 mins and came back.
Voltage on p8 V2 has levelled off at 0.380V.
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Voltage on p8 V2 has levelled off at 0.380V.
That is a low, but OK reading... it doesn't bias the triode ideally....I'm assuming that they designed this stage to clip this way,,,and it could be some of what you're hearing..........this is where a scope comes in handy,,,you see the wave going in and then see the difference of the wave coming out.
The cathode resistor size is chosen to bias the tube...the voltage drop that occurs as a result of that resistor puts the cathode more positive than the grid, which is how the tube needs to operate....the larger the cathode resistor, the more positive the cathode will be in relation to the grid, and this will get you away from a bias point that causes clipping........it puts the triode closer to center biasing, and "leaves more room" for a "hotter" input signal.
Did you try replacing the 470ohm cathode resistor with a 1K?......if you really want to hear a change go to a 2.2K, and see how that sounds, and YOU can decide if you like it better that way, with less clipping.
Also,,,did you verify your paths coming off of the clean/rhythm switch?
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I had a quick look in the limited time I had and it looks ok.
Didn't have time to solde anything. Had my guitar lesson.
Tonight I'll have more time
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So...
given that idiot me had forgotten a resistor, I'm just wondering if that could have put extra strain on any other components causing them to fry/ partly fry?
Or are the 2 resistors mentioned below the only targets?
We have the 470 before p8 V2, the 1m coming off the effects return jack...
Anything else a possibility?
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given that idiot me had forgotten a resistor, I'm just wondering if that could have put extra strain on any other components causing them to fry/ partly fry?
Probably not,,,but I'm most concerned about where you put the 47K when you put it in....go back to reply #100 and confirm that your path looks exactly like that........did you ever replace the diodes?
We have the 470 before p8 V2, the 1m coming off the effects return jack.
The resistors themselves are probably fine....check your wiring and solder joints...the 470 is just low for that spot, and it might work better for you to put a slightly higher value (reduce some buzz)...
As far as the 1M, I suggested replacing it with a pot so you could dial in the signal level hitting the grid of that stage....you might find that slightly reduced signal wont clip as hard......to try it without making it permanent, you could put a 1M across the existing 1M and that will drop the value to 500K (clip it in or just solder it across the 1M) and see how that sounds.
Anything else a possibility?
Yes, the other 70 components that we haven't ruled out yet :icon_biggrin:
I would try a new tube in the V2 location (if you had one) ....just because that tube is biased "on the edge" I would want to see if a different tube handled it better....
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Yeah that's how it looks. It was the 47k you have not erased that I forgot.
I'll try to get a spare tube today. Or could I swap the tubes around to see if that's the issue?
I'll play around with the resistors tonight.
1M down to 500k
470k up to ??? What do you suggest here?
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Yeah that's how it looks. It was the 47k you have not erased that I forgot.
I'll try to get a spare tube today. Or could I swap the tubes around to see if that's the issue?
I'll play around with the resistors tonight.
1M down to 500k
470k up to ??? What do you suggest here?
Yes, you can try swapping the tubes around and see if that changes anything...
-1M down to 500K is good
-And 470 ohm up to 2.2K and you should definitely hear a difference in the clipping of that stage.......you can always lower it back down and try 1K by putting a 1.5K across that new 2.2K
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Oh, and yes I changed the diodes. Changed other diodes too for peace of mind.
Sweet I'll let you know how I go.
Thanks again
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Ok here's what I've got...
I swapped V2 and V3... noticeable difference, not MASSIVE but noticeable. Less fizz/ fuzz/ buzz (whatever you want to call it), probably at a level that i would think was normal if i had bought the amp. Voltages much the same though.
I don't have a 500k resistor so i put another 1M in parallel to the existing one just to see what would happen. I think it made a slight difference but so small i can't really be sure if it actually did or not.
I don't have a 2.2K resistor currently either so i tried a 1.5K in place of the 470ohm one... and THERE IT IS! The 1.5K made a huge difference, it seems to have just pulled the gain level back a touch so it no longer sounds fuzzy, just gives that ever so slight break up. Voltage on pin 8 V2 is now 1.275 volts.
With the 470ohm in place (and the missing resistor) i can clean it up by winding the gain back a bit (this affects the tone though) or by using a bit of compression, however that makes the last little bit of the gain dial useless to me. Now, with the gain cranked its seems spot on. Introducing compression now though maybe cleans it up a touch too much (ill have to play around with it to get it right). All that said, i prefer how it is now compared to that fuzzy crappy sound.
Im very happy that the source of the buzz seems to have been located (knowing me i have now spoken too soon) and i thank everyone who has donated their time and knowledge to helping me sort this out. The truth of the matter is that i have learned more from the trouble shooting process than the build itself.
I guess it all boils down to taste now doesn't it? Decisions decisions...
The purist in me would prefer to leave the amp as it was originally designed, but i honestly can't see how that buzzy shithouse sound is useable, I've never liked that fuzz type of OD. I tend to range from that gainey Frusciante pushed clean, to ACDC type crunch, to all out high gain 80's metal type stuff... In other words all MARSHALL, and that fuzz just does not say Marshall to me, it says Hiwatt. Funnily enough i scored a Hiwatt custom 20 at a steal just before i started the build. I had never had anything to do with Hiwatt previously and i only bought it because it was hardwired and cheap. I ended up getting rid of it (for a profit) because i hated the FUZZY OVERDRIVE, and shortly afterwards decided to build my own. I wouldn't say my amp sounded exactly like a Hiwatt but it was heading into that territory.
So again, i hope this victory email is not premature, and again, i would like to thank everyone who has assisted me. MUCH APPRECIATED. Lets hope this is case closed. :icon_biggrin:
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The truth of the matter is that i have learned more from the trouble shooting process than the build itself.
And that's how it goes Jaymz.....that's the most important part of this.
Since you built that amp,,,it's only right that you fix it.
Congratulations on finding and fixing the problem.....we have all learned this way, by trial and error,,, and we will all continue to learn.
:occasion14:
Cheers!!! mate