For Sluckey - question on Mark Huss's 6V6 Plexi schematic

[dude]

Sluckey in the schematic you made from Mark's, you made a few changes. The change I see on your schematic is the coupling cap to the Bright Vol. Mark had a .022 going to normal vol and a .0047 going to bright.
Yours has a .0022 to bright and you X out the .0047 (I assume you have  "no connection" there from your .0022 to the 470K R in parallel with the bright cap 470p). Meaning no connection, as you have it X out?


So yours lets more highs pass on the bright channel than Marks? Do I have this right? I didn't see two caps there in Marks drawing. I'd post the schematics but can't copy them. Not saying you made any mistakes, just experimenting with mine


al   

 

[sluckey]

You shouldn't compare my Plexi 6V6 to the Huss amp. I only mentioned his amp because it was the first Plexi 6V6 I ever saw. Mark's amp was my inspiration. But... I followed the preamp component values for the ***REAL PLEXI***, so compare my preamp values to the Marshall JMP 1987 schematic.

[dude]

Just was asking, yeah I see the 1987, your values are the same. I was just experimenting as these preamp values are detrimental to the tone.
I appreciate all your help and thanks.


al 

[Ritchie200]

as these preamp values are detrimental to the tone.

Says who?  Personal taste?  Marshall sure did sell a crap pot full of them and they are generally regarded as the R&R standard.  Not too bad for substandard tone.  You might find that statement will cause some spirited discussion!  If you were talking about a Tele, I would have to agree wholeheartedly! 

Jim

[dude]

Hey Jim, yeah maybe I used the wrong word. I agree the original 1987 caps sound terrific, just experimentation. Changing caps and listening, I love the Plexi's tone, just trying different values and listening, best way to learn is with your ears, at least for me  . I've built a few amps and this 6V6 Plexi is at the top for tone, IMO.


have a good one,
al



 

[tubeswell]

Wonder what happened to Mark Huss? Haven't heard from him in ages over at MEF - must be a few years now.  (Edit: Oops - I just saw his last post from June 2018, so still active)

[dude]

  (Edit: Oops - I just saw his last post from June 2018, so still active)

What's MEF?

[sluckey]

That's something the good ole boys cook in the tool shed behind the double wide.

[d95err]

  (Edit: Oops - I just saw his last post from June 2018, so still active)

What's MEF?

I believe it's a reference to: music-electronics-forum.com

[dude]

Just curious, do any of you guys find the "Treble Knob" to be on the brighter side, not cutting much treble as you turn it down. Standard Hoffman schematic for 6V6 Plexi...?


al   

[shooter]

do any of you guys find

time isn't linear anymore, guessing 2years back, maybe 6-8 of us built some form a the "plexi"
the BIGGEST take-away I, and others figured out, 1 input, mix bright and normal.  Seems consensus was either channel by itself sucked, blended together and you get magic sauce!   

[dude]

Seems consensus was either channel by itself sucked, blended together and you get magic sauce!   

I hear ya, wouldn't say they suck alone but best tone is mixed, too bright turn the normal up, bright down .

Just the tinkering in me, always trying to fix something that maybe is meant to be... The JTM45 was based on the Fender bassman, I changed the tone stack a little closer to the Bassman and the overly bright treble knob is now much better.
But both channels is the only way to go.


al
don't fix it if it ain't broke
 

[sluckey]

Just curious, do any of you guys find the "Treble Knob" to be on the brighter side, not cutting much treble as you turn it down. Standard Hoffman schematic for 6V6 Plexi...?

I just played mine for a while today. Treble pot works just as it should. Very little treble on zero. Very bright when maxed out.

[dude]

Yours is pretty much the same as Doug's I think.  Are your coupling caps to vols .0022 (bright) and .022 (normal) with 500p parallel with 470K voltage divider to bright vol and 500p to treble? That's what I have, I tried a 250p to treble but still not much cut on treble knob. Have Mallory 150 caps and mica caps. Treble on 1 have almost as much treble as on 7...? Speakers or guitar could be an issue, what speaker do you have, mine are two GH1230's, Celestons and a strat, single (vintage) coils. Isn't my speakers, maybe the strat? I'll try a Les Paul tomorrow. Thanks for the feedback.


al
If it ain't broke don't fix it.

[sluckey]

My amp is wired exactly as shown in the schematic on my website.

Treble on 1 have almost as much treble as on 7

Then something ain't wired right.

[dude]

After going over wiring to tone stack, I can find no miswire. If I disconnect the cap to treble pot I have no treble, lowering this cap from 500P to 250p then to 180p, the treble is being cut with with each lower ecurmen. This amp definitely is over bright, not in a very bad way, just with treble up to 8 or 9, ice picking "with a strat". The treble works as it should but the range is on the very bright side but with the two channels mixed this can be corrected to a degree.  I now take this as not a fault in the amps schematic or this particular amps wiring but due to the guitar and the pick/ups in it. I initially had a celestion blue dog and GH1230, bright, changed to two GH1230's better, tried guitars other than the strat I was playing, much better. 


IMO, with my complaint of an overly treble response, the guitar used can affect the brightness in a "big way". Maybe this strat seems overly bright just in this circuit, which it does and therefore: a guitar and it's pickups can make a circuit sound overly bright.


al
if it ain't broke don't fix it       

[shooter]

just with treble up to 8 or 9

granted my career was NOT guitar, but I don't think I ever wondered, even once, why my system calibrated perfect on 3, but not 8.  I am continually amazed that it bothers guitar folk 

[dude]

Probably because I'm a 40 year guitar player along with being a tone freak  .

[sluckey]

There's not a nickle's worth of difference between the Huss, Luckey, or Hoffman schematic. I would expect all 3 to sound very similar. Which layout did you follow? Or did you roll your own? Did you use the proper taper for the pots? Can you post some pics?

The stock bright channel is really ice-picky. That's why I removed the .0047 bright cap from the volume control. Probably why Huss and Hoffman didn't even show one on their schematics. I'm using a strat with S1 switching and usually play through a 2x12 with a Celestion Heritage G12H(55)(bass) and Celestion Heritage G12H(75)(lead). The treble control on my amp does not behave as yours does. I really suspect something is not quite right with your amp. If not a wiring error, maybe a wrong value or faulty component.

[shooter]

Probably because I'm a 40 year guitar player

I had a 25yr guitar guy demo for me one of my builds, after an hour of guitars, pedals, etc he was very happy, except, he said with his strat and my treble knob on 9, it was a little ice-picky.  He played a twin AB763 standard gig amp.  I drug it out, plugged him into the bright channel, set the treble to 9, volume on 7 and told him to play, I made my point, we shared a peace pipe 

[dude]

I followed your layout and schematic which is the same as Doug's and Huss's except Huss's coupling caps to vols are lower, I saw in your schematic you took that .0047 bright cap out, Doug's didn't have it either. The treble pot is 264 K (a 250KA). I changed the 500p to ceramic 200p to try to cut the brightness on the treble pot but had the original in at first 500p.  I also changed the coupling caps to vols as per Huss's in an attempt to cut brightness but had .022 and .0022 originally. I now have .022 to normal and .0047 to bright. If these pic's are too grainy, I'll try to send better pics in single posts. If I have a problem in this amp, I would suspect a "faulty component" but in my experience that's reaching for straws...?  The bias, master preamp vol works as should as per your schematic. I install a PPIMV on stand-offs as you can see, it's not a LaMars, I have 220K grids to power tubes and bias. But without it "same problem" overly bright.


***IMO, the entire tone stack is "weak", if this is a clue? Let me know if these pic's are useless. Thanks for taking a shot at this.


al 

[dude]

More pic's

[dude]

OK, I just updated the pic's for better quality and important shots.
It ain't pretty, that AO43 board with the cone eyelets has a tendency to drip solder, I checked with mirror. ok. THe four caps over the PI is the PPIMV on stand-offs, works well but I like the pre-master better, probably will take it out although mixing the two gives a nice option.
Very tight ,ask me any question.


al

[sluckey]

The treble pot is 264 K (a 250KA).

Put the correct pot in it and see if that improves the treble action. While you're at it recheck the other pots to see if you have any others wrong.

[dude]

I'll check all the pot values, the treble pot is labeled 250KA but it's a 20% pot, so 264K is in that range. I'll drop in another that's 20% reading the other way. Maybe I'm out to lunch but others say this amp too bright and treble pot doesn't help much. I'll check all the pots out and replace if needed. Maybe just that treble pot is funky, I'll replace it anyway, can't hurt.


I have three other AO43's, this is my prototype, made some layout location mistakes as I can't get pots out without pulling BD up a bit, another can filter cap would give more room, use a custom made BD from doug, cleaner component soldering, lots of stuff I would have done differently but just want to get that biting treble fixed if it's not common with this amp. Thanks for looking.


al

[sluckey]

The value of the pot is not an issue. But you used the wrong taper. Use a 250K LINEAR TAPER POT like the schematic specifies. The mid pot should also be a linear pot.

[Ritchie200]

I find this interesting because my old small box 50's were pretty smooth on the treble input.  They were plug and crank and play.  They were super easy to get that great Marshall wood from.  I never jumped the "bass" side.  I also played a strat through them.  I also ran a treble booster into it.  I cant remember the settings (that was almost 50 yrs ago! holy crap!) but I would have remembered having to turn it way down.  I don't think the circuits were any different? I don't have time to dig into my Marshall book...


Jim

[Ed_Chambley]

Any Marshall tone stack performs better to me using the corrrect taper as Sluckey mentioned, BUT I INSURE ALL POTS are over.  For instance, 1 meg being 1.1 or even higher.  If you change the shrill trebel side using a larger cap you will lose the chest thumping upper mid.


Where the higher frequencies from the normal channel intersect the lower from the bright is where this lives.  Tone is subjective to player and GUITAR as Jim states even though he knows nothing about Telecasters.  Not sure what type of car guy Jim is, but my Father when alive would rather push a Ford Truck than Drive a Chevy.  Jim prefers strats with old dead strings, do not listen to anything avbout trebel from anyone who does this.


Jim acts like this about Stratocasters, but he often forgets if it were not for the invention of the Telecaster and ALL the COUNTRY Players in Bakersfield providing feedback the Stratocaster would not exist.  Until Hank Marvin came along, the Strat was considered a country instrument.  Don't let the newley turned 60 year old Jimbob sway you in your quest for tone.  I agree the Marshall 1987 Circuit is a grand Rock circuit.


Also, I have had speakers that do not respond to a Marshall tone stack well.  If you have a Greenback, use this as a benchmark and go from there.


No go plug a Les Paul or 335 into that thing and crank it up and wish it had EL34's in it.

[Ed_Chambley]

I find this interesting because my old small box 50's were pretty smooth on the treble input.  They were plug and crank and play.  They were super easy to get that great Marshall wood from.  I never jumped the "bass" side.  I also played a strat through them.  I also ran a treble booster into it.  I cant remember the settings (that was almost 50 yrs ago! holy crap!) but I would have remembered having to turn it way down.  I don't think the circuits were any different? I don't have time to dig into my Marshall book...


Jim

Happy Belated Birthday. I got stoned with 20 somethings forgot to call and wish you one!  I will tell you this and should make proud of my lady.  They were taking Sabbath and I was not saying anything simply because I can bore the crap out of most taking music history.  My lady chimes in and says"you know Tony Iommi got 2 of the tips of his fingers cut off the last day he was to work at the sheet metal plant."  "still it didn't stop him from inventing Metal, he simplly made fingertips out of a plastic dish soap bottle, tuned the guitar down a step and played the devils notes to Geezer's fasination with horror movies."


They all started lookin' suspisious at her and I jumped up and said now wait a minute Jim, you know she been living with me most of her life.  OOPS, wrong song.

[shooter]

I got stoned with 20 somethings

I my new career as beerbaitngas seller, I've gotten to know n become friends with that demographic,  Kinda fun playin  the cool 'ol man gig 

[dude]

My mistake, I'm losing it in my old age, I meant linear pots, both Treble and Mid pots are 250KB and 25 KB, read correct within 20%, more like 10%. What I'm sure of is this amp is on the very bright side, mixing the the normal up helps but treble pot doesn't cut highs much. Wondering If a faulty component could cause the treble not to work as usual but can't think of a anything.  the sweep (swipe?) is good tested both.
They Ed, I built this amp to take EL34s and 6L6s too, sounds great with EL34s and biased in the middle between hot and cool but still that treble pot doesn't cut the highs that much.
Maybe the GH1230s , I thought them to be on the tight bass side? Any other suggestions, lifting the cap to the treble the knob is inoperable, have a 181p ceramic there now, better but still doesn't cut much. Could presence have something to do with it, 47K feedback and to 16 ohm tap. Maybe disconnect and see?
Al

[sluckey]

Disconnect the NFB wire from the OT. Any better?

That's all I got. I will repeat though. Your treble control is not behaving nicely. Mine does. Get some new tone caps with leads long enough that you don't have to splice. I would use a silver mica 470pF or 500pF. 180pF is wrong.

[dude]

OK, I'll disconnect the NFB, check if that has any affect. I have new tone caps, I'll replace them all after I see if NFB has anything to do with it. I'll find the problem as long as I know I have a problem but I'm 95% sure that treble control is not working like it should, nothings 100%.
Look at your file on your 6V6 build with Huss's schematic, the tone stack, he has the bass 1M pot's end connected to the .022 cap along with the wiper, yours and Doug's doesn't, you have no connection...? Am I reading Huss's schematic wrong or is his schematic wrong...? What do those arrows mean?
I'll let you know if NFB is affecting the treble.

[Ed_Chambley]

Looking at the photos I cannot tell for sure.  Check to insure your treble pot has 3 connections to the board, one of which (the wiper) connects to the LTPI through a .022uf cap.  Lug 1 to the intersection of your 180pf and slope 33k and lug 3 to the .022uf.


It looks as if the mid pot is connected to the LTPI, but it is probably I just cannot tell for sure. 


I agree the 180pf is small.

[dude]

Might be getting somewhere, NFB has no effect on treble, disconnected, replaced the 180p treble cap with mica 500p, reflowed the extended leads on tone caps for now.
With the Bright Vol down all the way, normal up,  I have decent control over highs with the treble knob, pretty much normal. But when I turn the Bright up a quarter turn the brightness comes in but then the Treble doesn't cut some of it as maybe it should...? The higher up on the bright vol the worst it gets. Both at halfway, not much treble control with the knob, again turn the bright off, control over treble.
I'm  coming to the conclusion nothing is wrong with the amp itself. Could be the 6V6s, old stock RCA's that test very good, maybe they're on the bright side and my strat single coils are on the bright side. The 12Ax's are again vintage, test good, old GE's and the like, could be the first preamp tube as with both channels on overly bright. A lot of times I've ran a 5751 there to tame some gain. I know Sovtek WB 12ax's are way less bright sounding than their WA's. Very well could be the vintage tubes I have, GE 12Ax7's are bright sounding to my ears. Maybe this amp is sensitive to that first strage 12ax..? I'll experiment, the second 12Ax7 feeds the tone stack and get back. You can't get the Sovtek WB's anymore but I still have a few. I'm one of those players that plays much better when my tone is there, always been that way, to me you got tone or you don't, no middle ground but this amp is a Rock monster, especially once I tame that brightness, way up my ears bleed.   ED, thanks, yeah I just replaced the treble pot, I had it right. sloppy work but this is conversion once I get it right I'll rearrange everything and use doug's BD material and make it pretty.

al 

[sluckey]

he has the bass 1M pot's end connected to the .022 cap along with the wiper, yours and Doug's doesn't, you have no connection...? Am I reading Huss's schematic wrong or is his schematic wrong...? What do those arrows mean?

The bass pot works the same either way. Putting a jumper between the wiper and the unused end of that pot is the preferred wiring.

The arrows indicate the end of the pot that the wiper will move toward when the knob is turned up (clockwise). I wish all schematics would do use the arrows.

[Ed_Chambley]

I got stoned with 20 somethings

I my new career as beerbaitngas seller, I've gotten to know n become friends with that demographic,  Kinda fun playin  the cool 'ol man gig 

I write this stuff for shock value mostly.

[shooter]

I write this stuff for shock value mostly.

ya, I'm getting the internet jest of individuals here, was timely though, Sky n Lidia, young 20's happened to stop by and well, sample the fall harvest, they even like my art 
back to treble trouble 

[Ed_Chambley]

I am still looking at photos and the schematic.  Wicked, I cannot see anything, but it should work.  Plexi and Shrill seem incompatable.  They will do it, but dull out with trebel down.  Did you bypass your Master Volume?

[dude]

Ed, I've give it a shot without the pre-master vol. But I've played without the PPIVM and still not much treble effect with knob (as far as I can remember?), would be much harder to disconnect the Post Inverter MV, as pretty sure it was weak before I installed it...? But I'd do it if that could be the problem.
Whatever is going on seems to be affecting the entire tone stack, I was turning the Mids off and full on, hardly any difference, same with Bass and Treble, they work but very weak...? Could a leaking coupling cap cause this, pots are not scratchy and do work but very suttle. Maybe a faulty component  somewhere?


al   

[dude]

Found the problem!

Ed gave the suggestion to disconnect the master volume.  I couldn't see how the pre-amp MV could be causing any problems and Sluckey said his amps tone stack responded properly with that MV. So, I took the time to bypass the second master I installed, PPIMV. and the tone stack "came alive", it lives. I want to thank Sluckey for taking the time to help me troubleshoot the amp and especially posting that his tone stack was working properly. I was starting to think that's what you get till Sluckey said there's something miswired or faulty. Also, thanks to Ed for giving me second thoughts about the PPIMV causing problems.


Now that I fixed the problem, I'd like to know why this PPIMV caused the entire tone stack to be weak, working but very weak? This is the layout, I used, from an Allen Old Flame, only difference I used .047 caps in place of the .1, was that the reason...?



EDIT: The more  I look at that schematic, the two .047ufs are in "SERIES", so that would give .0233uf, close enough to .022...?  If I had the wrong values in there, would not using .1ufs cause the tone stack to be weak...? There are advantages to have that PPIMV, mixed with the preMV...? Shed some light...

al

[PRR]

> two .047ufs are in parallel

Series.

> so that would give .0233uf

Into 220k, that's 33Hz bass-cut. That's plenty for guitar.

This stage is far from the tone control and, one way or another, has little effect on tone. Something else happened. Maybe a ground wire was not connected, and got moved/fixed when you messed with the PPIMV?

[Willabe]

Found the problem!

You stuck with it and beat it! 

[Ritchie200]

Haha! What he said!  You are half way there now...   This is one of those character building exercises!

Jim

[d95err]

When you had the poimv, did you crank the coventional master volume and overdrive the PI? If you have distortion after the tone stack, then it’s normal that the tone controls are less effective than if all distortion is before the tone stack.

[dude]

d95, aware of cranked PI's effect on tone stack, thanks.
Guess I'll put this thread to rest.
Took out the PPIMV, amp and tone stack plays as should. PRR, thanks for the info but can't see anything I accidently fixed. Seems to be something with that PPIMV, really don't need it, maybe I miswired it..., but  I can't find it?
At least I got the tone stack working properly and that's what counts. Maybe the way I install the PPIMV with standoffs, wires running over the top of the bd, too crowded anyway. That PPIMV works very well in my Allen Old Flame, Super Reverb topology, maybe for some reason not in this amp...? There are several other PPIMV, maybe I'll experiment but for now I'm happy. This was a character building exercise,


al
If it ain't broke don't fix it.

[dude]

Just wanted to add one more thing to this experience, after reading about Negative Feedback, R values and which tap to use on Aiken's site, I came to conclusion that nothing was wrong with my PPIMV nor my tone stack. It was lack of knowledge on my part and not underingstanding how negative feedback works. Basically I had way too much NFB, I had a 100K on the 16 ohm tap, a ton of NFB. Overly bright, no mids or bass. Now I've got a good understanding of NFB, just changing the tap from 16 ohms to 4 ohms with the same R is changing the NFB drastically, change the resistor, higher more FB, lower less, the higher the tap the more NFB, vise versa. Too much NFB with will give a bright sterile tone with a less responsive tone stack. Maybe someone would like that brightness cut but I found with this amp using a 27K on the 4 ohms tap is just about right for my ears, some may want to use the 8 ohm tap. Too much NFB can take the mojo away from an Amp.


I'm changing MV's, bright caps, coupling caps all to no avail because I didn't understand Negative Feedback. Sometimes you get to the point where you think you have a handle on stuff but there's   more to the story than meets the eye.  Enough said!


al         

[Ritchie200]

Yeah, you never learn anything when everything goes right!  Now you know every detail on negative feedback and more important, what it sounds like when something is not quite right.  That is too cool - at least to me on the sidelines!  I think we have all had those AHAH! moments.  I always say I learn something every time I come here.  THAT is too cool!

Jim

[dude]

THAT is too cool!

Hey man, thanks, I feel a little better now.
al

[purpletele]

So let's hear it.