Blues Jr Conversion Really Loud

[Tbone55]

Hello There,

I have a Blues Jr that I converted using the Hoffman conversion kit that seems to be extremely louder than it was. I did use a different OT than the stock one that was in the amp. The replacement OT was for another Fender amp and is a bit  more powerful than the stock one.

The problem isn't so much that the amp is louder but that there doesn't seem to be any real range of volume adjustment. Its really loud with the volume and master volume at 2 and does get louder if you turn it up further but not by a lot. I have no idea what I should be checking to determine why this is happening and I come to humbly ask for help.

I would greatly appreciate any help on what I should do to diagnose this.

Thanks in advance. Cheers!

[uki]

Check the whole circuit, voltages for all tube pins, that is a good start, some nice pictures will help !

[EL34]

Do this first

https://el34world.com/Forum/index.php?topic=17701.0

[tubeswell]

Did you use Audio Taper (Log) pots for the volume controls etc?

[mresistor]

People are going to ask for high resolution photos, voltages on the tube pins etc.   which is helpful to diagnose trouble in an amplifier.

[Tbone55]

Check the whole circuit, voltages for all tube pins, that is a good start, some nice pictures will help !

Weird thing. First it was too loud and now when I went try it again there was no sound coming out. I reposted again with a different thread because of this and it has the voltages I measured vs what the voltages were when I built it. I think I've got a bad resistor on B+ output of the 47uf500v filter capacitor that's causing the problem. Have a look at my other post if you can and if you need more voltages I'll get them.

Thanks kindly.

[Tbone55]

Did you use Audio Taper (Log) pots for the volume controls etc?

Ye, they are all audio taper pots. Ran into a different problem and did a other post. Have no sound coming out if the amp now. If you'd care to look at it I've provided voltage readings now and from when I built the amp. I think I have a defective resistor that's causing the problem.

Thanks.

[Tbone55]

People are going to ask for high resolution photos, voltages on the tube pins etc.   which is helpful to diagnose trouble in an amplifier.

Thanks kindly. The amp stopped working. No output. I re-posted again and included pin voltages for the power tubes now and when I first built the amp. I think I have a bad resistor in the B+ circuit right after the first filter capacitor, 47uf500v. The voltage after the resistor drops off dramatically affecting the power tube plate voltage. If you care to look ar that post and tell me what you think that'd be great.

Thanks kindly.

[EL34]

Did you do what I said in reply #2?

[Tbone55]

Thanks Everyone.

The amp is now working again and just as loud. Guess I'll have to leave it as for now and just turn the volume on the guitar down. 🤣

[Tbone55]

Well, I'm back. The loudness problem is still there but today when I turned the volume knob it worked the way it's supposed to.....for a second. Then the volume jumped back up. I fiddled wiyh the volume knob a bit more and managed to get it to the same thing again. For a bit it actualy functioned the way it's suposed to.

Off hand I'd say there's something not right with the pot but I took a resistance measurement across it and it read 2.5ohms at max volume and 860kohms at the lowest setting. Is there anything else I should check or do before getting another pot? Maybe I need to just spray the pot with some contact cleaner?

Thanks.

[Lectroid]

Tbone55,

The first two replies suggested that you sit down and verify that every connection is correct.  That was excellent advice.  Were this my amp, I would immediately think the same thing: bad connection--a mis-wired terminal or a bad solder joint.  No way anyone here could do that; only you can do it.

But the mistake could be anywhere, given the symptoms you report and the lack of any more information to go on.  Verbal descriptions don't help much in diagnosis. Without giving any more data, you make it much harder to figure out your problem.  If you provide the pics, schematic, layout, and voltage list, you probably will  get more interest and suggestions.

Good luck.

[Tbone55]

Thanks for your reply. I've gone through all of the connections and measured the values of the components in that part of the circuit and they all seem to be ok. I've also re-checked the connections to make sure that they're wired to where they should be and that checks out. I'm going to try and resolder the connections and see if that makes a difference.

If I need to replace the pot is there any difference in which 1meg pot I replace it with? My closest supplier has CTS & Fender 1meg audio taper pots with different tapers of 10% and 30%. I think the 30% taper are what Fender calls their vintage pots.

Thanks for your help.

[Tbone55]

I'm just replying because I can't attach any of my images. They're larger than the site will accept and I can't change the resolution on my camera or tablet. If I can get this straightened out I'll send them along with my voltage readings.

[Tbone55]

Here's an image of my chassis.

[Tbone55]

Here are the schematic and layout for the board including the voltages I've measured.

[Tbone55]

Here's the other image with the voltages as well.

[dude]

You said the audio taper volume pot measures 2.5ohm max and 860k min, close enough and the pot is 1M.  Disconnect the leads to the pot, measure from two outer ends, should be 1M or close, 860K is fine.  Measure from one outer leg to wiper, should go from 0 ohms to 1M slowly not a fast jump, do this on each other leg. If not a slow increase the pot is bad, replace. 

[Tbone55]

You said the audio taper volume pot measures 2.5ohm max and 860k min, close enough and the pot is 1M.  Disconnect the leads to the pot, measure from two outer ends, should be 1M or close, 860K is fine.  Measure from one outer leg to wiper, should go from 0 ohms to 1M slowly not a fast jump, do this on each other leg. If not a slow increase the pot is bad, replace.

Hello Dude,

Sorry I couldn't get back to you sooner. Had some family things to do. Here are the results. I did as you said and unsoldered all of the conections going to the volume pot.

Resistance measured across outer terminals - 879kohm

Resistance Measured from wiper to each outer terminal. Readingscwere taken at each volume level number.

Volume Level     Resistance           Resistance
            1                 2.1ohms                  885k
             2                17.06k                      860k
             3                 50.8k                        825k
             4                 79.5k                        799k
              5                108.3k                      772k
              6                 135.2k                     745k
              7                  160.2k                    716k
              8                  297k                        529k
              9                  528k                        295k
             10                 717k                        21.1k
             11                  881k                       2.2ohms
             12                  882k                       2.0ohms

There sees to be a big jump in the second resistance column from vol level 9 to 12. What's your opinion?

Thanks.

[AlNewman]

That does seem a bit strange.  If your overall resistance from leg to leg measures 879k, Your resistances from outer legs to wiper should all add up to 879k.
I'm looking at 8-10, and it doesn't add up.
Maybe it's a dead spot in the pot?

[Tbone55]

You could be right. All I know is that the volume jumps dramatically from 1 to 3 and then doesn't seem to change much until you get around the 8-9 mark. I'm of the opinion that theres something wrong with the pot. I'm going to get a new pot tomorrow and I guess I'll find out. There are two different pots I was looking at that have different audio response curves. One is based on vintage fender pot with a 10% curve and another one with a 30% curve which is more modern. Not sure which one would be preferred.

[Tbone55]

So I purchased a new CTS 1meg audio taper pot and installed it. These are the resistance readings at each volume level.
                    New Pot            Old Pot
Vol Level    Resistance    Resistance
        1            961k                   885k
        2            960k                   860k
        3            943k                   825k
        4            921k                   799k
        5            903k                   772k
        6            883k                   745k
        7            852k                   716k
        8            803k                   529k
        9            593k                   295k
        10          319k                   21.1k
        11          11.95k                2.2ohms
         12          0.2ohms           2.0ohms

Theres an obvious difference in the taper between these two pots. With the new pot installed the volume doesn't change from 1 to 2 but then jumps at 3. From there forward the volume diferences are very small until you get to about 9 where you start to get breakup. Because of the higher resistance of the new pot the sound level change is not as drastic as it was between 1 and 3 with the old pot. There's about am 80k difference between the two overall which to me is pretty significant.

What says the forum.

[dude]

Is the new pot Liner or Audio?
If a pot across the outer legs is 950k, then in a Liner pot the middle would be half. But Audio pots are use in most amps for vol, as the taper is more suited to one’s ears. Giving a graduated change to your ears as you turn up, so the middle won’t be half. The new pot seems to be fine, l don’t think it’s the pot. Check your wiring, did you wire the pot backwards, didn’t EL34 suggest to check all the wiring. I know going over connections can be frustrating but follow Doug’s suggestions, go slow, mark each connection on the layout when your sure it’s correct. When the layout is fully marked and you’ve done this a few times check the solder joints, anything under the bd loose.
A bad component.., best l can suggest, maybe more could chime in, good luck.

[Tbone55]

New pot is audio taper. Pot does seem to be working properly. I've gone over the wiring as suggested by Doug highlighting eac connection as I went along. Everything seems to be as it should be. The amp is better than before and I think that's due to the new pot having a higher resistance. I'm going to play around with it some more. Maybe someone else might chime in that's had a similar expereience.

Thanks kindly for your help. Cheers!

[Esquirefreak]

Newer CTS pots are somewhat known for having a weird taper with a dead spot at very low volume. I think Alpha pots have a more usable taper.

/Max

[Tbone55]

Newer CTS pots are somewhat known for having a weird taper with a dead spot at very low volume. I think Alpha pots have a more usable taper.

/Max

Thanks kindly Max. That's exactly what my CTS pot appears to be acting like. From 1 to 2 there's nothing then at 3 the volume kicks in. I'm going to have a look at a Fender Pure Vintage 1meg pot tomorrow and see what its taper looks like. My problem now is that I had to enlatge the mounting hole tp accomadate the CTS pot and if I go back to an Alpha pot the whole is now too big. Maybe I can glue a washer with a smaller hole in the chassis if I go back to an Alpha pot.

Cheers!

[dude]

Doug sells small washers to fill the gap when going from 3/8” hole to alpha shaft size, next time you order with Doug get some. But you can center the alpha pot easy and tighten, if room use a small star washer on the inside.

[Tbone55]

Doug sells small washers to fill the gap when going from 3/8” hole to alpha shaft size, next time you order with Doug get some. But you can center the alpha pot easy and tighten, if room use a small star washer on the inside.

Thanks kindly dude for that info. I'll add that to my next parts order. As it so happens I just discovered something that might be the reason my volume is so loud at such low volume levels but I need some expert advice.

There's a 1meg resistor that goes across the tip and sleeve terminals of the input jack. I was starting to test some component values and figured I should begin where the signal comes in. This resistor is only measuring 0.1ohms. There's obviously something wrong with resistor but since I'm not experienced enough to understand what the purpose of this resistor is maybe you could explain if this could be the source of my problem? I think it has something to do with impedance but not sure.

Cheers!

[dude]

This resistor is only measuring 0.1ohms

Plug a jack in and measure again, no jack resistor shorted to ground.

[Tbone55]

This resistor is only measuring 0.1ohms

Plug a jack in and measure again, no jack resistor shorted to ground.

Plugged in a jack and it measures 963k. Oh well. The color code of the resistor is brown, black, black, green. Am I wrong but wouldn't this indicate a 10meg resistor, not 1 meg? It's measuring correctly  but shouldn't the multilier band be yellow?

[Esquirefreak]

Alpha makes pots for ⅜" holes as well. I think you may be over complicating things.

I usually use either Bourns or Alphas, depending on what local stores have in stock. Both have worked very well in terms of taper and quality. I do prefer the slightly higher torque of the Alphas for amps, though. And Bourns for guitar pots.

/Max

[Tbone55]

Alpha makes pots for ⅜" holes as well. I think you may be over complicating things.

I usually use either Bourns or Alphas, depending on what local stores have in stock. Both have worked very well in terms of taper and quality. I do prefer the slightly higher torque of the Alphas for amps, though. And Bourns for guitar pots.

/Max

I didn't know that. My local parts suppliers are hit and miss. I think you're right about me over complicating things. I have another amp that I built from scratch and the volume control works perfectly. The volume increases very gradually from 1 to about 6 and then starts to get much louder with some breakup. That's my comparison. Anyway, I'll just recheck the wiring and components one last time. Maybe I missed something.

Thanks kindly for your help.

[tdvt]

Just as a side note, several of us have had issues specifically with 1M CTS pots, see THREAD

I had a few failures myself with 1M version, typically a dead spot on the bottom of rotation & now actually avoid using CTS these days. The Alphas are cheaper, smoother & seem to be reliable.

I DO make a point to get the 3/8" versions but keep some of Doug's little adapter bushings around for the 8mm.

[Tbone55]

Just as a side note, several of us have had issues specifically with 1M CTS pots, see THREAD

I had a few failures myself with 1M version, typically a dead spot on the bottom of rotation & now actually avoid using CTS these days. The Alphas are cheaper, smoother & seem to be reliable.

I DO make a point to get the 3/8" versions but keep some of Doug's little adapter bushings around for the 8mm.

Thanks for the onfo. It's hard for me to get Alpha pots where I am. The places that carry electronic components either have CTS or some really cheap non brand stuff. It's sad when you spend more money to get what's supposedly a better made product and it doesn't work like it should. I may have to order some Alpha pots and those adapters from Doug as well as a few other items. I'll check to see if he has them for 3/8ths" hole as well.  The other amp I built doesn't have this problem with the volume knob but I built it back in 2018. Maybe components were better then like everything else.

Cheers!

[dude]

From the Blues Jr's that I played, if I remember correctly, didn't have a gradual volume raise like the other amp you mentioned. The Blues jr doesn't have a lot of clean, breaks up fast to my ears. What you have maybe be normal for the that amp. From what others mentioned, go with the Alpha pot..?  If no 8mm washer, just use a small star washer on the back side and tighten so it doesn't move, beware the threads can strip if overly tightened. 

[Tbone55]

From the Blues Jr's that I played, if I remember correctly, didn't have a gradual volume raise like the other amp you mentioned. The Blues jr doesn't have a lot of clean, breaks up fast to my ears. What you have maybe be normal for the that amp. From what others mentioned, go with the Alpha pot..?  If no 8mm washer, just use a small star washer on the back side and tighten so it doesn't move, beware the threads can strip if overly tightened.

Thanks. You're probably right. I honestly can't remember what the amp was like before I did the conversion so maybe what I'm hearing is normal. I wind up turning the guitar volume down to compensate. I ordered some Alpha pots today but not the ones for 3/8ths holes. I don't know where I could get those. Will do as you've suggested when installing it.

Cheers!

[mresistor]

What is your location  country   etc   Tbone?

[Tbone55]

What is your location  country   etc   Tbone?

I'm in Canada. I did find a supplier for the Alpha pots in my province but not for the ones for 3/8" holes. I've usually ordered my stuff through Doug because it's actually been easier. We get nicked for some ridiculous delivery rates here. Costs me more for delivery than the actual parts.

I've been thinking about trying a different pre amp than the 12AX7. Maybe put a 12AT7 or 12AU7 in the V1 position to soften it a bit. It just breaks up a bit too soon and I really have lower the volume level on my guitar like down to 5 to keep it clean. Your thoughts?

[Esquirefreak]

Try a 5751. Really nice tubes 👍

/Max

[mresistor]

Also you might want to try a 12AY7 


There's this place in ON CA that has 3/8" Alpho pots.  https://nextgenguitars.ca/products/alpha-standard-solid-shaft-pot-choose-taper-resistance.html

[Tbone55]

Thanks kindly for the tube info guys. I may have a 12AY7 kicking around.

Fuñny but I ordered the Aplha pots from Next Gen. I didn't see where they had the one's for 3/8" hole. No matter, I'll put the one I ordered in and just make sure there's a lock washer on it. I'm going to change the pot first and see how the volume control reacts before I do the tube swap. I'll give an update once I do.

Cheers!

[Tbone55]

I got my Aplha pots late yesterday. One measured 1025k the other 965k. I decided to install the 1025k pot. The amp still gets loud at 3 but there's some volume now between 1 and 3. Still have to turn my guitar volume down to about 5 in order to keep the sound clean.

My next step is to replace the 12AX7 in V1 with a 5751 to try and tame the amp down. My question is, which brand would you recommend? My current V1 tube is Electro Harmonics and V2 & V3 are JJ's. The cheapest available us from JJ and the most expensive is a Sovtek. There's a really big difference in price between these two. Which make is a decent price with decent quality that doesn't break the bank?

Thanks.

[Esquirefreak]

I use the old GE "5 stars" so I can't comment on new production 5751.

Btw, it might be worth a shot lowering the plate resistors of the first stage to cut the gain down.

/Max

[Tbone55]

I use the old GE "5 stars" so I can't comment on new production 5751.

Btw, it might be worth a shot lowering the plate resistors of the first stage to cut the gain down.

/Max

I never thought of that. Any idea what value I should use to do that? I have absolutely none.

Thanks.

[Esquirefreak]

Try lowering the plate resistor of the first stage to 68k or 47k just to see if it helps? Or try a splitload 47k/47k? That way you keep the gain but reduce the signal level going in to the second stage.

You could lower the second stage Ra value as well if you want to experiment.

Cheap enough to try before buying new tubes 👍

/Max

[shooter]

my guitar volume down to about 5 in order to keep the sound clean

as a non-guitarist tech I ran into this problem often.
The guitarist seem to think there's "magic" in the guitar volume, "I sound awesome with guitar on 6, amp on 8"


as a tech I laugh, tell them to spent 10 minutes tweaking between ALL the knobs til you sound awesome again.  You see the light come on, then you spend the next 30 minutes waiting til they rif themselves back to conversation 

[Tbone55]

my guitar volume down to about 5 in order to keep the sound clean

as a non-guitarist tech I ran into this problem often.
The guitarist seem to think there's "magic" in the guitar volume, "I sound awesome with guitar on 6, amp on 8"


as a tech I laugh, tell them to spent 10 minutes tweaking between ALL the knobs til you sound awesome again.  You see the light come on, then you spend the next 30 minutes waiting til they rif themselves back to conversation 

Well, as an amateur guitarist and amateur tech all I can tell you is if I can't put the volume knob on my amp past 3 with the guitar volume at max without the sound breaking up my only option is to turn the guitar volume down to clean it up. That's the way it was done by guitar players in the simpler days. I can spend 30 minutes tweaking the knobs on my amp and it wouldn't get me anywhere.

The other amp I built doesn't have the problem my Blues Jr does. I can turn the volume control up to about 7 with the guitar volume at max and there's almost no breakup. Past that point breakup really starts to come on. All I have to do at that point is turn my guitar volume down to clean up my sound. That amp also uses 12AX7 in the preamp section.

Obviously different amplifiers will have different characteristics.

[AlNewman]

So, you can't leave the preamp volume low, and raise the master volume to keep it clean?
There's some good mods that can be done.
I have a Blues Junior I never liked the sound of, so I kind of emulated a super reverb type build.

One great mod is to change the stock tonestack into more of a vintage TMB style by changing the Mid pot to a variable resistor, and changing the values in the tone stack.  That gives you better control of what frequencies you'd like to push.

Also, I think cooling the bias from stock sounds great, and your tubes will last longer. 

I did an awful lot to mine, but it is clean...  It's still loud, but I have a lot more control on the front end, and can get a lot of juiciness if I want it.  I can plug it into my deluxe reverb cab, and it would be hard to tell them apart.

[Tbone55]

So, you can't leave the preamp volume low, and raise the master volume to keep it clean?
There's some good mods that can be done.
I have a Blues Junior I never liked the sound of, so I kind of emulated a super reverb type build.

One great mod is to change the stock tonestack into more of a vintage TMB style by changing the Mid pot to a variable resistor, and changing the values in the tone stack.  That gives you better control of what frequencies you'd like to push.

Also, I think cooling the bias from stock sounds great, and your tubes will last longer. 

I did an awful lot to mine, but it is clean...  It's still loud, but I have a lot more control on the front end, and can get a lot of juiciness if I want it.  I can plug it into my deluxe reverb cab, and it would be hard to tell them apart.

I can turn the master up while keeping the volume low to keep it clean but I'm trying to play at low levels while in my house. Maybe comparing it to my other amp isn't a fair comparison and it's just the nature of the beast.

I apologize but I don't know what TMB stands for but it sounds like some of the mods you talked about would be worth looking into. You mentioned using a variable resistor for the mid tone pot. Is that like a trim pot? I'd certainly like to try some of the suggestions given.

Thanks kindly for your help. Cheers!

[acheld]

Treble
Mid
Bass