My Champ has a sound problem

[Mikante]

This was discussed before, my champ has some problem and i can not find out what it is.
I have tried anything, tubes, speakers, guitars. I have checked every single components and soldering too, everything is as it should.
What is driving me nuts is the fact that clean and right before the edge of breakup the amp sounds incredibly good. As soon as it gets hot and i push the volume a tiny bit further im getting some sort of overcrowd in the high/mid frequencies. it is like if those frequencies which sound fine with the volume down are then summing up when playing and become really annoying. It is much more notable when i play d or a chords. It only happens when playing, otherwise the amp is dead quiet.
It gets even worse into full overdrive.
Could it be a bad filter cap? They are all looking good and showing the right value on the multimeter. I have no idea.
The filter caps are very close to the power transformer, i don t know if this could ever be a problem.

[bepone]

there are many things here..also you need to check with the scope what is going on.

this amp doesnt have good overdrive? it is only acceptable, also sound depends a lot from the speaker.
for better drive you need also more gain stages.. also PP amp which has better OD.

then, you can use pedals? did you try to put very bit g1 grid stoppers (220k) to each tube? S.E> works better with lover voltage..

many times i linked here, there was old article in audioexpress magazine about, good to read :

https://audioxpress.com/article/Glass-A ... of-a-Champ
and
https://audioxpress.com/article/you-can ... of-a-champ

[Littlewyan]

If you can record the problem it would be really useful and some gut shots please

[Stevem]

Please post up a number of really good gut shot photos of the amp.

There are a whole array of things that could be causing this issue and a few of them might needa tone generator and a O- scope to track down .
Hopefully it's just a layout problem that needs to be addressed.

[Mikante]

there are many things here..also you need to check with the scope what is going on.

this amp doesnt have good overdrive? it is only acceptable, also sound depends a lot from the speaker.
for better drive you need also more gain stages.. also PP amp which has better OD.

then, you can use pedals? did you try to put very bit g1 grid stoppers (220k) to each tube? S.E> works better with lover voltage..

many times i linked here, there was old article in audioexpress magazine about, good to read :

https://audioxpress.com/article/Glass-A ... of-a-Champ
and
https://audioxpress.com/article/you-can ... of-a-champ

I ll take a look, thank you.
The overdrive sounds good too but the problem i described gets even worse. The amp has a 470r screen resistor on the power tube. I have also tried grid stoppers on each tube and i don t like it, beside my personal taste, it didn t solve the problem.
220k isn t a bit too much? I have seen values for the grid stoppers on fender amps and they never go over 10k for pre amps and 1.5k for the power tube.

If you can record the problem it would be really useful and some gut shots please

I don t have an audio interface right now, i have tried recording with my phone but the audio is too compressed and mid scooped, you just can t tell by listening to it.

Please post up a number of really good gut shot photos of the amp.

There are a whole array of things that could be causing this issue and a few of them might needa tone generator and a O- scope to track down .
Hopefully it's just a layout problem that needs to be addressed.

It looks so messy right now, i have been working on this amp for so long

[bepone]

I ll take a look, thank you.
The overdrive sounds good too but the problem i described gets even worse. The amp has a 470r screen resistor on the power tube. I have also tried grid stoppers on each tube and i don t like it, beside my personal taste, it didn t solve the problem.
220k isn t a bit too much? I have seen values for the grid stoppers on fender amps and they never go over 10k for pre amps and 1.5k for the power tube.

we are just speculating about your problem, what kind of is. so pls record something via phone and post here. if all is ok with the topology, tubes and working points, then problem is just normal.

if is only "harsh" sounding on high volume,you are hitting hard g1 grids of V1b, and output tube and there is nothing to prevent clipping and you are getting "transistor" overdrive in valve circuit, full of middle and high content.

how to battle this - via high value g1 stopper, put somewhere from 220-470k in series with g1 in preamp section which is geting most of the signal, then current which will flow in the g1 during excessive gain, will shape and compress input signal which is good.

then champ with or without NFB? if is without - this is even worse! why is that? because SE amp cannot drive single speaker, due to high internal resistance of pentode. pls connect NFB which will tame the speaker raising impedance, so in this way you will have less harshness in OD..

then how to kill it naturally? also is possible via 15" speaker high power, try something of 400W if you have close.

to get good overdrive in small amp, single ended, with few tubes, is hard task, and quality without pedals is not so great, i would add 1 ECC83 more in the preamp circuit to shape it more..

[bepone]

overdrive and how to manipulate and shape, is described in the book of M. Blencowe, Designing tube preamps for guitar and bass..

[Mikante]

I ll take a look, thank you.
The overdrive sounds good too but the problem i described gets even worse. The amp has a 470r screen resistor on the power tube. I have also tried grid stoppers on each tube and i don t like it, beside my personal taste, it didn t solve the problem.
220k isn t a bit too much? I have seen values for the grid stoppers on fender amps and they never go over 10k for pre amps and 1.5k for the power tube.

we are just speculating about your problem, what kind of is. so pls record something via phone and post here. if all is ok with the topology, tubes and working points, then problem is just normal.

if is only "harsh" sounding on high volume,you are hitting hard g1 grids of V1b, and output tube and there is nothing to prevent clipping and you are getting "transistor" overdrive in valve circuit, full of middle and high content.
transistor like is also a good way to describe it

how to battle this - via high value g1 stopper, put somewhere from 220-470k in series with g1 in preamp section which is geting most of the signal, then current which will flow in the g1 during excessive gain, will shape and compress input signal which is good.

then champ with or without NFB? if is without - this is even worse! why is that? because SE amp cannot drive single speaker, due to high internal resistance of pentode. pls connect NFB which will tame the speaker raising impedance, so in this way you will have less harshness in OD..

then how to kill it naturally? also is possible via 15" speaker high power, try something of 400W if you have close.

to get good overdrive in small amp, single ended, with few tubes, is hard task, and quality without pedals is not so great, i would add 1 ECC83 more in the preamp circuit to shape it more..

Thank you so much for the explanation, i will definitely try to add a bigger value grid stopper, for g1 you mean pin 2 and 7 on the 12ax7 tube right? As i said, it is not just the overdrive and clipping. So i think this will only make it sound better in terms of distortion.
The negative feedback is helping a lot, with the 22k stock value the problem i described is at its worst. So i tamed these frequencies by going for a 1.5k resistor, much better but still unpleasent.
Here is a picture of the once clean and tidy circuit board

[sluckey]

Your soldering skills may be a factor.

[bepone]

-mikante-
v1a side pin 2 no need, it is ok to put 15k there,

even with that layout maybe it is possible to fix, your volume wire is close to anode wires,

put shielded wire from volume pot to the grid v1b- and on the pin 7 put 220k-470k, then completely remove wires to the cathode switch from v2b because they are interfering too much

[maxkracht]

Better lead dress and/or shielding should definitely help. Getting rid of some solder blobs and chopsticking around could help find issues as well.

If you replaced the crossed out jack next to the speaker jack with a switch, you could move the NFB away from the input, loose a few inches of wire, and have additional NFB settings.

[Mikante]

Your soldering skills may be a factor.

I knew this was coming
I have ordered new turrets and parts, i will be cleaning this mess no questions about that.

-mikante-
v1a side pin 2 no need, it is ok to put 15k there,

even with that layout maybe it is possible to fix, your volume wire is close to anode wires,

put shielded wire from volume pot to the grid v1b- and on the pin 7 put 220k-470k, then completely remove wires to the cathode switch from v2b because they are interfering too much

Ok i will follw your suggestions, by the way, you re saying you would add 15k grid stopper on v1a and 220k on v1b?
I had grid stoppers and they only adjusted the overdrive behaviour, no improvements for the problem i have, they where small value resistors though, 10k on both pre amp grids and 1.5k on the 6v6gt grid.
I have a shielded wire but it is very thin, i will try.
The cathode wires are going to the 3way switch to chose different bypass cap values and to the feedback resistor. This arrangement has been done lately and it didn t make any difference for that problem, but i can make it better and have only one wire coming out the cathode pin.

Better lead dress and/or shielding should definitely help. Getting rid of some solder blobs and chopsticking around could help find issues as well.

If you replaced the crossed out jack next to the speaker jack with a switch, you could move the NFB away from the input, loose a few inches of wire, and have additional NFB settings.

Yes i was planning to put it back where it was, as you can see there was a switch there to chose between two values of negative feedback, but then i found out that the 22k resistor was making it worse.
About the solder blobs, you are right but i have no problem of crackle sounds or anything associated with bad soldering, i have also tested each joint individually with the a chopstick with the amp on and loud, no problem whatsoever.

[Phil_S]

This has an excellent section on how to solder...for anyone who might need it. I found it very helpful when I started doing this stuff. Look around page 10.

[maxkracht]

I think Bepone means a low value is fine for the grid stopper off of the input. Lower than 15k you could run into RF issues and might need to make other adjustments. 68k is fine, no need to change.

For chopsticking, I meant both checking solder joints and moving wires around. Where the wires are in relation to each other and other components matters. This is why shielding the wire going to the second grid could help and why moving the nfb resistor could help.

[Mikante]

Thank you i understand now.
I have added a 220k before pin 7 and replaced the bypass cap switch and feedback resistor.
Replaced the blu wire with a shielded one and ground it both sides.
Pictures is coming.
Is there a way to attach a video without going through youtube? I made one.

At the end i was saying that the volume was not even past half.