Volume affected by treble pot

[ninoman123]

I built my TMB exactly like the layout thats here. (Plus the missing cathode ground) It works well except that when the volume is turned to 5 the volume is low, but when turned to 0 the volume goes way up. When turned to 10 the volume is very low. Even with the MV and Volume controls turned to 10 its low when treble is on 10. Is this how it should work? I checked the schematic and its wired like that too. I can understand a small boost when treble is turned up but I doubt it should affect the volume this much. Should I try switching the lugs on the treble pot? Thats all I can see wrong. Nothing is shorting to ground that shouldnt be either. I checked that too. Any advice or am I just being paranoid?

[rjgtr]

It sounds like the tonestack is miswired. Check a couple other layouts. Even a Fender or other Marshall style amp.

[ninoman123]

I compared it to the 18 watt layout and its the same thing. It only does this when the Master Volume is turned up to 10. Otherwise the treble pot acts normally. The amp is pretty much dead quiet when turned down below 10 on the master volume. Even at 9 its quiet. The volume pot is almost worthless too because I have to keep it at 10 always in order to get any volume at all from the amp.

Switching the NFB switch does change it some but I still get the weird effects from the tone stack.

I have this same wiring on my P1 and it doesnt do that. This amp is quieter than my P1 and this amp only uses 1 EL84. Ive double and triple checked the wiring but I see nothing wrong. Maybe Ill check again.

[rjgtr]

Maybe you should swap out the volume pot. It could be bad.

[ninoman123]

Thanks Ill try that. This thing used to work just fine but I fired it up today and didnt get much. Ill check again for shorts and Ill try to swap that pot and see if I get any change.

[ninoman123]

Pots seem ok. Checked them with my DMM today and they read the same as they read on my P1 and it has the same tonestack. Checked all my grounds and I have nothing to ground that shouldnt be. Maybe I have one of the leads on the treble pot to the wrong place. Has anyone else that has used this layout found this problem or just me?

[Plexi]

Sounds like you might have an oscilaiton..that kills the signal and will drop out the volume.. Lead dress is important..

That is not how the amp should work.. if its built right,you should be able to crank everything and have no problems..

Richie

[bevins]

Can you post some pics? Maybe something we could see that you are overlooking.

I noticed you said it worked before, then in your next post you mentioned about maybe having it wired wrong. If it is wired wrong it probably would have never worked right.

Bob

[ninoman123]

Everything acts normally until the master volume is turned all the way up. Then the treble starts acting as a volume control.

If I dime the MV down to like 8 or so then everything is 100% fine. Why would it be doing it at the last part of the pots rotation? I moved around wires inside the amp and it only changed the hiss and hum of the amp, not the MV problem.

Is there a good article or thread on lead dress? I tried searching the fourms and found nothing.

I appreciate the help.

[ninoman123]

Anyone know? I tried replacing the MV volume pot and got the same result. Should I replace the treble pot too? Every schematic Ive seen has the tonestack wired like this. So I must have something wrong in order for it to be acting so weird. The thing is...I cant find anything wrong! Argh! Theres no hum no hiss, just this thing. Frustrating. Any suggestions?

bevins- Wiring is 100%. Triple and quadruple checked. I can post pictures but not right now. Camera is out of town. Plus the wiring is kind of hard to see inside the chassis because of the chassis lip. Im confused...this is such a weird problem.