Crate GTD 120/212 Problem - Treble Changes Volume

[Enzo]

"No reading" means the meter it turned off, there is always SOME sort of reading.

[vintagekiki]

Okay, I took out C30 and tested ... ...

Tips from practice

Some components are designed for single use (small value capacitors, resistors of small dimensions and power) and they are simply not tested, but if they are "suspicious" and if the measurement "in the circuit" does not give a reliable value, they are replaced with new ones. Among other things, these components are extremely cheap.
It is very likely that during desolder and re-soldering due to heating of this component, it will change its value.

[Hicks86]

Okay, sorry. It said OL. I'll just replace the thing and see if that fixes the problem.

[g1]

Yes, better to just replace it. The part you linked from allelectronics should work fine. If it's not a major disassembly/reassembly to replace parts, you can even try the amp with that cap removed.
The tone will be different, but it the treble control no longer acts as a volume, you will know the cap was bad.

[Hicks86]

Haha! Picked up a cap at Frys while I was out today, it was the last .0047 in the store I might add, and its working again as it should!! I'm so stoked! Thanks everyone for the awesome guidance! I was about the junk the thing and all it took was less than a dollar to fix the thing! Thanks again!!

[johnhoef]

Hi everyone....thought I would write here in hopes of continuing this thread. My situation also involves a Crate GTD120. The problem is with the clean channel. It works, but the volume control does very little until it reaches the very loudest position. The circuit is very simple, involving IC3 essentially. I replaced the op amp IC3, caps C32, C34, and C29. Checked the operation of Q21 and Q25...they work normally. I checked all resistors in this circuit. In other words, ALL components in this circuit are either good, or replaced with new. Yet, the volume control is still not operating properly. I am truly at a loss as to what to do next!! Any ideas? Would an OPA2134 in place of the TLO-72 solve the problem?

[Helmholtz]

Hi everyone....thought I would write here in hopes of continuing this thread. My situation also involves a Crate GTD120. The problem is with the clean channel. It works, but the volume control does very little until it reaches the very loudest position. The circuit is very simple, involving IC3 essentially. I replaced the op amp IC3, caps C32, C34, and C29. Checked the operation of Q21 and Q25...they work normally. I checked all resistors in this circuit. In other words, ALL components in this circuit are either good, or replaced with new. Yet, the volume control is still not operating properly. I am truly at a loss as to what to do next!! Any ideas? Would an OPA2134 in place of the TLO-72 solve the problem?

Did you consider a faulty vol. pot?

[johnhoef]

Forgot to mention, I also replaced the volume pot!

[Helmholtz]

The pot is not wired like a typical vol.pot. It's in the NFB path of IC3:B and has its wiper grounded. Did you connect the replacement exactly like the original one?
Any change in behavior?

What's the DCV at IC3:B pin 7?

No sense "upgrading" the opamp.

[The Dude]

It's best to start a new thread for your amp.

[johnhoef]

Indeed, not only is the volume put in the negative feedback path, but not even wired in the usual way! The volume pot is indeed wired correctly. It's PC mount, so rather difficult to miswire! Change in behavior? Between the old pot and new? No. The voltage on pin 7 is .012 volts.