removing sound controlls...

[trigger]

ok i have an old amp here that i am just tinkering around with, i am removing the sound controls(bass, treble, and balance).

ok my question is, when i remove the pot, (has resistors connected) can i measure the resistance of the pot (with resistors) and replace the pot (with resistors) with a new resistor and expect the same sound that was produced when the pot (with resistors) was in the circuit? is it that simple or i am i over my head here?

the amp has 2 el84, 2 12au7 and the amp will most likely be salvaged for parts but for now its just a project to keep me busy.

the area circled in green is what i am removing.

[wicked1]

We usually remove the tone controls because we want a shorter signal path, and nothing messing w/ the sound. So in that case, you'd find where the signal enters the tone control circuitry, and where it exits, and take out all the stuff in between. You might have to study some schematics before you understand what's going on w/ all of it. Unless you have the schematic for that amp. Then post it here.

I've just been reading about tone controls and have this link handy..
Tone Controls
it might show you what you're looking for. And in your case, most of the tone shaping circuitry will be in those red/maroon rectangles attached to the pots.. you probably wont find all the individual caps and resistors cause they're potted in that rectangle.

[adason]

trigger,
what you are about to do will most likely sound the same, or very similar, so similar that you might not even hear the difference
if you want cleaner sound, you want to bypass the tone controls completely

[pointy]

you can replace all the resistors in the amp.....................and it will sound better!

[Soonerorlater]

Trigger,
Even with your tone controls set flat your tone controls may still attenuate your signal. Bypassing them might therefore increase the signal carried to the next stage.

Also, some amps with tone controls have an extra gain stage to compensate for the attenuation caused by the tone controls. This stage would also become unnecessary. Without a schematic its hard to tell. The valve line-up and picture suggests you have a nice single-ended stereo amp. Can't resist a little speculation here but one side of the 12au7 may have been used as the extra gain stage for the tone controls.

As for removing the balance IMHO this should be considered as a separate issue, I'm just an old Noobie so I welcome any corrections from the more venerable on this forum

Best Regards
Bill

[trigger]

well after removing the yellow circled area, i am experiencing the issues mentioned by bill above.
after removing the balance control pot i am experiencing the fact that the amp dose not fire up until the signal is grounded for a second.
the second is perhaps an extra gain stage as bill also mentioned, after removing the tone controls (with resistors) the amp became much louder and sharper, losing some of the low end.
any help is appreciated, though i am experimenting and will sort it out, i may draw up a schematic. thank you for the advice, this form ROCKS!

[Soonerorlater]

Trigger,
First off, congrats on your pot surgery and double congrats on solving the problem its removal caused. I wonder though whether or not you have removed all the tone shaping circuitry. From your picture it looks like you have from the left a dual volume pot followed by bass and treble pots then a single balance pot and then the switch. Both bass and treble pots need to be bypassed along with their capacitors and resistors (inside the red/maroon rectangles as wicked1 says) Be careful not to remove by mistake any capacitors directly in the signal path that are there to block Dc from getting through to the next stage.

On the other hand perhaps you would rather rest on you laurels having satisfied your curiosity about tone controls.

If it was my amp I would solve the problem of those poor tolerance resistors (and those suspicious looking ceramic capacitors) by gutting all of the signal circuitry and replacing it with one of the many schemes designed and developed by the members of this forum,

Best Regards Bill

[trigger]

i am currently stumped,
the balance pot i removed has 3 wires, 2wires(stereo signal) 1wire ground(center lead on pot).
the 2 signal wires need to be grounded out for a second in order for the sound to be amplified?
this confuses me, is a resistor needed? any thing that will help me better understand whats going on with the balance control, will be much appreciated.

[rotaspec]

Originally Posted by trigger

i am currently stumped,
the balance pot i removed has 3 wires, 2wires(stereo signal) 1wire ground(center lead on pot).
the 2 signal wires need to be grounded out for a second in order for the sound to be amplified?
this confuses me, is a resistor needed? any thing that will help me better understand whats going on with the balance control, will be much appreciated.

It may be the amp is now be oscillating at frequencies you can't hear, and stops once you ground the stage. You are then getting signal in there before the oscillation can start again, then negative feedback is taking over and preventing the oscillation starting again.
A resistor to ground could very well help, but without a schematic it would be hazarding a guess as to what value. If it's from a grid to ground, around 500k would be a starting point. A small grid stopper (a few hundred ohms to a few k) in series with the grid signal, positioned as near to the grid pin as possible, is also a good thing.
Once sorted, a little SE amp like this can sound VERY good. Just don't expect huge bass response with those little o/p transformers.
I have a SE amp with one ECL86 per channel (essentially a 12AU7+EL84 in the same envelope) that came out of a console, and after a few mods it sounds fantastic.

Gary

[kavermei]

Please post a schematic, without it we're just shooting in the dark!...