Hi,
I have a problem with a amp I'm building wherein the signal is heavily attenuated if I have a balance pot in the chain.
The chain is: a tone control, the balance, then an ACP+ with a 20k volume pot.
Heavily attenuated means ~1/3 the output level from the amp with the balance in the chain compared to it removed. I know the balance will attenuate a bit (and I see that when testing it in isolation), but not this much!
I've attached schematics of the tone control and balance.
I have a sneaking suspicion the problem is the impedance of the balance pot compared to the ACP's volume pot but I still haven't deeply understood the interaction of impedances practically.
I'd be grateful for ideas to fix this. I'm tempted to just build an active version (as per Doug Self's small signal book) but wonder if it could be done passively (and whether it'd help).
I have a problem with a amp I'm building wherein the signal is heavily attenuated if I have a balance pot in the chain.
The chain is: a tone control, the balance, then an ACP+ with a 20k volume pot.
Heavily attenuated means ~1/3 the output level from the amp with the balance in the chain compared to it removed. I know the balance will attenuate a bit (and I see that when testing it in isolation), but not this much!
I've attached schematics of the tone control and balance.
I have a sneaking suspicion the problem is the impedance of the balance pot compared to the ACP's volume pot but I still haven't deeply understood the interaction of impedances practically.
I'd be grateful for ideas to fix this. I'm tempted to just build an active version (as per Doug Self's small signal book) but wonder if it could be done passively (and whether it'd help).
Attachments
You have a 100k pot and 33k. The dual gang pot has to be centred (50k + 50k) for equal output from each channel. That gives around -3dB attenuation.
If you now load the wiper with the 20k volume pot you drop the level by around -8dB. If you drop the values by a factor of ten (10k pot and 3.3k) you get to around -3.5dB attenuation.
If you now load the wiper with the 20k volume pot you drop the level by around -8dB. If you drop the values by a factor of ten (10k pot and 3.3k) you get to around -3.5dB attenuation.
I did a lot of research here on balance pot but ended up just using one of these
https://partsconnexion.com/audio-note-100k-ohm-stereo-balance-potentiometer/
problem for me was solved I stopped over thinking it
https://partsconnexion.com/audio-note-100k-ohm-stereo-balance-potentiometer/
problem for me was solved I stopped over thinking it
Thanks @Mooly. I didn't mean for this to be a tutorial on how to calculate this (which I'd like to be able to do for my understanding), but I happened on the post below (here) by you so I hope it's not too large a request to ask if you could explain...
I would think in this case I replace the 3900 Ohms with my balance pot arrangement and the 430 Ohms with my 20k pot. However, I can't reproduce the -8dB you quote with any arrangement of half-track and 33k resistances in the balance pot that occur to me. Could you explain how you got to -8dB please?
I would think in this case I replace the 3900 Ohms with my balance pot arrangement and the 430 Ohms with my 20k pot. However, I can't reproduce the -8dB you quote with any arrangement of half-track and 33k resistances in the balance pot that occur to me. Could you explain how you got to -8dB please?
From what I understand yes
heres more about itAudio taper (logarithmic):
This design ensures a smooth and even volume change throughout the rotation of the knob, providing a more natural listening experience.
Stereo balance precision:
Designed specifically for stereo applications, it allows for accurate left-right channel balance adjustments.
a bit more about it
feature a conductive track made from thick silver, a wiper made from solid silver and heavily silver plated connection pins.
feature a conductive track made from thick silver, a wiper made from solid silver and heavily silver plated connection pins.