Ok, so I can't get this out of my head and it hurts. I don't even plan on building a preamp anytime soon. Yes, I know things like balance and tone adjustments are out of style but I'm thinking and learning still.
From what I see a preamp is usually input selector -> volume pot -> differential input -> gain stages -> output.
Where would one inject a balance control?
From what I see a preamp is usually input selector -> volume pot -> differential input -> gain stages -> output.
Where would one inject a balance control?
Trying to be helpful, I offer that you should consider the entire signal path, the circuits you are using to control it, and the end goal of a balance control, which is to allow an easy to control gain difference between channels. You can put any of this anywhere, maybe you can fold this function into other parts of the circuit that already exist, maybe it has to be an isolated stage… and so on.
One of the goals of 'nice' analog circuit design, as I see it, is the ability to provide all of the behavior / functionality that you need, while using a minimal set of components and hardware to accomplish that. IMHO, analog always seems to work better when you use minimal circuitry (which is of course able to provide the functions and features needed).
As an example, let's say you have a programmable attenuator style volume control. Your balance control could simply be a gain offset sent to the left and right channel gains, added to the volume control setting. In this case, you don't need a separate circuit to do balance, you just use one variable gain stage to do both volume and balance.
If you're using mechanical pots or mechanically switched attenuators, then you need a separate volume control and a separate balance control, but maybe the two circuits can be blended together to avoid a buffer stage. For example, if you have a volume control pot, you can add a balance pot before or after so that the resistances work out right. If you can't do that, you need to add a buffer between the controls, but again, this should be avoided, and is probably avoidable without much hassle.
I know this is going to partly add to your confusion by providing even more options, when you seem to want fewer, but it's the right way to think about analog circuit design IMHO. Think carefully about how you can provide the function you need with what you already have, or with some otherwise compact and simple (i.e. elegant… ;-) set of circuitry.
Best of luck!
One of the goals of 'nice' analog circuit design, as I see it, is the ability to provide all of the behavior / functionality that you need, while using a minimal set of components and hardware to accomplish that. IMHO, analog always seems to work better when you use minimal circuitry (which is of course able to provide the functions and features needed).
As an example, let's say you have a programmable attenuator style volume control. Your balance control could simply be a gain offset sent to the left and right channel gains, added to the volume control setting. In this case, you don't need a separate circuit to do balance, you just use one variable gain stage to do both volume and balance.
If you're using mechanical pots or mechanically switched attenuators, then you need a separate volume control and a separate balance control, but maybe the two circuits can be blended together to avoid a buffer stage. For example, if you have a volume control pot, you can add a balance pot before or after so that the resistances work out right. If you can't do that, you need to add a buffer between the controls, but again, this should be avoided, and is probably avoidable without much hassle.
I know this is going to partly add to your confusion by providing even more options, when you seem to want fewer, but it's the right way to think about analog circuit design IMHO. Think carefully about how you can provide the function you need with what you already have, or with some otherwise compact and simple (i.e. elegant… ;-) set of circuitry.
Best of luck!
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