Volume control

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I'm partially deaf in one ear, not many headphone amps have balance controls or volume to adjust l/r channel level. Anyways I wondering if would be possible to build something so I can individually adjust l/r channel volume?
Any ideas or suggestions?

With the O2 headphone amplifier here

http://nwavguy.blogspot.com/2011/08/o2-details.html

http://www.diyaudio.com/forums/headphone-systems/193977-objective2-o2-headphone-amp-diy-project.html

the voltage gain on each channel is set by a resistor you can change (R17 & R21 for the low gain setting in the schematic in that first link). If you make that change once to match what the "bad" ear needs then the two different gains will track as the volume control is turned up or down.

If your input source level is high enough that you don't really need voltage gain (many O2's are built with 1x gain and just used as a current buffer) you can use a 10K resistor in place of the 274R input resistors and 22pf in place of the 220pF input RF filter caps (R3, R7, C11, C12), which will form a 50/50 voltage divider with the O2's input 10K resistors. In other words it will knock the source signal down by half. You can then re-amplify it with the gain settings as need be, such as 1x for the "good" ear and 1.5x for the other.
 
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You could also have a pot for your good ear on the input. A good cheap pot, like a Panasonic EVJ, can be had, with panel mount parts, for $2. The greatest problems with these pots are channel imbalance and scratchy noise when changing volume (even if capacitor-smoothed). Since it shouldn't need much adjusting, and will be used mono, that's no big deal.

A stereo volume control is two potentiometers sandwiched together, and with a single wiper mechanism. They are usually installed right at the input, or between the preamp and buffer. Between the pre and buffer has some benefits (like being quieter, typically, when turning the knob, and keeping the input impedance apparently very high), but right at the input is not going to break anything.

Instead of a PCB-mount input jack, use a panel-mount for the input, wire the good ear's channel to it, then the output of that channel to the amp board's input. Just in case, wire from the other side's input in parallel to the amp input, to have matching left/right impedances, in case too much mismatch would do funky things with the source. If more than an inch or so of wire is needed to make it work, be sure to twist separate signal and gnd leads to and from the pot.

You could also have both channels adjustable, with two pots on the input, of course, simply ignoring one channel on each pot.
 
You can actually buy finished headphone amps with separate left and right volume control as wel, e.g. these guys have been offering corresponding versions of their headphone amps for many years. Technically it's not hard and basically amounts to splitting one stereo pot into two single ones (or just using one of two sections each if you can't find single log pots). You can do this with most any (DIY) headphone amp that uses a (wired) volume pot. The O2 is normally intended for use with a PCB-mounted pot, but people have been putting them in larger enclosues with wired pots as well.
 
I'm partially deaf in one ear, not many headphone amps have balance controls or volume to adjust l/r channel level. Anyways I wondering if would be possible to build something so I can individually adjust l/r channel volume?
Any ideas or suggestions?

I have the exact same problem. Sucks, doesn't it? Years of being a musician are to blame for my ~40% loss in my left ear. I don't know if you're opposed to building a simple headphone amp or not, so here are some solutions I've come up with:

The first headphone amp I built was a Cmoy and I built it with separate left and right volume controls rather than a dual volume control. Worked pretty well as far as the balance problem, but as far as sound quality, I wanted more.

As agdr mentioned, the O2 is an option. I messed around with the gain resistors until I found what worked well for me. (In fact he may have given me this idea....)

Another thing I tried was simply a piece of perfboard with two audio jacks, a pot for the right channel, and pass-through for the left channel. Use the pot on whichever side you hear better out of, so you can reduce the volume to match the volume on your bad ear.

Hope this helps. PM me if you'd like, hearing loss/degredation sucks.

EDIT: I forgot to mention that, at least in my experience, it's better to reduce volume to your good ear rather than amplify the bad ear. I've destroyed a very expensive pair of headphones by over-amping my bad side.
 
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I'm partially deaf in one ear, not many headphone amps have balance controls or volume to adjust l/r channel level. Anyways I wondering if would be possible to build something so I can individually adjust l/r channel volume?
Any ideas or suggestions?

Agreed, just attenuate the good side to match the other. Since the relative good/bad attenuation would be fixed,
you could just use one resistor in the right place, where (and whether series or parallel) depends on your components.

It could be as easy as hacking it into one side of a pair of RCA cables. You could use a pot first, adjust it for the best balance,
and then replace it with a resistor.
 
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