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Using gain to set balance (PPA)

post #1 of 4
2/14/10 at 1:29pm
Thread Starter 
Hi all, I'm about to build a PPA (board is ordered, thanks Tangent!) and had an idea, I searched the forums but couldn't find a single post about it:

I have a slight hearing imbalance and was planning to add a balance control, but what if I socket the R4 resistors and use them to set the gain of each channel in a way it'll account for my imbalance? I could set L-gain to 5.1 and R-gain to 5.0 and then change resistors until it's perfectly balanced. That way I have a ppa custom build for my ears! Is there any reason it will not be possible to use a different gain setting for each channel?

Besides that, does anybody have a recommendation for cheap opamps I can try and experiment with before ordering the expensive OPA627's?
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post #2 of 4
2/14/10 at 10:12pm
if you don't want to add a balance pot the hacker's way would be to tack solder a resistor in parallel with R4 to reduce gain (actually a linear pot to adj 'til you've got it right and remove, measure and then solder the right parallel R)

by paralleling you reduce the risk of the feedback path opening and saturating - possibly burning your Cans with the DC - the pop would be pretty loud too

TL071 is one of the cheapest fet singles that would be reasonably compatible, OPA134 another possibility, AD823 is similar speed to 627 but a dual
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post #3 of 4
2/15/10 at 5:06am
I'd also ask an audiologist whether it's a good idea to throw more SPLs at the damaged ear. That seems likely to make it get worse faster.
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post #4 of 4
2/15/10 at 7:20am
Thread Starter 
Thanks for replies!

I'd like to keep the feedback resistors socketed so I can easily tune the gain later on. So I will solder a pot in parallel with a feedback resistor to set the balance, then measure pot+resistor and pop a resistor with the combined value in the socket. My main concern was whether different gain levels for each channel could lead to adverse effects further down the line.

About the damaged ear: I'll just throw less SPL's to the good ear to preserve it I only listen to headphones at home where it's dead quiet so listening volumes are very low. On all the 'commercial' gear I owned gain was too high making it difficult to set low volumes. Now I can play around with gain and even suit it my ears which is really great.
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