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C-Moy Question

post #1 of 9
Thread Starter 
I have made a cmoy and it works fine. I currently have a gain of 5 but still use less than quarter turn on the volume control to take the volume level up to suitable listening levels. I would therefore like to make it unity gain. However I am a little unclear on how to do this. From what I have read this involves shorting the R4 resistor (see link). Is this correct? My other question is (if i'm right about the first bit). Does it matter what the value of R3 is?? This is probably a really dumb question but any help is appreciated

TestSpecimen

http://tangentsoft.net/audio/cmoy-tu...angent-sch.pdf
post #2 of 9
Unity gain simply means that an OPAmp will work with any gain level you use. If you want a gain of 1 then just jumper where you would normally have a resistor. You can try jumpering it but if you get excess noise then try a gain of two. remember that if you get headphones with a lot of impedence (ohms) then you might end up changing that to a higher gain later.
post #3 of 9
Thread Starter 
I'm still a little unclear. Yes i want a gain of 1, but do i jumper R3 and R4? or just R4?
post #4 of 9
If you want unity gain in a cmoy, just remove R3. Be aware, though, some opamps won't be stable at unity gain. No problem with OPA2132 or OPA2134, but if you're using other opamps, be sure to read the datasheet to determine what's the minimum gain required.
post #5 of 9
Sorry to sidetrack your thinking - Are you using a audio log or linear log pot? The linear log pot will cause the volume to increase too quickly.
post #6 of 9
Thread Starter 
Ok thanks. I have OPA2132, OPA2134 and OPA2227P which i think are all unity gain stable so i should be ok
post #7 of 9
Thread Starter 
not sure what those are but i'm using the ALPS 10K (RK097) pot recommended in the tutorial
post #8 of 9
Looking at your sig, it appears all you're using with the CMoy right now are IEM's - fairly efficient ones, at that. You may want to live with that quarter turn until you get one of those headphones on your wish list. You'll need the rest of it then - or a lot more than 1/4 turn, anyway.
post #9 of 9
Thread Starter 
Yeah maybe, but thats a dreamy wishlist and i'm a student so it could be a while. Anyway it will be easily reversible so i'm not too bothered. I like messing about with stuff like that anyway
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