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M^3 (Mcubed) Variable Gain

post #1 of 9
3/6/10 at 10:52pm
Thread Starter 
I saw that the M^3 can have a variable gain with another Alps pot where the bass boost pot goes, and it sounds like an awesome idea. I did see though that the C1 values change depending on your gain, so what caps should be put in with a variable gain that will go from 2 - 11?

(Btw, this may be buried in the M^3 forum but I couldn't find it).
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post #2 of 9
3/7/10 at 11:24am
Quote:
Originally Posted by smrtby123 View Post
I saw that the M^3 can have a variable gain with another Alps pot where the bass boost pot goes, and it sounds like an awesome idea. I did see though that the C1 values change depending on your gain, so what caps should be put in with a variable gain that will go from 2 - 11?

(Btw, this may be buried in the M^3 forum but I couldn't find it).
I would guess you would want C1 to be set to the default 5 gain setting of 33pF. But that also depends on which opamp you are using.
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post #3 of 9
3/8/10 at 4:55pm
Thread Starter 
I was just going to use the default AD8610AR op-amps, but I have Grados so I wanted to lower the gain from the stock 11 anyway, and the variable gain was cool depending on what 'phones I have in the future (my old man has a pair of Sennheisers I bought him) plus if I use it for a pre-amp, etc.
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post #4 of 9
3/8/10 at 6:56pm
Use 33pF for variable gain as long as it doesn't go lower than 5. If your want lower than gain of 5, then I suggest 47pF.
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post #5 of 9
3/13/10 at 9:38pm
Would the signal run through the variable gain pot?

Also if wiring it for balanced mode would you just wire up a 4 gang pot to the L/R for each board? Thanks.
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post #6 of 9
3/13/10 at 10:44pm
Quote:
Originally Posted by stew1234 View Post
Would the signal run through the variable gain pot?
Since the pot is in the global negative feedback loop, yes.

Quote:
Also if wiring it for balanced mode would you just wire up a 4 gang pot to the L/R for each board? Thanks.
Yes, see the "Other options" section of the M³ website.
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post #7 of 9
3/14/10 at 1:58am
I feel pretty dumb, I just took another look at the zoomed in board picture and for the longest time I was thinking that for the alps pot 2 pins corresponded to L, R and Ground instead of 3 for L and R. That clears up a lot of my confusion recently over wiring the volume pot for balanced vs. single ended.

Thank you again AMB for the help.
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post #8 of 9
3/14/10 at 3:17am
Thread Starter 
thanks for the help AMB, but on the site it says that using the variable gain you can have a gain ranging from 2-11. What caps should I use for that then?
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post #9 of 9
3/14/10 at 4:02am
If you're asking about C1[LR], use 33pF or 47pF.
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