mic headphone amp base on cmoy

[severthee]

good day, i recently built a headphone amp for 2 mic using the simple cmoy design.i split the left and right input into xlr 1 and xlr 2. each has their own 10k pot.i dont know how to wire them balanced so i just shorted ground and cold of the xlr for now. .

i added a spdt switch right next to the xlr input hot wires , to switch between split mono (hard panned to left or right) or stereo(dual mono or mixedsignal?).the stereo mode is a bit weird, because the levels of both mic are affected.

i moved the spdt switch to the headphone output. while it was doing what it was supposed to do in stereo(mixed signal on both left and righ ear) levels of xlr 1 and 2 are independently controlled. the sound was dull, lots of noise, distortion. i am not sure how to describe it. out of phase perhaps?

should i move the spdt swich right after the 10k pot to achieve what i want? both xlr signals on both left and right ear, but volume is independent from each other.

did some reading and found a thread in another forum where it was suggested to invert the cmoy to be a 2 channel summing mixer. how do i go about this? does that mean i direct xlr 1 to input A + of the opamp and the xlr 2 to input B-?? or xlr1 goes to input A+ and xlr2 to he input A-?

lastly, one of the xlr needs to be send thru, so i did a parallel wire to the xlr out. i realized that there will be a long xlr going to the PA. I was wondering how to wire that xlr to the opamp as a balanced wiring (hot, cold, ground) because right now i shorted the ground and cold pins to test and make the mic headphone amp to work.

looking forward to any suggestions.thanks in advance!

p.s. im using the same exact schematic for cmoy, no change in values. i just change the input to two xlr. using a TL072 for now but it needs 18v to

[J M Fahey]

Please post the schematics you are talking about.

No clue about what "cmoy" means .

Thanks.

[pdf64]

Yes, it may be obvious to you what you mean, but different people will interpret your text differently.
Sketch out the full schematic of what you've built, take a good photo / scan of it of the sketch, upload it to a hosting site and provide a link.
I built a few cmoy amps some years ago and can't now remember the circuit. But its performance / operation will vary according to the particular op amp used, implementation, and power supply.
So detailed photos of what you've built may be useful.

[severthee]

Thanks for the reply

here is the schematic
http://tangentsoft.net/audio/cmoy/mi...angent-sch.pdf

and here is the layout
http://tangentsoft.net/audio/cmoy/mi...ayout-0150.pdf

only thing i changed is i took out the 3.5mm stereo jack and dual gang pot. I split it to two xlr with a 10k pot each xlr

[pdf64]

... i moved the spdt switch to the headphone output. while it was doing what it was supposed to do in stereo(mixed signal on both left and righ ear) levels of xlr 1 and 2 are independently controlled. the sound was dull, lots of noise, distortion. i am not sure how to describe it. out of phase perhaps?...

I think that you may have connected the outputs of the opamps directly together?
If so, bear in mind that opamps will tend towards zero output impedance, so each will tend to short the other to ground.

I suggest that you change it back to switch the inputs to mix the channels; add a resistor, eg 1k, between each input socket and its 10k volume pot.
Connect the shorting switch for mixed channels across the node of the 1k resistors and 10k pot.

[Enzo]

OK, I see what we are discussing, but what is "CMOY"? Someone's name?

[Jazz P Bass]

CMOY was developed by Chu Moy.


https://en.wikipedia.org/wiki/CMoy

Here is the "Bass Boost" version.

cMoyBBx203R_Schematic.pdf

[severthee]

yes it's Chu Moy

@pdf64 i put the spdt back at the inputs but the pots were acting on each other.. havent tried your resistor suggestion yet.
but when i moved the spdt right AFTER the middle lug of the pots and before the C2, it seem to be working how i wanted (both xlr1 and xlr2 are now coming out of both left and right headphones. with the 10k pot independently controlling their levels). the only quirk is, when the pots are anywhere 7 to 9 oclock(7 being the minimum or 0 volume) they're shunting each other to the ground. but anywhere passed 9oclock, the inputs are independent of each other

i will have to try the resistor as suggested

lastly, any ideas how to wire one of the xlr into a balance signal? do i have to duplicate the 10k pot, c2 ,r2 and just connect it to the negative input A of the opamp?

[diydidi]

I think you are better off converting the balanced signal from the mic to a unbalanced signal first. Use one opamp for each XLR input. Besides you'll gain 6db's by doing this. Then you can add a pot on each opamp output, and then feed each pot to a summing/ mixing circuit. This will use 2 opamps per channel. You can configure the last opamp for some gain.