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Cmoy testing-is this right?

post #1 of 24
4/10/10 at 4:32am
Thread Starter 
(See post #20)

I just tested my Cmoy amp by using alligator clips and I got sound! But the bass is really lacking and the sound is a little tinny, is that normal (because I'm using clips?) or did I do something wrong?

Will this clear up when I wire up the panel components or should I check something before moving on?

Thanks.

Sidenote: the ground jumper on the board was too short to hook up both clips to it so I hooked one clip to the jumper and the second clip to the first clip. I'm don't really see how that would effect the sound but I'm just checking.
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post #2 of 24
4/10/10 at 8:58am
While alligator jumpers aren't on the list of Audiophile Approved Cabling Solutions, they shouldn't cause huge impacts on sound quality. I think it's more likely that we're dealing with a mismatch between your expectations of what the amp should sound like and what it does in fact sound like.

The easiest test you can make to see if the amp is behaving is to measure the amp's current draw.
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post #3 of 24
4/10/10 at 2:30pm
Thread Starter 
Quote:
Originally Posted by tangent View Post
While alligator jumpers aren't on the list of Audiophile Approved Cabling Solutions, they shouldn't cause huge impacts on sound quality. I think it's more likely that we're dealing with a mismatch between your expectations of what the amp should sound like and what it does in fact sound like.

The easiest test you can make to see if the amp is behaving is to measure the amp's current draw.
When I plug the headphones directly to my source, it sounds better than going through the amp. Since this amp is mainly for learning, I'm not sure if that's normal.

For current draw, I got 10.4mA on my multimeter.
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post #4 of 24
4/12/10 at 1:11am
Thread Starter 
Quote:
Originally Posted by nate911 View Post
When I plug the headphones directly to my source, it sounds better than going through the amp. Since this amp is mainly for learning, I'm not sure if that's normal.

For current draw, I got 10.4mA on my multimeter.
Just verifying this is okay before I continue...
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post #5 of 24
4/12/10 at 1:38am
Quote:
Originally Posted by nate911 View Post
For current draw, I got 10.4mA on my multimeter.
What opamp are you using?

download the data sheet for the opamp. Look for a spec called "quiescent current draw". Add a ma or 2 for the virtual ground (you can get a better number using V/R=I where V=rail to rail and R=BOTH virtual ground resistors {if you used 5Kohms*2 for virtual ground R=10Kohm}) and everything should line up. If it doesn't you have problems *in* the opamp or circuitry around it. If it does make sense your problems are elsewhere Most likely how the thing is hooked up somewhere IME.
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post #6 of 24
4/12/10 at 1:52am
Thread Starter 
Quote:
Originally Posted by nikongod View Post
What opamp are you using?

download the data sheet for the opamp. Look for a spec called "quiescent current draw". Add a ma or 2 for the virtual ground (you can get a better number using V/R=I where V=rail to rail and R=BOTH virtual ground resistors {if you used 5Kohms*2 for virtual ground R=10Kohm}) and everything should line up. If it doesn't you have problems *in* the opamp or circuitry around it. If it does make sense your problems are elsewhere Most likely how the thing is hooked up somewhere IME.
I'm using the one Tangent recommended--OPA2132PA...it seems to use around 8mA looking at the datasheet. I used all of the resistor values he recommended and currently am at a gain of 6 (if that matters).
What's IME mean?
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post #7 of 24
4/12/10 at 2:06am
IME=In My Experience.

with a 2*9V supply, and 2*4.7Kohm Virtual ground resistors that part of the circuit sucks down about 1.9ma.

8ma+1.9ma=close enough to 10.4ma.

I would tripple check all of your connections.

What do you mean with the part about the alligator clip not being long enough to get to the ground jumper?
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post #8 of 24
4/12/10 at 9:41pm
Thread Starter 
Quote:
Originally Posted by nikongod View Post
IME=In My Experience.

with a 2*9V supply, and 2*4.7Kohm Virtual ground resistors that part of the circuit sucks down about 1.9ma.

8ma+1.9ma=close enough to 10.4ma.

I would tripple check all of your connections.

What do you mean with the part about the alligator clip not being long enough to get to the ground jumper?
The place where the ground jumper clips onto the board (the bottom-center of the protoboard)...the jumper I placed is too close to the board and I couldn't clip both alligator clips on it. So I clipped my first one to the jumper as normal, then connected the second clip to the first clip instead of directly to the jumper (because I didn't have room).

I'm running off one 9V battery now by the way.
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post #9 of 24
4/13/10 at 6:41pm
Thread Starter 
Also..I'm using sockets for the R3 resistor so I can find the best gain before I solder it in..would that have any effect on the sound?
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post #10 of 24
4/14/10 at 11:55pm
Unlikely.
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post #11 of 24
4/15/10 at 8:49pm
Thread Starter 
Quote:
Originally Posted by tangent View Post
Unlikely.
Okay. I may just be expecting more of the amp I guess

Thanks.

Also, grounding wise, is coating the bottom of the tin with electrical tape sufficient?
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post #12 of 24
4/15/10 at 10:32pm
You'll need to either sand the sharp bits off the bottom of the board (not sand flat, just sand blunt) or use 3 or so layers of tape. A common failure mode seen with mint tin CMoys is that they fail when you squeeze the amp, and it's due to sharp bits from trimmed leads pushing through too little tape insulation.

Something tougher like 10 mil plus Teflon or poster board is a better idea.
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post #13 of 24
4/15/10 at 11:13pm
Thread Starter 
Quote:
Originally Posted by tangent View Post
You'll need to either sand the sharp bits off the bottom of the board (not sand flat, just sand blunt) or use 3 or so layers of tape. A common failure mode seen with mint tin CMoys is that they fail when you squeeze the amp, and it's due to sharp bits from trimmed leads pushing through too little tape insulation.

Something tougher like 10 mil plus Teflon or poster board is a better idea.
Alright; I'll just use some Teflon tape on the bottom of the tin then. Thanks!
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post #14 of 24
4/16/10 at 1:38am
That'll be like 2 mil. It's also difficult to handle that thin; 5 layers doesn't sound like fun to me. I'd rather use electrical tape. Or, better, poster board.
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post #15 of 24
4/16/10 at 10:48am
Thread Starter 
Quote:
Originally Posted by tangent View Post
That'll be like 2 mil. It's also difficult to handle that thin; 5 layers doesn't sound like fun to me. I'd rather use electrical tape. Or, better, poster board.
Oh, forgot about the 10 mil part heh. Poster board sounds easier to find I think...thanks.
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