CMOY troubleshooting

[jchanhm]

Hi everyone,

I've been lurking on Head-fi for a few years off and on. You guys actually helped me choose my first set of audiophile headphones (HD595s. Loving them

) I've been recently thinking about doing some DIY projects, and last week I ordered parts for a CMOY based on Tangent's guide.

I just finished putting the amp together, and am on the part of the procedure where I use alligator clips to test the amp prior to putting in the panel components. When I did this, I got no sound out of the headphones, so I unplugged it and tested everything out.

Headphones are fine, so are my wires. So I checked the power supply for the amp. I'm getting a little over 5V in and out. Following the schematic, I traced the positive voltage into pin 8 of the op amp, and found that there is no voltage coming out of the op amp, except at pin 4, where it connects to the negative half of the power supply.

(I'm using a cheapo analog multimeter, so I'm not really trying to read the voltage exactly).

Can anyone give me any advice on how I can go about debugging this thing?

Thanks in advance!

 

[tomb]

Couple of things:

What opamp and power supply are you using? An OPA2132 or 2134 requires + or - 2.5V. If you are supplying 5V total, you're right at the minimum before it even goes through the circuit. A CMoy needs at least one 9V battery, two are better. You may not be feeding the opamp enough voltage to work.

About your measurements - I'm not sure you're supposed to get any voltages out of the other pins without a signal. Here's the pinouts for the 2134, but every dual opamp is the same (that a DIY-er might use):

.

If that's not the problem, try posting some photos. Someone usually spots something.

 

[Pars]

Pull the opamp out of the socket. Measure your voltages from pin 4 to virtual ground (center two rows of the board where the 4.7K resistors come together, etc.) and from pin 8 to virtual ground. These should be half the battery each (pin 4 is V-, so assuming a 9V battery should be -4.5Vdc... pin 8 is V+ so should be +4.5Vdc... assuming you have the red lead on pins 4 and 8 and the black connected to ground).

 

[jchanhm]

Oh!!

I just got home from work, hooked up all the clips again... And it works! Not only that, but it sounds really nice from the cheapo headphones I used n___n happy happy.


Anyways, I'm wondering -- If I didn't hook up all of the wires correctly, ie. say I was missing R.out . Would that cut the whole circuit and cause the amp to stop working? I'm guessing not.. In which case, I'm wondering.. Since I didn't change any soldering on the board from the last time I tested my amp, is there any explanation why I would have gotten no output at all before? I know I didn't mess up say, clipping ground to virtual ground, or plugging in r.out into r.in.

 

[Nordic]

Tgats the beauty of learning with these little circuits, if it was a gainclone, you would probably have seen a nice cloud of smoke...

 

[Daroid]

Quote:

Originally Posted by jchanhm Oh!! I just got home from work, hooked up all the clips again... And it works! Not only that, but it sounds really nice from the cheapo headphones I used n___n happy happy. Anyways, I'm wondering -- If I didn't hook up all of the wires correctly, ie. say I was missing R.out . Would that cut the whole circuit and cause the amp to stop working? I'm guessing not.. In which case, I'm wondering.. Since I didn't change any soldering on the board from the last time I tested my amp, is there any explanation why I would have gotten no output at all before? I know I didn't mess up say, clipping ground to virtual ground, or plugging in r.out into r.in.

R_out is only limiting the current, and won't jack your circuit up if you forgot to use it in one of the channels. It could be anything that caused it not to work before, it's hard to say. Maybe V at -ln and +ln was identical.

And a good advice - use your multimeter to check for performance before plugging in headphones. If something is not as expected, you can be sure that it doesn't work in practice.

The only thing you can measure with a multimeter really is the DC-ofset at the output (measuring mV DC ground to left, and ground to right on the output). If it oscillates the opamps will heat up and break sooner or later. An oscilloscope will tell you this right away.