[Tim]

Here's the deal. I have my cmoy all hooked up the a breadboard according to the schematics at Headwize. I'm pretty sure all the components are hooked up right as I've gone through it 2-3 times.

Now, I am using the BurrBrown OPA2134PA opamp. I have a mini to mini with one end hooked to the headphone out of my portable cd player. The other end is hooked to the amp via alligator clips. Alligator clips hook from the amp to a cheap pair of phones as well.

The Problem: I can't hear any music, and when I turn the volume up I here a horrible clickity clack clack click. Painful to the ears.

I have no idea what might be wrong

Please help!

Tim

 

[tangent]

Clicky sounds, huh? That could be a very high level of DC offset, since that basically forces the headphone driver in one direction most of the time, and when the driver pops violently back and forth like that you get clicky sounds. Put a DC voltmeter from ground to one of the output channels to see what kind of offset you're getting.

Also, measure current draw of the amp, or touch the chip after it's been running for a minute or so. Is the chip hot, or is current draw near the max output for the chip? If so, it's oscillating.

If neither of these indicate the problem, start taking the amp apart. First, remove it from the enclosure, if it's encased already. Just put it on the workbench with cables flopping everywhere. If the problem goes away, you've probably got a grounding problem (metal case only) or a weak connection that's stressed when everything's cinched down in the case.

If it still has problems when "naked", unhook the amp section from the power supply and test the power supply. Is it splitting the voltage evenly? In this simple setup, you should get a near-perfect split. Hook it back up to the amp section, then remove the chip and power it up. Measure from ground to V+ and V- -- do you still get an even split? Now put the chip in and re-test. It should still give an even split. Finally re-test with the headphones plugged in -- the split should shift away from ideal, but not a great deal -- 1 to 2V at most, with a 9V battery. If you're getting gross shifts, you've probably got assembly problems -- cold joints, etc.

If voltage is splitting nicely, remove the I/O jacks and alligator clip the bare wires to the headphone and input plugs. If the problem goes away, you melted the innards of the jack during soldering, and now something's shorted. You'll have to replace the jacks.

I've probably forgotten some other common problems, but this list should get you started.

Good luck!

 

[Tim]

Ok I got it working...kinda. There's sound, but it's only coming out of the left channel. I can tell that power is coming through both channels but no sound in the right.

 

[vagicle]

Hi, i'm also working on my first cmoy & i'm having the same kinda problems. It all works fine if i just hook up the input & the headphones with alligator clips, but if i try to hook it up via the input/output sockets with alligator clips coming from the 3 little tabs, i only get sound out of my right channel. I don't think i've shorted them because i haven't actually soldered the sockets yet, and i've tested the voltage and that seems fine too.

any suggestions?

thanks in advance!

 

[jasong]

Try putting just one of the jacks on the amp at a time. If it works with both sides (input and output) alligator clipped, then the amp is working, it would seem that the problem is the jacks. Alligator everything together first, test; then add in the input jack, test; if everything is cool, add the output jack.

--Jasong

 

[vagicle]

okie doke, thanks for that - i've got both channels working now

but now there's a new problem! i keep getting a slight distortion (esp. in the low end) and hiss, which wasn't there when i only had sound coming from the right channel. I've discovered that my voltage split is no longer even (one side is around 4.9, the other about 3.5) for some reason - it used to be even, and sometimes it still appears to be so, but it'll tend to fluctuate occasionally. so i thought that might be why it's getting distorted.

so my main question is - how do i go about finding the bad connection? in the tutorial it says to check the resistance, and i have a DMM, but i'm not entirely sure what range of values i should be looking for. i've tried looking in the archives but can't find anything about *how* i should be checking connections (perhaps this is really basic common sense stuff & hence isn't here!)

thanks - & sorry for being a pain in the butt newbie

 

[CaptBubba]

If you are using the resistor voltage divider in the cmoy article, you are going to get some drift in the power supply levels, allthough that is fairly high. You could try using a railsplitter, use 2 9V batteries, or (as I did on one of my amps having this problem) try fiddling with the resistor values and capacitance until the problem goes away. I had to reduce the resistor values and increase the capacitance and the problem went away for one of my amps.

To see if the voltage offset is what is causing the distortion, you can try this: Use 2 9V batteries instead of one, if this cleans up the sound then you need to focus more on the power section than the amp itself.

Basically, figure out what is working first, then fix what isn't.