[finleyville]

Greetings all,

Well I finally assembled my META and am having major problems. When I try to use it there is MAJOR hum from my regulated 18V wallwart and even audible hum from a 9V battery. Also it doesn't amplify anything. Even stripped down without a volume pot and C2/3, I don't hear any music unless it is at max volume from the PCDP. Then it is only very soft.

I re-checked all my resistors and they are the correct values. I don't think I have the trace flaw underneath the board. My voltage offset between the +/- rails is .03V; so no problem there. Luckly I used header pins for all the panel mounted items and socketed almost everything else except C1, C5, D1, TLE2426, Rled. R8 and 9 are jumpered. I even tried switching opamps from the AD8620 to a simple OPA 2134PA thinking it was a poor soldering job to the BD adapter.

With over $125 in parts alone, I don't want to give up on this one. Any help is greatly appreciated. Thanks...

 

[morsel]

Judging from your lack of complaint of sound in one channel only, I'm guessing you have a systemic problem.

Check for solder bridges or cold joints, incorrect component orientation or value, reverse polarity on the power supply, and other common errors of that nature.

With no signal present and the pot all the way down, check power, input, and output voltages at various points in the circuit, including all the ICs, to make sure DC power, ground, and biasing is ok.

Do any of the ICs get hot to the touch? If so, turn off the power while you figure out what is wrong. A hot IC could have a shorted output, or the chip may be dead, or both.

Apply a signal to the input, preferably a 1kHz sine wave, and scope the pot, c1, opamp input, buffer input, and buffer output, noting the signal amplitude. The amplitude on the far side of the opamp should be the input amplitude times the gain.

If you think you have a short, disconnect the power and use your DMM in resistance mode. Remove socketed components if necessary to narrow the list of possible culprits when checking for shorts.

If you don't have a scope, try the AC setting on your DMM. If you don't have a signal generator, use a CD or PC program to generate a sine wave.

Once you have a better idea where in the circuit your problem lies you can scrutinize that area more closely.

 

[finleyville]

Morsel,

Thanks for the reply. Actually at first I did only have sound out of one channel. By working backwards and removing parts, I think it worked itself out... By the way, what does that indicate?

 

[morsel]

If your problem is only in one channel and the other channel is fine, it suggests your problem has to do with the signal path or power of one channel, as opposed to something more systemic such as reversed polarity on the power connections, no power to a dual opamp, etc.