[thedoctor]

Quote:

Originally Posted by Eisenhower I fixed the tle and mounted the opamp correctly, nothing gets hot anymore But, I tried hooking up a pcdp and a pair of cheapo headphones like tangents guide said and when the battery isnt hooked up, it sounds like just a pcdp, but when the battery is hooked up, the signal gets very faint and crackley.

been so long since i've built my CMOY, but isn't you supposed not to hear anything without the battery plugged in?
and do you have a multimeter with you? do check for DC offset. if you're using the same Opamp as before, then most probably it's already dead when plugged in the wrong way.

 

[The Monkey]

Are you using the same opamp as before? I think it could be fried. Try another.

 

[Eisenhower]

I swapped it out. Ill check the DC offset, how much is too much?

 

[thedoctor]

Quote:

Originally Posted by Eisenhower I swapped it out. Ill check the DC offset, how much is too much?

20mV perhaps? that's the first sign something is wrong.

you have a multimeter? good. my usual steps to check amps :
- check the voltage to the Opamp +ve pin (grounded to virtual ground/signal ground, both input and output jack is doable).
- check the voltage to the Opamp -ve pin (also grounded to virtual ground).
- plug an Opamp in, and check for DC offset.
^ do this with a source plugged in, without a headphone plugged into the amp.

the +ve and -ve voltage should sit close to each other (maybe about 5% if you use resistor divider, less if you use TLE2426). if it does not, check the voltage divider, the TLE might already be fried.
if the virtual ground is sitting at half the voltage, and DC offset is normal, then there's a wiring problem. check your wiring.

 

[Eisenhower]

Quote:

Originally Posted by thedoctor 20mV perhaps? that's the first sign something is wrong. you have a multimeter? good. my usual steps to check amps : - check the voltage to the Opamp +ve pin (grounded to virtual ground/signal ground, both input and output jack is doable). - check the voltage to the Opamp -ve pin (also grounded to virtual ground). - plug an Opamp in, and check for DC offset. ^ do this with a source plugged in, without a headphone plugged into the amp. the +ve and -ve voltage should sit close to each other (maybe about 5% if you use resistor divider, less if you use TLE2426). if it does not, check the voltage divider, the TLE might already be fried. if the virtual ground is sitting at half the voltage, and DC offset is normal, then there's a wiring problem. check your wiring.

Alright, I finally got around to checking connections. just to clarify, I measured them by putting the dmm's ead on the jumper on the bottom of the board (virtual ground, correct?) and the positve on whatever pin (with the battery connected, with the opamp out)

Im not sure which pins +ve and -ve are,
but, with the battery at 7.9 v,
at pins 4 and 8 I measured 3.93v
The rest of the pins measured 0 or .01mv

For the TLE, I measured voltage from virtual ground to the leads, I measured 3.93 on both.

 

[The Monkey]

What opamp are you using?

 

[Eisenhower]

Quote:

Originally Posted by The Monkey What opamp are you using?

opa2134pa

btw, just to make it clear, the opamp isnt hot anymore, the problem is that when I hook up headphones, the sound is very distorted and fainter than without the battery hooked up.

 

[Fiola]

wow, it's been a while eh? I thought this thread looked awfully familiar, heh.

Anyways, like thedoc said, i don't think your suppose to hear anything if the amp is not on but with source connected. So, given that, I would say you have shorts on your implementation and thus things are going wonky. try tracing through all the points with your meter (assuming you have one) on continuity mode and see if it beeps where it shouldn't have.

 

[Eisenhower]

I couldnt find any shorts with my MM, I also traced the back with a razor to get rid of any bridging. didnt fix it though.
Maybe I fried something, are my pin readings okay?

btw with both the battery and opamp out music still plays through it

 

[Pars]

Your voltage split is OK, at least without phones plugged in, but since you are using a TLE this shouldn't be an issue. Pin 8 is V+, pin 4 is V-. I assume that on pin 4 you were measuring a -2.93V (black lead on V ground, red on pin 4)?

Also, remove the opamp from the socket, and with the amp powered off (no battery) with your DMM ohm out each socket pin to Vground while consulting the schematic. If any value seems odd, figure out why. Look at this post for some info. Also, ohm adjacent pins out to each other. You should not find any continuity, at least low (< 10 ohms) readings.

 

[Scimmia]

Get a resistance reading from the input on the amp side of the input cap to the output, it should be = R2 + R3 + R4, as far as I can tell from the schematics. That should be enough resistance that you wouldn't hear it bleeding from input to output without power, or it atleast should be VERY soft. If you can hear it, the reading's probably pretty low, in which case you can step through it, eliminating one resistor at a time to find out where the problem lies.

Edit: That's with source, phones, and battery disconnected, and opamp out.

 

[Eisenhower]

Alright I got some more measurements.

first I checked the resistance of each pin to ground:
pins 5 and 3 at 10.93 k ohms***
pins 2 and 6 at 1.003 k ohms

If Im right, according to the schematics, shouldnt pins 5 and 3 read at 100 kohms?
/\just to clarify, Im presuming pins 5/3 are + In, and pins 2/6 are - In.

Also I did as scimmia said, I measured from the inout lead of the cap to the output of the matching side, It read 2.6 M ohms for the right and 2.4 M ohms for the left. capital M for mega. Thats large enough, correct?

 

[Eisenhower]

I fixed it...

or rather, it wasnt broken at all...

...I was hooking the source up wrong

Thanks for your help all, I apologize for being an idiot.

 

[Pars]

Quote:

Originally Posted by Eisenhower Alright I got some more measurements. first I checked the resistance of each pin to ground: pins 5 and 3 at 10.93 k ohms*** pins 2 and 6 at 1.003 k ohms If Im right, according to the schematics, shouldnt pins 5 and 3 read at 100 kohms? /\just to clarify, Im presuming pins 5/3 are + In, and pins 2/6 are - In.

Yes. Are you sure you have 100K for your R2s? These need to be a minimum of 10x your pot value.

Quote:

Originally Posted by Eisenhower Also I did as scimmia said, I measured from the inout lead of the cap to the output of the matching side, It read 2.6 M ohms for the right and 2.4 M ohms for the left. capital M for mega. Thats large enough, correct?

The information that scimmia posted is incorrect. With the opamp out, you should see an open between pins 3 and 5 (the + inputs) and the outputs (pins 1 and 7, IIRC). With the opamp in, who knows... probably depends upon which opamp it is, and probably isn't relevant or discernable anyhow. I would also check to make sure that you get ~10K when ohming between the - inputs (pins 2/6) and the outputs (1 and 7) to ensure that you have the correct gain resistors (R4) in. If you get an open, you are missing R5/jumpers, but since it sounds like you have it working, I guess these must be in.

 

[Eisenhower]

It works great,

one last question, My alps pot/switch is backwards, IE when I turn it on it starts out at the loudest setting, then tapers down.
Did I just solder my wipers in backwards? should I just switch them?