[rokk]

I just got the last component for my PIMETA amp, and it seems to work just fine except for an loud humming in the right channel. It's much more audiable in my grado cans than my old sennheisers.

i've looked over the design/layout but i cannot seem to find what i did wrong.

I wish a had a digital camera to take a pic of the PCB.

Anybody got suggestions about what to try?

 

[n_maher]

How about a list of things you've checked so far?

For starters:

Check for shorts, bridges, cold joints?

Power supply voltages at opamps?

DC Offset?

 

[rokk]

I checked all the solderings and i can see no shortcurcuits. Another i noticed now is that the opamps are getting Hot. They should not be warm to the touch.
So something is indeed wrong.

I cannot check the DC offset etc right now as my multimeter is not in the apartement atm, i gotta wait til my friend who borrowed it comes back.

Thanks in advance,

 

[n_maher]

Quote:

Originally Posted by rokk I cannot check the DC offset etc right now as my multimeter is not in the apartement atm, i gotta wait til my friend who borrowed it comes back.

Unfortunately I think that means you are stuck waiting to trouble shoot the amp. There isn't much we can have you do without a DMM.

Nate

 

[rokk]

Quote:

Originally Posted by n_maher Unfortunately I think that means you are stuck waiting to trouble shoot the amp. There isn't much we can have you do without a DMM. Nate

Figured, Just thought i'd give it a shot to try to see if i overlooked something.
I'll see if i can get the DMM back during the weekend.

Btw. I'm using AD843's but i guess that does not matter?

Thanks again for your response!
I'll get back with a DMM.

 

[NeilR]

A lot of humming issues seem to be related to incomplete ground paths, especially the inputs. When you get your meter you might want to measure continuity of the input grounds to the board's ground plane. You should measure the input side ground from the other end of an interconnect plugged into the input to make sure everything is sailing right through that long "signal" path.

 

[FallenAngel]

Just a little note, the AD843's run pretty hot, they shouldn't be burning hot, but they do run some warm temps.

 

[rokk]

Quote:

Originally Posted by FallenAngel Just a little note, the AD843's run pretty hot, they shouldn't be burning hot, but they do run some warm temps.

That explains some of my worries as i've never used the 843's before!
Would some kind of heat dissapation do them well or are they ok being pretty warm but not really Hot to the touch

 

[ATAT]

843s are fine warm.. rule of thumb for me is that an opamp shouldn't dissapate enough heat to cross teh threshold of pain.

Basically, touch the potentiometer.. does that stop the buzz? then its a grounding issue.

 

[rokk]

There is no reduction or change in the noise if i touch the potentiometers casing or metallic knob. The noiselevel seems to be static as well, it does not increase when the volume is increased.

 

[rokk]

I've had it running for a while now afterbi solved the problem (it was a defective DIP8 socket it seems). And it runs pretty hot, the opamps that is, i can touch it but if it gets hotter it'll be pretty hot to the touch. So it seems to runs Hot rather than warm. Would cooling be an alternative or should i just leave them be?

Update: i can still touch them but it aint so pleasant anymore...
Should i grab some heatsinks?

 

[rokk]

Seems i'm having bad luck with this PIMETA.

It worked fine and sounded pretty good for some while now.
But i decided to take it out of the box for replacement of 4 capacitors, but when it was out i decided to listen some before the change and it gives weak sound on one channel and the other is VERY weak and starts distoring with a continues LOUD cracking noise which spreads across both channels and you have to turn it off.

I'm checking whatever i can check now, but everything seems to be in order strangely enough.. still have'nt got my DMM back :\

Hope not one of the opamps are 'dead', you can hardly buy them in sweden..
And the buffers are just silly high priced.

 

[Polaris111688]

If the capacitors didn't explode or anything, check to see if you have any of them in backwards.

 

[tomb]

If you had it in a case and it worked OK, then pulled it out and before changing anything else, it was messed up - the standard answer is a bad solder joint/loose connection.

 

[The Monkey]

What kind of case, if any, is it in?

Also, I see that you don't have a digital camera, but do you have a scanner?