opamp question

[nosamiam]

Hi all,

I'm working on the Bass Paralooper from Moosapotamus' site http://www.moosapotamus.com/paraloop/paraloop.htm and I've run into a snag.

It's doing the gating-and-no-sound-unless-I-give-it-a-LOT-of-signal thing that's described on the FAQ.  That, plus it makes a clicking sound which matches the blinking of my blinking LED.  So I'm trying to figure out what's going on with the opamp(s).  My question is, how are the opamps functioning? Are they linear amplifiers or comparators?  What is a comparator for that matter?  And is there an easy way to tell by looking at the schem? (Ok, I guess that makes it questions.

While I'm at it.... While I was populating the perfboard, I bent a couple of pins on the opamp sockets to hold them in place.  Seeing how well that worked, I just incorporated all the pins into the layout by bending them in the appropriate directions so they would lay flat.  Bad idea?

Thanks for anyone who takes the time to explain this to me

[Paul Marossy]

Bending the pins on the socket usually won't hurt anything. Those are external to the socket itself. Do a google search on opamp comparators and you should get quite a few links about them that will explain what they are.

[niftydog]

what you have there is a fairly crude, low pass filter with buffers all over the place.

almost all of the op amps are "voltage followers". They have no gain - all they do is buffer the signal. (high input impedance, low output impedance)

The last op amp is an amplifier with a gain of 2.

Blinking LED? I am unsure as to what you're refering to, but my guess is that the paralooper isn't the cause of the clicking sound, it's almost certainly the blinking LED that's to blame. If you can live without a blinking LED, just rip it out and problem solved.

There is an "easy" way of telling what an op amp is doing, but it's only "easy" if you know what you're looking for/at. Try reading through some tutorials such as this to get an idea of basic op amp configurations.

Now, some basic troubleshooting is required here. Confirm with a multimeter that all the op amp power pins are getting the proper voltages. Confirm that all the ground points are connected together. Now, my suggestion would be to build an audio probe, or get an oscilloscope. No prizes for guessing which one is cheaper!

Once you have a probe, check systematically through the circuit, listening for audio at each step of the way. Then, you'll have a good chance of finding the error.

BTW, comparators "compare" voltages... in a nut shell. The link I gave you will give you more info.