In Timer, Op Amp & Optoelectronic Circuits & Projects by Forrest M. Mims III there is a percussion synthesizer on page 71. The author says "bell and drum sounds can be produced", but I was unable to make any noise that could be described as a bell or a drum. I followed his tuning directions, but mostly sounds like an out of tune radio. Has anyone built it before? Is it possible that stray capacitance from the breadboard could causing problems? Any other ideas?

 

The schematic

 

The bread board

 

Simulation shows the circuit should work, but the adjustment of R3 is critical. Try with R2 ~= R4, and R3 ~= 30% R2.

 

Thank you for the clue. Your settings do give the best results.

Last night I discovered that the speaker was a significant part of the problem. I am now getting sounds that might be described as a drum.

However, I think there still might be another issue. I suspect stray capacitance from the bread board is taking the edge off of the sound. I am going to try spacing out the components.

 

I doubt the breadboard capacitance is a problem at low audio frequencies. More likely the opamp is clipping.

 

I spaced out the components around R2/R3/R4 and also replaced the used ceramic capacitors with new film capacitors. That improved the sound a lot.

If spacing is not an issue then one of the old caps must have been leaking?

I will look into the op amp clipping.

Thanks again. Do you do a lot of audio work?

 

one of the old caps must have been leaking?

Maybe. Or could have just been a poor contact with a breadboard socket.
No, I don't do much audio work.

 

Hello,

Perhaps you are interested in the PDF's on this page of the ePanorama:
http://www.epanorama.net/schematicsforfree/Audio/Musical/Circuits/index.php

You will find a drum machine and a polytonic percursion synthesizer over there.

Bertus

 

If you are interested in Drum synthisizers...

Here are two drum schematics I found somewhere on the web sometime ago. One is for a tom tom but with some tweaking you could probably make it sound like a bass drum or a bell. It only has 5 components so it´s easy to breadboard (yet I've never done so myself ).

The other one is actually two similar circuits and they sound like two bongo drums or a single bongo hit at two different places. Like the other circuit you can with some tweaking probably make it sound like a bell or a bass drum as well. I've only made a simulation of it but the bongo sound was surprisingly realistic.

And if you have LTspice I included the asc files.

 

Awesome. Thank you very much to both Bertus and Sinus23.