No PAiA Theremax Volume (banging head)

I'm having the exact same problem with my Theremax.

Right now I've got a nice sound coming out with the jumper between the diode and volume pot. But without it, nothing audible until I crank the amplifier's volume WAY up and dial down L4 (volume oscillator). I hear a faint pitch that I can tweak with the pitch control, but still not getting any control from the volume antenna.

Any suggestions on where I can start to look on the circuit to isolate where the problem is coming from?

It seems that your volume osc doesn't oscillate or if it does, not on the frequency it should. You should check this with an oscilloscope.

Many, Many years ago, before I got my first scope, and was building audio kit, the problems of 'no sound' dogged many projects I undertook.. A neat simple tool which helps a lot is a small Piezo (high impedence) earphone.. Put a croc clip on one end, and a resistor (at least 1k, 10k is better, 1M variable resistor is best) between the other end and a probe..

With this, you can clip to ground, and go probing the circuit to find where there is audio, and trace any breaks / faulty pots / wiring errors etc.

But BE SURE you ONLY do this with battery or low voltage circuits!

Fred, I´m not sure he will hear the volume oscillator working at 796 kHz with a crystal earpiece...

I recently bought a UT-81B pocket LCD oscilloscope/multimeter for only 160 EUR from a chinese dealer on ebay. The 8MHz bandwith at 40MHz sample rate is enough for working with theremins and the display is fine when working in stand-alone mode.

The only problem for me is that the included PC optical/serial to usb interface and software work only under MS Windows and I could not yet find a solution running under Fedora8 Linux.

"Fred, I´m not sure he will hear the volume oscillator working at 796 kHz with a crystal earpiece..."

True! :) There are quite a few limitations using a xtal earpiece, and nothing beats a scope.. but, debugging problems on the audio circuitry (after the mixer / filter) where frequencies of 20Hz to 10kHz are present, an earpiece is better than nothing..

I have removed this posting and edited the last - I fear I may unintentionally hijacked this thread.. Sorry!

Fred,
I love the 5/8/2008 4:07:23 PM post about the earpiece tracer! It is now in my bag of de-bugging tricks!

There are many PAiA Theremax 'guys' here at Theremin World that can offer help in this thread, if they can, or want. Coaching a new builder thru a medium experience kit build like the Theremax can be--- well--- a challenge.
I think your particular talents could be best focused on the TheraSynth. ;) Hey-Hey!

Good Luck!

tesaltheremin

"I think your particular talents could be best focused on the TheraSynth. ;) "

Thanks Tesla - You ar right!

I suppose I get into these 'other' threads as a easy distraction from what I 'should' be doing.. It is a form of relaxation rather than 'work'.. Also, it is extremely useful to see the kinds of problems people have with kits.. I intend producing kits, and am compiling a list of frequent problems people are having, so that I can find ways to avoid these on my products.

Main areas I have identified are a)Power supply problems- wrong polarity etc.. I intend to supply my boards with at least a few components fitted, and a bridge rectifier on the power input is a definite (this way no-one could cause difficult-to-fix faults by supplying wrong polarity voltage, or AC).. b) Most problems seem to be related to external wiring - so I will probably supply pre-wired (soldered) sockets and potentiometers etc..

Also, adding a simple debugging tool with the kit might not be a bad idea - And could save me lots of time in supporting people who have construction problems.

All this observation etc does take time away from my 'primary' task - sorry to everyone waiting for the products! .. But I am a pedantic sort of person - And I want to get things as close to perfect as possible!

This is all from me re my stuff - Tesla is right, and I also think I have been guilty of clutterring this thread with irrelevant trivia.