Audio Output Problem - loud cracking and barely audible tone.

Update - It wasn't (at least not entirely) the ESPE01.  Although the tone output is normal volume now and is modified by motions over the volume antenna, the crackling sound was still there.  I performed the volume tuning procedure again (we still only get -10v to +10v on U3 pin 12).  After doing that (the depth of the slug did not really change that much from where it had been previously) the unit is back to not producing sound other than the crackling. 

rsutor said: "Frustrating as this has been it was fun to work on and I really appreciate the help!"

The theremin has attitude, always treat her with respect.

crackling is an interesting symptom. If it is coming from the power supply section you should hear it in the sound over the AM radio.

If not it is in the audio section which begins at pin 7 Audio to the 1/4" jack.

You said -Shorting the +12v pin to the VCA Out pin causes the crackling to be louder but does not alter the theremin tone at all.
So doubt it is in the Volume Control section, since your adjusting it you may have created a volume issue. Do the above VCA to +12 short test again. Leave it that way until you get your theremin tone back and you fix the crackling. This bypasses what the Volume Control circuits do.

If the LM13700 is in a socket maybe re-seat it. Sweep your Waveform and Brightness knobs to each side.

I hate troubleshooting. Anytime a theremin gives a day of satisfaction it is a real treat.

Christopher   

rsutor, have you tested the continuity of the RF chokes on the volume side?  They have really fine wire and are easily damaged.

Beyond that, I think you'll need a scope to get to the bottom of this.

Love your avatar!

Dewster yep.  The chokes on both sides have continuity all the way through to their respective antennas.  At this point, I think Im agreeing with you that diagnosing further is beyond my skillset and available tools.  This board looks to be for an etherwave standard (theres a diode attached across the terminals that wasnt on the board in the one I have).  Can I remove that diode and use it as a replacement mainboard for my etherwave plus?  As much as I feel replacing the mainboard is cheating, its cheaper than buying an oscilloscope.

Thanks,
-S.

They stop selling that board 10 years ago, it would be great to know if it is available again. The webpage has changed a bit. I keep asking with no response does Moog sell parts? Why would they not? You could remove the six antenna coils and sell the set for $100 on ebay and get your money back for a new board.

Christopher

well hell.  Yep.  That button says "Notify Me"  not "Add to Cart".  Durnit!

Did you remove the ESPE01 wire from the pin 7 Audio connection. This is where the crackle noise can easily be injected.

Christopher

I fully removed the ESPE01.  To install it, you lift the leg of C6 nearest to and the leg of C2 furthest from the header connection on the mainboard and connect the raised leg to a lead coming off of the ESPE01.  You then remove the Audio cable from the header and solder it to an open hole on the ESPE01 then drop the module into the header connections on the edge of the board soldering ground, -12v, +12v and the audio pin to the pads on the headers.  When I removed it, I removed the audio wire from it, disconnected C2/C6 from the leads and reattached them to their positions on the board, then removed the ESPE01 from the header pads and lastly reattached the audio wire to the audio header pad where it was originally.  This reset the physical configuration of the EW back to its pre-install condition. 

Interestingly enough, Im not sure if this is a recent addition (I suspect not and I just missed it) but on the product page for the ESPE01 there is a warning that says:
"Important! 
The latest production run of the Etherwave circuitboard and the ESPE01 module seem not to be compatibel. Please do not install the module if you have a new Etherwave Standard or PLUS. By approximation this warning concerns Etherwave PLUS theremins with serial numbers higher then 7500 and Etherwave Standard theremin with serial numbers higher than 30.000.
Do contact us if you need more information.

The Etherwaves themselves work fine, but with the ESPE01 module it does not behave as desired."

Im guessing this has alot to do with the problem I was having with the ESPE01 installed.  Now to figure out what the current problem is! 

Thierry has been awful quiet. I bet that warning was "very" recently added.

I am sure he knows what gets damaged. If the LM13700 is in a socket that is at Mouser for $2

If not in a socket you will destroy the PCB trying to remove it incorrectly.

The theremin she has attitude like the rest of us.

My latest research, not complete yet, might be a solution if you can not purchase a new EWS board or fix the current issue. It is an external mod in a small wood box that replaces the complete EWS Pitch side with my Lady Vocal sound but it still uses the EWS Volume side. DIY less than $100  I give the PCB away at no cost if you are in the States. You are north of me.

Thierry needs tell us what can go wrong as my add-on may not work in a newer EWS.

Christopher

Edit: Thank you Thierry, that is the answer I was hoping for. If the Pitch Field changed dramatically tells me the antenna circuit stopped resonating.

Thierry has actually an overload, day job wise, until Sept 24 including.

The warning which Wilco put on the ESPE01 website does concern a different problem (restricted pitch range on newest Etherwaves with ESPE01) which he met on only 2 or 3 new instruments and I’ll investigate after the date above.

Nothing to do with the problems in this thread.