Audio Output Problem - loud cracking and barely audible tone.

Hiho.  Ive got a problem with the Etherwave Plus I purchased for my wife about a month back.  I see many posts about volume issues and have read through them and tried some of the things listed.  I'm not a complete novice to DIY electronics (I have a DMM and know how to use most of it) but there are some things being discussed that I do not understand.  Heres the detail.

I purchased the ESPE01 and installed it a day before the issue began.  The theremin did function correctly (with the expected greatly increased field) immediately after I completed the work.  The next morning, after moving the unit to another room the problem started.  The issue is that the theremin emits only the quietest of sounds through the audio jack if the amp connected to it is turned all the way up or through the headphone jack (to a set of headphones) if the headphone knob on the unit is turned all the way up.  Additionally, when moving my hand toward the volume antenna I get a crackling white noise that increases with what I would expect would be the volume.  If I move my hand away completely from the volume antenna the crackling noise is silenced (it seems to follow the anticipated behavior of the output volume of the unit even though the sound its modifying is the crackling and not the tone itself).  The quiet sound of the theremin tone itself is constantly and quietly audible behind this and it is not modulated by motions around the volume antenna at all.

I have verified that the power cord is outputting 14v between the 3:00 and 9:00 pins and have tried the unit in multiple locations on both an amplifier (on the audio output) and headphones (on the headphone output) both of which worked fine previously.  I have opened the unit, verified that the solder connections I made are still connected (the pads have continuity to the leads on the espe01 and none of them are shorted. Ive also checked the capacitor leads this way.  I verified that D1 shows uf in the reverse direction and .587v in the forward direction (I know this is less than the 0.7v mentioned in another post but I also understand DMMs built in diode check function use very low voltages which may not be able to fully open the diode.  I checked the other diodes on the board to verify and they behave in the same way).  I then used the "Tuning the Volume Circuit" process using the voltmeter function listed in the manual.  I was never able to get the voltage between U3/Pin12 and Ground to read -12v even when L11 was brought almost fully out of its seat.  The max reading I could get was -10.9v.  When I moved it back in to 0v, it was still 1/8" protruding out of the body of L11 which was far higher than it had been when I started.  The voltage range did vary from -10.9v to +10.9v as I moved my hand towards and away from the antenna.  This did not change the behavior of the tone output although It might have made the crackling behave more predictably

I would like to be able to troubleshoot further but the next things it look like I should check involve 'nodes' and I dont know what they would be.  Case in point, node "D1/R14/C12".  I gather that would be a point on the board which is a junction of those 3 components but I dont see where that would be.  I would be most appreciative if someone had some more suggestions for things I could check (and maybe some additional guidance about how).

We're loving the instrument sofar and the added performance the ESPE01 gave us (even for the one night) made practicing the hand motions much more intuitive.  Its a real drag to have lost the thing immediately after.

Thanks in advance for any help we might receive.
-S.

bump

rsutor said: "I purchased the ESPE01 and installed it a day before the issue began."

You got cute banana's

What I enjoy about the theremin is how temperamental she can be. Most likely... something about the ESPE01 install went bad. Possibly the install or the device itself is defective. Cracking sounds could be a bad solder joint or connection.

This is where the audio begins, your volume side seems to be responding correctly.

Test: Place an analog AM Radio next to your theremin tuned to around 570 kHz or 858 kHz and if you hear the theremin heterodyning sound this tells you the theremin is working up to the ESPE01. 

I have never seen a schematic of the ESPE01, seems to be a secret. Is there a way to bypass it completely?

There was another bass mod design that could be bypassed with a simple two pin jumper.

A simpler way to get a similar effect or better with "no bass mod" is to just solder a 100pf across D4, I prefer a 47pf to keep some of the texture in the upper end of her voice.

Then there was my design I called "Switched on Clara" , my latest work just replaces everything in the EWS box. I always thought it is too much risk to make that modification so my latest stuff is a beautiful life line when all else fails.

Hear a switch (clicking) fully turning on my mod  Clara.wav   This is an EtherWave Standard with no external effects, just a little bit of knowledge.

Good Luck

Christopher

rsutor:

1. Does the pitch follow your pitch hand movements correctly?  If so,
2. Jumper pins 1 & 2 on the header you installed the ESPE01 on, this should bypass much of the volume axis circuitry.
3. Is the volume much louder and the pitch normal sounding now?

If 1 & 3 are true, then I'd maybe check the continuity of the big RF chokes going to the volume antenna.  You've definitely ruled out D1 on the volume side?  I've heard that ESD can kill it, and your unit not working after moving it to another room sounds suspicious.  Then again, you just did surgery on it, so anything could happen I suppose.

rsutor:1. Does the pitch follow your pitch hand movements correctly?  If so,2. Jumper pins 1 & 2 on the header you installed the ESPE01 on, this should bypass much of the volume axis circuitry.3. Is the volume much louder and the pitch normal sounding now?If 1 & 3 are true, then I'd maybe check the continuity of the big RF chokes going to the volume antenna.  You've definitely ruled out D1 on the volume side?  I've heard that ESD can kill it, and your unit not working after moving it to another room sounds suspicious.  Then again, you just did surgery on it, so anything could happen I suppose.

dewster did you make an error? Pin 2 VCA Out should go to Pin 6 +12v if you want the sound full on. Also he did indicate he thinks the volume side is working.

dew you use to be like my little brother, what happened along the way?

Christopher

From: UNDERSTANDING, CUSTOMIZING, AND HOT-RODDING YOUR ETHERWAVE [LINK]:

"Using a clip lead or a temporarily-soldered wire jumper, connect the two leads of C28 together. (C28 is a small capacitor, about 3" to the left of the PITCH ANTENNA connection on the Etherwave circuit board.)"

The leads of C28 go to pins 1 & 2 on the header (so sez the schematic in that doc) and pin 1 is GROUND, pin 2 is VCA OUT.  Full disclosure: I don't think I've ever done this - but why would Moog Inc. instruct one to minimize the volume when adjusting the pitch side?  Or did the header change on the EW Plus?

Mixer audio should be on pin 7 of the header, you might try hooking that to your amp through a 0.1uF or so cap to see if that's OK.

Anyone know where I can get the EW Plus schematic?

Today I was fixing the first version of SUBSCOP with a similar problem.
As a result of the study, it turned out that the GND contact in the 3.5 socket is broken.
After replacing it, everything works fine.
Not long ago I installed Thierry's  module in MOOG EWPlus. After installation, it turned out that one leg of the module was bent during transportation and the soldering of the contact on the module itself was damaged. In this case, the module did not work correctly. After soldering this contact, the module resumed.
Try to check the quality of soldering contacts on the module. Perhaps my recommendations will help solve the problem. Good luck

Thank you both for your replies.  Ive done some more digging using your responses and heres what Ive found:
- AM radio hears the Theremin pitch and it reflects expected pitch changing behavior when waving my hand around the pitch antenna.  Interestingly enough, when I touch the VOLUME antenna, the pitch changes (drops by a varying amount, at least a whole tone but higher up its a 3rd or 5th).

-Shorting the +12v pin to the VCA Out pin causes the crackling to be louder but does not alter the theremin tone at all.

Ive read elsewhere that a diode can test OK with a DMM but actually not be as its failure might only impact a specific frequency range.  Is there another test I could do to rule in/out D1 other than replacing it? (Radio Shack being long gone Im gonna have to hunt for a replacement source).  Are there any further tests you would recommend?  It seems both sides of the device are functioning properly its just that the volume side is not modulating the signal.

Thanks again,
-S.

Radio Shack, you're in the States? We need to talk in the future. All my beautiful sound is a theremin designed only using RS parts.

You keep verifying that the issue is the ESPE01 install. I hope you figure it out but if all else fails remove it and add a 47pf capacitor across D4. You will then have a nice upper voice instead of whale mating sounds. Adding a lower octave does not mean you will have better linearity, that is a different aspect of theremin design.

If there is a ESPE01 schematic available then a bypass method without removal might be revealed.

Test: Just as a guess but you probably removed a 15pf capacitor for the input connections, put that back in and pull the wire in the Pin 7 Audio hole. Be very careful as the copper foil is like tissue paper.

Maybe in the process of removal you will spot the actual issue, a bridged solder spot at the 8 pin terminal?

Edit: 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."  
This demonstrates you should for forget about D1 on the EWS board being a problem. IMHO

Christopher   

It was the ESPE01.  Ive uninstalled it and the unit works as expected again.  Thank you for your time and expertise helping me debug the unit.  Ill contact Thierry to see what it would take to get a replacement.

Its been awhile since Ive had to dust off the soldering iron and multimeter.  Frustrating as this has been it was fun to work on and I really appreciate the help!

Thank you,
-S.