my theremin is mute...

well, I finished all the soldering on my theremax and overall it looks good (to me). Most of the parts I was able to solder really quickly so they didn't get too hot. The case is a bit of a different story as it's just in a cardboard box :P (I will try to post a picture soon because it's a bit goofy looking, looks incongruous with what I expect it to sound like)

It powers on (yay!) but no noise comes out (boo.) I've tried following the steps on calibration by turning the pots after using the jumper cable, but no sound at all that way. I've also tried that youtube video about fast calibration, but no luck there either (the other LED doesn't light up while turning the pots). I've also tried poking the base of one of the transistors per the manual but don't hear any static.

So I'm wondering if it's one of the following:

1 - The wiring on the panel. I was initially using the shielded wires supplied with the kit. However, I realized when I got to the steps after wiring that I was supposed to use the bare wire on the panel! agghh... would this make a difference?
2 - The 20 gauge wires. Because I used up my shielded wires on the panel, I didn't have enough wire when I got to the following steps where you hookup the power connectors and ground and stuff. So instead of using a 11" of .20 cable, I had to snip up some other cables from my PC parts box and use those. I suspect the cable was .18 instead of .20. Would this affect it?
3 - The main board cables soldered underneath. I thought the board would be ugly with the cables soldered in the topside, so I soldered them to the underside... is that ok or will it cause problems?
4 - Cable length. I gave an extra .5" or 1" on each of the cables because I didn't want it to be tight or snap. Is this ok or bad?
5 - The amplifier. I tried plugging it through my receiver's CD IN jack, which works when I plug in my SX-150 through the same jack. Just to be safe I also tried plugging it in through my PC on a known working input (again the SX-150 works on that). Tried volumes from minimum all the way through max but nothing on either (other than when I plug in an SX-150, which works).

Lastly... would it be something else like a dead component? (I sure hope not...)

Looking for any suggestions. Thanks for your help everyone.... this is the part I was dreading :( hope I can get the box working soon with your help.

The easiest procedure would be taking a DMM and verifying all DC operating points on the circuit board. Second step: take an oscilloscope or at least a grip-dipper (a friendly HAM radio freak in the neighborhood may be helpful) and check the oscillators. Perhaps your Theremax makes a sound but outside the audible range.

The systematical diagnostic way would be almost the same as for an AM radio.

Finally it will be more and more difficult in the future to find people who are experienced in this domain. Even normal Radio and TV technicians know today more about I2C bus and micro-controllers than about classical heterodyning circuits... Same problem as finding someone to fix the ignition of your 1964 Dodge.

N.B.:

I bought this pocket DMM/Scope (http://cgi.ebay.com/Uni-T-UT81B-SCOPEMETER-MULTIMETER-OSCILLOSCOPE-ut-81B_W0QQitemZ270331933807QQcmdZViewItemQQimsxZ20090118?IMSfp=TL090118115004r10470) one year ago. It surely isn't a high precision device but you have all functions and a sufficient frequency range for servicing and adjusting all kinds of theremins. And the price is more than OK.

... funny you should mention grid-dip meters, Thierry. I thought that might be the perfect theremin tuning tool, also. Unfortunately my Heathkit Solid-State Dip Meter is dead. I hope to work on it after I finish off the theremin.

Don

Can't help, I am one of these old fashioned guys who ask still if there was really a need for inventing pocket calculators. And so, grid dip meters aren't strange to me.

Thanks Thierry. I'm dreading testing every component... any chance it's an issue with one of the things I did above? (those might be easier to fix!)

...and what's a DC operating point and how would I test it with the meter?

I'm guessing you'd be better off to find a competent tech. to take a look at your theremin. If you have a very limited knowledge of electronics AND a thing you just built ... the possibilities are many!

If you haven't done so already, take some time to carefully look at each soldering connection. If it's a "cold solder", it will look dull, grainy and or lumpy. A good solder joint is shiny and smooth.

Also make sure you haven't splashed solder between things that are not supposed to be connected together ... in other words a "solder short".

Those are where most troubles lie for beginner's.

Don

The DC operating point of the transistors has to be calculated in function of the circuit design if not given by the manufacturer. That means you should know which DC voltages you should measure at each of the three transistor pins if the device is working correctly. If there are too important differences this may help to find out what goes wrong.

There are some troubleshooting and test instructions at the end of this document (http://vinic.free.fr/tmax/fab/thereils.pdf)

Thanks for all the replies. So I went through my theremax again and made these changes:

1 - installed the correct unshielded wire where I'd incorrectly used braided shielded wire (I salvaged some of the unshielded wire which I'd kind of used to substitute for solder lugs... don't ask :P)
2 - swapped 20 gauge wire in where I'd incorrectly used 18 gauge (previously I'd run out, having used the shielded wire incorrectly earlier. I bought some 20 gauge from radio shack. it turned out to be wire for multimeter leads! oops, oh well, it's a bit thicker, but...)
3 - tested the resistors that I thought were "troubled" from too much soldering - they were measuring the right levels more or less within a couple of notches (I think this multimeter reads everything high?)

So I powered it on, and this time after running through the pot turning routine... heterodyne tone! I was able to eventually calibrate it, more or less, and now the volume works (more or less) as does the pitch rod! So everything's working correctly now.

Thanks for your suggestions on checking with a multimeter, Thierry. It's a good tool to have and I'm sure I'll use it on my other electronics kits. Time to find some hacks to improve the Theremax's linearity! (wow, finger movements are totally inconsistent between the low range and high range on this baby... I hear using brass rods really helps - that'll be my first stop!)

Since I don't have the assembly instructions and your theremin in front of me to look at, I can't comment precisely about use of shielded cable for what spot, but in general the wire gauge is not relevant for theremins. AWG22 is fine for any and all chassis wiring.

Shielded cable is usually only needed if you are running a sensitive, low-level signal near a source of interference. In all but a few cases, just twisting the signal and return line together is more than adequate for canceling interference inside the box.

So my guess is that you had something else going on there (small bits of wire shorting to something, or cold soldering connection) in addition to not having the tuning right.

Cable length, however, can and does cause some problems. You want to keep wires as short as possible, but still allow enough length to be able to work on it.

Don