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TM3030 V/oct tuning flat / cutoff range / picking up radio
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author TM3030 V/oct tuning flat / cutoff range / picking up radio
th0mas
Hi

I am close to finished building two TM3030s. I've got three questions for anyone who can help smile

For U6 on both I'm using SSM2010s I bought on ebay. Anyways, when I calibrate the powersupply and then go to tune the unit, I turn the trimmer all the way in one direction and am still about a semitone flat over 2 octaves.

After reading the forum for awhile I believe my best bet is to lower R2?
Would 33kohm suffice (I know I have them laying around)?

Secondly I found while adjusting the freq trimmer and cutoff pot that my favourite range was with the trimmer all the way open and would still like a brighter sound. Should I increase R49 or decrease it? Judging by the schematic I think, decrease?

And finally, my units both pick up radio. It's not a constant hum but rather it plays radio only while the envelope/filter is open. My pots are not board mounted as I put them in a desktop case, so most wires to the pot are twisted, unshielded, and maybe 4-8 inches in length. Any suggestions? It's a plastic case but I could line it with aluminum tape or similar if that should help. I work with RF engineers and they suggested a combination of wire length and high impedance is usually the cause of radio interference.

Otherwise the design was easy as pie to put together and sounds great so I'm very excited to fix these little details grin
Synthbuilder
th0mas wrote:
Anyways, when I calibrate the powersupply and then go to tune the unit, I turn the trimmer all the way in one direction and am still about a semitone flat over 2 octaves.


This has come up before and I sure as heck don't know why it is happening. You should be getting around 1V/octave from the output of your DAC - pin 7 of U7. That should give a +1V jump for every octave you rise on your controlling keyboard. It might be worth checking that before changing R2.

But lowering R2 may well fix things if there is a problem with the SSM2210 or the temp co resistor's nominal value.


th0mas wrote:
Secondly I found while adjusting the freq trimmer and cutoff pot that my favourite range was with the trimmer all the way open and would still like a brighter sound. Should I increase R49 or decrease it? Judging by the schematic I think, decrease?


Lowering it should do the trick.

th0mas wrote:
And finally, my units both pick up radio.


The RF guys are right. Like any audio project it really should be in a metal case. But screening a plastic one will certainly help.

Tony
th0mas
Sigh.

My multimeter's battery was old, so calibrating the PSU was out to lunch and in reality my PSU was at ~5v. Fixing that and the tuning range (and filter brightness) problems were solved. Sadly I only figured this out after modding one unit's R2 value.

Thanks for your help and sorry for the waste of time.

Doh!
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