[sdiy] TB-303 smps interference

[cheater00 .]

I was told that the alu foil shorts the H field. I thought this only
happens if the metal is ferrous. I guess one learns something new
every day.

Here's a shot of the the H field from the smps and the hum, with the
hum at the bottom:

http://imgur.com/a/idtGJ#42

You can see that it's nearly the same waveform.

The hum does not show up in the line output.

I have tried using a thick layer of aluminium foil, grounded or not,
put in a ziplock bag as insulation, and inserting it between the smps
transformer and various neighbouring components. Placing it between
the coil and the parts immediately south of it (in the direction of
the key pcb) removed just a tiny little amount of the ripple. I
believe that's a transistor and a couple poly capacitors. Maybe I
should try putting a ferrous material there to see what happens.

As the LED blinks, both waveforms change pitch just very slightly.
When the LED is off, the pitch is higher. If DC-coupled, the ripple on
the headphone output also has a higher DC offset than when the LED is
on.

Changing the VCO pitch doesn't change anything. However, if I start
the sequencer, the waveforms change in frequency a lot! You can see
some slides. I'm thinking this must be related to the oscillator
pitch. Perhaps a DAC is running wild? Or can it be that the uPD
microcontroller outputs some signals more often for higher pitched
notes?...

Cheers,
D.