Midibox SID Standby Noise

[KeenVox]

Hi all,

I hope to find some Midibox Sid users to give me some insight about the SID behaviour in a MIDIBox SID.

So I designed my own Midibox loosely based on the Sammich with a minimal Control Surface on a LCD screen. So far everything seems to work as it should, but I get kind of a strange noise floor at the audio output right after startup.

I used it with an Armsid, Swinsid and original 8580 SID and get different results without touching a button or a note on my keyboard:

Armsid: a high pitch sound - 9 Mhz sinewave on my oscilloscope

Swinsid: a pulsing sound and crackles on the higher volumes - 250khz squarewave on my oscilloscope

8580: same sound like the Swinsid but with a bit of white noise in the background

I tried different variants on the power supply input (filtering, linear regulators etc.) but it makes absolutly no difference. I even checked that no datalines or powerlines are anywhere near the audio output traces on my pcb.

The last thing I can think of is that the "startup" patch somehow sends an signal to the SID to produce the sounds or it's simply the "normal" noise floor of a SID which even gets emulated by the Armsid and Swinsid.

All youtube videos I found don't seem to have the problem as far as I can hear. But on the other hand, all start directly with an melody, so there's now way to hear any sounds in "standby".

If anyone could share their experiences with me it would be greatly appreciated!

 

Thx

Kevin