Unwanted modulation

I have completed building the Ambika, and started testing the voice cards, calibrating the VCF trimmer as I install them. It was first going well, but when I got all the 6 voice cards in, I notice a modulation on all cards. It is sort of like an extra “buzz” on all cards, like a modulation source I can´t turn off. Very noticeable on the filter with high resonance. So far my guesses are:

1. Too weak line lump external power supply. It is rated 9V AC, 6VA

2. Maybe the ripple from the external power is leaking in, and I need to install the C12 cap in the power supply section of the motherboard?

3 Is there a deep-menu modulation source that I have not found yet? The modulation is equal on all programs. I tried many different programs, and tried turning off all modulation, but it is still there.

Any ideas?

Try a different PSU first.

Try a power supply with a higher amp rating. 9V at 1.5 or 2 amps will solve this issue.

OK, thanks, I will try a different PSU. Would I damage anything by inserting 15 V AC on the input?

Not for the first few minutes, but then the regulators would heat a lot and ultimately die. And if it’s in a plexi case, you’ll burn the plexi.

Don’t use anything else than a 9V AC PSU able to deliver 1A or more.

You are quite right: I tried running it with different power, and with higher voltage and/or higher current, everything works just fine. Curiously, when running it from the original 9V power it is the power pack itself that gets hot.

Thanks - all working now.

9V AC, 6VA implies ~660mA, so that’s certainly not enough for the Ambika and the transformer inside risks being damaged. Don’t use this wallwart!