Ambika output distorted (sounds fm/ring modulated)

I just finished building a Ambika kit with 6 voices. This was a kit from the store with all the included parts, I did not source anything myself apart from the power supply.

Everything sounds good until I put the 5th card in, and it gets worse on the 6th card. 4 cards sound fine. It does not matter which card I put in as the 5th card, the output changes on both combinations that I tried, so I guess it’s not any one card that is the problem.

It is most noticeable in the resonance. I’ve taken a few screen shots of spectrum analysis with both OSCs off and filter and resonance set to 63 (like when tuning the voices) and there you can where 1 - 4 voices sound fine with a pure sine wave, but 5 has a lot more frequencies and 6 even more.

I’m wondering if this could be a power problem as it gets worse with more load on the system. The sound is also like this from the individual outs so I’m guessing it’s not a distortion in the mixer.

My 9Vac power supply is stated to be 666 mA. I have a photo of that as well.

Your PSU is struggling, you need 1A as stated in the manual and written on the PCB itself.