Why is Ambika Power Supply AC/AC?

It’s January 2019, I just moved to the UK from the US and brought my Ambika with me. This also means that I need a new power adapter.

I have seen other posts here that reference parts from UK distributors, but they are all discontinued now.
Here’s one that I found after a fair bit of searching:

This begs the question, why did Mutable design this to take an AC/AC adapter instead of AC/DC?

If you use an AC/DC adapter, you have to use one of the following design strategies:

1/ Use single-supply op-amps, and design all your circuits to use a virtual ground. I gave it a try and it was noisy.
2/ Use a switched-mode power supply to generate a negative rail from the positive one.

After my bad experiences with 1/, I thought that 2/ would be a noise hell too and didn’t explore it. I was wrong – since then I’ve built a couple of things that use Traco Power DC/DC converters and provide +/- 12V to power analog circuitry, and their output is very clean.

Denis from OTO machines was using AC/AC adapters on the Biscuit and told me this turned out to be the best option for him in terms of quality, so it was one more argument to go that route.


Thank you very much for the insight into the design!