[quote name='Shambo' post='974907' date='Oct 2 2010, 12:36 PM']I'm the owner of a Demeter Opto Compulator pedal which, when 9v battery powered, easily fulfils my simple compression needs. However, when I try to power it with an ac/dc adapter by the mains, it emits a clearly audiable whistle. I'll admit the adapter wasn't the most expensive in the shop, ('Lynx Multi Power Supply' from Dawsons), but I didn't want to spend a fortune to power just a compressor and a tuner. It powers my TC Polytune perfectly well on its own BTW.
Have any other forummers experienced something similar before I throw money at getting the cherished pedal fixed, or should I just buy a pricier adapter? [/quote]
Why not take it to a shop to try a pricier adaptor? If that works, great, if not then get it looked at. Not to ask a stupid question, but is the adaptor you're using actually compatible? (but I don't know how it could not be...)
If it works fine with batteries, then I'm thinking it's more likely to be the adaptor than the pedal...