Not quite a PASS amp yet but will hopefully be part of it.
Chances upon this (not that I was looking for an arc welder) 70 years old, beautifully designed and extremely well constructed 9KVA arc welder.
The top and the base are made of cast aluminium. Centre is 1.5mm thick sheet aluminium, finished in hammerite green.
It is a 3-phase only arc welder, on the label it says 130A@20V output, 9.2KVA, either I have to re-attend my secondary school physics class on ohm’s law or the man who did the calculation failed his maths.
I was looking at the Pass Amp 20 years ago, so this looks like a perfect low cost entry 🤣
When I hooked it up to the 3-phase supply it didn’t blow the apartment to pieces. The output measured 65Vac. Opening it up revealed that the transformer was wired to 2 phases, 450Vac across the primary, neutral not connected, 3rd phase omitted.
So I re-wired it to single phase, L1-N, 230Vac and the output fell to 41Vac. With that if I add a bridge rectifier and some electrolytic capacitors I should be able to get well over +-25Vdc.
So I ordered a Pass A5 clone today, with the +-25 Vdc I should be able to get 40W
@8 ohm? to drive my Sonus Faber Concertino with 86dB sensitivity.
The reason why I chose not to build an A2 instead was I may buy a “proper” toroidal transformer later if I cannot get rid of the transformer hum later.
Found an old thread by John Biles that someone suggested that the EMF emitted by the transformer would cause Leukaemia, this is in a grounded and fully enclosed aluminium case and perhaps that itself is a Faraday’s cage? Just to be on the safe side I am going to buy a EMF tester.
Wish me luck!