I am going to build a Leach amp as a subwoofer amp. What transformer rating would I need for the single amp? I would guess 3-4Amps. Any suggestions?
Also, the power supply diagram on the Leach web site shows 4 output fuses- 2 on each rail-Why?
what impedance are you driving.
Standard Leach is 120w into 8r, assuming 6 ohm minimum impedance, this gives Ipk about 42/6 = 7A from each rail alternately. So the average is about 3.5A, right in your suggested range giving a transformer of about 300va.
But if you drive 4r then all ratings need to be doubled. i.e. 14A/7A/600va.
You could probably do it economically with 200VA as Ihalf =Io/pi
but the smaller the transformer usually the poorer the regulation and the greater the bounce at power envelope infrasonic frequencies and I doubt this ampwould cut it with it's RC rail filters even with the cascode. This is serious modulation. It throws the onus onto the power supply, giving worthwhile (audible) improvement with overbuilding, to compensate. When people say it benefits from supply overbuilding you can rest assured it's weak in the PSRR dept and/or conditions are onerous. Sub amp conditions are.
A chip front end with reg supplies would eat it for b'fast IMHO.
You know, i like to talk cars.
I am eagerly awaiting the arrival of the Corvette Zee-O-Six here.
This one will put the stuff made in Modena, Italy, in the shades.
Not because it has the biggest engine, that they already did in the 70s : worst Vette ever.
Because they made a lot of this one lighter, with SOTA technology.
On top of that this one even has decent mileage, they might even put the technology on it that will make it drive on 4 cylinders when needed for better mpg.
You can put the biggest transformer in any amplifier, maybe it will do better on a straight line, but wil it do better in the curves.
I am doing the Leach right now.
With discrete voltage regulation on the front end, by using a raised voltage through a small step-up transformer that will have a second life.
With discrete voltage regulation on the driver stage, same way.
Fat chance that i would ever use such an amplifier on a subwoofer, but to quote Mr. Ball : Eat It for Brekkie !!