DIY balanced power

by tubino
(Toledo, Ohio, USA)

Some years ago I scored a 2500VA Plitron toroidal transformer with balanced output (60-0-60), which provides isolation plus common mode noise rejection. I put it in a chassis with outlets in the back, and on the front a power switch and two vintage meters (AC output voltage and an ammeter).

First problem I had was that load or no load, switching it on would trip a 20A circuit breaker just due to the inductance! I had to put a current inrush limiter to stop that.

Next problem was that my usual load of 1-5A was too low for a device intended to deliver 1:1 input-output voltage, no sag, under full 2500va load! As a result, my already too-high house AC was even higher!

The solution was to use a 20A 6.3vac transformer as a bucking unit. I wired it using the 107 primaries, to increase the amount dropped, and as a result I get a nice 118-120 range in my household. Success! Oh, and it DOES improve sonic too!

Ken Thank you for sharing with us your experience with isolation transformer, and also the solutions to the problems you encountered. It is definitely useful the the readers here.

I wonder if you've any pictures to share with us on your project?

I did a balanced isolation as well, but I am using 2 identical toroid transformers that were idling in my storeroom connected together as follow:

Trans 1 (240V input : 16-0-16 output) -> Trans 2 (16-0-16 input: 120V-0-120V balanced output)

I connected trans 1 primary to mains, trans 1 secondary to trans 2 secondary, and trans 2 primary as output.

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Feb 01, 2012
Photos of the project
by: tubino

You can see some photos of the project here, with construction comments in the captions:

I didn't take any of the bucking transformer, but I squeezed it inside the chassis. This unit is now in my living room system. Even with 845 class A amps, the current draw is ~25-30% of capacity.

Ken: Very nicely done. I love the look!

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