ADA8000 External Mains Power Modification

[subsonic]

@cgrafx
Thanks for the idea.

The transformer is used as an autotransformer (http://en.wikipedia.org/wiki/Autotransformer) or in german "Spartransformator" (http://de.wikipedia.org/wiki/Autotransformator)

I've tried to draw an easier version of the schematic.

[subsonic]

I did some tests with my two ADAs.

Both work stable at 190V.
The older one starts humming at 185V, the new at 180V.
At 190V the temperature at the voltage regulators for +/-15V is about 15 or 20 degrees lower than at 230V (open housing).

I think I will build a power source for 200V similar to cgrafx.

This http://www.thomann.de/de/the_tracks_...tage_meter.htm should be an applicable housing. It has a voltage meter, which could show the reduced voltage.
A 2*18V 50W toroidal transformer http://www.reichelt.de/Ringkerntrafo...=0&OFFSET=500& should allow 200, 215 and 230V, when used with this schematic:

                 .------------.
            S2   |            )|
                 o -30V    18V)|
         .---o--__          .-'
         |       o----------+
         |         -15V     |
         |                  '-.
    S1   |  reduced           )|
         o                 18V)|
  .-o--__ o-- off           .-'
  |      o------------------+--------o
  |         full            '-.
  |                           )|    200V
  o                           )|
                          230V)|    215V
  230V                        )|
                            .-'     230V
  o-------------------------+--------o


(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The 50W transformer sould be sufficient for at least 4 ADA.
When I consider this http://de.wikipedia.org/wiki/Autotransformator only the reduced part of the voltage is transformed.
If we need approx. 80W for 4 ADA at 200V, then the calculated output for the tranformer is 10 W ( transformer output = 80W * (1-200V/230V). Of course you should add some watts for transfomer losses.