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EI30 Transformer board



Every DAC board and also decoder includes power supply part. Only one part which missing is power transformer. It is possible to use for example toroidal transformer with a power switch and fuse holder on a chassis. I offer here one of many variants where is used small EI transformer on the PCB, small fuses on the primary and secondary sides and also small power switch and screw terminals.

Circuit description

Circuit includes terminal X1 for connection of power cable. Voltage goes to the switch S1 and via fuse F3 to primary winding of power transformer TR1 with EI30 size. From the transformer goes two secondary windings via fuses F1 and F2 to the output terminals X2 to X4. Output winding S1 designed for positive voltage rail is doubled for possibility to connect also S/PDIF decoder.

Schematics diagram

Schematics diagram schematics in Eagle 6 format


First we assemble power switch. We can also assemble small two pin connector instead of him and connect power switch on the chassis via wire. Next we assemble fuses and also terminals which first join them together. On the end we solder power transformer.

Component view

Component view

Printed circuit board

Board is designed single-sided with wide routes. It allow to create them in amateur conditions. I ordered it at small local company Kohout Spoj.

Printed circuit board PDF format Eagle6 format


Parts are commonly available. Fuses are in a radial variant to the PCB. It is possible to buy a sockets for them. His values coresponds to used transformer and expected consumption. In a case of selecting of DAC with TDA1543 circuit will be current requirements much higher about 500mA and we must select fuses and transformer with a appropriate values. Transformer with size EI30-2 produces many manufacturers. I choosed transformer from a HAHN company with 2x9V secondary windings which is enough for DAC with AD1865. For DACs with 12V voltage regulators for example PCM1794A we buy 2x15V transformer and for DACs with 8V supply we use transformer with 2x12V secondary windings. Informations about required voltage we can study on the concrete DAC page.

List of parts
name value and type quantity
F1, F2 PCB radial fuse T100mA 2x
F3 PCB radial fuse T50mA 1x
S1 switch P-KNX125 1x
TR1 2x9V (2x12V, 2x15V) EI30-2 power transformer 1x
X1-X4 Screw terminal AK300/2 4x



On the transformer board is probably nothing tricky that board works on the first connection. We must be very careful because on the board is present main voltage. It is a good idea to place board far away from the analog output part of DAC for preventing of hum caused by induction of transformer magnetic field to the output part.