Internal rewiring of Parasound Halo A21 120V --> 230V voltage conversion


Hello everyone,
I recently acquired a gorgeous Parasound A21 which I imported from the US, and as I am really into DIY and opening things to check how it's made, I deliberately looked for a 2nd hand amp from the US, so I would have to switch the voltage operation by myself. I believe I have almost solved the problem, but considering the different sources I found online (none were exactly for the A21, rather for A52), I came to doubt the final moves.
The circuit board is a B4170A, I have already moved the jumper cable JP13 to JP14, the former being for AC120 V and the latter for AC230 V.
Now I'm facing the change into the big transformer wiring. I have a red wire on P4 and a white on P1, both connections labelled as AC120V. The target connectors are P5 and P6, labelled as AC 230V.
The last two transformer wires, yellow and black, are plugged onto "To Transformer TP12" and "P3" respectively, along with a "AC120V" written above both.

There are 2 more wires, P2 and TP11 which connected to the external fuse. ( I have already swapped it for a 6.3A slow blow one)

I know that for 120V operation, the transformers are connected in parallel, and they must be linked in series for 230V operation. The thing I do not know which one exactly are primary and secondary and all the cable are pretty well coated with plastic and I'm not sure how could I do an efficient continuity test.

I believe that I should plug P4 to P5, and P3 to P6. Does anyone know exactly which cable must be switched to please ? Also, I think I could/should change the internal fuses but I have not thought about those yet...
As a safety measure, I have created a power outlet linked in series with a 500W incandescent light bulb, to avoid surge on the A21, if I would come to mismatch some cable, which I'd rather avoid, thanks to this forum hopefully.
Thank you all for reading and hopefully understanding my issue, I wish you all a very pleasant day !
Zeka
zeka
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I’m adding to this thread because the information above was helpful. Hopefully Google will help others to find this.

I have a Parasound HCA-1200, purchased in the mid 1990s in the USA, which was designed for 117VAC, and is marked that way on the back of the unit. I now live in Germany where the line voltage is 230VAC, and have been operating the amplifier using a voltage conversion transformer. I got tired of that and decided to convert the amplifier to operate directly off 230VAC.

The good news is that the power supply torroidal transformer has two primary windings, which are wired in parallel to run on 120VAC. To convert the amplifier to run on 230VAC is very simple: rewire the primary coils in series. Here are the steps, which closely parallel those above.

WARNING: I ASSUME NO LIABILITY FOR THE INSTRUCTIONS BELOW. IF YOU DO NOT HAVE EXPERIENCE WITH ELECTRICAL WORK AND ELECTRONICS, AND DO NOT KNOW HOW TO WORK SAFELY WITH LETHAL AC VOLTAGES, DO NOT ATTEMPT THIS. FIND SOMEONE QUALIFIED TO HELP YOU.

(0) Remove power from the amplifier and open it up.

(1) Locate the transformer primary wires. These come from the transformer in a bundle of four wires, which are black, red, clear and yellow. (The clear insulation is transparent.) You are not going to touch any other wires than these four! The red and clear wires are connected together to the mains power coming from the front panel power switch. The yellow and black wires are connected to the central (power supply) circuit board near a 10 ohm 30 watt resistor.

(3) You are going to leave the red and black transformer primary wires connected as they are.

(4) Disconnect (unsolder or cut) the clear transformer primary wire from where it is connected to the red wire and the incoming electrical power.

(5) Cut the yellow wire near the power board. Fold over the end of the stub of yellow wire coming from the power board and put some heat shrink tubing over it to prevent it from shorting against anything.

(6) Strip some insulation from the yellow wire coming from the transformer, and use a sharp knife to scrape off the insulation varnish.

(7) Solder the yellow wire to the clear wire. Insulate with heat shrink tubing.

That’s it! If you want to test this in a safe way, I put a 100 - 200W incandescent bulb in series with the power plug when you plug it in. The lamps will flicker from startup current then should dim and the amp front panel lights should light up.

Here is a schematic, the relevant part is the power supply transformer wiring in the bottom left.  (The schematic in the forum has the wrong aspect ratio, but if you download it in a separate window it is correctly proportioned.)

HCA-1200 schematic showing transformer primary wiring for 117V / 230V variants

 

Best regards,

Bruce