Note 1: Liquiphonics assumes no responsibility for the following circuit diagrams.
Also, bear in mind that it has been designed for myself and so may contain parts you may not need.
This is the circuit diagram (or schematic) for the dual supply, variable output voltage, high current, single potentiometer controlled power supply unit I will be using for testing the Liquiphonics’ HiFi design. The diagram also shows the ILP MOS248 MOSFET power amplifier monoblocks I’ll be including.
The heavy lines show the large gauge wire used to connect the amp power lines and earthing. This thicker wire is to ensure PSU ripple doesn’t get into the signal and to sink any RF interference in the earth wiring. Some connection dots are larger than others, this is a bug in the app I use called Inkscape. It is excellent though, especially as it is free, so I’m not complaining.
I haven’t reinvented any wheels, all this information has come from the web, either the manufacturers application notes for the LM317 and LM337 positive and negative variable regulators or circuits from other people who have been good enough to share their work on the web (thanks).
Click the image below to open a larger version of the schematic, feel free to download it.
The VDR absorbs any voltage surges, probably destroying itself in the process. The fuse should always be in the live power line only; if you put a fuse in both lines and the negative line only blows, the whole circuit will still be live. The Mains Filter is an off-the-shelf unit I bought from RS Components 30 odd years ago when I originally put this power amp together (the one I am now restructuring and adding to to make this Lab PSU). It has a rating of 3A continuous. The DC Filter helps to reduce the audible hum/buzzing from the mains transformers. I have a vague memory that the mains transformers were rated at 7A continuous (so more than enough for the job then). These are followed by 2 x 22,000µF electrolytic capacitors per channel. The rating of 63V is a little close but a higher one would be even more expensive. Generally speaking, given the same amount of capacitance, more capacitors of lower value is better than fewer capacitors of higher value as the ripple current is spread between them thus reducing their temperature and increasing their working life.
ICs 1, 2, 4 and 5 (LM317 and LM337) have a maximum current of 1.5A which is a little low. 2N3055 transistors have an absolute maximum of 15A collector current so should be good for a lot more than the ICs can give. IC3 and 4 allow the use of only one potentiometer for changing the ±voltage outputs by ensuring the negative voltage automatically tracks the positive voltage. I am having to use a rather expensive OP454 as it can handle the high voltage rails I’m using – these op amps get their supplies from the outputs of the transformer. Check the maximum Supply Voltage rating (Vcc plus and minus). If you have reduced supply values you may be able to use something cheaper such as a TL072 . To ensure good tracking make sure the potential divider resistors of R5/R11 and R16/R22 are 1% or as close to each other in value as you can.