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Improvements for old linear power supply - should be fairly straightforward!
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tophat:
Hello everyone,
This is the first post to this forum. I am currently working on an audio amplifier with a power supply as shown below.
It is different to the schematic because someone has doubled-up R58 in parallel so it is now approx 2R3.

The power resistors are dissipating quite a lot of heat - as would be expected in this design!

I was just wondering if anyone had any thoughts about why the circuit was designed like this in the first place, using the resistors and the specific differing values of electrolytics, etc.

Would I be correct to increase the capacitance and use a better quality of electrolytic in general, to avoid having to use the series resistors?

Many thanks for any thoughts on this, cheers , Jim
ArthurDent:
The heat has to go somewhere so the designers decided to lower the heat dissipation in the regulators by putting a 5R8 ohm resistor before it. The two capacitors and the resistor in between the two caps form a crude pi filter that reduces the ripple somewhat. Apparently someone though the 5R8 dropped the voltage a little too much and reduced its value. Without knowing if they also made other changes that increased the load on the regulators, I wouldn't dare guess why they made that change. 
themadhippy:
Daves video explains wot the resistors doing,you could try without the resistor  or maybe try the ideas in the video
ArthurDent:
"Daves video explains wot the resistors doing,you could try without the resistor..."

If you're saying it is a capacitance multiplier, that is incorrect. All four regulators are used as out of the databook regulators. What is before the regulators is just voltage dropping and filtering.

Bypassing the resistor will cause the first positive regulator to run hotter.
themadhippy:

--- Quote ---If you're saying it is a capacitance multiplier, that is incorrect
--- End quote ---
What im saying is at @7.20 he explains what the resistors are upto,and the problems they cause.
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