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Old 27th January 2006, 12:15 PM   #1
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Default Regulated Power Supply for power amp

Dear All,

I am considering a regulated power supply for my power amp.
Does any one have hints/links/clues/considerations ?

When designing one, do i need to place the big capacitors in front or behind the regulator ? And why ?

grtz

Simon
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Old 27th January 2006, 10:01 PM   #2
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By big capacitors, if you mean the large electrolytic supply smoothing caps after the rectifier, then they go before the regulator. A regulator needs a relatively steady supply voltage to get the best out of it.

What sort of power supply do you need? Split rail? What voltage and current rating?
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Old 28th January 2006, 11:33 AM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
many do not recommend a regulated PSU for a power amp. Partly due to the PSU cost being greater than the amp cost. But mostly due to interaction between the reg. active stages and the amp. active stages. Quite difficult to eliminate all the little (or big) instabilities.

A regulated front end and unregulated output stage is often popular, much cheaper and very much easier to debug.
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Old 28th January 2006, 12:59 PM   #4
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Quote:
Originally posted by AndrewT
Hi,
many do not recommend a regulated PSU for a power amp. Partly due to the PSU cost being greater than the amp cost. But mostly due to interaction between the reg. active stages and the amp. active stages. Quite difficult to eliminate all the little (or big) instabilities.

A regulated front end and unregulated output stage is often popular, much cheaper and very much easier to debug.
Loop stability is mostly a problem for low dropout regulators in which the output capacitor is part of the feedback loop -- if mama bear isn't happy, papa bear ain't happy either.

In one of the Nelson Pass "Audio Amateur" (predecessor or AudioXpress) designs he recommended regulation as the particular circuit had poor power supply ripple rejection (PSRR). There is an article on the PASS DIY website which describes MOSFET regulators for this amp.

I did some testing of LM3875 and LM4780s with regulated and unregulated supplies -- my observation (measurements) was that at low levels the THD was about 0.001% lower for the regulated version, but about 0.001% higher at the high end. At high output levels there was no difference except that power was consumed by the regulator. YMMV
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Old 28th January 2006, 08:16 PM   #5
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Hi,
overall regulation has good and bad points.
It's more expensive to regulate and peak power is more limited.
On the other hand, it seems to give the bass more oomph.

If possible, regulating only the first couple of stages (input and voltage) is useful and much less expensive.
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Old 28th January 2006, 10:58 PM   #6
CBS240 is offline CBS240  United States
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I fiddled around with a reg circuit for a project in the works, running off of a +/-72V, half wave rectified source. It functions pretty well and has very little noise, and good load rejection. I was worried about zener noise due to very small current in the 25V ones, but the circuit seems to correct for it, being inside the loop. Output is adjustable from like +/-55V to +/-65V, with about 30mA max. The circuit can be switched on and off with +5V logic. The only transistors that are not SOT-23 SMDís are 2N6038/35(TO-126) and 2N2716/27(TO-237). 2N6038/35 are Darlington. All resistors except the two 6.8K on the collectors of the voltage source for the op-amp chip are also SMD. This way it can all be squeezed onto a small PCB. The SMD components are pennies a piece, so cost isnít as high as it seems from the schematic. Iím sure there can be many variations of this circuit, but that depends on who is making it I suppose.


EDIT> Although it works quite well, any suggested improvements are always welcome.
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Old 28th January 2006, 11:54 PM   #7
Eva is offline Eva  Spain
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Placing the main storage capacitors before the regulator reduces the amount of voltage ripple that the regulator has to reject, but forces it to deal with big AC currents. On the other hand, placing most of the capacitance after the regulator increases input ripple voltage but reduces current requirements dramatically.

Nevertheless, I prefer splitting the latter option, or at least, splitting the capacitance equally between both sides.
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Old 29th January 2006, 12:27 AM   #8
Eva is offline Eva  Spain
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Ops... Last paragraph should read: Nevertheless, I prefer the latter option, or at least, splitting the capacitance equally between both sides.
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Old 29th January 2006, 10:04 AM   #9
WBRO is offline WBRO  Poland
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~blu_line

Look at the my beardini.prv.pl web page. You will find good regulator supply from Naim clone project (by Neil McBride).
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Old 29th January 2006, 10:09 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi Wbro,
is there an English language version of your site? so I can navigate.
Or can someone tell how to switch on the translator?
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