Regulated Power Supplies for Low Power Amps

[Serow]

Here is a good headphone amp power supply taken from one of Kevin Gilmore's articles here at Headwize. Note that the part number of the transformer listed is incorrect; Kevin mentioned that it should be 72VA dual 36VAC secondary, while the listed part is 56VAC CT 24VA.



Eric

[ced]

Hmm, stop me if I'm wrong but the LM317/lm337 will only take a max of 40V dc from input to ground so not sure this circuit would be too healthy. Any comments?
Ced

[Geoff]

Ced

The LM317/337 are floating regulators and can be used at higher voltages provided the input to output differential voltage does not exceed 40V.

Geoff

[paulb]

There should probably be zener protection diodes across the regulators (input to output), or something to keep them within ratings while the circuit is starting up. Short-circuit protection will also likely be a problem here.

[sonnya]

PaulB is right about what he is saying.
It depent on how large your output caps are. Under all circumstances they will be exposed to overvoltage for a short time under powerup if you don't use Zenerdiodes as PaulB describes.

Sonny

[Chucko]

What possible advantage could there be to feeding the LM317 and LM337 regulators twice their output voltage? "Margin for error and undervoltage", sure, but you're p***ing away half of the input power in the form of heat at the regulator! This strikes me as excessive, even above and beyond the normal standards of audiophilia.

Then again, to quote the designer: "The ultra-regulation of the power supply (figure 3) is so over the top and unnecessary that most, if not all, people building this amplifier would not even notice the difference."

I think you could cut the input voltages down to -+/- 36VDC and never notice the difference.

BTW, what about supply bypassing within the amplifier itself?

[traderbam]

At first I thought that Gilmore's circuit was totally over the top for a headphone amp. Then, having had time to reflect and really think hard about the factors that have driven this elaborate, 317-frying design, I conclude that I my initial instincts were not incorrect. Is this the result of a lurid fetish for electronic components? Perhaps this mollycoddling is an indication of the frail integrity of the amplifer on the end of it! Good grief.
BAM
(having a bad day )

[hifiZen]

As far as regulators for preamps go, i agree with paulb on this one. Each different amp circuit will have a different level of sensetivity to the power supply, and various combinations of active regulation and passive regulation will produce different results.

With opamp based circuits, I have had good results with plain old 317/337 regulators followed up by simple passive circuits like C-R-C filters, even just with small resistances, and the addition of ferrite beads etc. For really low noise supplies, the opamp with external pass transistor designs work well.

seangoesbonk: you might also want to consider the OPA134 and OPA627 opamps. The OPA627 is about the closest thing to a technically perfect opamp as I have seen. IMHO the Burr-Browns sound a little nicer, and i think you'll find that once you factor in current noise, these opamps are also quieter (depending on source impedance of course) and have higher input impedance. At the moment, my favorite preamp design uses an OPA134/627 with external discrete SE class-A MOSFET buffer inside the feedback loop to drive current to the laod. I'd point you to my website, but it's STILL down... grr. gotta fix that soon.

[ergo]

There are versions LM317HV/LM337HV of this regulator that accept upto +57V voltage difference between input and output. Might be this is what should be used...

Ergo