Reducing noise in voltage regulators

[lohk]

Thanks Andy and Hoffmeyer, that is all very interesting indeed.

(Andy, I am also starting to read the thread in the other forum, but there are a lot of posts... )

But once more to the POOGE schematic:
Do you think it is possible to create this PSU to the same specs with "normal" components like a combination of BD135 / ZTX 653 / ZTX 753 / LM329 ? How critical is the value of C3 (820n) ? Is D1 a red LED ? All values for a 24V output ?
Are you going to publish your SMD PCB layout one day ?

Preamp rectification: Did you make noise measurements with different types of bridges, half bridges, fast diodes ? Is a big transformer

I am thrilled anyway. I think we (at least I ) never were so near to understand why different power supplies make so much different in sound with certain simple potentially good sounding circuits. And more and more I realize how important is the right combination in grounding, arrangement and power supply capabilities. Now slowly the people at N.A. will have something to think about, and they will have some new series of tests I suppose.

Serious work Andy !

Klaus

[ALW]

Klaus,

(Andy, I am also starting to read the thread in the other forum, but there are a lot of posts... )

Take a look at the Jung / Didden results though, they're awesome, but can be made even better, particularly in line rejection.

Do you think it is possible to create this PSU to the same specs with "normal" components like a combination of BD135 / ZTX 653 / ZTX 753 / LM329 ? How critical is the value of C3 (820n) ? Is D1 a red LED ? All values for a 24V output ?

Pretty much, I'll post some suggestions once I've had chance to do a bit of modelling for you - the Sulzer reg is MUCH better though, and proabably easier to build and smaller, primarily because the capacitor values needed are smaller.

I actually think C3 could be eliminated if a good low-ESR cap was used (OS-Con, Rubycon ZA etc.).

The LED in mine was Yellow, because I had a load of them salvaged from old strip-downs, but RED or green is likely to be fine.

The values shown will give circa 23V.

Personally I'm beginning to form the opininion that the raw supply, subject to some basic requirements is much less critical with a really good regulator. With the performance constraints of standard regulators the raw supply being massively over-engineered brings benefits, but they are primarily to make the regulators life easier and enhance it's failing performance.

The raw supply needs to be able to supply the current requirements, with a sensible margin, I don't feel special rectifiers are required (their prime aim is to prevent the ringing present in the transformer when the diodes switch off sharply) when a simple, but properly designed snubbing network can do the job better and cheaper. Please note caps across the rectifiers are bad news and can make things worse - they just shift the resonant frequency (which can be calculated by measuring the transformer inductance and capacitance), making it lower and potentially more intrusive.

On a toroidal transformer I had it's self resonant frequency was a couple of Mhz, an RC snubber can damp this within a cycle or so. It's clearly visible on a 'scope if you look at the transformer secondary waveform on one trace, the raw DC on the other - as the diode goes out of conduction the transformer breaks into a self-resonant oscillation.

Here's a good article explaining here: -

http://131.109.59.51/technical.html.

I'd like to try some different transformers next - standard toroids are very wideband devices, offering little filtering to mains-borne noise. Electrostatic shields help, but not very effectively. Split windings, with no overlap (and therefore no inter-winding capacitance) helps a lot.

Things don't always sound better though, and I haven't tried ti yet.

Andy.

[Geoff]

Andy

Could you please check that the link in your last post is correct. I cannot get it to work (page not found error).

Thanks

Geoff

[jam]

Andy,

Have you tried c-core transformers?

Jam

[Hoffmeyer]

Hi Geoff.
If You just type: http://131.109.59.51/
then it should be ok.

[Geoff]

Thanks, Hoffmeyer. Problem solved.

Geoff

[Musher]

Hello

I need to get good regulation for my Pass X series project's front-end. I am aiming at +/-47V, and just wonder which one of the circuits discussed previously in the thread would be best for my purpose. If any is.

Current needed is 400mA. The raw supply will be +/-64V with no load and +/-56V with 1A load (which I see is more than needed, so practically it will be at +/-60V or so).

Transformers will be two 63VA 20+20V in series, resulting in one 126VA 40+40V with 15% Uo, that is 46+46V with no load.

Or would I be just fine with a capacitance multiplier?

Also, I don't think I will hunt for any special parts, so ordinary polyester and electrolytic capacitors, 1% metal film resistors, ordinary diodes and zeners and commonly available transistors are in. Do you think I will miss much?

I am indeed a person who doesn't want to find out how to order electrolytic caps and special resistors of certain brandname, product line or model. Maybe it's this country, maybe it's money, maybe it's just that I'm too anxious to wait for such to arrive.

-Kimmo Sundqvist

[capslock]

Andy,

you keep referring to the Jung / Didden results. Do you have a link or a schematic? I had heard before about the Jung regulators but found no schematic. Have built and measured one?

Is there any literature on the Sulzer circuit? I am a little surprised that in won't oscillate. After all, the op amp is pretty wide-band compared to the time constant of any possible change in the output voltage. The non-inverting input is AC-grounded, but more so than the inverting input. Won't noise or transient cause wild oscillations?

Greetings,

Eric

[JonMarsh]

The Op Amp is operating as a unity gain buffer at high frequencies, due to the AC feedback provided by C3. Loop gain is rolled off. These regulators have been around for eons; I used this same circuit in a musical instrument preamplifier power supply in 1977.

Best regards,

Jon

[capslock]

Yeah, I remember seeing similar circuits in some app notes etc.

I realize those circuits work, but I'd like to develop an intuitive understanding why.

I can see that there is unity gain HF feedback to the inverting input. But what does the op amp do, once it detects an error signal? After all, there is a substantial capacitve load at its output...