PS tests - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th December 2011, 10:50 AM   #11
magnu is offline magnu  Sweden
diyAudio Member
 
Join Date: May 2010
Location: Stockholm
Well to get a power supply to have a "good" sound, it shall not influence the output at all.

Noise and ripple is something you can not do that much about beyond a reasonable level. The amplifier itself must have some immunity against these factors.

The interesting thing is the interaction between the load (amplifier) and the PSU.

I would be most worried at frequencies around and below the cut-off frequency of the PSU regulation loop
  Reply With Quote
Old 13th December 2011, 08:59 PM   #12
tvrgeek is offline tvrgeek  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Md
I agree, a perfect amp would have no sound of it's own. Being able to characterize what actually contributes to most amps HAVING sound is the goal. I was surprised at the level of mains harmonics I was seeing on various supplies when build a test rig and looking at my various low power amps outputs, both regulated and unregulated supplies. I was looking at the output at 1 watt with a 1K tone for the simple static test into a pure resistive load. 120Hz may have been -90dB, but 240 or 480 Hz at -60! How much of this is easily dealt with by diode selection, suppressor cap selection, and so on. It is oft said to lose the 1N4000 series or similar high power and put in high speed Schottky. OK, I want to see a picture on my scope or spectrum analyzer.

Load interaction with a complex load I do suspect to be relevant. It should be no surprise the cleaner the power supply looked, the less character the amp had. Mind you, I am starting with pretty good amps. Of the unregulated power amps, I have a H-120, Rotel 840, Creek, Amior, and a home built FET. I wish I had a Bryston for reference. I have a handful of low voltage regulated supplies from my Heath bench, switchers, old 3 terminals and battery. The battery was of course harmonically perfectly clean, but I would not say the best sounding on my RA-1 head amp and Grado's. I prefer objective measurements to "sounds better" When they correlate with subjective ones, I figure I am in business as I will then know what to build to. Of course, the physical implementation effects the parastatics and we must look at "all things being equal". If yo u are wondering, I like the Creek and Rotel. I was surprised how much character I could ascribe to the Hafler. The Amior is, well lets say it is a good thing they went back to building boom boxes. It may become a box and transformer for a gain clone. Great place to play with power amp supply differences.

Lots of ideas here and I will need to think about how to test some of them. I think it worthwhile.
  Reply With Quote
Old 13th December 2011, 09:24 PM   #13
magnu is offline magnu  Sweden
diyAudio Member
 
Join Date: May 2010
Location: Stockholm
Well,
with an unregulated power supply, you can connect a load (resistor), that draws max power. Now you can measure the ripple and noise.

You can modify the PSU, to get more ripple and investigate what that does for the amplifier.
  Reply With Quote
Old 13th December 2011, 09:46 PM   #14
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Yes, measuring PSU impedance as a function of frequency could be useful. I guess you want to avoid peaks in or near the audio range, and the syllabic rate too. Transient response is essentially an alternative way of measuring the same thing.
  Reply With Quote
Old 13th December 2011, 09:53 PM   #15
magnu is offline magnu  Sweden
diyAudio Member
 
Join Date: May 2010
Location: Stockholm
Transient respnonse is not enough.

The true professionals measure the regulation loop phase margin, bandwidth. Without control of these factors, some loads (music) can make the PSU regulation loop to oscillate.
  Reply With Quote
Old 13th December 2011, 10:13 PM   #16
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
If some music causes instability then this suggests that at some frequencies the PSU has negative output resistance - not good! An impedance test would show this. A transient test might show it too.
  Reply With Quote
Old 14th December 2011, 02:52 AM   #17
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
Originally Posted by magnu View Post
Well to get a power supply to have a "good" sound, it shall not influence the output at all.

Noise and ripple is something you can not do that much about beyond a reasonable level. The amplifier itself must have some immunity against these factors.

The interesting thing is the interaction between the load (amplifier) and the PSU.

I would be most worried at frequencies around and below the cut-off frequency of the PSU regulation loop
Yes, the interesting thing IS the interaction between the load (amplifier) and the PSU. But so much depends on the power distribution network in the amplifier, where the rails' and the ground returns' inductances and the decoupling capacitors' abilities to accurately supply the transient currents have to be there, no matter how good the power supply might be. So what do we actually need to test, for the power supply alone?

What are a power supply's requirements and the desired specifications, for this application? Answering those questions would tell us what requirements and specs to test, and might also suggest how to test them.

The power supply must be able to accurately provide all of the music signal that drives the speakers, as a possibly-large and dynamic CURRENT signal, with high fidelity. I like to try to keep in mind that the high-power "signal path", which is the only one that we actually hear, is, after all, current that comes straight through the power supply and the power amplification devices, which are really just "precision current valves" (i.e. controllable resistances) that are controlled by the small-signal portions of the amp (which is also influenced by the power supply). They don't pull or push anything; they simply "allow" current to flow from higher to lower voltage locations, when they are opened and closed to varying degrees. The decoupling caps must provide all of the current for at least the start of every transient, since the inductance of the power rails makes it literally impossible for the power supply to get the current moving in time to meet the demand accurately.

With that type of picture in mind, what does the power supply really need to do, and, what are the most-important performance qualities that it should have, and with what actual specifications? i.e. What are the requirements and the desired specifications, for this application???

Answering those questions would tell us what requirements and specs to test, and would probably also suggest how to test them.

Personally, when designing a power amplifier, I think that it makes more sense to think of "the power supply" as including everything up to the active devices' power and ground pins, since THAT is where I hope to see the "perfect" impedance vs frequency plots, and that way I can design the decoupling and rails' inductances and the bulk/smoothing caps (and regulation, if used), etc, all together as a single system (which needs to be able to allow current to dump into some of the pins and swallow whatever current comes out of some of the other pins, all with perfect accuracy, on demand). I just think it's much easier to know and define the requirements for (and later test/measure) what is needed at the power and ground pins of the active devices, than at some "artificial" point called "the psu output" that is basically in the middle of the power and ground rails of the system as a whole.

That might seem unhelpful, at first, but I'm hoping that it might help to separate-out what is required of the PSU, alone.

Sorry to have blathered-on for so long about all of that.

Cheers,

Tom

Last edited by gootee; 14th December 2011 at 03:08 AM.
  Reply With Quote
Old 14th December 2011, 07:54 PM   #18
tvrgeek is offline tvrgeek  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Md
Tom, you are about as brief as I. We agree completely, the power supply is part of the signal path and everything must be looked at as a whole. I was trying to be a little simpler to start thinking what really basic practices we assume have what really basic effects, like diode selection, or would returning to pi filters have better performance with respect to harmonic suppression but cause transient regulation degradation.

I bet you have seen the same thing, the cap right on the heat sink at the transistor being high a high ESR type. Least we forget for most cap technologies, capacitance is not always the largest variable parameter of the part. Caps are hard. Thermal, voltage and frequency variable RL circuits effected by humidity that have some amount of capacitance. Yea, that's a cap. Z5U or X7R's used as integrators, tant's used as coupling.

I am intrigued with the idea of raising DCC above chassis ground by 10 to 100 Ohms. I have not seen that before. I have seen them only AC coupled. Where can I get more on that subject?
  Reply With Quote
Old 15th December 2011, 04:58 AM   #19
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
Tom, you are about as brief as I. We agree completely, the power supply is part of the signal path and everything must be looked at as a whole. I was trying to be a little simpler to start thinking what really basic practices we assume have what really basic effects, like diode selection, or would returning to pi filters have better performance with respect to harmonic suppression but cause transient regulation degradation.
Sounds like a good idea. One thing I've noticed is that so many people seem to focus on keeping the power supply voltages clean and it seems like they're forgetting that the current is the signal. The decoupling caps can't even respond to transient demands for current unless the voltage across them dips. We can increase their values to make the dips as small as desired, of course. But why? What are the trade-offs?

Quote:
I bet you have seen the same thing, the cap right on the heat sink at the transistor being high a high ESR type. Least we forget for most cap technologies, capacitance is not always the largest variable parameter of the part. Caps are hard. Thermal, voltage and frequency variable RL circuits effected by humidity that have some amount of capacitance. Yea, that's a cap. Z5U or X7R's used as integrators, tant's used as coupling.
Yes! Caps are where it's at! Caps and the inductances of the traces and wiring...

This is very interesting:

Cornell Dubilier Electronics

I wish they had some small electrolytics, there.

Quote:
I am intrigued with the idea of raising DCC above chassis ground by 10 to 100 Ohms. I have not seen that before. I have seen them only AC coupled. Where can I get more on that subject?
I have seen some discussions here, about that. I would try searching for "star ground". But I'm guessing that if the grounding topology and layout are done correctly then you probably wouldn't need to use that technique. I've been wrong, before, though.
  Reply With Quote
Old 15th December 2011, 03:42 PM   #20
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
This looks like a corker of a Thread. I will be back to read it through more thoroughly.

This is here to bookmark it for me, so that I see it popping up in my "searches"
__________________
regards Andrew T.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Listening tests Rob M Everything Else 119 26th January 2014 07:40 AM
PS Audio PS Elite Integrate Amp jimmy50 Solid State 14 5th May 2012 06:07 PM
Tape Tests percy Analogue Source 15 17th August 2008 10:23 PM
X-BOSOZ first tests wuffwaff Pass Labs 116 16th January 2006 04:00 PM
Some tweeter tests ucla88 Multi-Way 18 19th April 2004 04:49 PM


New To Site? Need Help?

All times are GMT. The time now is 07:41 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2