Power Supply Questions

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simon
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#16 Re: Power Supply Questions

Post by simon »

Sounds like you've picked it up just fine Steve. I read this when I first started using it, might help also?

https://www.dhtrob.com/overige/pdf/dhtrob_psu.pdf

FWIW, which isn't a lot, without looking at your PS in detail my gut feeling is you have more C than you need - the three sectioned filter will cut ripple a lot - I'd guess you've very little left at the second stage.

If you've a little more hum by halving the C then it might be worth considering earthing? Your schematic shows a star earth - don't know how you've actually wired it up but it might be worth running wires from each cap -ve in series and then to ground at the last cap to minimise noise in the signal ground. But you know all this so.
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#17 Re: Power Supply Questions

Post by simon »

Cressy Snr wrote: Sun Jan 14, 2018 11:04 pm Maybe I can get some suggestions as to how to speed up the step-response further, or maybe it's fine.
Ah, now you're getting in to PSUD games :-). I've generally found that a 2 section LCLC supply with a 200uF first cap and maybe as small as 20uf second cap works well for pretty pictures in PSUD - small ripple and generally a good looking response. Adding resistance can help with ringing, but will slow the response. But it's easy to play, and agonise over what's best! And in reality, can any difference really be heard? That's the conundrum. Have fun! :-)
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#18 Re: Power Supply Questions

Post by Cressy Snr »

Here is the PSU responding to a stepped 1:10 current load at the output stage, (5sec) followed by the driver stage, one second later:
Red trace - output stage.
Green trace - driver stage.
Yellow trace - input stage.
Image
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#19 Re: Power Supply Questions

Post by Cressy Snr »

I think that doesn't look half bad, but what do I know :)
The 5U4G used to get a blue glow between cathode and plate on power-up, as the heaters began to operate. That was before I halved the value of all the capacitors.
Now there is no sign of said glow from the rectifier as the power up sequence starts.

Simon....re the star earth; each cap in the PSU has its own ground wire running to the star point.
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#20 Re: Power Supply Questions

Post by Cressy Snr »

Paul Barker wrote: Sun Jan 14, 2018 1:35 pm Isn't there a wine your thing for macs? Psud runs ok in wine.
Thanks for that little pointer Paul.
PSUD runs perfectly.

The trouble started when I quit PSUD.
Where the hell was the program itself?
After much cursing and googling, it turns out that WINE uses a hidden folder to store the Windows programs it installs on the Mac.
I found a handy command line string to get to the virtual C: Drive that WINE puts your stuff in.
Opening Terminal I pasted the following command into the terminal window:

open ~/.wine/drive_c/Program\ Files

This caused the Finder to open the hidden folder into a window, where C:\ Program_Files revealed itself and there sat PSUD's icon. It was then a simple matter to make a couple of shortcuts, from the desktop; one to the programs folder and another to the specific app PSUD.

Double-clicking the PSUD shortcut on the desktop opened WINE which then loaded PSUD up.

So now I can get at the program from the Mac desktop - hours of fun await :lol:
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#21 Re: Power Supply Questions

Post by simon »

Cressy Snr wrote: Mon Jan 15, 2018 7:26 pmeach cap in the PSU has its own ground wire running to the star point.
Okay. Might be worth trying a single earth point on the last cap? As I understand it that should give the cleanest ground. Routing all cap negs to that star earth is supposed to inject more noise as there's more noise in the supply closer to the rectifiers. By 'daisychaining' the ground wiring the star earth shouldn't have the noise injected. Anyway, just a thought.
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#22 Re: Power Supply Questions

Post by Cressy Snr »

simon wrote: Mon Jan 15, 2018 10:18 pm
Cressy Snr wrote: Mon Jan 15, 2018 7:26 pmeach cap in the PSU has its own ground wire running to the star point.
Okay. Might be worth trying a single earth point on the last cap? As I understand it that should give the cleanest ground. Routing all cap negs to that star earth is supposed to inject more noise as there's more noise in the supply closer to the rectifiers. By 'daisychaining' the ground wiring the star earth shouldn't have the noise injected. Anyway, just a thought.
Carried out your suggestions Simon and the hum levels are now negligible. Thanks. :)
No crap being injected into the star point now, I presume.
TBH it's the first time I've done star earthing and I obviously got it wrong; a bit more to it than just running all the earths to one point.
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#23 Re: Power Supply Questions

Post by Cressy Snr »

PSU startup sequence looks OK (I think)
Image
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#24 Re: Power Supply Questions

Post by Cressy Snr »

Step-response now.
Couldn't find the right resistors for the first RC section (C2) so ended up with 22R instead (it was all I had in the right wattage)
Still looks decent to me.
Image
Last edited by Cressy Snr on Tue Jan 16, 2018 1:32 pm, edited 1 time in total.
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#25 Re: Power Supply Questions

Post by Cressy Snr »

The above, is now how the amp is configured.
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#26 Re: Power Supply Questions

Post by Mike H »

I can't figure what's causing that step? Looks odd to me. The previous one looked much more sensible.

Incidentally you should really find out what is the ESR of each cap, they can't all be 2 Ohms.
 
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#27 Re: Power Supply Questions

Post by Cressy Snr »

That step is deliberately programmed into the software as a 1:10 current step. The step values can be seen at the current taps.
This is done to try to provoke the simulated supply into low frequency ringing.
The step-down should be a steep exponential curve that levels off with no wobbling when it does do.

There are three steps placed at one second intervals so that The output stage steps, then the driver, then the input.
According to Morgan Jones, 4th ed, in a poorly designed supply, not only will the supply ring, but the ringing will leak into the next RC filter as each one steps and show up as a pronounced wobble. He used screenshots of PSUD to illustrate a good and a bad supply.

As to the ESR of the caps, I dont have an ESR meter and can't find any data for the ESR of JJ caps, so there's not much I can do about that.

The charts show different things; the upper chart is the startup to correct voltage at each current tap.
The lower chart is the step response of the supply.

I should probably have put that the above two charts show how the amp is now configured.
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pre65
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#28 Re: Power Supply Questions

Post by pre65 »

I have a feeling that the cap ESR would be significantly less than 2R.
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#29 Re: Power Supply Questions

Post by Cressy Snr »

This is why I started this thread, I'd really like to know about this stuff and want to learn.

So what difference do ultra-low ESR caps make in a choke input supply?

I can see them making a difference cap input supplies or in switch mode power supplies, or am I missing something re their effect in choke input supplies?
Last edited by Cressy Snr on Tue Jan 16, 2018 7:38 pm, edited 2 times in total.
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#30 Re: Power Supply Questions

Post by Cressy Snr »

Here is the real PSU as it is now, with actual measured voltages and incorporating Simon's suggestions for earthing arrangements.
Image
The measured voltages are not that far off the PSUD prediction, so that's good.

I can be reasonanky confident that I now have a supply that starts up without drama, doesn't eat tube rectifiers for breakfast, doesn't ring like a subsonic bell and has (I believe) a reasonably quick response to transient loads - useful bit of software.

I'll audition the results later tonight as most of today has been spent modifying, simming, measuring and making sure nothing is about to blow up.
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