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Old 29th August 2012, 03:00 AM   #861
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GooTee,
Bravo on your dedication and defining the situation in a way that anyone should be able to understand. Take the night off and we expect all the answers tomorrow..... Just kidding.
I think that you have very concisely stated the problem and what needs to be done to answer the questions. I myself am impressed with your effort and work.

Steven
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Old 29th August 2012, 03:10 AM   #862
gootee is offline gootee  United States
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Thank you, very much, Steven.

I might argue with your definition of "concise". <grin> But I think that sometimes it's good to try to regain our awareness of some type of "frame of reference". Or maybe I'm the only one who needs that. <grin>

Does anyone want an explanation of how the simulation's marker voltages and measurement commands work? (Be careful about what you wish for. <smile> [Actually, although it looks a little "hairy", it wasn't that bad and just sort of fell together in about an hour or two, AFTER I finally figured out how the TRIG and TARG statements were supposed to work.])

Regards,

Tom

Last edited by gootee; 29th August 2012 at 03:13 AM.
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Old 29th August 2012, 03:25 AM   #863
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I'm going to go listen to some music, with my incredibly-wonderful Magnepan speakers.

Every time I hear them, it's almost as exciting and awe-inspiring as touching a woman for the very first time.

Well, not really. But they are exquisitely-great. And I just want to keep doing it, again and again.

Cheers!

Tom
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Old 29th August 2012, 04:46 AM   #864
fas42 is offline fas42  Australia
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Quote:
Originally Posted by gootee View Post
So, DF, Terry, Fas, and other experts: Square-wave testing, with peak values equal to the peak sine values previously used, as in post 846, should be comparable to using a sine load current's or voltage's peak value instead of its RMS value, as the DC load current or voltage when calculating ripple and the needed reservoir capacitance using the standard approximate formulas, correct?

So it's like using double the power as a worst-case design margin, and throwing in huge fast transients, too.
Tom, sorry I haven't been more active lately, you know, life and all that! Anyway, I had a play with your pulse source, but what I did just to make things fair to the circuit was to drop the slew rate to that equivalent to a 20kHz waveform: made rise and fall times 20usecs. This is as nasty as one can encode a CD, so theoretically, if Iggy Pop had another go at mastering, this could end up in the stores! The end result? Double the power dissipated in the load, 200W, so the answer is, yes. And not that much worse voltage sag.

But what would be worth playing with now is ESR: at full power the voltage sag varies dramatically once you go over 30mR. This is where the parasitics really start to intrude very significantly, may be much more important than the nominal capacitance.

Frank

Last edited by fas42; 29th August 2012 at 04:50 AM.
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Old 29th August 2012, 05:10 AM   #865
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Quote:
Originally Posted by fas42 View Post
Tom, sorry I haven't been more active lately, you know, life and all that! Anyway, I had a play with your pulse source, but what I did just to make things fair to the circuit was to drop the slew rate to that equivalent to a 20kHz waveform: made rise and fall times 20usecs. This is as nasty as one can encode a CD, so theoretically, if Iggy Pop had another go at mastering, this could end up in the stores! The end result? Double the power dissipated in the load, 200W, so the answer is, yes. And not that much worse voltage sag.

But what would be worth playing with now is ESR: at full power the voltage sag varies dramatically once you go over 30mR. This is where the parasitics really start to intrude very significantly, may be much more important than the nominal capacitance.

Frank
No worries, Frank.

The maximum slew rate of a sinusoid will depend on the peak-to-peak amplitude. For a +/-40V sine, the peak slew rate occurs at the zero crossings and is about 5 volts per microsecond. So that rate should also be able to be sustained from peak to peak, which should be able to be encoded even on a bandwidth-challenged CD, in a triangle waveform. Remember that after amplification, the slew rate can be much higher than what's in the same signal when at line-level. Anyway, at 5 V/us it would only take 16 us to go from -40 to +40 Volts.

That will certainly make it easier to do the decoupling.

Ah yes, that generic capacitor model. It's been in the back of my mind the whole time, making me wish I would take a closer look at it. It was just a quick-and-dirty convenience when I first started using it.

What I should probably try to do is get a complete series of values of the frequency-dependent cap models from the Cornell Dubilier site and somehow set them up in a subcircuit so that the desired value cap would be connected automatically, so I could still do the automated sweeps of capacitance values.

Last edited by gootee; 29th August 2012 at 05:28 AM.
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Old 29th August 2012, 05:53 AM   #866
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Here are the files for simulating with square waves.

I hope I didn't leave out anything important.

(These should still work with sine waves, too, but you'd probably want to at least un-comment the .four command and comment-out (with leading semicolon) the meas_cmds.txt "include" statement.)

At some point, I need to go in and set it up with someplace where binary values are set, to select the configuration, and everything else is set automatically, maybe using the u() unit-step function of each binary parameter multiplied by each alternative value and then all of them could be summed, so that the one selected would be multiplied by 1 and the others all by 0, so the sum would be the correct value for the selected case.

Cheers,

Tom
Attached Files
File Type: zip PSU_Test_28AUG2012.zip (14.7 KB, 12 views)

Last edited by gootee; 29th August 2012 at 06:07 AM.
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Old 29th August 2012, 10:11 AM   #867
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Quote:
Originally Posted by gootee View Post
It says 150 Watts PER RAIL (i.e. per voltage rail; one positive and one negative, for a total of 300 Watts if BOTH rails are operating). The RMS Power (dissipated in the load) of the square wave is done as if the negative portion were folded around the axis to be positive. With only one rail, the negative parts would be missing so the power would be half of the total given (half of 300 W).
Oh, awesome! If given a fairly big transformer, 5400uF is the minimum capacitance that works okay with the 150 watts. That totally makes sense.
Quote:
Originally Posted by fas42 View Post
But what would be worth playing with now is ESR: at full power the voltage sag varies dramatically once you go over 30mR. This is where the parasitics really start to intrude very significantly, may be much more important than the nominal capacitance.
I have observed that the standard/economy power caps are much more successful upon power supply boards than high efficiency (low esr) caps. To get the same bass, it takes a huge amount more of the high efficiency (low esr) caps than it would the standard/economy caps. And the only thing more astonishing than the effectiveness difference is the price tag difference which is a bit counter-intuitive. Is it because the slightly more lossy (ordinary) cap is a more effective noise filter?
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Old 29th August 2012, 10:26 AM   #868
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Question Big "local" cap near output device

Quote:
Originally Posted by Nico Ras View Post
Tom,

About two years ago MiiB (Michael) and I was exchanging ideas on an amp design and he came forward with a PCB layout that had a reservoir cap of 10000uF between each power device. i.e. there was a large cap sitting a few mm from the active device.

I thought this was quite a novel idea at the time. I have not tried it in reality but it seems to tally with what you are promoting here Tom. It may not only be what is in the power supply but how it is distributed that makes the difference.
@ Tom: thank you for your kind feedback. It wouldn't make sense to me either, but I have to build in order to get hands-on experience and be more confident on my impressions/thoughts.

@ Nico, Michael (MiiB): I found the quoted post of yours. Did any of you ever build that amp?

One could generalize the thread to Power Supply Reservoir Size and Place ...

Stefano
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Old 29th August 2012, 10:29 AM   #869
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To add a bit more meat to what I said before about the ESR of the smoothing capacitor, here is what happens to the voltage rail when Tom's model is driven by a full power 1kHz sine wave into 8ohms, for 2 different values of the ESR, 30mR and 300mR, nothing else varied:

SagPerESR.jpg

Hopefully what you're for using on your amp are around 30mR or better, but if they're a bit dodgy or long in the teeth then the other value may be closer to what you have ...

Frank
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Old 29th August 2012, 10:39 AM   #870
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Quote:
Originally Posted by danielwritesbac View Post
I have observed that the standard/economy power caps are much more successful upon power supply boards than high efficiency (low esr) caps. To get the same bass, it takes a huge amount more of the high efficiency (low esr) caps than it would the standard/economy caps. And the only thing more astonishing than the effectiveness difference is the price tag difference which is a bit counter-intuitive. Is it because the slightly more lossy (ordinary) cap is a more effective noise filter?
Looking at that last post of mine, what you're saying doesn't make sense at first glance. But this whole power supply linking with circuit with associated parasitics thing is a can of worms, I believe; every case is different, and quite a bit more delving will be necessary to fully understand all the aspects that impact the final, perceived sound ...

Frank
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