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In Reply to: RE: ALT. 1. posted by drlowmu on January 09, 2015 at 08:29:58
"Don't hijack my thread. Just answer the question I posed, IF you seek to participate ."
First of all, it's not your thread. The OP was xcortes. And all I am doing is asking you to explain some points relating to the posts that you made on this thread.
As I said before, "what really matters as far as the amplifier is concerned is the output impedance of the power supply at audio frequencies, and how that impedance varies as a function of the audio frequency." Without knowing that information for the two power supplies, I don't know how to answer your question about which would sound better.
Chris
Follow Ups:
The amp is held constant, ALL we are discussing is the B+ Filter to the Finals, three or four parts choices, and what will perform best, on the basis of instantaneous pulsed power delivery.I am amazed that you don't know, but that is all you really need to say.
Lets see if others will answer and tell us why.
How "deep" does this SET AA Forum go ?? Who responds, and what they say as to "why" will be telling.
Paul Joppa has always been interested in us respectfully commenting on designs he has posted, as a way of possibly improving a circuit's audio performance.
Jeff Medwin
Edits: 01/09/15
"The amp is held constant, ALL we are discussing is the B+ Filter to the Finals, three or four parts choices, and what will perform best, on the basis of instantaneous pulsed power delivery."
I'm not sure what you are driving at when you say "The amp is held constant."
As I have tried to point out several times, the nature of the power demands of the amplifier, as it plays the music, governs the criteria that one needs to consider when designing the power supply. For a class AB amplifier, the net current draw by the amplifier can grow a lot larger during the course of a loud, and maybe and prolonged, crescendo in the music. By contrast, in a single-ended amplifier, which is class A, the net current draw, averaged over the timescale of the audio frequencies it is reproducing, is essentially constant and independent of whether the music is loud or quiet.
Thus, the design criteria for the power supply can be very different in the two cases. For a class AB amplifier, your criterion of looking at how the power supply responds to a stepped load would be quite relevant. For a class A amplifier like an SET, on the other hand, the power supply will not encounter any such prolonged increases in the loading. The important thing for a power supply for an SE amplifier is that it should allow the audio signal to pass through it with minimal let or hindrance. Thus, the important point is that the output impedance of the power supply in the audio frequency range should be small in comparison to to the impedances associated with the output stage of the amplifier itself, so that there is no significant frequency roll-off.
One can fairly easily make some estimates of the impedance at the output of the power supply, but one would probably want to use SPICE in order to do a better job.
Armed with such information, one would be in a better position to say which of the two power supplies you presented would be better. Neither of them looked very good to me.
Chris
and increasing the values of the caps in the CLC version
Dave, since you are doing those simulations in SPICE, I wonder if it is fairly straightforward to include the transformer and rectifier in the sim also? One could then look at the behaviour when the power supply is loaded with a constant quiescent current and a superimposed sinewave current (so I = I0 + I1 Sin(w t), simulating a typical load of an SE amplifier reproducing an audio frequency f=w/(2 \pi)). It would be interesting to see how the magnitude of the audio "ripple" on the power supply output voltage behaved for various frequencies f in the vicinity of the resonance in the low audio spectrum in the drlowmu supply.The reason I am wondering about this is that the approximation of putting that 100 ohm resistor to "represent" the power transformer and rectifier is a bit of a rough and ready one. The behaviour of the impedance curves changes significantly if one alters that 100 ohm value. I think the qualitative feature of the resonance is always going to be there, however.
I'm not familiar with using SPICE, and although I can handle LCR networks fairly easily (when I'm not making stupid typos!) using Mathematica, it's a rather tougher proposition to try to deal with rectifiers without the aid of a dedicated program like SPICE.
So it might be interesting to see what SPICE would reveal, along the lines I was suggesting. Oscillatory loads are much more relevant than stepped loads for probing the relevant features of a power supply for an SE amplifier.
Chris
Edits: 01/09/15
Here is my attempt to simulate the drlowmu power supply, using the same set-up as I think you have in your SPICE simulation. I took the two chokes, 1 H and 1.1 H, to have DC resistance 9.5 ohms each, and I copied your 100 ohms as a model for the power transformer plus rectifier. (I'm really not sure how good a model that is, which is why I've been a bit hesitant about making strong claims about how the PS would perform.) Anyway, with 30 uF and 50 uF for the two capacitors, my calculation in Mathematica then gives this result for the impedance as a function of frequency.
Chris
(This is a corrected plot. Had a typo before.)
Edits: 01/09/15
Guys,
ALL I did was change the Finals filter in Paul Joppa's schematic. This is hardly a supply I would use, as an overall supply. Nor is it an amp I would build.
I was only changing out the high HY high DCR choke, and asking everyone, "which will sound better and why? " !!!
Have fun, hardly anyone has answered my question above.
Jeff Medwin
I'm going to watch the results of these sims be hashed out amongst the group here... and enjoy Dave and Chris' bringing simulations to the table...
I'd just like to point out that it'd be next to impossible to speck a choke at 1.1 henry, vs 1 henry... that has to be an error on jeff's part in the sim.. I can't imagine that .1 henry difference making a significant difference, just know that the chokes will measure differently under different current levels and that he couldn't speck two difference chokes, one at 1h and one at 1.1h.
Jeff we've had debate over different chokes meausuring differenctly...using a LCR or a real bridge, etc.
that is the main probelm with tuning in PSUD2 to these extremes...its difficult to get an accurate indutance on the chokes, it is all guess work.
on another note, I'd still stick with the two 1h chokes and believe Dave's simulation shows lower impedance across the board, albeit with the resonance around 50-60hz... which might help dynamics :)
Rage,
I wonder,..... what if one 1 HY choke is wound with 10% more turns than the other, and maintains a similar gap?
Jeff
Out of Depth.
from my limited experience inductance doesn't necessarily work that way.
is this extra .1 henry essential to your tuning?
"from my limited experience inductance doesn't necessarily work that way."
Indeed. The inductance goes like the square of the number of turns, so an increase of 10% in inductance would be achieved with roughly a 5% increase in the number of turns, not 10%.
Chris
Well, we do have the resonances in the same spots :-)
what concerns me in your sim is that it drops below the series resistance values at low frequencies and mine levels out at the series resistance numbers.
dave
"what concerns me in your sim is that it drops below the series resistance values at low frequencies and mine levels out at the series resistance numbers."Sorry! You are quite right. I had a stupid and inexcusable typo in my Mathematica routines. I've corrected the two plots now.
Chris
Edits: 01/09/15
Thanks Dave,Not too many of us amateurs are comfortable with Spice. Could you please tell us ( me ) what that means?
Also, could I ask you what "you" think might sounds better between the two filters, and why ?
Thanks, you are a benefit to us all.
Jeff Medwin
Edits: 01/09/15
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