| planet10 |
| quote: | Originally posted by JoeBob
Adding an L would smooth things out, but are there any obvious downsides I don't know about? |
On a SS amp with low voltage & high current you have to worry about the voltage drop across the choke (and the power it will have to dissipate).
dave |
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| millwood |
| quote: | Originally posted by JOE DIRT®
try the test out with a random signal (pink noise) |
I don't know what additional insight one gains by doing this. Simulations, by definition, aren't real and 100% reflective of reality. But as long as it captures the key "themes" of the issues one is interested to study, they have done their jobs.
And in this case, I think pedja's simulation so far has answered the questions vs. cap size. Using pink or purple or white noises does not foundamentally or directionally change the conclusions we have so far.
It seems to me, after having gone through all the charts, that it is clear that unless there are some particular designs in the lm chip, it is unlikely that it will benefit from small PS caps. |
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| DrewP |
AFAIK, Pi filters are really good for class A amps where the current draw from the psu is a constant value. The whole point with a choke is to not allow sudden rushes of current through.
In an amp with a class AB output stage such as the LM3875 (although all stages up until the output stage appear to be current sourced class A stages) the need to pull a quick slug of current from the power tranny would be compromised by the presence of a choke.
Yes a choke would cut HF PSU noise but I think it would kill dynamics by destroying the fast recovery attributes of the PSU as well. (assuming that one believes in the benefits of a fast recovery PSU)
Drew |
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| JoeBob |
| How about the use of a very small choke? Just to filter out high-frequency noise? |
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| janneman |
| quote: | Originally posted by DrewP
AFAIK, Pi filters are really good for class A amps where the current draw from the psu is a constant value. The whole point with a choke is to not allow sudden rushes of current through.
In an amp with a class AB output stage such as the LM3875 (although all stages up until the output stage appear to be current sourced class A stages) the need to pull a quick slug of current from the power tranny would be compromised by the presence of a choke.
Yes a choke would cut HF PSU noise but I think it would kill dynamics by destroying the fast recovery attributes of the PSU as well. (assuming that one believes in the benefits of a fast recovery PSU)
Drew |
Drew,
With the choke filter, it's the last cap that furnishes the "slug of current". Since the diodes only conduct 20% or less of the time, the xformer couldn't do it for 80% of the time anyway, even if there is no choke.
Jan Didden |
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| IanHarvey |
It might be interesting to repeat the simulations with a low-value resistor (say 1 or 2 ohms) between the diodes and the filter caps.
This will lower the mean voltage on the caps (and so the charging pulses should be longer and less spiky), but without the voltage ripple of the small capacitor version.
Cheers
IH |
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| Joe Rasmussen |
| quote: | Originally posted by ALW
You should do an FFT of your raw PSU if you think it's just 100Hz ;)
Andy. |
I have! Or just connect a little speaker with a suitable DC blocking cap across your reservoir cap and listen to it. Then ponder that you must be listening to that minus x dB down.
Have you ever done it with a choke input PSU ? Very instructive! Nice enough to hum along to.
;)
But this whole discussion about reservoir caps can only be resolved by doing the obvious.... try it. Even better vary its value as we often vary other parameters and then listen to it. Why should these be any different?
Personally I suspect the whole thing come down to dynamic behaviours that are very difficult to predict and even more difficult to model. The way it affects the ability to portray pitch and pace in the mid-bass area alone seems to point to a possible resonant interactions between the dynamic behaviour of the circuit and the ability of a frequency based LF PSU to hang in there. The PSU does not have a constant source impedance (even with regulators difficult to achieve) and the constantly changing load imposed on it... and a merry dance indeed!
But don't bother figuring it out when the solution is: Just experiment - it will be better for your sanity.
Batteries anyone? How about setting up a trickle charged batteries where the averaged trickle is set above the averaged out (over time) current requirement? (Then allow for suitable peak current ability and test PSU Z on peak load) I have done it to Turntable power supplies (TT using DC motors). Could work a treat?
Certainly the noise floor would be dramatically lower, that should have other benefits like reduced haze and greyness this potentially adds to the sonics of most amps.
I make some interesting tube amps that use an infinitely high AC Z, an inverse bandwidth power supply. The amp circuits rides the power supply (and hence is isolated) and it is the power supply itself that is left to sort it out. There are many ways to tackle same or different problems. Maybe that is why we like our chosen toys ?
Joe R. |
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| DrewP |
| quote: | | With the choke filter, it's the last cap that furnishes the "slug of current". Since the diodes only conduct 20% or less of the time, the xformer couldn't do it for 80% of the time anyway, even if there is no choke. |
Yes, the cap provides the slug to the amplifier chip but then how quickly is it refilled?
On our 50hz (Australian) supply, if as stated (and I have every faith that this is true) the diodes conduct for 20% of each half wave (which occurs 100 times a second). So, you're trying to top up the second PSU reservior (the one after the choke) with a short term current pulse that lasts 2ms (20% of 10ms).
So once the final reservior is depleted of its charge, how quickly can it be refilled with a choke in the way?
You folks out there who love doing simulations and drawing beautiful curves and graphs for us, please simulate a 100hz square wave with 2ms on pulses and 8ms off pulses trying to flow through a series choke being fed by a low impedance transformer and show me how compromised and fubarred the output to the final psu cap after the choke is.
My prediction is that the result will not be fast refill of the reservior.
Drew |
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| RichardN |
Would probably work best if the amp was amplifying. Listening to the steady state noise probably isn't that instructive.
The original Gain has the transformer and diodes in a separate box. I wonder how much the characterisics of this connection scheme (impedence and inductance of the wiring etc.) have been used to alter the characteristics of the high frequency burst as seen by the power opamp. |
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| millwood |
| quote: | Originally posted by Joe Rasmussen
But this whole discussion about reservoir caps can only be resolved by doing the obvious.... try it. Even better vary its value as we often vary other parameters and then listen to it. Why should these be any different? |
there is no question an actual prototyping will give the ultimate answer but if simulation can get us 80% of it using 20% of the resources, it is a pretty good starting point.
the proliferation of simulation in recent years is a good supporting evidence of that.
| quote: | Originally posted by Joe Rasmussen
Batteries anyone? How about setting up a trickle charged batteries where the averaged trickle is set above the averaged out (over time) current requirement? (Then allow for suitable peak current ability and test PSU Z on peak load) I have done it to Turntable power supplies (TT using DC motors). Could work a treat?
Joe R. |
maybe the opposite is more useful in an amp. batteries have high output resistence. so one way to go might be to use a battery in parrallel with a conventional PS (isolated with a diode) that outputs slighly below or at the battery's voltage. Under slight load, the battery is the only one contributing. Great.
Under heavy load, the battery's voltage drops, and the conventional PS, with its low impendence, starts to kick in, providing the neccessary "headroom".
| quote: | Originally posted by DrewP
My prediction is that the result will not be fast refill of the reservior.
Drew |
I agree with your intuition. a pi filter is a low-pass filter. and it will not react quickly with a high-frequency current drain.
I will do some simulation later today. |
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| millwood |
On the idea of using a low-value resistor in place of the inductor in a pi filter. I have seen it mentioned 20 or 30 years ago (I am quite sure that some tube amps actually use this set-up for filament).
But I am not quite sure how well it works with amps as you essentially increased the output impedence of a PS. during the 80% of the time when the cap is discharging, that's like increasing the ESR of that cap substantially. It may induce parasitic oscillation as well. |
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| millwood |
the PS circuitry here.
I varied the inductor from (almost) zero H to 100mh (the upper limit of what one might use in real life). |
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| millwood |
this is the output for no inductor (I think I set the inductor value to 0.00001mh).
the green curve is the charge current going through the diode (right scale), and the blue one is the voltage over the load (right scale).
as you can see, voltage fluctuats from 32 - 35v, or 10%.
note that the "fuzzy" voltage line is due to driving a 20khz current source. |
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| millwood |
here is the case with a 100mh inductor.
the voltage fluctuates from 32v to 33 v (3% variation). the thick voltage line, again, is a 20khz signal on top of the basic 50hz carrier.
it does seem to be that case that using an inductor helps smooth out the 50hz carrier but unfortunately, the 20khz variation gets a low worse: 0.2v variation vs. almost nothing in the prior case.
conclusion? inductors are better for PSs that deal with more steady load. |
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| millwood |
| sorry, I attached the wrong chart. here is the one for a 100mh inductor. |
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| kropf |
I promised some measurement results, so here they are. They are probably not as extensive as you had hoped.
First, the amp vitals. LM3875 inverted configuration, dual EI 24VAC transformers in a separate box, vanilla 400V, 35A diode bridges, 2200uF caps next to the chips.
The main test I ran was to place an 8ohm resistor across the +/- terminals of one of the diode bridges. IIRC, the positive rail, although with hindsight the negative rail would have been a better choice given the 30 dB worse PSRR at 1 kHz. Qualitatively, with my ear very near the speaker, I could hear little difference in hum/hiss even though one rail had been dropped asymmetrically to 22.7V from 35V and had a huge 5V(p-p) 120Hz ripple.
Unfortunately, the dynamic range of the scope was only about 80 dB, so it was not possible to resolve really low level detail.
Freq. Level
------ --------
0 Hz 0 dB (22.7V)
60 Hz below noise floor at -60 dB
120 Hz -22 dB (1.8Vrms)
240 Hz -47 (0.1Vrms)
360 -48
480 -69
600 -63
720 -70
840 -79
960 -76
So, given the much larger current drain, these values match Pedja's sims fairly well. I didn't try a measurementat high frequency to see diode RF noise.
I then removed the 8ohm load resistor and played a 1 kHz test tone. Significant harmonics of 1 Khz appeared on the supply rail due to the split supplies, although at a lower level than the -50dB of the 1Khz signal (output about 1 Watt). 4 kHz was below the noise floor. These harmonics could conceivably give the chip PSRR problems at high frequencies and high output levels.
Jeremy |
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| apassgear |
| quote: | Originally posted by janneman
With the choke filter, it's the last cap that furnishes the "slug of current". Since the diodes only conduct 20% or less of the time, the xformer couldn't do it for 80% of the time anyway, even if there is no choke.
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I have good experiance using input chokes on class A amps, they get as clean as you ever thought and it's a test that I would do with these class B chip amps provided I had a test bed for it and extra secondary voltage needed for this setup.
Looking for a good sound I would test different cap sizes and types, and use something like 10 to15 mH gapped chokes
Thing is I have not built this chip amp yet to do some testings, when I do I'll report back.
Keep on with these nice ideas, pedja's modellings are very enlighting even for my humble understanding. |
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| millwood |
| quote: | Originally posted by kropf
Freq. Level
------ --------
0 Hz 0 dB (22.7V)
60 Hz below noise floor at -60 dB
120 Hz -22 dB (1.8Vrms)
240 Hz -47 (0.1Vrms)
360 -48
480 -69
600 -63
720 -70
840 -79
960 -76
Jeremy |
so essentially having huge amps doesn't help much (diminishing rate of return).
I got similar results on a discrete amp I am working on. Injecting 5v/50hz ripples to the supply rail (otherwise 36vdc) induced an increase of 0.004% in THD on an 8ohm load, with just some simple RC decoupling for the input and vas stages.
I basically concluded that 6600uf per rail will be sufficient for my application, even for driving 4ohm loads.
I did a quick simulation of the "audioamp" circuitry in switchercad. with a 2vac/50hz ripple in the positive supply rail (10vdc), thd is 0.2759%, vs. 0.2708% without the ripple.
this is a pretty typical simple discrete amp, without any current source or curren mirrors. so real amps should perform a lot better than this. |
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| Pedja |
Hi Jeremy,
Thanks for the results. One thing I forgot to post earlier: all the graphs with log Y axis I posted are relative to 1V (0dB) and not to the carrier. So, the absolute levels in your measurements are showing better figures then they would be if scaled as those in my simulations. However, since the current drawn in your case was notably higher (fluctuates between 3A and some 4.3A if I am not mistaken) the things still could fit to each other.
I ran shortly that 2200uF/8 Ohms load case and the spectral content of the harmonics relates very well to your measurements, though cap’s ESR and parasitic series resistance could change this content somewhat. But what puzzles me is that you get 5V p-p swing around the 22.7V. I see swing between some 23V (or 22.7V you mentioned) and 34V (it can’t reach 35V anymore even at the peak) so it seems to me I am missing something about your circuit.
(Generally I also believe that our results are likely in agreement, just need to synchronize them.)
| quote: | | I then removed the 8ohm load resistor and played a 1 kHz test tone. Significant harmonics of 1 Khz appeared on the supply rail due to the split supplies, although at a lower level than the -50dB of the 1Khz signal (output about 1 Watt). 4 kHz was below the noise floor. These harmonics could conceivably give the chip PSRR problems at high frequencies and high output levels. |
Yup, something like harmonic distortion at PSU lines. And seems to me like there is an IMD here also.
Pedja
Ps: Two more notices about the previous graphs that I forgot to give along the road. All FFTs are done for 10th cycle (90ms-100ms period). If some ask why not the logarithmic freq axis - MicroCap can’t show the logarithmic X axis to display a negative values. |
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| Pedja |
| quote: | Originally posted by IanHarvey
It might be interesting to repeat the simulations with a low-value resistor (say 1 or 2 ohms) between the diodes and the filter caps. |
Here they are.
1000uF, 0.1 Ohm ESR, 350mA drawn
10000uF, 0.1 Ohm ESR, 350mA drawn
So I should correct my previous answer to Jan. According to what I saw looking at more cases now, series resistance contributes to noise if used with a higher capacitances. With smaller cap it could be beneficial. It seems this should be tuned.
Pedja |
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| kropf |
| quote: | Originally posted by Pedja
[B]
I ran shortly that 2200uF/8 Ohms load case and the spectral content of the harmonics relates very well to your measurements, though cap’s ESR and parasitic series resistance could change this content somewhat. But what puzzles me is that you get 5V p-p swing around the 22.7V. I see swing between some 23V (or 22.7V you mentioned) and 34V (it can’t reach 35V anymore even at the peak) so it seems to me I am missing something about your circuit.
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The PSU was actually charging and discharging between 20.2 and 25.2 V. I think the explanation is in the transformers. I am using 120VA EI transformers. The resistance of the secondaries must be limiting the charging rate and the load regulation may be rather poor for these transformers, since they were running very near the VA rating . The trace on the scope looked more like a triangle than a sawtooth. A toroidal transformer could probably charge at a higher rate. I also have a 1 meter run of 18 gauge wire from the PSU to the amplifier. It shouldn't be too hard for me to calculate the resistance of the wire and determine if there was a significant voltage drop across it.
Jeremy |
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| tbla |
| please use "monstersize" trafo when performing those tests - so you are absolutely certan that there is no limitations.....ei regulates better than torroid btw......but anyway, very interesting test - thanks. |
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| JoeBob |
Wouldn't a film cap in parallel with the main psu capacitors shunt alot of the high-frequency content to ground?
I know alot of people don't like bypass caps, but here sounds like somewhere they might come in handy. |
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| theChris |
| such is reccomend on the datasheet, but not located near the main caps but rather near the chip itself. |
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| janneman |
| quote: | Originally posted by JoeBob
Wouldn't a film cap in parallel with the main psu capacitors shunt alot of the high-frequency content to ground?
I know alot of people don't like bypass caps, but here sounds like somewhere they might come in handy. |
Not really. The cap is the CAUSE of the hf content. If you read the earlier posts, you will see that increasing the cap generally increases the hf content, because the current pulse gets narrower/sharper and that means a higher hf spectrum.
It would be different if the hf signal was fed to the cap via an impedance, then you would have the normal low pass filtering action.
Jan Didden |
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| Joe Rasmussen |
| quote: | Originally posted by JoeBob
Wouldn't a film cap in parallel with the main psu capacitors shunt alot of the high-frequency content to ground?
I know alot of people don't like bypass caps, but here sounds like somewhere they might come in handy. |
I agree with Janneman, it might actually make it worse. A classic Dr Jeckyll vs Mr Hyde. It may increase the peak current at HF and be worse, on the other hand it may present a Lower Z at those freqs to the subsequent load. Which is preferred? It may be a 'horses for courses' situ. Almost near unpredictable. This is why you cannot really design overall 'by the book' and why a combination of gut feeling and thorough experimentation cannot be substituted. What comes to mind is a time (and I suspect that it still does happen) when there were those who said that all amps sounded the same. Yet Matti Otala (the TID guy) said there are thousands of reasons why they sound different. I have never heard two amps sounding the same. That's the honest truth. So power supplies make a difference, that we can all agree? So why be surprised if some use it to shape the kind of sound they like? Provided the end result works, right?
Joe R. |
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| millwood |
| quote: | Originally posted by Joe Rasmussen
So power supplies make a difference, that we can all agree? So why be surprised if some use it to shape the kind of sound they like?
Joe R. |
there is no question that power supplies make a difference. But how many of us can hear it at -50db over 1Khz, on an amp with over 40-50db psrr?
I cannot.
Materiality is the key, everyone. |
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| carlosfm |
Guys, I don't want to start a discussion here, we're just debating this, and this is an interesting one.
But it seams to me that what is good for digital is not good for analog.
Would you put a single electrolythic cap on the PSU pins of a DAC?
I would bypass it with a small ceramic/polyester cap near the chip's pins.
Is this bad for a GC?
Wouldn't a PSU be better if it has low impedance at high frequencies? |
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| Pedja |
Beside the content and level of the HF noise generated by the larger cap value, the problem with larger_main+small_bypass_cap is the way in which these two caps are integrated. The larger cap has inductive rise at some point (which is for us too low). So we put one small cap that can keep the impedance low further above. So we’ll indeed have further above that our wanted low impedance, but the meeting point of two caps might be one new resonant frequency.
As Carlos pointed out, in the digital (and high speed opamp) circuits it is usually beneficial to put small bypass close to the chip, because here you have more HF problems than in classic slow analog circuits. Bypass in the analog circuits can make more problems than it solves.
Pedja |
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| carlosfm |
| quote: | Originally posted by Pedja
As Carlos pointed out, in the digital (and high speed opamp) circuits it is usually beneficial to put small bypass close to the chip, because here you have more HF problems than in classic slow analog circuits. Bypass in the analog circuits can make more problems than it solves.
Pedja |
OK for power op-amps.
Modern signal op-amps are very fast, and do benefit from bypassing.
Like the LM6171.:eek:
Excellent, BTW.;)
And my beloved OPA627.:D |
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| Pedja |
I took some steps toward the real world. One result of it is attached. Supply is made of 400W, 2x22V toroidal transformer, double bridge formed by SB560 and 2x4700uF per voltage, then I have the regulation. Drawn current is 80mA. Absolute level is not scaled either to DC or to 1V. I think it is anyway good for better understanding of what comprises the waveform regularly called a 100Hz ripple.
(Interesting thing: the higher noise floor you see below 300Hz went down for 10-15dB when I added 1 Ohm series resistor after the rectifier. So, the RC filter on work or something else…)
Short experiments with some parameters told me that the situation might not change exactly as predicted in the simulations but the simulations were far from being totally wrong either. Once again, take them as the orientation of how some parameters influence the things but remember that the transformer and diodes actually used as well as the parasitic properties will determine the final results.
I might do one day more extensive and systematic measurements of this kind, varying as much of parameters as possible, but it could last. So, no comparison from me for now but someone else might send a classic 1000uF GC supply FFTed (at the moment I don’t have any such GC at hand and I could only improvise) so we can compare it (of course “generally” and not “directly”) with the graph above.
Pedja |
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| millwood |
I think my take away from this is that 1) there is little high frequency content in voltage. and 2) paired that with an amp having decent psrr, PS ripple shouldn't be a major problem.
However, i would add that when large caps are used, current going through the diodes / bridge may carry a lot of HF content. Thankfully, that gets BETTER under heavier load. |
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| carlosfm |
:angel:
Amen.
Oh, yes, a small value resistor after the bridge helps.;) |
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| millwood |
| quote: | Originally posted by carlosfm
Oh, yes, a small value resistor after the bridge helps.;) |
a 50w rms / 8ohm amp can drop upwards of 3amps. For a 1-ohm resistor, that means a drop of 3v peak per rail.
I am not sure sure if that is worth a 10 - 15db drop in the <300hz range, where psrr usually is pretty good. |
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| carlosfm |
| quote: | Originally posted by millwood
a 50w rms / 8ohm amp can drop upwards of 3amps. For a 1-ohm resistor, that means a drop of 3v peak per rail.
I am not sure sure if that is worth a 10 - 15db drop in the <300hz range, where psrr usually is pretty good. |
Yes, I agree, 1 ohm is too much, but 0.1~0.22 should be OK.
I was talking PSUs generically.
As for op-amps (even power op-amps in GCs) I always put a 0.1 cap between + and - pins on the chip.
That makes PSRR at high frequencies a little better. |
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| janneman |
| quote: | Originally posted by carlosfm
Yes, I agree, 1 ohm is too much, but 0.1~0.22 should be OK.
I was talking PSUs generically.
As for op-amps (even power op-amps in GCs) I always put a 0.1 cap between + and - pins on the chip.
That makes PSRR at high frequencies a little better. |
It doesn't do diddly for PSRR. PSRR is an attribute of the amplifier itself.
It MAY do a little to reduce hf ripple, but with .1uF it will be minimal.
Jan Didden |
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| Joe Rasmussen |
Hi Guys
Pedja sent me an email earlier in the week. When I mentioned that I had done FFT measurements of power supplies, he asked, as I recall it, if I could supply one of the JLTi or gainclone, using 1000uF caps etc.
Can't supply exactly that at the moment, but will as soon as possible and post it here.
What I will furnish is an FFT measurement of a hybrid amp (tube front end & Mosfet outputs) capable of 115W into 8 Ohm and 180W into 4 Ohm. This is an amp called the JR-100 that I designed for a company called Audio Fidelity about 12 years ago.
A few details so that the measurement can be seen in correct light. Power supply is +&- 50V DC, from 500VA tx, uses standard 35A bridge (nothing special) and 15.000uF/63V electros. The bias current is 300mA. The measurement was taken across the plus 50V rail, so it is single ended (I could do it across both rails - but needs to configure for balanced input on my equipment - trickier to wire up - but could be illuminating to do).
A 'true' AC measurement shows that total ripple is 55mV. Because it is a 'true' measurement, this includes the 100 Hertz ripple and all harmonics in total.
The measurement is calibrated. The 0dBu line at the top is 0.775V (following the normal convention). That means we can roughly calculate the AC value of every harmonic. For example, the 9th harmonic at 900 Hertz is -60dB, that means we can calculate its AC value as -60dB relative to 0.775V RMS. Your calculator will show that to be 0.775/1000 = 0.775mV out of 55mV total.
Please feel free to make your own comments and observations. Certainly there are similarities with Pedja's, but I don't think his is calibrated in msg #131?
Joe R.
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| janneman |
Joe,
This is no load, just the 300mA bias?
Did you do any measurements under (sine or music) load?
(I know, you give us the world, and immediately we want another one. Sorry)
Jan Didden |
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| carlosfm |
| quote: | Originally posted by janneman
It doesn't do diddly for PSRR. PSRR is an attribute of the amplifier itself.
It MAY do a little to reduce hf ripple, but with .1uF it will be minimal.
Jan Didden |
Hi Jan,
Yes, you're right, it reduces ripple, nothing to do with the chip by itself.
Anyway, what value would you suggest?
Thorsten suggests 1uf, but that's a big cap to put under a circuit between + and - pins of an op-amp most of the times (at least if it's a polyester cap). |
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| Joe Rasmussen |
| quote: | Originally posted by janneman
Joe,
This is no load, just the 300mA bias?
Did you do any measurements under (sine or music) load?
(I know, you give us the world, and immediately we want another one. Sorry)
Jan Didden |
If I was to do that, there would be a near infinite set of parameters to define. If under load, what fequency or frequencies, single or multiple? What ouput level? 1W? 10W? 100W? What load, 8 Ohm, 4 Ohm or some reactive load simulating a speaker As for using music, how do you do FFT measurments under music/dynamic conditions when what you see above is averaged out over 1000 samples? The very nature, and shortcoming (?), of FFT measurements precludes it.
I do believe, at least hope, that one day a meaningful standardised (or set of) dynamic tests can be devised. With the increase of computing power, such type of tests may become a reality? That will get away from the severe limitations of static measurements.
That may be the 'another world' you wanted? Make that both of us!
Joe R. |
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| millwood |
| quote: | Originally posted by Joe Rasmussen
If under load, what fequency or frequencies, single or multiple?
Joe R. |
probably should be done under random noises with some concentration on the lower frequencies (a pink noise for example?). |
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| millwood |
| quote: | Originally posted by Joe Rasmussen
Hi Guys
Joe R.
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I think it will be hard to argue, given the magnitude of the noise and its frequency distribution, that a reasonably decent amp with 50db psrr will suffer from an average PS whose fft looks like the one you presented. |
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| sss |
| quote: | Originally posted by Mesh
When ever i have built power amps, ive always used large filter caps. How come the gainclone only has 1000uF per channel?
What happens if you use lots of uF's in a gainclone |
yup , that was the original question :)
well Mesh,
did u ever think why a simple op amp circuit doesnt need a 10000uf filter caps ?
thats because the size of the filter caps is depended on power output .Most chip ams are rated at < 50W so less capacitance needed , plus chip amps got good psrr and low "on" current .
One more reason : those chip amps are intended for applications that require small space ,thats why in the application notes u see small filter caps , this is the minimum size required .
there is nothing wrong with using large filter caps for any amp but too much wount do any good eather . |
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