That's inversely proportional to the primary inductance then. Do you see high primary inductance as a worthwhile feature of a power trafo ? What makes the sintered core worth paying extra money for? (I can't see that the power saving is worth having seeing as its only the loss factor of that primary inductance which is going on the bill for the average domestic consumer who pays by the W rather than the VA.)
You know I feel I must relate to you something that happened to me at college . Our college was mostly ex RAF ( 1974 ) . Peter Platt my electronics teacher was asked by me to recommended a capacitor for a power supply I was building . I kicked off by saying perhaps 1000 uF . Peter struggled and said much smaller as the instantaneous current would be gigantic . He got so bogged down he almost said 1 uF . In despair he called across the courtyard to Mr Evens who was passing for help . Evens taught electrical engineering . He looked at the blackboard and said " Peter you forget one thing , there is no such thing as a perfect capacitor thank goodness so 1000 uF will be fine " . Peter then said pay attention when doing electrical engineering , sometimes it will be your best training . I went on to qualify as an electrical engineer . I took my electronics as an endorsement .
Dvv and all came to 2 x 22 000 uF / 100 W I seem to remember when this came up last ? The idea of 4700 uF next to each output device appealed to me . PSU's can be engineered by ear . One company said it's 10 000 uF better than others of 22 000 uF . I would beleive that can be true . Not on ripple but balance of performance . I buy large capacitors . It seems to me ones that claim Audiophile qualities are often larger . It might be true if not going too far to use for example 100 ( 80 ) V types when only needing 63 V . Some say this is very bad practice as the cap will reform and have a higher value ( perhaps not so bad ) . It has always seemed to work for me . I am convinced it produces a better sound and not too expensive . The sound seems less bloated and cleaner at HF . My theory is the needs of higher voltage also give better overall performance .
I loved the idea of feeding Audio into the PSU to test it , well said FAS42 .
Dvv and all came to 2 x 22 000 uF / 100 W I seem to remember when this came up last ? The idea of 4700 uF next to each output device appealed to me . PSU's can be engineered by ear . One company said it's 10 000 uF better than others of 22 000 uF . I would beleive that can be true . Not on ripple but balance of performance . I buy large capacitors . It seems to me ones that claim Audiophile qualities are often larger . It might be true if not going too far to use for example 100 ( 80 ) V types when only needing 63 V . Some say this is very bad practice as the cap will reform and have a higher value ( perhaps not so bad ) . It has always seemed to work for me . I am convinced it produces a better sound and not too expensive . The sound seems less bloated and cleaner at HF . My theory is the needs of higher voltage also give better overall performance .
I loved the idea of feeding Audio into the PSU to test it , well said FAS42 .
Sintered material toroidal core will start to saturate WAY after the usual fare. I do not mean at say +20% of the standard, more like at 220% of the standard. Hence, its short term power peaks are much greater than with normal fare.
Or, if you prefer, instead of using a say 500 VA standard, you could use sintered 300 VA with the same, or even somewhat better effect.
This can become critical when you need high power, but are really pinched for space. Most amps use much lower values anyway, I believe only Krell has used (don't know if they still do) sintered core toroids in some of their models.
There's an interesting paradox with sintered cores. Over time, they actually IMPROVE in performance, they become more efficient. Of course, this is no tremednous effect, something like 1...2 %, but I know of nothing else that pulls off that trick. The explanaito I was given was that when you pass large currents over sintered material, they tend to compact over time, reducing the miniscule air pockets and improving efficiency.
I have verified this with my line filters. The same filter, after say two years of operation, WILL measure better by 1 or 2 dB without fail, in respect to its initial values. All the L elements of my filter use sintered materials. I don't mind the price premium.
Once, a long, long time ago, somebody told me that one can expect 0.7 Amps RMS from a 1,000 uF value in peaks. However, that man wasn't one bit interested in audio.
And he surely didn't know Wayne, with his Incredible Speaker Band.
The simple fact is that most, if not all, of our discussions are related to the most extreme and severe conditions of operation.
While that may be good engineering practice, it is way out of touch with how the vast majority of audio power amplifiers are actually used in practice. I'll wager that 99% typically dissipate an average power of less than 1 W, although obviously there may be peaks of 10 or more Watts.
I will also wager that in fact, if not for the advertising which has totaly distorted the public's perceptions, 99% of audio users would in fact be perfectly happy with a 50 WRMS/8 Ohms amp, IF it was done right, meaning not regarded as a poor man's product. It suited the manufacturers to make more money by promoting power, as this enabled them to bundle this with more useless commands and features and make some extra profit, arther than to work on quality, which would incur greater costs with no obvious effect.
But such an amp would not have like 4,700 uF, or if you are lucky 6,800 uF capacitors, it would have 15,000 uF or even 22,000 uF caps. Yet, these caps, as well as the transformer, are INSIDE the case, and cannot be shown off to prospective customers, while silly little LEDs and switches can be paraded and peddled to the gullible public.
Now I'm intrigued even more - what I've learned about transformers is that the flux in the core goes down slightly under load. So other than asymmetric loading of a trafo (say using a half-wave rectifier which presumably we avoid anyway) what can lead it to saturate under load?
In my understanding the flux in the core is the integral of the applied voltage, minus the primary losses. So the flux isn't a function of secondary load, providing the load is AC (symmetrical). So does core saturation occur because the amp (+attached speaker) effectively becomes an unbalanced load?
That's a dam good question . Any DC component on the mains also . I suspect as people more often feed current into the grid from soar panels it will increase . Someone said the local incinerator power plant in Sweden was causing near DC spectrum ( hetrodyning ) . He was getting a rolling noise like sea waves ( loud then quiet ) .
Well, given how evil soma loads can become, I wouldn't be surprised one bit.
My own AR94 speakers are no gentle lillies at all, they are bad at around the 200-300 Hz range, i.e where the lower bass is being cut off by a solitary inductor, if memory serves. Impedance drops, and phase shift is around -45 degrees.
Now, that isn't good, but imagine what happens with Wayne's system, which is low impedance to start off.
We have a real misunderstanding going on here now, MGH! Not quite sure how it happened, shows you how important one's choice of words is, but what I've bolded above is exactly what I would suggest strongly that you do do! In other words, bypass the amp end, don't bypass the supply end. Are we in sync now ...??
Frank
Ok for my clarification .... Bypass caps at amp end only (psu output to board ) and not at main caps ...
Yes ...?
dvv,
50W enough? pretty much in the ballpark. I'm a regular guy myself, but what's 6dB between friends?
a.wayne will love this discussion (if you haven't already gone through that, haven't read the last few pages)
I'm using 6volt rms when playing loud , ok its nominal 1ohm (300-22k) , only man amplifiers need apply ...
Yes DIY, 3way direct drive ribbon (no transformers) hybrid.
Bel Canto class-d mono's did not work , as well as others . Krell,Threshold ,PS audio, adcom(565/555) are the few that has worked , i did not like the sonics of the adcoms ..
The PS audio works amazingly well considering 3pr output ....
Bel Canto class-d mono's did not work , as well as others . Krell,Threshold ,PS audio, adcom(565/555) are the few that has worked , i did not like the sonics of the adcoms ..
The PS audio works amazingly well considering 3pr output ....
That's exactly what all systems should sound like: I found it amazing, 20 years ago, trying some monster amp that would crush my toes if it fell on them, start to collapse as you pushed the volume up. A "miserable", 20W, chip amp should give you that impression if it has a decent power supply; it's what's called "engineering" ...
Frank
Hi dvv,
The calculation example that you quoted was not calculating the required reservoir capacitance for a power supply. It was merely to help illustrate what types of calculations could be performed, with an equation that had been derived.
In that particular example, the result meant that IF you needed a capacitance to supply all of the current for the first zero-to-peak rise of a 5-Amp-Peak 30 Hz sine wave, then if that capacitance was not at least 53050 uF, the voltage across the capacitance would drop by at least one volt.
The result was subsequently verified with an LT-Spice simulation.
That equation was actually just an approximate result; a sort of "worst-case estimation" equation:
(13b): C ≥ a / (πfΔv_MAX)
where a is the 0-to-peak amplitude of the capacitor's sinusoidal current waveform, f is frequency in Hertz, and C is capacitance in Farads.
The more-complete picture, for the scenario being considered in that derivation, is this one:
(17): C ≥ Δi / ( 2πf∙(Δv - (ESR∙Δi)))
Equation (17) gives the capacitance value, C, that would be required in order to supply the current for the first quarter-cycle of a sine signal of frequency f (in Hz), with 0-to-peak amplitude Δi Amperes, while causing the voltage across the capacitor to dip by no more than your choice of Δv Volts.
To use equation (17), it will be easier to first set ESR to zero, calculate a C value, find an estimate for ESR for that C value at the frequency being used, and then re-calculate the C value with the ESR value.
If we still want to just account for the whole sine wave, we should be able to simply double the C value given by equation (17), since we're considering only the positive or negative half-cycle, but not both, and the other half of the half-cycle of a sine wave is symmetrical and thus encloses the same area (its integral), i.e. the same amp-seconds value, as the first half.
[Edit: Note, too, that positive capacitor current was defined as current flowing into the positive-voltage-designated lead of the capacitor. So, typically, for this scenario, both Δi and Δv will be negative.]
For more of this exciting story, including some of the considerations involved when Δv - (ESR∙Δi) gets close to zero, go to
http://www.diyaudio.com/forums/power-supplies/216409-power-supply-resevoir-size-169.html#post3320547
Tom
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What's in a name ...?
I remember a hulking GAS being quite a disappointment ...
Krell was OK, but tends to sound fairly rough. ME, an Australian brand with an intelligent power supply for its time, a vast array of paralleled small value smoothing caps, did pretty well ...
Frank
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