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Interesting New Amplifier from Thomas and Stereo. Large capacitor banks good or bad?

stevec67 said:
Yes, indeed. I have seen designs where there are banks of big caps stabilising a PSU power rail, and smaller caps in parallel with them. The argument given is that the smaller caps in parallel with the bigger caps give the best of all worlds. It sounds plausible, like all these things, but most hifi BS sounds plausible, which is why it gains traction and people (I'm no different BTW) who don't have any detailed electronic knowledge pick up on one thing and decide that this is the solution.
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Any solid state amplifier out there has the small capacitors close on the power amplifier board(s). The last thing you want is the fast Class AB half wave switching currents travelling all the way back to the reservoirs.
 
stevec67 said:
Yes, indeed. I have seen designs where there are banks of big caps stabilising a PSU power rail, and smaller caps in parallel with them. The argument given is that the smaller caps in parallel with the bigger caps give the best of all worlds. It sounds plausible, like all these things,
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Is it easier to re-oxygenate by taking quick shallow breaths or slower deeper ones.

Multiple small capacitors or fewer bigger ones.

This is of course a highly imperfect analogy (anyone know why?? Answers on the back of a postcard..) but maybe there is at least some truth or anti-truth in it.
 
Those familiar with Doug Self's Blameless amplifier articles, will have seen how managing where those dirty half wave Class AB currents flow is important.
Having many small capacitors can easily make this worse.
Small capacitors also have shorter service life than large cans and owners should be mindful of the capacitor desoldering challenges seen in the MDAC
 
rontoolsie said:
Is it easier to re-oxygenate by taking quick shallow breaths or slower deeper ones.

Multiple small capacitors or fewer bigger ones.

This is of course a highly imperfect analogy (anyone know why?? Answers on the back of a postcard..) but maybe there is at least some truth or anti-truth in it.
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I'd say it was highly imperfect because the two systems are massively different and the physics of charging capacitors is very well understood, so drawing an analogy with an even more complex and totally different system is a hiding to nothing. For an analogy to work it has to be something that you understand. Electricity in a wire is like water in a pipe going downhill. OK, got that. We all understand how that works. Capacitors are like buckets of water at intervals in the pipe. OK, got that too. But you don't go the other way. "Oh, removing balls from a bucket is like radioactive decay. They are both first order processes where the rate is proportional to the concentration, hence N=No e^-kt. So now you understand how many balls are left. Clear?"
 
stevec67 said:
I'd say it was highly imperfect because the two systems are massively different and the physics of charging capacitors is very well understood, so drawing an analogy with an even more complex and totally different system is a hiding to nothing. For an analogy to work it has to be something that you understand. Electricity in a wire is like water in a pipe going downhill. OK, got that. We all understand how that works. Capacitors are like buckets of water at intervals in the pipe. OK, got that too. But you don't go the other way. "Oh, removing balls from a bucket is like radioactive decay. They are both first order processes where the rate is proportional to the concentration, hence N=No e^-kt. So now you understand how many balls are left. Clear?"
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The correct answer is that there is 200+ml of dead space in your airways before any air exchange can occur...so a breath of 250ml only gives 50ml of fresh air (80% is wasted)but a breath of 1000ml give 800ml of fresh air (only 20% is wasted).

There is no such equivalent in an RC circuit.

I did say it was an imperfect model!

I am well familiar with solving the differential equations of charging and discharging RC circuits.
 
Just big enough so that the caps never empty, so it depends on max power and output level. Ime 500uf per watt per rail suffices. My own 180w monos have 160,000uf per channel on 400va traffo and very short routed psu, with sufficient local capacitance right by the output devices.

It depends on the circuit.
 
Some people would argue that 320,000 uF of capacitance fed by "only" a 400 VA transformer is a mismatch in extremis.

Krell would argue that you need a 3 kVA transformer.
 
...and would be wrong...

Good PSRR, first, is the answer - always.

This is exactly like that fad of c. a decade ago, where the 'only ' answer was battery suplies - all led by people who couldn't design for good PSRR, let alone design a suitable, sufficient voltage regulator.

There was even one then prominent-advocate-company doing this as add-ons [Vince somethng or other], where sterophile (iirc) test on 'their' supply showed rampant egregrious mains harmonics, far in excess of even a stupid -basic trafo-rect-cap - on a battery supply - simply because apart from anything else - they didn't even understand how to wire things up.
 
Jean Hiraga did that in his famous Class A amplifier in 1979.

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My bad, its 80,000 and 400 va per channel.

I used to own a ksa200, mk1, full time class A. Cost £600 to recap it, 10 years ago. No better in the bass than a ncore400 with the sq/rt of SFA reservoir capacitance in the matching smps
 
quickie said:
Not watched video. What design is it.?

I was talking to Colin Wonfor last week about the Claymore and power supply capacitance.

I've got one of his old designs here that uses quarter of a farad and it definitely doesn't sound bloated and slow :)

Saying that, I remember paying around with NVA amps many moons ago, and while they responded well to huge toroids, anything more then 10k uf on rails made them sound flat and boring. Go figure.
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Just completed all 4 version of the KIT PCB.
5W SECA sounds amazing caps 2 off 47,000uF
SECA A/B amp caps 2 off 22,000uF 5W class A 15W class A/B gives 18W Build this one Paul I put mine in chassis you sent me THANKS
A/B 15W Amp caps 2 off 10,000uF gives 18W
A/B 30W Amp caps 2 off 10,000uF gives 40W
Tested on Mintrals and Ruark Sabre, all stereo.
When next chassis come will do bridge balance in version at 80W A/B 10W A class.

When you come to set them up A/B bias first at 100mA and SECA at 1A.
Also adjust DC bias to less than 1mV

Have fun
 
But then, much more capacitance is needed in a class A amp, with high standing bias, or else the ripple will be too high.
 
irb said:
But then, much more capacitance is needed in a class A amp, with high standing bias, or else the ripple will be too high.
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I found that with a Threshold Stasis clone I built. I ended up with just over 400,000uF, anything below that just resulted in a general hum from the speakers.
 
I'd be interested to see the performance of a multiple small series/parallel cap bank vs a pair in good big uns in series under typical power amp conditions. Actual vs simulated results.
 
30 or so years ago, McCormick had the DNA series of power amps...DNA standing for Distributed Node Amplifier.

What set these apart was that the reservoir capacacitors were pretty much piggybacked over the output devices..so many small capacitors instead of one or two bigger ones.

Is there some technical reason why this was not eventually industry standard? Superfically this makes sense to place the capacitors as close to the load as possible, just like you do with voltage regulators. I do not know enough about amp design to have an opinion one way or the other.
 
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