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Old 22nd July 2012, 05:28 PM   #201
Krisfr is offline Krisfr  United States
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One more point and I will not ask any more questions.....

Should each rail have its own transformer and bridge rectifier and which is better

400 100uf caps
40 1,000uf caps
4 10,000uf caps
1 40,000uf cap

should each output transistor have a local cap and a bypass cap of about .1uf ?
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Old 22nd July 2012, 05:35 PM   #202
gootee is offline gootee  United States
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And now were back to bigger is better.....which contradicts my findings...Sorry.
There is feedback in this equation.. that compensates for rail-sag... It seems like there's a delicate balance in things...If I just add capacitance my system losses its speed and sense of space.
Yes. I would think less about capacitance in the PSU and maybe think more about getting decoupling capacitances as close as possible to the power output devices.

For speed (and the timing and phase accuracy that give the detailed soundstage image), you would need something like at least 10uF or 20uF per volt of rail voltage, with one inch or less of total connection and lead-spacing length, at each power output device.

Better yet, use multiple smaller caps that add up to that value, in parallel, with star-like connections that don't share conductors, to lower the total inductance (and ESR) below any of their individual inductances (or ESRs).

The total inductance and ESR would each be divided by the number of parallel caps. I would try to use at least three caps in parallel. (Note that the total connection length can be longer, with multiple caps, but I would still try to keep each cap's total connection plus lead-spacing length at one inch or less, if possible, or at least keep the total for all of them at one inch per cap or less.)

Then add more capacitors as close to each device as possible until you get a total of up to about 2200uF per max output amp, for each device. You don't have to go that high but it would improve the bass and mid response. If possible, make all capacitor connections like a star, where none of them share any common conductor. That will lower the total inductance (and ESR), very drastically. Using more smaller capacitors in parallel is better, especially if they can be placed to not share conductors until they get to the power and gnd decoupling points. But obviously there is limited space. So just do it as well as is practical.

Last edited by gootee; 22nd July 2012 at 05:55 PM.
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Old 22nd July 2012, 05:36 PM   #203
gootee is offline gootee  United States
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Quote:
Originally Posted by Krisfr View Post
One more point and I will not ask any more questions.....

Should each rail have its own transformer and bridge rectifier and which is better

400 100uf caps
40 1,000uf caps
4 10,000uf caps
1 40,000uf cap

should each output transistor have a local cap and a bypass cap of about .1uf ?
Assuming 40000uF is needed, somewhere in between 40x 1000uF and 4x 10000uF. How about 8x 4700uF?
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Old 22nd July 2012, 05:41 PM   #204
MiiB is offline MiiB  Denmark
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In speed I mean the ability to resolve micro-dynamic details. Like nails touching strings or lips forming words... all taking place in time and context with the music.
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Old 22nd July 2012, 06:08 PM   #205
gootee is offline gootee  United States
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Originally Posted by MiiB View Post
And now were back to bigger is better.....which contradicts my findings...Sorry.
There is feedback in this equation.. that compensates for rail-sag... It seems like there's a delicate balance in things...If I just add capacitance my system losses its speed and sense of space.
Interesting: So if the rails are held too tightly to a fixed voltage by too much reservoir capacitance, then maybe the decoupling caps that supply the fast transient currents can't respond as well, since the rail voltage would need to be able to drop just to make them send out the needed current! So then at least part of the current will have to try to come through the rail inductance, instead of from the decoupling caps. But for fast transients, it can't get there in time to provide an accurate transient response, because of the rail inductance. Also, the rail voltage gets disturbed by more than it would have (by the current trying to come through the rail inductance), possibly partially defeating the purpose of adding the reservoir caps in the first place.

(AS USUAL, we might know what kinds of things could be happening, but we have no idea of the relative magnitude or potential signficance of each one.)

So maybe the conclusion should be that if psu reservoir capacitance is raised to the overkill level, then the decoupling capacitances should also be raised to the overkill level, to increase the sensitivity of their current-output response to the smaller voltage variations caused by the too-large reservoir caps. <grin> (Or maybe the total decoupling capacitance should be kept equal to the total reservoir capacitance?)

This does point out the fact that more decoupling capscitance gives faster response and better dynamic accuracy, since when a power output device "opens wider" (lowers its resistance), and the rail voltage then dips a bit, more decoupling caps would produce more current, faster.

I wonder if there is a point where there could be so much decoupling capacitance (with low-enough inductance and ESR) that the whole system would become "too sensitive". Or maybe it would just keep getting better.

Last edited by gootee; 22nd July 2012 at 06:37 PM.
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Old 22nd July 2012, 09:35 PM   #206
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Quote:
Originally Posted by Krisfr View Post
One more point and I will not ask any more questions.....

Should each rail have its own transformer and bridge rectifier and which is better

400 100uf caps
40 1,000uf caps
4 10,000uf caps
1 40,000uf cap

should each output transistor have a local cap and a bypass cap of about .1uf ?
Since "there is not a perfect formula" and We go for experience... I would go for low E.S.R caps 105c 6.800X6 or 4.700X8 per rail. some people go crazy and go for 1.000.000uf per rail (LOL) thinking they will get "better" sound than a "normal" and moderated power supply.
for the transformer...if your amp gets 650watts at 4ohms We multiply 650x1.41 and we get 916VA so I would go for a 1K transformer...1.600VA I think is an "overkill" again!!!
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Old 23rd July 2012, 12:56 AM   #207
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So 34 x 4700uF per rail for 500W/8 is overkill ?
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Old 23rd July 2012, 02:57 AM   #208
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So 34 x 4700uF per rail for 500W/8 is overkill ?
Well, Krell amps use hefty power supplies...I guess 160.000uf per rail is "normal" with 3kVA transformers for them. For Krell there is not such as "overkill".
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Old 23rd July 2012, 03:38 AM   #209
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Another example is with Bryston.
Bryston 14BSST is 600watts at 8ohms using 44.000uf per rail.
Bryston 28BSST is 1,000watts at 8ohms using 80.000uf per rail.
so, as We can see here, Krell likes "overkill" power supplies compared to Bryston amps.But does that mean Krell amps sound better than Bryston amps because krell uses "overkill" power supplies?...I do not think so!!!There is not an exact capacitance for power supply. other way "all" 100 watts or so at 8 ohms amps will have the same capacitance in all power supplies.
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Old 23rd July 2012, 04:20 AM   #210
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I use 12 x 27,000 uf Panasonic 105C caps for each channel (324,000 uf) fed from seperate posivitve and negative RC snubbed TO 247 60 amp discrete hexfet bridges. Multicap 2uf film and foil bypasses then 1 mh chokes and then 4 x Blackgate 10,000 uf FK with 2,200 uf N/100v bypasses near the output stage. Thats for each channel in a Krell KSA 100 chassis. Front end is run from seperate PI filtered transformers and preregulated supplies - output is just 100 watts Class A per channel Borbely Milleniums all jfet/fet discrete direct coupled and servoed.
A 1/2 second AC line soft start is mandatory. Transformers run barely warm to the touch.

Runs parralled modified Martin Logan CLX (1/2ohm in the top end with a Raal ribbon) with Dynaudio subs - tomorrow i test 2 JL 113 Fathoms with it.

The Borbely is smooth and very dynamic despite just 100 watts, the Bryston 4B SST 2 was gritty , unresolving, even harsh on the same load despite more power.

Last edited by ticknpop; 23rd July 2012 at 04:33 AM.
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