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In Reply to: Gaincard power supply opinion posted by manx on April 16, 2000 at 22:56:00:
manx wrote:"Ever since I saw the earlier postings on the Gaincard, my nipples have been ROCK HARD! ;-) As a result, I'm starting a couple experimental amp projects using a similar approach. One thing I was hoping to get an opinion on is how Kimura san could get away with only 1000 uF of filter bypass in the power supply (actualy noted to be placed in the amp itself). Is this due to the amps power supply rejection capability or to the placement of the caps close to the I.C. or is there another way of reducing ripple current that would be placed upstream of the caps?"
There may actually be some larger caps in the power supply unit. I mean, it (the Power Humpty) does seem rather large for only having to house a 170VA transformer and a rectifier bridge. But even if that's not the case, I can't say I understand his reasoning for using such a small value cap for the power supply filter.
The literature says:
"If energy supply depends on the capacity of filter/condensers, you can easily lose the freshness of sound. The high capacity transformer of Model 4700 (170 VA) regulates enough energy to support the extremely small filter/condenser (1000 uF) of Model 4706, enabling it to trace avalanches of fff."
I don't understand why he seems to think that a power transformer with relatively high internal resistance and plodding along at only 60 Hz is somehow superior with regard to "trace avalanches to fff." 60 Hz power transformers are decidedly "slow" devices. It's good to have a high VA transformer so it doesn't load down when refreshing the filter caps, but no matter what the VA rating, it can only refresh the caps every 1/120th of a second (assuming a full-wave bridge rectifier) and higher frequency transients could easily draw down those little 1,000 uF caps resulting in significant voltage drops on the supply rails.
Also, within a given voltage rating, the smaller the cap the higher its ESR, making it "slower" with respect to a larger cap with a lower ESR (or a parallel array of smaller caps adding up to a higher total capacity). So I fail to see the advantage here other than being able to say "World's smallest filter/condenser" which might impress those who don't understand the consequences.
If you want to "trace avalanches to fff" and want to do it at frequencies higher than 120 Hz, you want a low-impedance, high-capacity voltage source.
se
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Follow Ups
- Re: Gaincard power supply opinion - Steve Eddy 01:27:24 04/17/00 (2)
- Re: Gaincard power supply opinion - manx 13:40:39 04/17/00 (1)
- Re: Gaincard power supply opinion - Steve Eddy 15:00:51 04/17/00 (0)
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