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Old 26th October 2012, 03:39 PM   #1531
DF96 is offline DF96  England
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Quote:
Originally Posted by danielwritesbac
Do amplifier topologies vary widely on power supply requirements,
Apart from PSRR the critical feature (for reservoir cap size, the topic of this thread) is voltage drop in the output stage (including any emitter resistors), especially when compared with the difference between off-load rail volts and required peak output volts. If you increase the voltage drop then you have to increase the cap size so the supply voltage droop under load is reduced.
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Old 27th October 2012, 03:29 PM   #1532
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Default assumptions

How valid are the claims below ?
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Old 27th October 2012, 03:51 PM   #1533
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they are unlike any I can recall seeing before.
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Old 27th October 2012, 05:12 PM   #1534
DF96 is offline DF96  England
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Both appear to say nothing of any value. The first one appears to confuse core flux with winding temperature issues. The second one is insufficiently coherent to be criticised. Where did you find them?
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Old 28th October 2012, 01:25 PM   #1535
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I think the second attachment of post 1532 is showing a futile attempt of continuing to pile on more capacitors to the too small transformer. That is counterproductive. Some of Tom's spreadsheets listed those conditions as impossible, invalid, or a negative number.
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Old 28th October 2012, 04:27 PM   #1536
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Hello,

And where these assumptions are coming from ??
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Old 28th October 2012, 11:19 PM   #1537
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Quote:
Originally Posted by danielwritesbac View Post
I think the second attachment of post 1532 is showing a futile attempt of continuing to pile on more capacitors to the too small transformer. That is counterproductive. Some of Tom's spreadsheets listed those conditions as impossible, invalid, or a negative number.
Though, piling on more capacitors, of the right type and in the right area is highly productive. Because this markedly reduces, shall we call it, micro fluctuations ... higher frequency disturbances of the voltage rails, the sort of thing that loves jumping around inside a circuit via all the parasitic capacitances that are part of real components. If you're into "micro detail" in your sound then this just may be part of the answer ...

Frank
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Old 30th October 2012, 03:01 AM   #1538
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Quote:
Originally Posted by danielwritesbac
I think the second attachment of post 1532 is showing a futile attempt of continuing to pile on more capacitors to the too small transformer. That is counterproductive. Some of Tom's spreadsheets listed those conditions as impossible, invalid, or a negative number.
Quote:
Originally Posted by fas42 View Post
Though, piling on more capacitors, of the right type and in the right area is highly productive. Because this markedly reduces, shall we call it, micro fluctuations ... higher frequency disturbances of the voltage rails, the sort of thing that loves jumping around inside a circuit via all the parasitic capacitances that are part of real components. If you're into "micro detail" in your sound then this just may be part of the answer ...

Frank
And in my spreadsheet, the capacitances are what would have been _required_, in order to have no possibility of even a tiny bit of clipping. It had nothing to do with adding extra (or too much) capacitance to an already-OK situation. It only meant that the cases being considered were either impossibly underpowered, or almost so.
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Old 30th October 2012, 03:14 AM   #1539
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has anybody compared caps with varying ESR's as against mere cap values?
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Old 30th October 2012, 03:33 AM   #1540
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Quote:
Originally Posted by fas42 View Post
Though, piling on more capacitors, of the right type and in the right area is highly productive.
I was looking at some caps I pulled out of a poweramp I'm currently modding yesterday on my LCR meter and took a bit more trouble than normal to understand how the impedance was changing with frequency. They're 10,000uF/50V a fairly typical value for a mid-range amp.

What I saw was though the capacitance was close to the sticker value at 50Hz it fell at higher measurement frequencies. Here are the values I jotted down in my notebook:

50Hz 9,535uF
1kHz 8,035uF
10kHz 1,530uF
20kHz 495uF

Anyone else come across this? I tried a couple of other brands (Rubycon, Elna), similar results. The capacitance is down to 5% of its marked value at 20kHz, seemingly due to internal inductance which, in turn varies with frequency. I calculate about 0.5uH @ 1kHz down to 120nH at 20kHz.
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