F5 Power Supply Caps Seem Small

NV&H · 12th January 2009, 11:48 PM

I'm speaking without knowledge here, but the capacitors that Nelson uses for the raw ps in his F5 strike me as very small. Is that because it's a Class A amp at low power where average current doesn't change? Seems that once it began operating in Class AB mode, ps voltage would start to swing around a bit. Is that not true?

If so, would larger caps help? Any downside to that?

gary s · 13th January 2009, 12:20 AM

Nelson's design is 60,000uF per rail for the F5.

For 25 Watts Class A into a load that can go down to 1 ohm without misbehaving as Nelson so eloquently puts it, means the PSU is more than adequate.

Nelson has always been known to have beefy PSU's in all his amps.

It will not hurt at all to build your own F5 with more capacitance, mine has 100,000uF per rail and sounds so powerful and in control at all times.

Cheers

Gary..

NV&H · 22nd January 2009, 07:23 PM

The caps don't have to be as large on Class A amps because they have a bias current and so the average current doesn't really change much?

Nelson Pass · 23rd January 2009, 01:41 AM

Depends on how you look at it. The large quiescent current creates
large ripple so you see more supply issues there. On the other hand,
these same supply issues arise under high power conditions with
Class B or AB.

This is DIY however, and over-the-top capacitance is part of the
landscape because it's not that expensive and there is little
controversy over the benefits, especially CLC or CRC.

12th January 2009, 11:48 PM	#1
NV&H diyAudio Member Join Date: Feb 2005 Location: Charlotte, North Carolina	F5 Power Supply Caps Seem Small I'm speaking without knowledge here, but the capacitors that Nelson uses for the raw ps in his F5 strike me as very small. Is that because it's a Class A amp at low power where average current doesn't change? Seems that once it began operating in Class AB mode, ps voltage would start to swing around a bit. Is that not true? If so, would larger caps help? Any downside to that? __________________ NV&H

22nd January 2009, 07:23 PM	#3
NV&H diyAudio Member Join Date: Feb 2005 Location: Charlotte, North Carolina	The caps don't have to be as large on Class A amps because they have a bias current and so the average current doesn't really change much? __________________ NV&H

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13th January 2009, 12:20 AM	#2
gary s diyAudio Member Join Date: Nov 2002 Location: Australia	Nelson's design is 60,000uF per rail for the F5. For 25 Watts Class A into a load that can go down to 1 ohm without misbehaving as Nelson so eloquently puts it, means the PSU is more than adequate. Nelson has always been known to have beefy PSU's in all his amps. It will not hurt at all to build your own F5 with more capacitance, mine has 100,000uF per rail and sounds so powerful and in control at all times. Cheers Gary..

23rd January 2009, 01:41 AM	#4
Nelson Pass The one and only Join Date: Mar 2001	Depends on how you look at it. The large quiescent current creates large ripple so you see more supply issues there. On the other hand, these same supply issues arise under high power conditions with Class B or AB. This is DIY however, and over-the-top capacitance is part of the landscape because it's not that expensive and there is little controversy over the benefits, especially CLC or CRC.