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Old 14th May 2004, 08:38 PM   #1
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Default SET Power Supply Regulation

Viewing low power SET schematics (45, 300B, 2A3, others) thinking I'll dive in and build one, I wondered, hey, why not regulate the power supply (input/driver + output)? If regulating line-level power supplies increases the stage's musicality (unquestionably does), regulating a SET output power supply very likely will benefit the circuit by equal, perhaps greater amount. The SET topology, moreover, seems ideally suited to output power supply regulation given the modest current demands of the output tube.

Has anyone any experience regulating SET output power supplies? My personal preference leans to tube-based regulation, but I welcome any comments.
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Old 14th May 2004, 08:52 PM   #2
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Well, one thing to remember about SET is that it is class-A operation, and so the current draw of the output stage is fairly close to constant, thereby reducing the need for regulation. A class-AB push-pull stage, by contrast, has a constantly varying current draw, and actually would seem to benefit more from a regulated supply.

That said, you could go ahead and regulate. The problem is finding a regulator that can supply something like 400-600 volts and 120 to 150 mils of current, and not sound worse in the signal path (it is in the signal path) than the rest of the SET amp.

Good luck with the project, and keep us posted - Pat
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Old 14th May 2004, 09:12 PM   #3
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Quote:
Originally posted by tubesguy
The problem is finding a regulator that can supply something like 400-600 volts and 120 to 150 mils of current, and not sound worse in the signal path (it is in the signal path) than the rest of the SET amp.
Hi Pat,

I've recently thought about that notion that the power supply is in the signal path. I agree, an amplifier merely reforms and modulates electricity coming from the wall, so everything---the entire power supply, all the cables, etc---is in series with the signal path. All other things being equal, a simpler signal path is IME preferred. But it occurred to me perhaps the better amplifier might one having the simplest, shortest signal path per se, combined with a regulated (and thus a somewhat complicated) power supply. My experiences experimenting with mains regulation seem to bear this out. In my system, I have a balanced transformer plugged into a PS Audio P600 plugged into a balanced transformer plugged into an Exactpower unit. I noticed better sound adding each additional component, and have many times tested this perception by simply plugging my gear directly into the wall. Here's the interesting implication: all these components (P600 etc), which combine to form a rather complex power supply, are in series with the signal path. It seems, then, that power supply regulation be a good thing, assuming it's done right.

Tom
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Old 14th May 2004, 09:48 PM   #4
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Quote:
Originally posted by tubesguy
Well, one thing to remember about SET is that it is class-A operation, and so the current draw of the output stage is fairly close to constant, thereby reducing the need for regulation.
Pat, are you speaking from experience here? My intuition tells me amplification class is probably not relevant to whether regulation might improve a circuit. What we want to know is whether non-amplification-related variations in power supply current (and voltage) are reduced by power supply regulation. I realise that in a class A circuit those variations will be a small percent of overall current drawn. Those variations, on the other hand, might constitute a quite audible percentage of overall (amplification-related + non-amplification-related) current variations. Voltage stability is a somewhat separate but related concern.

Tom
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Old 14th May 2004, 10:27 PM   #5
jlsem is offline jlsem  United States
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Quote:
Has anyone any experience regulating SET output power supplies? My personal preference leans to tube-based regulation, but I welcome any comments.
My experience and that of others is that a brute-force regulated power supply is the way to go, i.e. LCLC with chokes about four times the value of critical inductance and not too heavy on Farads for the capacitors. High bandwith chokes are helpful as well.

John
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Old 15th May 2004, 01:15 AM   #6
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Hi,

Quote:
LCLC with chokes about four times the value of critical inductance and not too heavy on Farads for the capacitors.
If you must use alot of PS filtering_never hurts_put those big caps either in front or inbetween the chokes.
Use smaller value polypropylenes after the last choke for best sound.
Same goes for active regulation, bigger caps infront, smaller but fast caps behind the reg.

Beware not to put a large cap right behind a tube rectifier or you'll have yourself some fireworks.

Quote:
High bandwith chokes are helpful as well.
Most people don't seem to distinguish between chokes for PS duty and anode loading anymore, using one for the other.
To my mind this is a major mistake.

With SE designs everything you use in the amp is audible to some extend.
When you decide to regulate one end you'd better regulate the lot or nothing at all IMHO.

Cheers,
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Frank
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Old 15th May 2004, 03:26 AM   #7
jlsem is offline jlsem  United States
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Quote:
My experience and that of others is that a brute-force regulated power supply is the way to go, i.e. LCLC with chokes about four times the value of critical inductance and not too heavy on Farads for the capacitors. High bandwith chokes are helpful as well.
And I forgot to mention: a big fat power resistor to bleed off at least 10% of the current is also necessary for good regulation.

John
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Old 15th May 2004, 12:35 PM   #8
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How much resistance is there in the output transformer primary? 100-300 ohms? This resistance appears in series with the DC supply to the anode and even if you had a perfectly regulated supply the actual regulation would be limited by the transformer resistance.

A truly adventurous person might experiment with a bit of *negative resistance* in the power supply to dial out the effect of the transformer winding...
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Old 15th May 2004, 01:36 PM   #9
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Default The big ones in front ?

Hi Frank,

Quote:
If you must use alot of PS filtering_never hurts_put those big caps either in front or inbetween the chokes.
When simulating a power supply with PSUD I find that using the small caps in front of the choke and then the large cap behind the choke produces far less ringing. Is this something to consider, the ringing of a power supply ?

Greetings,
Jim
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Old 15th May 2004, 04:00 PM   #10
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Default Re: The big ones in front ?

Quote:
Originally posted by jim
When simulating a power supply with PSUD I find that using the small caps in front of the choke and then the large cap behind the choke produces far less ringing. Is this something to consider, the ringing of a power supply ?
Jim,

Yes!

http://www.vt52.com/diy/tips/tips_supplies.htm

Tom
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