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Old 19th July 2003, 11:26 PM   #1
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Default Switched power supply?

Hi.

Have any one tryed using a switched power supply in a tube amp? Is so, what was the result?

/Johan Ch
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Old 19th July 2003, 11:56 PM   #2
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Hi,

Big No,No in my book.

Yuk...,
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Old 20th July 2003, 12:38 AM   #3
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Default We shall light a candle...

I realise I'll be burnt at the stake (or perhaps filament) for uttering this heresy, but I would love to try a decent switched-mode HT supply. Yes, switched-mode used to be noisy. But so is "linear", and a small, regulated supply gets my vote every time.
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Old 20th July 2003, 12:44 AM   #4
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Hi,

Quote:
Yes, switched-mode used to be noisy.
Used to? What has changed since, he wonders and ponders while searching Epping forrest for a fair amount of filaments so he'd burn this little villain for his satanic ideas...

Care to tell us before you reach Joan of Arc filamentary ( penny drops as I type) status?

Cheers and a lot of fun,
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Old 20th July 2003, 12:46 AM   #5
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Generally, not something I'd use, but if there was one available, compact, cheap and quieter than my linear (I'm really doubtful) then I'd try it. SMPS are just a different set of design compromises.
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Old 20th July 2003, 01:11 AM   #6
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The switching frequency of switch mode PSUs is rising all the time. They now have to meet EMI regulations. It ought now to be possible to make one that is cleaner than your average (unregulated) linear supply yet for the same price. Subsequent (analogue) filtering would be cheaper/easier too.
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Old 20th July 2003, 01:18 AM   #7
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Hi,

Cost aside, never cared about thgat much anyways, what about the RFI this kind of supply would spit back into the mains?

But by all means give it a try...as long as I'm not the one having to play testbed.

And this would be for a heater supply, wouldn't it?

Cheers,
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Old 20th July 2003, 01:58 AM   #8
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Well, this just happens to be my area of expertise - smps design, that is - and I can't think of a better way to power a tube amp, with all of the different voltages it needs, most or all of which need to be isolated from the other. The noise? Fdegrove, your fears about noise and line pollution are well justified, but based upon rather dated technology. All the major players in SMPS control IC design have produced power factor correction circuits and the newer resonant mode controllers generate sine wave currents (or voltages, though that is much less common). Given that the minimum switching frequency for new designs these days seems to be 100kHz, it would be difficult to argue that any switching noise would contaminate the audio stream. The very real concern about loop stability of the error amplifier in a SMPS when powering solid state amplifiers (due to the very large amounts of negative feedback typically present) is not a concern in tube amps, and, in fact, having regulated and separated anode supplies eliminates motorboating without having to resort to smaller interstage coupling capacitors (the preferred technique back in the day, as I understand).

Much of the disdain for SMPS in tube equipment seems to be unfounded, knee jerk, or simply a prejudiced against all things silicon. The only good reason not to use one is that they are somewhat difficult to design and the voltage/current combinations most useful in tube amps are not going to be found in COTS* switchers!

* Commercial Off-The-Shelf
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Old 20th July 2003, 02:13 AM   #9
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Rest assured I'm working on an all-discrete version.. slowly but surely.. think I need to grab another pack of transistors though, all the ones I have in my box don't seem to work anymore... (And no "", they seem to die on their own!)

It's a multivibrator (squarewave clock/PWM) > driver > output (TO-220 with some 400Vceo or more) driving an inductor, with high-speed diode to cap the flyback pulse, stepping 12V to whatever voltage.. current best result is 100V 30mA or so, at maybe 60 or 70% efficiency (mostly lost in the crappy drive circuits.. I need some PNPs ). 80% shouldn't be a problem...

Tim
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Old 20th July 2003, 02:48 AM   #10
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Quote:
Originally posted by jeffreyj
The only good reason not to use one is that they are somewhat difficult to design and the voltage/current combinations most useful in tube amps are not going to be found in COTS* switchers!

* Commercial Off-The-Shelf
That's precisely why I think it will be hard to get one that's going to be quieter than my LCLC shunt regged linear supplies. I don't have the resources available any more to tackle such a design, and get good consistent performance out of it, that exceeds what I have now. For instance, the PCB design in these designs can be critical to performance, which for a DIYer is a huge PITA and expense. For a manufacturer, it's merely part of the development costs. Size and weight of my amps aren't an issue, and my linears have been refined to a very high degree.

So, as you have the expertise and tools at hand, how 'bout designing one for us? There's nothing off the shelf I've seen that will do. And I'll gladly test it for you. I'm not silicon-phobic, sometimes it's the best tool for the job.

Until there is actually a unit that physically exists, that is shown to be both technically and sonically superior and affordable, then a SMPS is not the best.

Thwack!*

*sound of gauntlet being thrown
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