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SET Power Supply Regulation

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Konnichiwa,

serengetiplains said:
Has anyone any experience regulating SET output power supplies?

I do.

serengetiplains said:
My personal preference leans to tube-based regulation, but I welcome any comments.:D

I found that regulated supplies, no matter the topology all benefit from a comparably large value, high quality output capacitor and from a comparably high internal impedance (much higher than commonly found).

By the time that was done and correctly tuned and other relevant issues where addressed I found very little sonic difference between a valve rectified & valve regulated supply, a choke filtered valve rectified supply and a solid state rectified and regulated (rather filtered, via a gyrator) supply.

Of course, you need to competently design each type of powersupply and no, the solid state version looks not at all like thge common circuits used.

For the most reliable DIY implementation I would stick to Valve rectified CLCLC/LCLC supplies. As long as they are implemented correctly they are much less troublesome than others. If space or money is a premium (which in DIY Gear it should not be) then I'd go straight to all solid state implementing all the tricks I learned over time....

Sayonara
 
diyAudio Senior Member
Joined 2002
Hi,

I found that regulated supplies, no matter the topology all benefit from a comparably large value, high quality output capacitor and from a comparably high internal impedance (much higher than commonly found).

By the time you're finished with that your "regulator" will have become a trickle charger for the cap, a mains to circuit buffer, a capacitance multiplier (if you're clever), an electronic choke (even more clever) , a ripple filter (clever but tricky), in short the circuit you're regulating won't even know it's there...unless the cap's too small.

After all that you'll be listening to your PS cap + the circuit at work almost as if you're running it from a battery supply but possibly even better.

Cheers,;)
 
Circlotron said:
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...


Graham,

How nice it is to have some fresh thought into a topic.
I'll consider your input, but it may take me some time....:spin:
 
Konnichiwa,

fdegrove said:
By the time you're finished with that your "regulator" will have become a trickle charger for the cap, a mains to circuit buffer, a capacitance multiplier (if you're clever), an electronic choke (even more clever) , a ripple filter (clever but tricky), in short the circuit you're regulating won't even know it's there...unless the cap's too small.

Yes, that is the logical conclusion. I found that adjsuting the timeconstant between regulator output and capacitor to a certain value and keeping the output impedance of the regulator below a certain value gave the best overall compromise and in this case the circuit is a regulator with a finite lowish impedance at low frequencies (usually a lower Z at LF than passive LC supplies) and at high frequencies it is tricklecharger for the Cap.

The key is in juggeling several interetsing requirements and getting the relative values and one absolute value right....

fdegrove said:
After all that you'll be listening to your PS cap + the circuit at work almost as if you're running it from a battery supply but possibly even better.

Yes, I did something like that once but found in thend that really big capacitors seem to sound worse at low frequencies than the regulator.... As said, all a matter of the correct turnover.

Sayonara
 
The line/phono preamp I'm building has 2 OC3's at its PSU output( per channel - current set by IXYS ss curent regulators). Each set of OC3's is bypassed by a 0.56uf film capacitor. At this point, I'm a little worried about noise coming from the 0C3's, not so much for the line stage, but for the phono.

Should I worry?

I've read that VR tubes dislike any significant capacitance following them. Is there any way around this. Will the .056uf bypass cap help reduce any noise that they do make?

Am I just being paranoid?

thanks

pete
 
diyAudio Senior Member
Joined 2002
Hi,

Will the .056uf bypass cap help reduce any noise that they do make?

Quite to the contrary.
Those caps are already too high in value; 0.047µF to 0.100µF maximum.
If the VR tubes tend to oscillate, upping the value of the bypass caps will only make matters worse.

Normally a VR tube in good working condition will produce 1mV of broadband noise, much less obtrusive than a similar stack of zener diodes.

I've read that VR tubes dislike any significant capacitance following them. Is there any way around this.

Yes, resistive or inductive isolation but you may just as well have used a series regulator in that case IMO.

Cheers,;)
 
diyAudio Senior Member
Joined 2002
Hi,

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.

True but that resistance isn't such a bad thing and it's also part of a big inductor that actually very effectively isolates the tube from its PS.
Shunt the inductance with a big cap and you'll see what I mean.

The only reason I'd forego the reasoning behind this and still opt for a regulated supply is the added benefits of it, not just the simplified notion most of us have about regulators that desperately try to regulate like don Quichotes fighting windmills.

As said before, SE amps are class A and don't require much regulation in the traditional sense of the word.
Nonetheless the sonic benefits are quite obvious IMHO especially so when the rest of the system is equally well isolated from the vagueries of the mains.

Cheers,;)
 
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