Some people prefer to have a regulator with a flat output impedance line in the audio frequency range. Have a look at the mosfet shunt regulator that we're talking about here, and notice where the line starts curving up (higher impedance). There's a variation of the low voltage Salas shunt regulator which I worked on a while ago, extending the low output impedance to much higher frequencies, such that it is completely flat in the audio frequency. Whether this is something you would like or not is besides the point. Some people do and even claim to hear a difference. However, this modification results in lower stability (gain margin) unless one is careful about, among other things, the input capacitance of the drive and shunt transistors (mosfet in this case).
1. What's the worst case Zo over the entire audio band (20Hz-20kHz) of the present Salas Shunt?
2. Tube based shunt regulator will have constant Zo over the audio band, however, will the Zo be lower than the worst case Salas Shunt?
3. Did anyone make a sonic comparison between lower un-constant Zo, versus higher but constant Zo? This question is the most important one when considering between tube and SS shunt regulator.
We should mention BJTs also if lower capacitances than in Mosfets are to be the main goal.
So, it's about 12mOhm at 20KHz and about 50mOhm at 100KHz. I doubt if tube shunt regulator would do better.
Indeed, the question is what's the main goal, lower overall Zo, or higher Zo which is more flat at high frequencies beyond the audio band.
I always find oscillation if trying to use a gas discharge tube directly
Loading a pentode gate should be fine though.. diagrams..
Mounting a tube socket + tube is much easier (hole punch + 2 M3 bolts) than a PCB and a heatsink (probably sitting at 400V) for me.
With the right gate drive I can't see why a power pentode like the GU50 should not make a perfect shunt
. It just needs to be told which voltage to shunt at...
Of course, bjts will bring their own advantages and disadvantages. As I said, some people will prefer a flat output impedance curve in the audio frequency, others will not be convinced. I don't even talk for myself, as I haven't gotten that far yet. But when it comes to technical stuff, we can choose. The guy asked for a shunt reg based on tubes, and it happens I have thought about it, but didn't go as far as to bother with a design. Just thinking out loud for now, that's all.
The boards arrived today. It took almost 7 weeks, but the boards are in very good quality. Warning released.
Although the bass is improced, these big caps seem to have picked up a very low pitched subtle hum only audible with high sensitivity headphones. Should I try grounding the cap
s cases or just go with a different style cap like clarity caps?
