Simplistic MosFET HV Shunt Regs

[Salas]

We use small ref filtering capacitor here and it does not go because it comes up fast, although I have shown it could be Zener protected in an old post for avoiding the odd smoke. I will see about it again when I will check the SSHV2 if with a bit bigger cap.

 

[iko]

Which cap are you talking about? Across the shunt mosfet I use a MKP 156nF cap, series with 1R, and the result is excellent. Any lower value cap could not be used in my case, and the 1R was compulsory too.

Before the reg I have a RCLC filter with low ESR, large C values.

 

[Salas]

The Vref filtering capacitor (c2). That one needs time to charge up and can give a spike when on/off. Also the wider the BW, the spike can be more vicious.

 

[iko]

The Vref filtering capacitor (c2). That one needs time to charge up and can give a spike when on/off. Also the wider the BW, the spike can be more vicious.

I see. I use a 33uF there. Anything lower was a bit too much noise and the slow startup too fast for what I wanted.

 

[merlin el mago]

Technically if you want the achieve the lowest output impedance that the design might allow you should use force/sense connections. However, we started talking about the Kelvin connection only when I introduced the bjt buffer before the shunt mostfet on the low voltage circuit, where the design promised low output impedance well beyond 20kHz. In that case, there was no way to achieve it without the Kelvin connection. If the current Salas HV schematic doesn't have the buffer, then you don't worry about low output impedance at 20kHz anyway. The HV shunt reg that I built recently has both the bjt buffer and the force/sense wires, and low output impedance in a wide frequency range.

Thank Iko, could you post your schematic?

 

[Salas]

I see. I use a 33uF there. Anything lower was a bit too much noise and the slow startup too fast for what I wanted.

Depends on the application's own gain and noise floor demands. I try keep it all MKP if possible since its mainly used for not that spectacular noise floor tube line stages and the like.

 

[AndrewT]

C2 is at zero volts at start up.
As the CCS starts to pass current, the voltage across Q4 & Q2 b-e rises rapidly to become enormous.
Expect the devices to pack in eventually.

 

[iko]

Thank Iko, could you post your schematic?

There you go: http://www.diyaudio.com/forums/power-supplies/197332-hv-shunt-regulator.html

 

[Salas]

C2 is at zero volts at start up.
As the CCS starts to pass current, the voltage across Q4 & Q2 b-e rises rapidly to become enormous.
Expect the devices to pack in eventually.

With the value used it holds fine for maybe 3 years now in so many builds, but if with bigger cap, a zener should be employed as discussed.

 

[merlin el mago]

There you go: http://www.diyaudio.com/forums/power-supplies/197332-hv-shunt-regulator.html

Thank you.

 

[merlin el mago]

Hi, I had given you that link before I think. I have changed nothing yet. P2P or vero are OK. At your voltage skip the zeners.

http://www.diyaudio.com/forums/powe...tic-mosfet-hv-shunt-regs-182.html#post2604016

Salas I suppose that I can implement four wire remote sense Kelvin in your HV reg?

 

[Salas]

Sure, I have shown schematic in the past. As in the other regs. SSHV2 will have as standard, if proven it mixes well. But I will have to go visit a friend that has #26 and horn speakers, and tweak there, compare SSHV installed already, gather opinion etc. Want to keep it comparably low parts count with gains in frequency etc. with no further stages, to can practically give better subjective impression also. A juggling act on trying to surely practically improve on a so widely liked and used circuit, not easy.

 

[merlin el mago]

Sounds very good SSVH2

 

[merlin el mago]

What about the quality of AZ1 Siemens?

?

 

[Joao@AltheaMusica]

Originally Posted by merlin el mago http://www.diyaudio.com/forums/powe...et-hv-shunt-regs-post2714890.html#post2714890
What about the quality of AZ1 Siemens?


Nice Rectifier and good sounding, but I prefer the 5xx versions because they are more practical (socket). If you are looking for more exotic rectifiers have a look at the 80 or 274.

 

[merlin el mago]

Originally Posted by merlin el mago http://www.diyaudio.com/forums/powe...et-hv-shunt-regs-post2714890.html#post2714890
What about the quality of AZ1 Siemens?


Nice Rectifier and good sounding, but I prefer the 5xx versions because they are more practical (socket). If you are looking for more exotic rectifiers have a look at the 80 or 274.

Thanks for the info

 

[regal]

I've been doing some more rigorous testing of my SSHV SPUD Single Feed OPT SET heamp.

With the spud tube (WE417) loaded at 100k (600ohm headphones on the 32 ohm secondary) I can easily output 1V (2.5rms in) with good THD (2H -60dB).

Now when I plug in the 32 ohm headphones on the 32 ohm secondary (equals a 5k load on the tube) well after .5V's and above the distortion get very high (2H -20db by .8v out).

Now 32 ohm headphones don't need .5V's and overall at normal listening levels this thing sounds great but I find it odd that this circuit runs out of steam so fast with the tougher load on the tube.


Could this be related to the undefined SSHV issue with inductive loade? Or is it more likely a transformer or poor operating point issue? Tried what is on the schematic as well as ~150V/15ma/1.8V. My SSHV is set for 40mA and has ~200V in. The second mofset reads about 280F on its tab.

 

[Salas]

If it could oscillate it, you would see a wide spray of harmonic noise across the FFT screen. If that's not happening its highly probable the THD is happening due to the audio amplifying section. But, can it be needing more current to set for such driving conditions?

 

[iko]

I don't think it's the shunt reg. My shunt reg (a different design but still shunt reg) works just fine with basically the same circuit as yours using a 6C45P-E.

What will the usual fft on a soundcard show if the tube is oscillating at a few MHz?

 

[Salas]

High harmonic content, both odd and even, without signal even.