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In Reply to: RE: 5687 & OB2 as an excellent HT regulator posted by NAQTEN8 on February 23, 2015 at 14:07:13
This (something like this) circuit works. I've heard it and I want it. It's sounds better than any other regulators or stabilizers I've heard so far for this purpose (spdif buffer in a CD transport). The guy who draw me a sketch which I used to draw a schematic was really sloppy so the sketch he draw is hard to read. This guy died, so I can't get the explanation from him.
What if R1 and R2 are used only as a voltage divider to which center we connect 5687 pin 8 (ground center tap). So let's get that out of the schematics for now.
I made a new schematics. R5 says 120-150K at the sketch. Could this work?
Follow Ups:
Question #1
What voltage output do you want?
Question #2
What tube is V2?
Question #3
Do you want it a variable output supply?
DanL
1. 90-100V
2. OB2
3. Yes
Here you go...
R4 is the voltage adjust pot.
DanL
Thanks a lot. I made this and it works amazing for the purpose. Whatever someone might think, sound quality went up quite a bit with this regulator.
You find a schematic for some obscure tweak or project. You build it and it always sounds great. Been there myself since the 1970s.
Not trying to be sarcastic here but it wouldn't hurt to analyze how the circuit is making the improvements you are hearing.
We actually see and hear with our brain, not our ears and eyes. They just collect the data. It's our mind that makes that data good or bad.
Yes, this version of the basic circuit will work.
With a fixed voltage (to ground) at the grid of the 5687, the output impedance of the regulator will be approximately 1/Gm of the tube (which depends on the cathode current and plate-cathode voltage). With roughly 200 V across the triode and 10 to 30 mA current, that output resistance ranges from 200 to 100 ohms (for a single triode).
Personally, I would break R3 into two 1k to 5k resistors in series, with a good film capacitor from the junction to ground. The 0B2 can handle 0.1uF directly across the tube, and the resistor after it will reduce instability caused by the shunt capacitance: the series resistance before the capacitor will improve the high-frequency noise filtering.
Thanks for explaining this to me (us). Will the effect of adding a film cap across OB2 be the same as adding a cap accross the zener diode? I never liked that, it sucks the life out of high frequencies. How is a value of this cap related to high frequency roll-off?
Putting a capacitor directly across a Zener diode, which shows a very low resistance when conducting, is not very efficient as a filter. A series resistor between the Zener and the capacitor improves the filtration dramatically (so long as the rest of the circuit allows the series resistance). Gas VR tubes have a maximum capacitance specification, typically 0.1 uF, above which they are liable to relaxation oscillation (cool flashing light, but otherwise useless).
But this is powering an SPDIF buffer is it not? Nothing you can do to this power supply can affect the audio frequency response as being suggested. Round the signal off too much or apply too much ringing and you will get errors. That is hear clicks and pops.
Want to "liquify" the high end just a tad? Well with digital audio you will need to learn DSP programming. Because tweaking a cap in the power supply ain't gonna do it!
The 0B2 can't be connected directly across B+. If the sketch really shows it wired like that, toss it. Maybe someone can figure this out if you post a scan of the original work.
--------------------------
Buy Chinese. Bury freedom.
I'll try to find the original sketch and post it here.
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