Tell him that Wavebourn said, "Size matters". I mean, value of the current that discharges the cap.
It seems to me that a choke input filter is wasted when there is a regulator following it. Don't get me wrong, I've built several HV regulators for preamps and power amps and like them very much. I just don't think the choke brings anything to the party here. If the regulator is working correctly not only does it hold the voltage at the desired value, it provides much better filtering than the choke could ever do. The other thing the regulator does is provide a broadband low impedance power source for the load. A C-L-C filter will have a low output impedance in a very narrow band and not be as stable of a voltage source for the load. It could be a contributer to the problem you are having. Try pulling the choke and trying it that way.
Since I'm moving to a simple choke input supply (basically what you see before the regulated supply in this PSU) I don't want to screw too much with this.
I can say I originally built it as the original schematic shows. There were always improvements in sound and never any drawbacks, but in this case the regulator section was not designed for what precedes it and that's the issue.
It would be nice just to be able to get another stable 5V out of it. I don't know if playing just with the VR plate voltage would do that or have a chain reaction in the reverse.
I can say I originally built it as the original schematic shows. There were always improvements in sound and never any drawbacks, but in this case the regulator section was not designed for what precedes it and that's the issue.
It would be nice just to be able to get another stable 5V out of it. I don't know if playing just with the VR plate voltage would do that or have a chain reaction in the reverse.
Yep - my thoughts too. A simple C-R-C into the regulator should be ample. Saves space weight and $.
I guess it is going to need attention. It just started oscillating after 8 hours of stability. I had to drop PSU output voltage again....
I really don't want to go backwards in terms of SQ. I just need to stabilize this PSU. Its been ruining flawlessly in this configuration for over a year. Not sure what's up.
I really don't want to go backwards in terms of SQ. I just need to stabilize this PSU. Its been ruining flawlessly in this configuration for over a year. Not sure what's up.
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I told you already many times what's up. You are still ignoring.
Good luck! (I swear not to chime in to this thread anymore)
Here's what I think is happening - as the current drawn through the EL84 increased (from 6ma to 12ma) you reach a point where the voltage drop across the tube decreased BELOW its ability to conduct at that current. It starts to "buck" as it moves across from conducting to not conducting - not due to the control circuit, but due to its own internal resistance.
Wavebourn's suggestion to INCREASE the voltage across the EL84 aligns with this - by increasing the idle anode to cathode voltage you increase the headroom of the tube and it can conduct the 12ma you need at 200V without dropping out.
The EL84 allows for up to 550V peak applied across the anode/cathode. The 300V is the operating maximum. So you have PLENTY of space to play in.
Wavebourn's suggestion to INCREASE the voltage across the EL84 aligns with this - by increasing the idle anode to cathode voltage you increase the headroom of the tube and it can conduct the 12ma you need at 200V without dropping out.
The EL84 allows for up to 550V peak applied across the anode/cathode. The 300V is the operating maximum. So you have PLENTY of space to play in.
Ahh (light bulb goes on) now I get it What I should've said to Wavebourne was I don't understand why this is suddenly happening at lower and lower voltages very close to the voltages its been running fine at.
When it destabilized today at 195v and now I'm down to 194 I was concerned something mysteriously else was happening. Its run fine at 193v for more than a year.
I'll look at adding more capacitance at C1 and see what happens. Do you think I need to put the .1 bypass back on C3?
When it destabilized today at 195v and now I'm down to 194 I was concerned something mysteriously else was happening. Its run fine at 193v for more than a year.
I'll look at adding more capacitance at C1 and see what happens. Do you think I need to put the .1 bypass back on C3?
That's funny because I did try to model it this afternoon in PSU II. I wasn't sure what to use beyond the 12mA load. I have to check the DCR of the PT to enter it correctly. But I wasn't able to come up with a good number due to the fact I didn't know what output voltage was target for the reg supply.
On cap value. Its true that a film cap is equal to double or triple the value of electrolytic, right?
On cap value. Its true that a film cap is equal to double or triple the value of electrolytic, right?
yep - and metal film resistors have twice the resistance of a cracked carbon... 
No. The value is the value. It MAY have a lower ESR (series resistance) but as pointed out earlier, in this application that makes sod-all difference.
Your model will need your current draw of the preamp (12ma) + the current draw of the regulator (effectively the 3-5ma of the VR tube and the bias current of the diff amp).
The voltage output of the regulator is irrelevant for the purposes of the model. You are looking to run the model and then increase the C1 value until you get the maximum realistic stable voltage across the load.
Taking the choke out would probably be more productive...
No. The value is the value. It MAY have a lower ESR (series resistance) but as pointed out earlier, in this application that makes sod-all difference.
Your model will need your current draw of the preamp (12ma) + the current draw of the regulator (effectively the 3-5ma of the VR tube and the bias current of the diff amp).
The voltage output of the regulator is irrelevant for the purposes of the model. You are looking to run the model and then increase the C1 value until you get the maximum realistic stable voltage across the load.
Taking the choke out would probably be more productive...
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