I found solution. Somehow I mixed MPSA29 pins differently that it should be. After changing them correct then no high frequency noise anymore. Sound also comes out. 🤣
Pin 6 - 224 V
Pin 1 - 144 V
Pin 3 - 2.35 V
Do I need to lower pin 1 voltage and how would be best to do that?
Pin 6 - 224 V
Pin 1 - 144 V
Pin 3 - 2.35 V
Do I need to lower pin 1 voltage and how would be best to do that?
Sounds like good progress.
I can see two things that needs to be adjusted, so that the circuit is well balanced.
It all depends on where your high voltage sits, is it +236V or +250V - let me know the correct voltage and then I should be able to give you specific advice.
I can see two things that needs to be adjusted, so that the circuit is well balanced.
It all depends on where your high voltage sits, is it +236V or +250V - let me know the correct voltage and then I should be able to give you specific advice.
OK then, what needs to be adjusted are these two resistors:
1) If you are getting 226V on Pin 6, then that is reasonable in the ballpark and close to 230V. You can tweak the 560K, likely 470K would also be OK. But I would leave it as is.
2) Adjust 2K7 to bring down the 144V on Pin1. Try replace 2K7 with 2K2 and let me know what voltage you end up with, something nearer 130V. I suspect it will then all be OK.
1) If you are getting 226V on Pin 6, then that is reasonable in the ballpark and close to 230V. You can tweak the 560K, likely 470K would also be OK. But I would leave it as is.
2) Adjust 2K7 to bring down the 144V on Pin1. Try replace 2K7 with 2K2 and let me know what voltage you end up with, something nearer 130V. I suspect it will then all be OK.
I have made changes.
Input voltage 253V (raised to get 130V on pin 1)
Pin 1 - 130V
Pin 6 - 228 V with 470k resistor
Pin 3 - 2.14 V
If the output voltage is close to 2 V then I kind a hear distortion specially in bass area. Could be HV regulator issue? I am using Allen Super Reg tp has voltage 0,15 V which should be 15mA?
Tube I am using is Telefunken ECC801S
I want to try the CCS version also FVP-6A. Can I use two BSS159N or BSP149H or DN2540N or 2SK209 or J113 for that?
Input voltage 253V (raised to get 130V on pin 1)
Pin 1 - 130V
Pin 6 - 228 V with 470k resistor
Pin 3 - 2.14 V
If the output voltage is close to 2 V then I kind a hear distortion specially in bass area. Could be HV regulator issue? I am using Allen Super Reg tp has voltage 0,15 V which should be 15mA?
Tube I am using is Telefunken ECC801S
I want to try the CCS version also FVP-6A. Can I use two BSS159N or BSP149H or DN2540N or 2SK209 or J113 for that?
What would be the maximum input voltage to still have nice signal out? I am using B version. I like to use it with up to 2V rms. What changes I need to make for this and how to lower the gain more or even option for unity gain?
Another question is about pin 3 cathode voltage 2.6V. What this voltage affects if I increase or decrease this voltage? Right now I have voltage on pin 3 - 2.14V.
Another question is about pin 3 cathode voltage 2.6V. What this voltage affects if I increase or decrease this voltage? Right now I have voltage on pin 3 - 2.14V.
The 'scope' is on "A" which is the output and more that 30V peak-to-peak:
Here I increased R4 to 680K. Makes Pin 6 sit on +226V. You may need to gradually increase R4 to see if that improves the situation. Are you sure the MPSA29 has not been damaged. Do you have a True Volt AC meter? Or a scope AC coupled, check that the voltage swing on pin 6 is clean and symmetrical. Check Source voltages on both IRF820 (or whatever you used there) and around +12V on each?
It should be able to swing 12V RMS on the output with a full 2V RMS input. If not, there has to be something preventing it.
Here I increased R4 to 680K. Makes Pin 6 sit on +226V. You may need to gradually increase R4 to see if that improves the situation. Are you sure the MPSA29 has not been damaged. Do you have a True Volt AC meter? Or a scope AC coupled, check that the voltage swing on pin 6 is clean and symmetrical. Check Source voltages on both IRF820 (or whatever you used there) and around +12V on each?
It should be able to swing 12V RMS on the output with a full 2V RMS input. If not, there has to be something preventing it.
So, I build SuperRegulator with slightly modified CCS part, with LF411 OpAmp and with 22uF PP instead of electrolytic capacitor (in the picture blue one):
And that was not good idea! At the output I got very nice sawtooth shape signal and whistling sound at the phono output:
Changed PP capacitor back to 22uF 450V electrolytic and whistling sound disappeared. So, it is not always possible to follow the rule that the electrolytic capacitors are evil. The better low ESR PP in this case causes such type of oscillation.
And still trying to figure it out and understand why I can not get a perfect square wave from phono stage 🙁
Yes, it has but there is a standard testing procedure with invers RIAA circuit and it fails. It fails even with LTSpice modeling.
https://hifisonix.com/wp-content/uploads/2016/12/Accurate-Inverse-RIAA.pdf
https://hifisonix.com/wp-content/uploads/2016/12/Accurate-Inverse-RIAA.pdf
Then your RIAA/amplification is not accurate. There cannot be those many variables, assuming your invers RIAA is accurate.
Since the actual measurements match the simulation, I conclude that the invers RIAA is more or less accurate (post #20). Phono Stage is identical to schematic as in the first post by Joe.
Quite so. The SuperReg is sensitive to capacitors and the opamp used, something I have observed too. The higher ESR is likely the reason it became stable and not the same bandwidth as the PP covers, slowing things down. Maybe this is a case where you do what needs to be done to make it work. Keep an eye on stability and if it stays that way, then so be it.
Hi all VSE fans.
I built the FVP5 25 years ago and I'm happily living with it since then.
I think it's time for an "upgrade". For some time now, I was thinking about upgrading to the all-tube FVP5A (aka SVP1), since Allen claimed that this sounded much better than the MOSFET version.
So, I came to this thread and found Joe's version very interesting. Actually, as far as I remember, in the commercial version SVP2, Allen used a voltage divider on some inputs to tame the high gain of the preamp. So, using a lower μ tube sounds a great idea.
My question is the following:
Since, as Allen has stated, in a cathode follower it is better to use a high transconductance tube, how about using a 12AT7 in the first (gain) stage and a 6922 in the SLCF stage, sharing the two triodes between the two channels for both tubes?
Regards,
Evangelos
I built the FVP5 25 years ago and I'm happily living with it since then.
I think it's time for an "upgrade". For some time now, I was thinking about upgrading to the all-tube FVP5A (aka SVP1), since Allen claimed that this sounded much better than the MOSFET version.
So, I came to this thread and found Joe's version very interesting. Actually, as far as I remember, in the commercial version SVP2, Allen used a voltage divider on some inputs to tame the high gain of the preamp. So, using a lower μ tube sounds a great idea.
My question is the following:
Since, as Allen has stated, in a cathode follower it is better to use a high transconductance tube, how about using a 12AT7 in the first (gain) stage and a 6922 in the SLCF stage, sharing the two triodes between the two channels for both tubes?
Regards,
Evangelos
Yes. that could work and makes sense. Use the T7 for what it does best, voltage gain. And then 6922 which should suit the SLCF.
On a slightly different note: I have just received some high voltage Darlingtons in TO-220 package and I will test them to see if they work and have sufficiently high hfe current gain to be used as the top half of the SLCF follower... will get back to you guys about that.
That did not work out, a TO-220 Darlington, the hfe >1000 dropped to under 20 @10mA. Shelve that idea.
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In that case, we stick to the MPSA29, until further notice.
When going with a 6922 for the SLCF, what changes must be made in relation to the 12AT7 version?
When going with a 6922 for the SLCF, what changes must be made in relation to the 12AT7 version?
The filament supply requirements needs to be looked at, if you have 12.6V for 12AT7 (which is usually normal) and the 6922 needs 6.3V - that needs to be figured out.
One could use a single twin-12AT7 for the gain stages, left and right. Then have two 6922 wired in parallel, one for each channel, but have the filaments wired in series and hence 12.6V. But I would be looking at using some decent current if using parallel 6922 as followers, like 12mA at least.
As the 6922 are in unity gain like the T7, the circuit pretty much stays the same.
Hi Joe,
Thank you for your response.
Actually, I was asking about the circuit values of the SLCF.
Regarding the heaters, I think I will use 6.3 V for both tubes and a separate +/- 15 V supply for the current sinks, so no need for 12.6 V heater supply (and just one 6922, with triodes shared between L and R channel).
Would there be a benefit increasing the cathode current of the SLCF when substituting with 6922? As it is now with the 12AT7, cathode current is round 5 mA and I was thinking about 10 mA with the 6922.
Regards,
Evangelos
Thank you for your response.
Actually, I was asking about the circuit values of the SLCF.
Regarding the heaters, I think I will use 6.3 V for both tubes and a separate +/- 15 V supply for the current sinks, so no need for 12.6 V heater supply (and just one 6922, with triodes shared between L and R channel).
Would there be a benefit increasing the cathode current of the SLCF when substituting with 6922? As it is now with the 12AT7, cathode current is round 5 mA and I was thinking about 10 mA with the 6922.
Regards,
Evangelos