ImPasse Preamplifier

[wuttichai]

Hello wuttichai did you first solved the problem with your power supply?
It seems that you have fried your LM317 because 415volt is excessive. The final measurements need the audio circuit to load the power supply.. I would start with this problem first.
One thing I also found out with my implementation was I needed the Cadj as per LM317 datasheet or else the supply had noise.
One more thing is to check before and after the LM317 voltage to ground and you need more than 5volt in order to be safe.

When I made my Impasse the component values for the power supply didn't work well for me and I had to change some of them in order to obtain the stated performance.

When you fix this, I believe you have to check the R5 in order to have both CSS perform as stated (about 8mA ,as Tony and Jack said above) and then you have to bias the 6dj8 by altering the voltage divider after the output of the 6SN7.
The voltages on the right channel at the 6Dj8 doesn't make any sense to me now, I would follow the above steps and measure again.

Hello nkostop , Thanks for the solution . I will fix the first problem

 

[nkostop]

A comment for anyone who might like to try, I removed the LEDs at the cathode and changed them with 470ohm resistor, so the bias is a little bit more "hot" and also there is some negative feedback. I changed the voltage divider before the second tube in order to keep the bias at the same current level as the first tube.
The gain is almost the same (it was too high already).
I firmly believe that the sound is much better now. (less muddy sound)
The tubes I am using is a VT-231 kenrad and a siemens E88CC. For the interstage capacitors I am using FT3 russian caps.

 

[jackinnj]

A comment for anyone who might like to try, I removed the LEDs at the cathode and changed them with 470ohm resistor, so the bias is a little bit more "hot" and also there is some negative feedback. I changed the voltage divider before the second tube in order to keep the bias at the same current level as the first tube.
The gain is almost the same (it was too high already).
I firmly believe that the sound is much better now. (less muddy sound)
The tubes I am using is a VT-231 kenrad and a siemens E88CC. For the interstage capacitors I am using FT3 russian caps.

Measure the voltage drop across the anode resistor with LED and with 470 R cathode resistor --

 

[nkostop]

Hello jackinnj! I didn't see your answer! I haven't mess with my impasse for a long time! Maybe I will do but why you ask?

Also I would like to ask a question, does anyone uses the impasse as a single ended preamp? What do you believe about this?

I made a test, I connected the impasse as single ended to my F4s using parallel mono instead of balanced and I think the sound is much better... I am not completely sure I will check it for some days... The gain is still very good for my 96db speakers for the neighbors to call the police!

Has anyone a similar experience?