Hi all,
Can I prevail upon the wisdom and knowledge here to do a quick check on my numbers?
I've knocked together the little buffer below (all credit to http://www.valvewizard.co.uk/accf.html) to drive the output of a PCF802 phonostage. It sounds very good..... but of course then you start thinking is there something I can do to make it better? A CCS at the cathode seemed like a good idea - and can I just check my calculations. I think I'm in a good spot with it but would appreciate a second look:
Va=233V (50V or so lower than the schematic, but its the transformer etc I had to hand)
Va-k=103V
Vg-k=-2.6V
CCS set to 6mA current
My grid leak resistor is 510k, and Rb is still 470R, input cap is 680nf and output is 2.5uF
The image below shows the load line from the original buffer from the valve wizard site for ease of reference.
Can I prevail upon the wisdom and knowledge here to do a quick check on my numbers?
I've knocked together the little buffer below (all credit to http://www.valvewizard.co.uk/accf.html) to drive the output of a PCF802 phonostage. It sounds very good..... but of course then you start thinking is there something I can do to make it better? A CCS at the cathode seemed like a good idea - and can I just check my calculations. I think I'm in a good spot with it but would appreciate a second look:
Va=233V (50V or so lower than the schematic, but its the transformer etc I had to hand)
Va-k=103V
Vg-k=-2.6V
CCS set to 6mA current
My grid leak resistor is 510k, and Rb is still 470R, input cap is 680nf and output is 2.5uF
The image below shows the load line from the original buffer from the valve wizard site for ease of reference.
1. Is the 12AU7 buffer driving the input of the PCF802 Phono Stage?
That seems like what you said.
Or, is the PCF802 driving the 12AU7 buffer? Probably what you meant.
2. The 12AU7 buffer has a DC voltage out.
You may need a coupling cap from the cathode to the output, and a resistor from the coupling cap to ground, before passing the buffer signal to the next stage.
That seems like what you said.
Or, is the PCF802 driving the 12AU7 buffer? Probably what you meant.
2. The 12AU7 buffer has a DC voltage out.
You may need a coupling cap from the cathode to the output, and a resistor from the coupling cap to ground, before passing the buffer signal to the next stage.
Clumsy language @6A3sUMMER mea culpa
The 12au7 is on the output of the phonostage - and yes, I have 2.5uF cap on the way out - valve wizard mentions this in the text of his site, but hasn't drawn it in the schematic, and its often commented on....
The 12au7 is on the output of the phonostage - and yes, I have 2.5uF cap on the way out - valve wizard mentions this in the text of his site, but hasn't drawn it in the schematic, and its often commented on....