Thanks. Indeed, so I dont know if I shoud slightly adapt their voltage reference as discribed in the building guide or not. It is just borderline....
OK, I just took a couple of pictures of my version of this great amp.
I added a "T" Plate under the Store board so I could double up on output devices (you can barely see it in the last picture.) Just paralleled the outputs after matching them, with separate grid resistors for each device. I made no other changes to accommodate the second pair per channel.
I am running at 28 volt rails and 2 volts across the .1 ohm resistor.
I think this doubles the damping factor, probably adds more feedback too.
It sounds great, one of the best sounding amps I have. (I have Mr Pass' Factory F7 to compare, among other DIY amps from the master.)
Just a note about the case. I found a cheap Nakamichi PA-7AII that had a bad channel, gutted it and built the Pass/Sony VFET inside. The heatsinks are massive. (I hope the irony is not lost, using a Stasis amp box to house a later Nelson Pass design.)
I need to wipe the old lettering off the faceplate and label it what it is: "Greatest Amp Ever" or "Pass/Sony VFET PP"
Rush
I added a "T" Plate under the Store board so I could double up on output devices (you can barely see it in the last picture.) Just paralleled the outputs after matching them, with separate grid resistors for each device. I made no other changes to accommodate the second pair per channel.
I am running at 28 volt rails and 2 volts across the .1 ohm resistor.
I think this doubles the damping factor, probably adds more feedback too.
It sounds great, one of the best sounding amps I have. (I have Mr Pass' Factory F7 to compare, among other DIY amps from the master.)
Just a note about the case. I found a cheap Nakamichi PA-7AII that had a bad channel, gutted it and built the Pass/Sony VFET inside. The heatsinks are massive. (I hope the irony is not lost, using a Stasis amp box to house a later Nelson Pass design.)
I need to wipe the old lettering off the faceplate and label it what it is: "Greatest Amp Ever" or "Pass/Sony VFET PP"
Rush
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Well I might have done it now.
My wife and I moved last year and I've been meaning to check the bias on my VFET amp since it surely bounced around a lot in the moving truck. After listening to it this morning I decided to go ahead and check it. Tweaked the left channel fine and when I was tweaking the right channel I turned the wrong pot. I stopped, turned it off, and decided to start from square one. I turned pots P3 and P4 counterclockwise, turned on and checked bias on the output (T16 and T17). I then started to bias the front end and noticed the right side heat sink and VFETs are cold compared to the left side.
I'm not sure what to do now. I assume the output stage should be generating heat even without the front end biased. I didn't hear or smell anything fry so hopefully the magic smoke is intact.
Any help would be appreciated.
My wife and I moved last year and I've been meaning to check the bias on my VFET amp since it surely bounced around a lot in the moving truck. After listening to it this morning I decided to go ahead and check it. Tweaked the left channel fine and when I was tweaking the right channel I turned the wrong pot. I stopped, turned it off, and decided to start from square one. I turned pots P3 and P4 counterclockwise, turned on and checked bias on the output (T16 and T17). I then started to bias the front end and noticed the right side heat sink and VFETs are cold compared to the left side.
I'm not sure what to do now. I assume the output stage should be generating heat even without the front end biased. I didn't hear or smell anything fry so hopefully the magic smoke is intact.
Any help would be appreciated.
Thanks for the nudge Dennis. Since there was a voltage on R32 I figured it wasn't toast. I went ahead and slowly brought everything up to bias and everything seems normal. Going to let it run tomorrow and check again and hook up a cheap speaker.
Phew, I was sweating bullets.
Phew, I was sweating bullets.