I am attempting to modify a Dyna PAS 3 in the spirit of Spice and the art of preamplifier design, Part 2
However, I am using mosfets instead of tubes in the out put stages. Based on advice and some simulation work, two ZVN0545As should work as drop in replacements for each 12xa7 being used as a cathode follower.
If this is correct, shouldn't I be able to use the stock PAS power supply? There are no new heaters, and the idle current in the fets would total an additional 4mA on the HV side.
However, I am using mosfets instead of tubes in the out put stages. Based on advice and some simulation work, two ZVN0545As should work as drop in replacements for each 12xa7 being used as a cathode follower.
If this is correct, shouldn't I be able to use the stock PAS power supply? There are no new heaters, and the idle current in the fets would total an additional 4mA on the HV side.
Yes - it should work and the additional current draw from the HV won't be a problem. But two possible issues . . .
1. The RIAA network will need to be recalculated due to the different Zout (and other factors) in the phono stage
2. You are likely to need to adjust R6C (line amplifier) so that you obtain the same voltage as shown at node 3B
1. The RIAA network will need to be recalculated due to the different Zout (and other factors) in the phono stage
2. You are likely to need to adjust R6C (line amplifier) so that you obtain the same voltage as shown at node 3B
How about reading the articles in Dynaco Tube Amplifier technical articles and upgrades ST-70 PAS 2-3 ST-35 SCA-35 EFB
before destroying yet another PAS ?
Thank you for your feedback, Joe. The second problem I knew about. The bode plot for the modified phono stage with the fet looked almost identical to the all tube circuit, but I'll take a closer look. I'm a relative beginner, so I'm trying to proceed with this mod very carefully.