(Theoretical because I'm not planning on doing this to my brand new Oktavas just yet )
I was recently looking at the dorsey mod schematic and at the schoeps schematic, and obviously the two are similar, but with a few differences. I was wondering how big these differences are.
The first one would be the DC-DC converter. How big of an advantage does the 60V polarisation voltage give over the 35V of the much simpler dorsey circuit? Does this improve sensitivity, linearity, noise?
The second is the choice of the input FET. The schoeps uses a BC264 which has an input capacitance of 4pF, and the dorsey uses a 2SK170 with an input capacitance of 30 pF. Considering the very high impedance at that point, isn't such a large input capacitance a bit of a problem?
At 16kHz the BC264 should have a input reactance of 2.5M (already quite small compared to the 1G precharge resistor), the 2SK170 on the other hand only 330k. Wouldn't it be better to use the BC264, despite the slightly higher noise figure?
I was recently looking at the dorsey mod schematic and at the schoeps schematic, and obviously the two are similar, but with a few differences. I was wondering how big these differences are.
The first one would be the DC-DC converter. How big of an advantage does the 60V polarisation voltage give over the 35V of the much simpler dorsey circuit? Does this improve sensitivity, linearity, noise?
The second is the choice of the input FET. The schoeps uses a BC264 which has an input capacitance of 4pF, and the dorsey uses a 2SK170 with an input capacitance of 30 pF. Considering the very high impedance at that point, isn't such a large input capacitance a bit of a problem?
At 16kHz the BC264 should have a input reactance of 2.5M (already quite small compared to the 1G precharge resistor), the 2SK170 on the other hand only 330k. Wouldn't it be better to use the BC264, despite the slightly higher noise figure?