fet cascoding
Mr. Pass, I found your latest vfet amp in Audio Express interesting. I have some of Sony's older complemetary vfets that I was thinking of cascoding. You used a mosfet to cascode to the vfet. My question is whether a bipolar would work as well as a mosfet for the cascode, especially in not contributing a sonic signature that would mask the vfet. In a complementary pair of outputs, how does the mosfet behave as a cascode in the crossover region where the mosfets are nonlinear but bjts like Toshiba's 1302/3281 are very linear? I'm going to dig out your old Audio Amateur cascode 60W amp to study it's circuit for this project.
Thanks.
Bob
Mr. Pass, I found your latest vfet amp in Audio Express interesting. I have some of Sony's older complemetary vfets that I was thinking of cascoding. You used a mosfet to cascode to the vfet. My question is whether a bipolar would work as well as a mosfet for the cascode, especially in not contributing a sonic signature that would mask the vfet. In a complementary pair of outputs, how does the mosfet behave as a cascode in the crossover region where the mosfets are nonlinear but bjts like Toshiba's 1302/3281 are very linear? I'm going to dig out your old Audio Amateur cascode 60W amp to study it's circuit for this project.
Thanks.
Bob
There's not a lot of difference between using a Mosfet
or a bipolar for the cascode transistor in my book. I
used a Mosfet because I have them laying around like
popcorn.
The cascode transistor imparts very little of its own
character into the signal. With a Mosfet, 100% of the
current through it comes through the cascoded gain
transistor, and the only influence it has is the small
variation in voltage on its Source, which in turn has
a small influence on the the gain transistor, mostly
linear.
With a bipolar, some of the current is sent off through
the Base, so you lose maybe 1% or 2%, but even that
is mostly linear, and doesn't have a lot of effect.
or a bipolar for the cascode transistor in my book. I
used a Mosfet because I have them laying around like
popcorn.
The cascode transistor imparts very little of its own
character into the signal. With a Mosfet, 100% of the
current through it comes through the cascoded gain
transistor, and the only influence it has is the small
variation in voltage on its Source, which in turn has
a small influence on the the gain transistor, mostly
linear.
With a bipolar, some of the current is sent off through
the Base, so you lose maybe 1% or 2%, but even that
is mostly linear, and doesn't have a lot of effect.
