nikongod
DIY-ku
- Joined
- Jan 24, 2005
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Quote:
Do you mean like an LM317, or some newer (and better) version? Unless you have a negative voltage supply the voltage overhead is kind of a killer in gain tubes. If you have a negative supply (which makes the cost of the long tail pair {LTP} look small) just build an LTP. In power tubes people who really care grid bias or use CCS on a LTP... In the case of gain tubes most people who want to use SS parts just use LEDs or rectifier diodes. Impedance is not as low (theoretically) but low enough for our purposes.
The long tail pair allows you a few neat things in a SE circuit.
Gain is always lower (usually half) of what you would get from a common cathode amp. Its hard to get gain low enough in a hybrid IMO so buying the next few lines while reducing gain kills 2 birds with one stone.
Input capacitance follows gain, which is lower, which means more bandwidth, which is nice.
If you care about phase (its audiophile BS) you can make a non-inverting gain stage this way.
The long tail pair allows neat feedback arrangements if you are into that sort of thing.
The downside of a long tail pair is that it requires many more parts than a simple common cathode or even cathodyne. But it often pays you back in performance.
I have never been a fan of current mirrors - they just seem weird to me. I would stick with plate resistors, but to each his own. If you stick with plate resistors I'm pretty sure you could convert the amp to LTP without adding any parts. Break the connection between the plates and just leave one hanging out with a 15Kohm resistor to B+. Break the connection between the grids and ground one. Done!
Do you mean like an LM317, or some newer (and better) version? Unless you have a negative voltage supply the voltage overhead is kind of a killer in gain tubes. If you have a negative supply (which makes the cost of the long tail pair {LTP} look small) just build an LTP. In power tubes people who really care grid bias or use CCS on a LTP... In the case of gain tubes most people who want to use SS parts just use LEDs or rectifier diodes. Impedance is not as low (theoretically) but low enough for our purposes.
The long tail pair allows you a few neat things in a SE circuit.
Gain is always lower (usually half) of what you would get from a common cathode amp. Its hard to get gain low enough in a hybrid IMO so buying the next few lines while reducing gain kills 2 birds with one stone.
Input capacitance follows gain, which is lower, which means more bandwidth, which is nice.
If you care about phase (its audiophile BS) you can make a non-inverting gain stage this way.
The long tail pair allows neat feedback arrangements if you are into that sort of thing.
The downside of a long tail pair is that it requires many more parts than a simple common cathode or even cathodyne. But it often pays you back in performance.
I have never been a fan of current mirrors - they just seem weird to me. I would stick with plate resistors, but to each his own. If you stick with plate resistors I'm pretty sure you could convert the amp to LTP without adding any parts. Break the connection between the plates and just leave one hanging out with a 15Kohm resistor to B+. Break the connection between the grids and ground one. Done!
