preamplifier with huge amplification

[homeskillet]

Another way to get high gain and good drive capabilities in a single stage is to try a resistively loaded pentode with a CCS assist.

Thank you. I'm going to try this. -Fred

 

[Rod Coleman]

Another way to get high gain and good drive capabilities in a single stage is to try a resistively loaded pentode with a CCS assist. You can use a high value resistor to get the gain up, the CCS provides additional current to get the pentode into a good operating point, and you can use the MU output of the CCS to drive the next stage.

Using 1/2 of a 6BN11 pentode with CCS the circuit had a gain of 192 and output impedance of 500 ohms. Distortion was .54% at 90Vrms.

I'm sure that with some of the other high transconductance pentodes the gain could be pushed higher.

Look at the Pentode + CCS driver page under Driver Experiments on my web page for more details.

Yes, why not. For a 300B SE driver, I think the sound of EL84(6BQ5) pentode-mode driver is much better than the horrible 6SN7 cascaded pair usually seen in this position (and in the referred KT90 cathode follower circuit).

Your example of 6BQ5 (EL84) with 500V supply and Av=125 is almost there. The KT90 version is probably a bridge too far, but with a 300V EL34 PSE, a 9W rms output to the load needs about 360V pk-pk of grid drive.

With EL84 as driver, maybe we could increase the supply to the cold-anode limit (550V) and it would just about do it. The high voltage required is the downside. Compared with the shunt cascode, which will drive even more output swing than this with Power Supply Voltages no more than 250V beyond ground (+ and - in this case).

But provided one can source some high-voltage parts for the CCS, the EL84 pentode is an excellent candidate. Or, for higher voltages,the EL34 as driver is more comfortable, with its 800V rating (probably safer at 600V for many modern types).

 

[homeskillet]

mu output on ixys regulator

I just tried to configure an ixys regulator as a mu follower.

Music comes out as shown but is this it? Thank you. -Fred

 

[nigelwright7557]

If you are using that much gain then great care will be needed with layout to stop oscillation. Use star grounding to stop feedback paths.
Make the input circuit as short as possible.

 

[homeskillet]

If you are using that much gain then great care will be needed with layout to stop oscillation. Use star grounding to stop feedback paths.
Make the input circuit as short as possible.

Hi. Do you mean me? If so, my version is not so high in gain. I know what you mean with high gain and layout/grounding. Good advice. Thank you. -Fred