TL Reverb driver idea - from triode cathode circuit??

[jazbo8]

jazbo8 - Thanks for the info. I looked up the thread, and some interesting stuff there. Along very similar lines to the reverb driver circuits on Merlin's website. I have actually made a couple of amps using this style of driver, plate driven with series resistor to simulate constant current. They sound good, but I'm trying for better!

I just want to circle back to your CF driver idea, if you want to make the load impedance have a lesser effect, then CF does not seem to be the ideal choice as the driver, as both Merlin and Polstra have demostrated. Also there are a lot of good information at Elliot Sound's site (middle of the page) for your reference.

[jimboyogi]

Hi jazbo8. Sorry for the slow response!

I was not proposing driving the reverb tank using a cathode follower. I was merely putting the tank transducer in series with the cathode bias circuit of a conventional gain stage.
My first iteration used a 1.5K ohm cathode resistor in series with the tank. The tank transducer has a DC resistance of 200 ohms, and an impedance of 1.4 -1.9K (say 2K) at 1kHz, and varying greatly with frequency, reportedly halved at 500Hz, doubled at 2kHz.
With the cathode resistor unbypassed, the impedance of the cathode circuit would then be 2.5K @ 500Hz, 3.5K @ 1kHz, 5.5K @ 2kHz.

The next iteration was using a 7V zener diode in place of the cathode resistor, so fully bypassed down to DC. So all of the AC impedance is now due to the tank.
Cathode circuit impedance now 1K @ 500Hz, 2K @ 1kHz, 4K @ 2kHz.

What I found with both of these circuits though, was that the sound was quite muddy. I'm not sure if this was due to the impedance change with frequency, or to some degree of core saturation from DC current in the transducer. Or a combination of these 2 factors. However I have moved on from trying to improve this circuit, and have gone back to an anode driven version :0

[nickb]

On the AC drive current, I did some testing a little while back and concluded that you can drive (and most amps do) much higher than the datasheet suggests.

The DC current is will move the magnet to one side resulting increased even harmonic distortion. The amount is small and IMHO not important in guitar amp applications.