pentode pre with a bias

[PPL]

Hears My Preamp I have been Playing with this last weekend, It has the bass and treble controls inside the feedback loop for fast articulate tone response. it is a (2) two stage design using a cascode Input driving a pentode Output in what I call my APHEX circuit.

I would like to have (2) two of these Inputs per Amp one the Clean Input shown and the other using similar topology however Voiced for Blues. I plan on putting this circuit on A PC Board for the DIY Guy's with the remaining power amp section Point to point.

If this develops into a full scale DIY Project would this Forum be a good place to base this?

[Andy Le Blanc]

Ya .... its a good place, besides its not like your cloning another fender.

Looks like there's ample open loop gain, the FB tone control should be nice.

C from the screen grid bypass to the cathode of the ef184 is a nice touch.
where do perceive its affect?

Have you measured Vout for a given Vin? It would be neat to see a harmonic distortion and freq. response plot.

You could also use a cathode follower after the pentode stage and drive the output and tones with a low impedance.

[PPL]

the C from G3 to the cathode is the standard screen Bypass cap, however again I returned this to the cathode rather than ground so as to improve its bypass capability and if needed re sized for HF Roll-off. I haven't got to the point of measuring this yet it is not quite ready for prime time.

(1) the overload clipping has fuz on top. changed to EF86 and this fuz almost went away.

(2) the treble Control causes Instability at 3 o clock or greater Rotation.

(3) ya i was thinking about that also and it occurred to me that Perhaps another phase inversion needs to take place. This application seems Right for an SRPP type of output stage with the gain from it only small. Another option is to use a Standard plate Follower ie a standard grounded cathode that has equal cathode and Plate resistors for unity gain.

[PPL]

I have got the Preamp almost together. I am putting it on a PC Board. I also tried connecting the Sup Grid (g3) to the Screen's (g2) and no misadventure results it dose slightly shift the DC operating points and these will have to be compensated for. As for change in Tone yes it did change it slightly. alot of work on screen Shadowing is going on now in the Hi-Fi world http://www.6moons.com/audioreviews/tome ... ara_3.html

Attached is my Progress on the Complete Amp system I am working on.