Test of Prototype.

With SS

& Tube preamps.

Because they have the same board connectors pinouts, swapping was very easy.
Controls settings are the same for different preamps while recording.
Fet_vs_Tube
Archive contains mix & only guitar tracks.
Legend:
SX_Y
X - track number
Y - preamp number
SX_YG - only guitar without mix.
Try to estimate who is who.

Another several samples
High input, gain at 3.5, TS, presence & depth at middle
High input, crunch
Low input, gain at 8, TS, presence & depth at middle
Low input
Low input + reverb in loop

The planned mini-head design
Budget version


Custom version

Additional samples
Mini head, gain at 2 hours, presence 2 hours, Depth & TS at middle positions
Mini head, gain at full position, Depth, presence & TS at middle positions

Prototype head (JCM800 preamp + 5W PA):



Sample
Mini Head Medium Power
Same controls setting except master volume turned to MAX position
Mini Head Full Power

ehx44 inside

Datasheet
http://www.ti.com/lit/ds/symlink/tpa3106d1.pdf

Quotebut in what point i can do the "shared cathode" thing? between the diode and Rk?

Something like this

QuoteAre you planning on selling these?

Only as part of complete devices.

Quotehow can you make(using LND150's) a shared-cathode stage like a superbass?

I don't see problems. Only careful selection of the values in source network (& maybe biasing of this network).

QuoteSo...are you going to start selling these things or are these just for your own use?

Bare boards are not planned for sale. Primarily I plan to use these boards in this design
http://www.ssguitar.com/index.php?topic=1981.msg19551#msg19551
Maybe I'll sell small amount of assembled boards as a kits (but not just now).

I got ordered PCB's for
Micro fet PA with speaker simulator

& mini mixer for it

I got ordered PCB's for JCM800 based on LND150

Schematic of simulation project & waveforms.

QuoteThe servo integrator time constant in fact is too fast !!!

It's right!
Some results of simulating two JFET stages with & without servo matched by gain & operating point. Both works without "grid current"
V(out2), V(bias2), V(servo2) - vith servo loop.
V(out1), V(bias1) - vithout servo loop.
First - oscillating of servo loop due to improper loop parameters.
Second - as I said, servo loop increases operating point shift even in steady loop state (noservo_servo_end.jpg).

QuoteI use diode clipping on the input because gate current causes the output to clip too sharply and gate current doesn't always start when the output clips.

2010
http://www.amtelectronics.com/support/articles/why_tube-like_cannot_measure_up_to_tube_inside/
Russian original text dated 2006.
http://www.sugardas.lt/~igoramps/article68/article.htm

By benefits I mean closeness to vaccum tube operation, i.e. absence of deep feedback, existence of "input clipping" (by gate-source diode).
I apologize for  hasty conclusions about comparing this idea with opamp limiter, but after the simulation would like to note the following.
Servo in this case acts as a positive feedback to the clipping duty cycle for stages with "shifted" operating point.
In stages with "shifted" operating point without servo clipping duty cycle does not change significantly without "input clipping".
Also it works as a positive feedback for "input clipping".
In stage with servo clipping duty cycle while "input clipping" changes faster than in stage without servo.
V(out1) & V(servo1) for stage with operating point shifted to saturation, V(out2) & V(servo2) for stage with operating point shifted to cutoff.