A chopped Mini-A with Jfet input stage

[Fuling]

Well, since the dynamic CCS is gone it doesn´t qualify as an Aleph at all, but what do you guys think about this:


Edit: I forgot to draw a few things on the schematic.
Output transistors are IRF9530/IRF530 with 220R gate stoppers, rails are +-12V and Iq=1,3A

 

[Fuling]

Or this (more questionable...):

 

[Zen Mod]

second version looks as safer bet
in both cases you need lag compensation across nfb resistor (15K ; 12K)
mebbe you can try with one range up-scaled nfb resistors (multiplied with 10) so you can use film cap in divider;

besides ,referencing bases of cascodes to intersection of two 47 ohms resistor is mebbe better........

besides besides-don't take me serious, I'm just toob boy

 

[Fuling]

I´m not so sure that the cascode circuit is necessary, only the change from IRF9610 to BF245C (or some other Jfet) should decrease the input capacitance quite a bit I think.
When I get the time I´ll hardwire a prototype and see how simple it can get before losing performance.

 

[Nelson Pass]

You will want to use Fairchild or Harris for the 9530 part,
as they have lower distortion in Common Source applications.

 

[Fuling]

Thanks for the advice!

I have a another circuit in mind too that I will post within a couple of days, something between this and a Zen.
When I look into my crystal ball I see a lot of prototype building and testing the next few weeks

 

[Fuling]

My latest "invention":

The AC and DC values are measured on a working prototype, not simulated. Max output voltage is 20Vp-p with 24V rail (missing in schematic).

 

[Zen Mod]

My latest "invention":

The AC and DC values are measured on a working prototype, not simulated. Max output voltage is 20Vp-p with 24V rail (missing in schematic).

nice

mebbe you can try dissimilar jfets for cascode?

 

[Fuling]

mebbe you can try dissimilar jfets for cascode?

I must ask: For what reason?
I need all the current I gan get to drive the mosfet, and BF245C seems like a good choice. I tried BF245B at first but then I only got 5mA instead of 9mA.

 

[Zen Mod]

here it is

 

[Fuling]

The idea is great, but I looked at the curves for BF245C and it seems that the high current will be a problem.
The whole circuits operation point depends on the lower Jfet´s Vgs and Id.
The upper Jfet operates at -1,1Vgs, which seems way too low (as Vds)for the lower Jfet.
Though, I guess I´ll give it a try since I have a prototype setup, if it works it might be great!

 

[Fuling]

My "semi-serious" attempt to get the circuit in post #7 working:

 

[Fuling]

Since this version is more or less a prototype, I didn´t want to spend much work on a nice alu chassis (well, I gave it a try but it failed) so I decided to just put all the parts in a simple MDF box.
I ditched the cascode on the input stage sinceit was probably not necessary and besides, I ran out of solder points