A while back (quite a while, actually) I posted a Class A design using an Ixys depletion mode fet as a substitute for the usual Aleph top side modulated current source, I actually had some boards done back when I was still using OSH Park for board fab (yes, they're purple...). I've returned to that design with a different scheme for biasing the topside current source. Attached is a picture of the partially assembled board waiting for a matched diff pair front end and some selected output mosfets. More action on this may happen over the weekend. When I get home, I'll post a prelim schematic (it's on my home computer).
Attachments
Here's the thread from long, long ago that inspired this current work:
https://www.diyaudio.com/community/...etion-mode-mosfet-now-available.261833/page-4
https://www.diyaudio.com/community/...etion-mode-mosfet-now-available.261833/page-4
OK, here's the preliminary schematic for the new board. The SIR311 is a GaAs IR LED made for purposes of illumination, available for cheap at yer favorite auction site. Anyway, I will be making a couple of mods to get around some issues I noticed after I got the boards back from China. I'll be doing some tuning with a couple of current probes to optimaze the value of Aleph current sense resistor for symmetric drive.
Attachments
Reviewing the above schematic, I need to change how the bias for the topside current source is referenced - more bodges for my board...
Ha Ha, nice to see someone else has to carve up their prototypes...
So far, I've been able to get by without any carving, though the aesthetics are still somewhat dubious., with components bodged on board topside.
This one will get off the ground as soon as I have time to sit down and select/match the mosfets for the diff input stage.
Input diff pairs in place, amp is mounted on temp heat sink - ugly pics to follow... Powering this thing up should prove interesting.
