But when I connect up the AN board ... R18 starts to smoke - and R4/R6 get very hot!(These are reses on the SLB board.)
Hence Hugh is thinking that maybe the AN 4R circuit is not compensated correctly and is oscillating. So I am waiting for my Variac to arrive, so I can reduce the input mains voltage to get +/-15v on the SLB DC rails. If R18 doesn't smoke ... then AN oscillation would seem to be the cause of R18 on the SLB smoking at full voltage!
Andy
My Variac arrived - so I fired up the suspect AN 4R board with my new Variac on the mains supply (160v instead of 240v - to deliver 15v DC rails). R4/R6 on the SLB still got blisteringly hot ... and R18 started smoking!
So I switched off.
Hugh then suggested the AN 4R must be oscillating - which is causing oscillation in the SLB. So I should increase C4 on the AN 4R circuit (attached) from 15pF to 22pF, to stop this oscillation.
I had to wait a couple of weeks for these caps to arrive but, yesterday, I installed the 22pF cap. Fired it up this afternoon (with the Variac) and - at last! - R4 & R6 on the SLB only got hot (not blisteringly hot!) and R18 did not smoke! Yay!
So, yes, it would seem that C4 in the AN 4R circuit needs to be 22pF - not 15pF.
X, are you able to mark up the schematic with this change?
Now I have to do the same on my other three AN 4R boards.
Regards,
Andy
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From previous posts, there will be 2 boards/kits, with each VFet. There will only be one per channel, either variety will be used. I appears (no proof at present) that you can use a pari of either one to make an amp. No matching. It seems that there will be kits with VFets, and bare boards to buy. February, May, whenever. It is not worth stressing over the time schedule (not that I don't look daily) Details to come, when Mr. Pass makes them available. Mark Johnson is doing his best not to mess up the surprise, shock, and awe!
Those boards/kits will come. Until, we enjoy, and love, the M2x. Endless discussion ensues. And we give thanks for the blessings bestowed.
Those boards/kits will come. Until, we enjoy, and love, the M2x. Endless discussion ensues. And we give thanks for the blessings bestowed.
Speculation- the first DIYStore VFET kits used 28v rails, from 22v transformers. Those were push pull circuits. We have not been told much other than hints by Mr Pass, and Mark Johnson. I would not be shocked if the new circuit used 24v rails though.
1) 2 schematics, one for 2SJ28, and one for 2SK82 (one per side, SE not PP)
2) kits + boards through DIYAudio Store
3) modular input cards by Mark Johnson (a la M2x)
I suspect that Mr. Pass has a stack of un-matched Vfets that can be used for a single ended amp. These hints are mostly scattered through the M2x thread. Mostly we just get teases.
1) 2 schematics, one for 2SJ28, and one for 2SK82 (one per side, SE not PP)
2) kits + boards through DIYAudio Store
3) modular input cards by Mark Johnson (a la M2x)
I suspect that Mr. Pass has a stack of un-matched Vfets that can be used for a single ended amp. These hints are mostly scattered through the M2x thread. Mostly we just get teases.
Yes, I put jingle bells in my wife's presents for Christmas just because of that.
I was just spouting what I remembered, I am still exploring the M2x, (with SLB PSU boards) and can wait on a new project at this point.
Ok so sounds like in all likelihood it’s another +/-24v and 1.25A bias current 25w class amp.
Btw, on some amps, if the parts can handle it and the design is tolerant, a happy accident +/-28v rail makes a huge improvement in peak power vs 24v - which is really often 22.5v under load and transformer sag. I think it becomes a 35w amp and that allows some passages on certain songs not to clip at the crescendo.
Btw, on some amps, if the parts can handle it and the design is tolerant, a happy accident +/-28v rail makes a huge improvement in peak power vs 24v - which is really often 22.5v under load and transformer sag. I think it becomes a 35w amp and that allows some passages on certain songs not to clip at the crescendo.