Carsten forwarded me a couple of question from the German forum, so I thought I'd post my answers here too. (Caveat: I'm not an expert. I think I understand this design, but if I get something wrong then someone should feel free to correct me.)
R19 adjusts how quickly the voltage output ramps up. A larger resistor causes C5 to fill more slowly and the voltage to come up slower (although it always ends at ~ 41V). I think Nelson’s version (47K5) comes up in something like 30 seconds, whereas mine (33K) comes up in 15 or 20 seconds. Both values will eliminate turn-on-thump, and one could choose to use even larger or even smaller resistors for slower or quicker times.
As long as the JFET + R5 for each channel puts the JFET in its sweet spot, there’s no requirement to match them.
The cascode MOSFETs (Q2) are adjusted with P1, so no matching required.
P2 controls how closely the CCS follows the output devices. There’s no good way to measure this without a distortion meter so you might want to match the CCS MOSFETs (Q3) between channels, but there’s a lot of wiggle room here and I’d be very surprised if you could hear any difference between them being matched and not.
You could match the C-multiplier MOSFETs (Q5) for Vgs so that the rails were the exact same between channels, but again I’d be very surprised if you could hear the difference.
On the other hand, if you have graded a tube full of MOSFETs (say, for an F5), then there’s no harm in using up the loosely matched pairs.
Cheers,
Jeff.
R19 adjusts how quickly the voltage output ramps up. A larger resistor causes C5 to fill more slowly and the voltage to come up slower (although it always ends at ~ 41V). I think Nelson’s version (47K5) comes up in something like 30 seconds, whereas mine (33K) comes up in 15 or 20 seconds. Both values will eliminate turn-on-thump, and one could choose to use even larger or even smaller resistors for slower or quicker times.
As long as the JFET + R5 for each channel puts the JFET in its sweet spot, there’s no requirement to match them.
The cascode MOSFETs (Q2) are adjusted with P1, so no matching required.
P2 controls how closely the CCS follows the output devices. There’s no good way to measure this without a distortion meter so you might want to match the CCS MOSFETs (Q3) between channels, but there’s a lot of wiggle room here and I’d be very surprised if you could hear any difference between them being matched and not.
You could match the C-multiplier MOSFETs (Q5) for Vgs so that the rails were the exact same between channels, but again I’d be very surprised if you could hear the difference.
On the other hand, if you have graded a tube full of MOSFETs (say, for an F5), then there’s no harm in using up the loosely matched pairs.
Cheers,
Jeff.
This heatsniks will do it:
Kuhlkorper, Gehause und Steckverbinder vom Hersteller
SK93 150mm height one pcs per chanell?
Kuhlkorper, Gehause und Steckverbinder vom Hersteller
SK93 150mm height one pcs per chanell?
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Google spreadsheet
Good day Jeff or Carsten!
It is not possible to get in the spreadsheet (Google) and finding any information like Bom and tuning the Jfet!? Google says it's dumped in the waste-bin!
Ed
Good day Jeff or Carsten!
It is not possible to get in the spreadsheet (Google) and finding any information like Bom and tuning the Jfet!? Google says it's dumped in the waste-bin!
Ed
Hi Ed,
I've attached my BOM, but Carsten added a bunch of good info to it, so hopefully he has backups of the Google drive....
Cheers,
Jeff.
Note: strip the ".txt" extension from it and it will load into a spreadsheet.
Note 2: the BOM is for a single channel, so you'll need twice the quantities.
I've attached my BOM, but Carsten added a bunch of good info to it, so hopefully he has backups of the Google drive....
Cheers,
Jeff.
Note: strip the ".txt" extension from it and it will load into a spreadsheet.
Note 2: the BOM is for a single channel, so you'll need twice the quantities.
