Thanks 'Teach
Many thanks ZM!
I'm too much a novice to actually toss my hat in that ring (tie together the two sides of my Aleph J) but if I don't understand what is being proposed and possible I'll be relegated to standing by forever while you smarter fellows have all the fun. I'll get there all in good time AND with your kind help.
I'll try to pay it forward when I can
Many thanks ZM!
I'm too much a novice to actually toss my hat in that ring (tie together the two sides of my Aleph J) but if I don't understand what is being proposed and possible I'll be relegated to standing by forever while you smarter fellows have all the fun. I'll get there all in good time AND with your kind help.
I'll try to pay it forward when I can

Idss again...
Many moons ago, the Mighty Zen Mod wrote:
I have some pretty well matched 2sj108V at about 18mA and
am wondering if they can still be used as is or if adjustments
to the circuit might be needed.
Thanks,
Dennis
Many moons ago, the Mighty Zen Mod wrote:
i
Jfets need to be somewhere in range of 8-15mA Idss , but they're biased by CCS , so no biggie there - as long their Idss is greater than bias itself
I have some pretty well matched 2sj108V at about 18mA and
am wondering if they can still be used as is or if adjustments
to the circuit might be needed.
Thanks,
Dennis
The thermistor in the mains connection is a soft start. You can replace it with another soft start if you wish. I prefer to use the thermistor in place of the resistors usually found in soft starts. If the relay bypassing the resistance fails, the thermistor resistance goes low and you won't have burning parts. Even a class AB amp will still work (with a little more fluctuation in the voltage the transformer sees.)
Thermistor soldered to the softstart board, or just inline, into the softstart?
one NTC , as Pa is using it , is soft start
as myriad times written before - best soft start circuit is certainly one relay based , but with string of NTCs instead of fixed resistors
that's much more versatile , covering plenty of xformer VA vs. cap bank size combinations , then common iterations , with fixed resistors
as myriad times written before - best soft start circuit is certainly one relay based , but with string of NTCs instead of fixed resistors
that's much more versatile , covering plenty of xformer VA vs. cap bank size combinations , then common iterations , with fixed resistors
As ZM said, NTC on the soft start board instead of resistors. Just use one. I believe that the soft start board uses resistors in parallel. NTCs should be used in series if you need more cold resistance.
they're usually connected in series , having 40R upwards
connecting them ( fixed ones ) in parallel , for abrupt load , is same clever as using paralleled fuses

NTC always series ; due to their nature , parallel is impossible
connecting them ( fixed ones ) in parallel , for abrupt load , is same clever as using paralleled fuses

NTC always series ; due to their nature , parallel is impossible
As ZM said, NTC on the soft start board instead of resistors. Just use one. I believe that the soft start board uses resistors in parallel. NTCs should be used in series if you need more cold resistance.
From this post from Toecutter:
http://www.diyaudio.com/forums/diya...supply-soft-start-board-v3-3.html#post3772857
Which resistors would you replace?
From the BOM:
1 R1 220R
1 R2 1M
4 R3,R4,R5,R6 180R
1 R7 2K2
gimme sch
those 180R are evidently peak eaters , but I simply can't believe that they're paralleled ( 4 times 180 being just too much , 45 being more in ballpark for soft start) ?
as I said - that's no-no
edit : attached example of proper one
just replace those 10R with NTC , preferably with even more resistance
those 180R are evidently peak eaters , but I simply can't believe that they're paralleled ( 4 times 180 being just too much , 45 being more in ballpark for soft start) ?
as I said - that's no-no
edit : attached example of proper one
just replace those 10R with NTC , preferably with even more resistance
Attachments
Last edited:
Well, if I already have the one from the store (same type from Toecutter's pic), am I screwed or is there a way to salvage it?gimme sch
those 180R are evidently peak eaters , but I simply can't believe that they're paralleled ( 4 times 180 being just too much , 45 being more in ballpark for soft start) ?
as I said - that's no-no
edit : attached example of proper one
just replace those 10R with NTC , preferably with even more resistance
The schematic is on the first page of the thread in the vendor/diyaudio section but I could try to link it here if it's easier.
Just use an NTC instead of one of the 180R reisistors and leave the others out.
http://www.diyaudio.com/forums/imag...SDP-2V20/P-SSSDP-2V20-softstart-schematic.pdf
http://www.diyaudio.com/forums/imag...SDP-2V20/P-SSSDP-2V20-softstart-schematic.pdf
Hi,
Good to read about the NTC's... was just wondering about what to use.
I have the PCB's stuffed so now it's onto ordering the toroids and getting it all in an enclosure.
I have read about the first capacitor in the Aleph J schematic, but I am not sure if I want to use it. Less is more, so to say. Is C1 needed when I use a preamp that has a capacitor in the output (a la Pass B1 buffer or a tube pre)?
I guess using a speaker protection module will be smart, or is this not needed with a J?
Good to read about the NTC's... was just wondering about what to use.
I have the PCB's stuffed so now it's onto ordering the toroids and getting it all in an enclosure.
I have read about the first capacitor in the Aleph J schematic, but I am not sure if I want to use it. Less is more, so to say. Is C1 needed when I use a preamp that has a capacitor in the output (a la Pass B1 buffer or a tube pre)?
I guess using a speaker protection module will be smart, or is this not needed with a J?
I ordered 8 2SJ74's from the shop and have just come to stuff them but they don't test within what I was expecting. The closest I can get is one pair at 11.2 and 11.4mA; and another pair at 14.2 and 14.3mA. The other four won't match any closer, indeed one of the group tested at 7mA.
Will it be OK to use these 2 pairs or should I order some more to try to get a better match?
Will it be OK to use these 2 pairs or should I order some more to try to get a better match?
Looks like you have a couple of good matches to me. Idss is a little higher than you'd expect but that allows you to increase the current in the differential and drive another output pair or two if your heat sinks are up to it. 

build more, worry less...
VDO, I built my Aleph J to spec. It was my first NP amp build and all went well. The amp sounds great no issues. No need to add or subtract 🙂
For that first cap I used a polycarbonate, they have a nice clean sound. I think ZM is a fan too. We have an option here to follow-the-leader and what a great leader: Nelson Pass!

VDO, I built my Aleph J to spec. It was my first NP amp build and all went well. The amp sounds great no issues. No need to add or subtract 🙂
For that first cap I used a polycarbonate, they have a nice clean sound. I think ZM is a fan too. We have an option here to follow-the-leader and what a great leader: Nelson Pass!

VDO, if your preamp has a cap output there is no need for C1, just jumper the pads. Just remember that the amp is DC then coupled if you change to a DC coupled preamp - that would suggest inserting it.
Looks like you have a couple of good matches to me. Idss is a little higher than you'd expect but that allows you to increase the current in the differential and drive another output pair or two if your heat sinks are up to it.![]()
Thanks Bob, good to know.
Hi Bob,JDG,
Thanks for the reply.
The J being DC-coupled answers my question about speaker protection as well...
Thanks again, Vranc
Thanks for the reply.
The J being DC-coupled answers my question about speaker protection as well...
Thanks again, Vranc
Just use an NTC instead of one of the 180R reisistors and leave the others out.
http://www.diyaudio.com/forums/imag...SDP-2V20/P-SSSDP-2V20-softstart-schematic.pdf
Since the resistors are paralleled, (4x180R), I assume I need a 45 Ohm (or higher) thermistor?
I can't seem to find any axial thermistors that fit the bill so should I just use a radial thermistor, bend the leads and cover with some shrink tubing?
Would this be appropriate or could you recommend something better?
(50R, 10%, Axial, GE, NTC)
RL3504-31.2-73-D1 GE M&C / Thermometrics | Mouser
Is there a limit to how large of a thermistor or should I try to stick near 45R?
- Home
- Amplifiers
- Pass Labs
- Aleph J illustrated build guide