Aleph J illustrated build guide

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#761
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 :cheers:
 
#762
Idss again...

Many moons ago, the Mighty Zen Mod wrote:

Zen Mod said:
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
Click to expand...

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
 
#764
BobEllis said:
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.)
Click to expand...

Thermistor soldered to the softstart board, or just inline, into the softstart?
 
#765
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
 
#769
#770
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
 

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#771
Zen Mod said:
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
Click to expand...
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?

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.
 
#773
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?
 
#774
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?
 
#776
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!

:cheers:
 
#780
BobEllis said:
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
Click to expand...

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?
 
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