Aleph J illustrated build guide

[Zen Mod]

yup

as explained several times in Babelfish J thread

 

[mpa]

I would seriously consider buying the back panel kit if you’re thinking of using one of the chassis (4u/5u) from the Diy store. It has the rca input connectors, speaker terminals, power switch AND all the mosfet mounting screws and washers needed. I don’t believe it has the split washers though which you’d need to source separately.

Many thanks for the advice guys, unfortunately I had already got the 4u chassis without the back panel kit but managed to source the IEC socket ok although I must admit, I've never seen a dual fused inlet before and it does concern me slightly! Does 2.5a slow blow sound ok for Aleph J with 500VA transformer 240v? (and DIY audio soft start) I was thinking of using a larger fuse on the neutral side.
Quick question as I am planning to populate my boards tomorrow, should R8 be a 500R pot as per the BOM or a 1k fixed resitor?

 

[Dennis Hui]

R8 should not be a 500R pot. The BOM I looked at indicates a 2K pot.
It is nominally set to 1K to ensure about 8-ish mA current through the
front end jfets. (So the pot value should be greater than 1K)

I built mine with a 2K pot, set it at 1K, and never touched it since. If
I were to do it again, I would have just gone with a 1K fixed resistor.

Cheers,
Dennis

 

[ItsAllInMyHead]

@mpa - FWIW, I did 1k fixed. re: your fuse choice, there are those more skilled than I to help you there.

Enjoy the build!


Patrick

 

[mpa]

Hmm, I'm looking at BOM REV C and it definitely says a 500R pot. Am I looking at an old version?
Thanks for the advice though, I'll just go with a 1K fixed resistor!

 

[Dennis Hui]

I was looking at the BOM here:

http://www.diyaudio.com/forums/atta...j-universal-mounting-spec-bom-aleph-j-ums.pdf

This one is Rev D. It looks like the link on the PCB page at the store is for Rev C. (Kinda confusing...)

 

[mpa]

Thanks! Already ordered from Rev C so hopefully there's not much difference but I guess I'll spend tonight checking.

 

[Dennis Hui]

I suggest you also compare against the schematics:

https://www.diyaudio.com/archive/gallery/data/500/AJ_Sch.png

 

[Mazeppa]

Just trying to help out, and trying to pay it forward. I’ve received a lot of advice and help with my projects, and am eternally greatful. My first build was in fact an Aleph J thanks to a little push from 6L6 (aka Jim) and Dennis Hui. I was petrified that the little knowledge I had wouldn’t be enough to get through the build, let alone a functioning amp. The help, advice and encouragement from the people on this forum from Nelson himself, 6L6, Zen Mod, Dennis Hui and Mark just to name a few is never ending and appreciated. Without the help I might not be sitting here as I type listening to my J. 😊

Hear, hear.

Now back to the bench, I'm upgrading the PS to dual mono for my AJ.
Best amp I've ever heard as is; but if it can sound any better, I want to know it.

 

[Extreme_Boky]

Many thanks for the advice guys, unfortunately I had already got the 4u chassis without the back panel kit but managed to source the IEC socket ok although I must admit, I've never seen a dual fused inlet before and it does concern me slightly! Does 2.5a slow blow sound ok for Aleph J with 500VA transformer 240v? (and DIY audio soft start) I was thinking of using a larger fuse on the neutral side.
Quick question as I am planning to populate my boards tomorrow, should R8 be a 500R pot as per the BOM or a 1k fixed resitor?

The fusses should be the same value, 2.5A slow blow is fine for 240V.

If you use dual diodes (the fast switching/soft recovery types) and you have a large capacitor bank and you decide to use thick&short wires (and you already have a 500VA transformer) the fuse may have to be increased to 3A...or more... see how you'll go.

 

[6L6]

, should R8 be a 500R pot as per the BOM or a 1k fixed resistor?

Omit the pot, use the 1K. The Zener is actually what's setting the current, the pot, if installed, can only made very small changes if desired. As others say, you set it to 1K and be done, so why even bother with the $4 pot when a $0.05 resistor does the same job.

 

[toto34]

Dear ZenMod,

Which value of gate resistance is needed for an IRF150 instead of an IRF240 (221 Ohms)?

Best Regards
Toto

 

[6L6]

221ohm will work beautifully.

Anything between 47-300R will work for a gate stopper resistor, it's fairly uncritical, use what you have on hand.

 

[toto34]

Thanks again for your advice

 

[elwood625]

With the DIY store sale going on now, I'm buying everything I need for an Aleph J amplifier. I have one question, C1, is it needed or not? If so, under what conditions would it be necessary to use it?

 

[Zen Mod]

if you're member of FAB Club , you don't need it


it helps leaving it in place if you're not sure of your preamp behavior regarding DC offset ( DC gain being minimized) and with tricky combinations of R and C in your PSU , so lowering Power On thumP!

 

[6L6]

I’d leave it in, for stability in all the points ZM listed.

 

[Extreme_Boky]

DC offset will hunt around... I do not believe it will ever be (even close to) zero without C1.

 

[elwood625]

OK. C1 it is. Why does the WIMA version have so many "fans"?

 

[Mark Johnson]

Dare to be different. Use a Kemet F461 polypropylene capacitor. Blaze your own trail.