Aleph J illustrated build guide

You could mount it soldier-style and have only the thin lead on that side, or

Soldier style? :confused: Please help a non-native english speaker. :)


hi 6L6,
i have toroidal with 25-0-25 / 20A
can i use with aleph J ? (previously it is okay with my aleph 30)
i am afraid it will run too hot for the J

thanks.

At least I would make the PSU CRCRC style to lower the DC voltage near 26 - 27 V.
FWIW 25 V AC = 35 V DC is way too much. Agree with 6L6 though, best to use
it for a more suitable project.
 
wengtech,

Whether you can use that transformer depends on your confidence in exceeding the 2SJ74's ratings. The rail voltage will be similar to what you had in your A30, 30+V. Assuming that your heat sinks are up to the output section heat (the same as similarly biased A30), you can probably get away with running the jfets, see NP's F5Turbo article, where he says that the 2SJ74s fail at 43V. You might consider doubling them up to reduce individual dissipation, use 2 on each side of the differential. Better yet, use the transformer for a cascoded F5TV3 as already suggested
 
ouch... too bad.
maybe it should be retired until i get the properly amp for it.
thanks for advice guys....

btw what about pre amp for the J ?
my opinion the aleph p1.7 and the pumpkins will be suitable for the J.

any suggest?

Depends on your source(s). If it's only going to be digital then I would suppose a B1, DCB1, Lightspeed Attenuator would also work.

As for myself, I will have a choice between DCB1 (Hypnotize) and Aikido + Tetra. In the meantime my 22 year old Rotel RC980BX is doing that job.
 

6L6

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IMG_0464.jpg

The bigger resistors are mounted soldier-style.

(I thought soldier style was the real term for that... maybe not...)
 
Soldier style: Standing at attention, with the body vertical. Took this native English
speaker and Navy veteran a second to figure that one out so don't feel bad ticktock.

The bigger resistors are mounted soldier-style.

(I thought soldier style was the real term for that... maybe not...)

Thanks, mates. I should have figured it out on my own and at least I'll never forget that.
:D I even have some resistors that way in my own Ono MC prepre. ;)
 
No push pull here, this is single ended country. ;)

The bias impacts where the amp becomes current limited vs. voltage limited. If you have low impedance speakers, you might see an increase in power output with more bias.

6L6 has done some measurements that show that higher bias decreases distortion. While measurable, you may or may not hear a difference.
 
So how much different in overall topology is the Aleph J from the Aleph 0?

While it will not leave Class A on an unclipped positive signal, a single ended Class A design would ordinarily clip at negative currents greater than the bias point, and for this occurrence the Aleph 0 has proprietary pull circuitry in the output stage which allow push-pull operation at negative currents beyond the bias point. This new topology has been designed to source greater negative current than previous amplifiers with single ended bias, in the belief that push-pull Class A operation is preferable to clipping.


So where is the J biased for the 25W@8 ohm rating?
 

6L6

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The J will make 25W into 8ohm at the .400V bias. I am not sure how the bias actually interacts with total power, but I do know that a 'normal' single ended output stage can not pass more current than the bias, but the Aleph CCS has the ability to change that somewhat... but I honestly don't know exactly what the circuit is doing to make that so.

Maybe somebody more familiar with how this stuff all actually works can help explain?

I do know that I can take some measurements and data points and pass that info onto the thread -- If I get a chance in the next few days I will get some full-power measurements into 8 and 4 ohm at various bias levels.
 
Yep, I think the dumbness sets in when I have to comprehend the interaction with the hybrid SE/PP section of the circuit. I think I just want to understand it as far as being able to bottom-line a total device dissipation-to-output efficiency. It seems like it's 35% in the best case of operation.

Sort of related: I'm getting a value of 21k for R7 in order to achieve the 400mV bias with the BOM parts. At 68k it was 520mV which was a bit too hot for my 4U chassis heat sinks. Even with the lower bias this thing still kicks out some heat. Winter is coming...
 
mica and insulation

I have read the mica and goop thread but I got myself into trouble when I bought micas from Mouser...

TO-220 was said to cover the interface for TO-247 but it is SO close to not covering it! How critical is insulating (electrically) the output transistors and the heavy duty diodes from the casework/heatsinks?

Can anyone point to a source of larger (like 25 x 20mm) micas that don't have to come all the way across the world to the USA? Digikey and Mouser don't seem to have them (which to me means I just can't find them on their sites...)

Cheers!