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Old 4th August 2013, 12:30 PM   #21
jdg123 is offline jdg123  United States
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Smile rare parts

The Aleph J will be my first SS build and it makes for a lot of questions. I have been reading through all that I can find on the Aleph J, most of it is kinda old by now so I can empathize with the stress of HiFi Rookie.

What I have gleaned is that many folks are distressed by the end of an era for JFETs like the 2sj74, we're all hoping that a different company will take up the banner and produce a similar product though market forces don't seem to indicate this will happen. In short, no one has the answer HiFi Rookie is looking for.

It may come with time.

As to the power supply, I can say it seems like two boards will be enough. I hope it is as I only ordered two.

Many would say dual power supplies are better and they are but if Papa uses just one you gotta know it will do.

Anyone who knows more than me (that is about all of you) please correct me if I'm off base.

Now I'll leave with a question on a practical matter, but first a thank you to all you guys who created the boards we newbies are buying! You are the ranks that support the good cause Papa spearheads! The question is about the BOM for the Aleph J: Is the BOM for one channel? Do I need a quad of 2js74 and an octet of IRFP240?

Newbies need lotsa help eh?

Many thanks to all the helpers!
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Old 4th August 2013, 01:20 PM   #22
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Rookie and jdg123 - One set of PSU boards will give you a dual rail power supply - one rectifier board and one capacitor board for each rail. Not dual mono, but you can run two channels from a single supply.

The single vs. dual supply question is one you'll have to answer for yourself. There are those who swear by them and those who are happy with a single supply. I suspect that whether dual mono provides an audible difference depends on the rest of your system and your own ears.

The 2SJ74 has been obsolete for a while, most of the ones you see for sale now are fakes. There is a member selling genuine parts, Spencer, I think. Search the Aleph J and F5 threads, he has full semiconductor kits IIRC. There are other parts that may be substituted, but have Vds ratings that are a bit lower (use an F5Tv3 style cascode with a lower cascode voltage? requires a different board) and other specifications are different. It seems that j-fets of all types are endangered species, particularly through hole types. I wouldn't be surprised if Pass Labs has a bank vault full of them.

jdg123 - Look at the schematic to answer your BOM question (more appropriately asked in the A-J thread). The Aleph circuit uses a long tailed pair input - 2 gain devices per channel and four IRFPs per channel.

Now back to discussing the PSU V3 boards

Last edited by BobEllis; 4th August 2013 at 01:26 PM.
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Old 4th August 2013, 03:30 PM   #23
Bones13 is online now Bones13  United States
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Answers one of my questions. Each amp board requires a dual rail PSU (v+, v-, and ground), so to do true dual mono power requires 2 toroids, and 2 sets of PSU boards.

So unless you go full out doubling everything, looking into a higher rated Toroid might be the easier option, as well as maxing your cap bank. Of course it's not the "ultimate", but lines have to be drawn sometime.

If I could find one sided cases, like the new ACA ones, sized for the Aleph J dissipation needs, building monoblocks would make more sense.
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Old 4th August 2013, 03:43 PM   #24
jdg123 is offline jdg123  United States
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Thanks BobEllis!

I apologize for asking a question I could have found through adequate searching. I did give it a few hours. I must learn more to even be adequate as a learner!

I do give back especially to other new folks when I have something of value to put out there but I know I am guilty of asking a question on the signal side of things and not specifically on the power supply. I am contrite.

About the question itself, please understand I don't really know what a long tailed pair is and that coming as I do from the tube side of audio it is common (and yet not so commonly specified) to draw one channel only leaving it "understood" that one has to make two channels for a stereo amp. This field is dense with symbols and conventions to learn. I have no guide. I appreciate your willingness to put aside irritations and help out the learners, very much.

Sincerely,

John
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Old 4th August 2013, 04:28 PM   #25
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You're welcome, John.

A long tailed pair is a differential pair of devices joined at the emitter/source/cathode. Have you seen a tube preamp where both sides of something like a 12AX7 are used with one side the input and the other connected to the feedback point and their cathodes connected (may be resistors between them, but the dual connection is between the connection and ground)? That's a long tailed pair.

Grossly simplified: The total current in the pair remains the same, so if one side turns on more the other conducts less. Therefore, the voltage across the load (resistor in the Aleph case but can be a current mirror or two) changes. The net result is you have the input signal amplified, both inverted and non-inverted available at the tail end of the pair.

There are conventions, but it is always wise to verify that the BOM is for a single channel or two. It's fairly easy to do by looking for a part that is used an odd number of times. A good sign that it is a single channel. If there are even numbers of other parts, find one that is used sparingly, like 2 pieces of 2SJ74. The BOM will usually specify the part ID(s) for them. If there are 2 pieces called out and 2 part numbers... Also you could look at the schematic, and count how many times that part is used. Simplistic, but sometimes hard to see when you're getting started.

Bones, Another thing that NP has done is use a single large transformer and double up on the rectifiers and caps. Sorry for giving you another option to consider.

Hope this helps.
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Old 5th August 2013, 01:37 AM   #26
Bones13 is online now Bones13  United States
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The toroids I see have 2 AC output pairs. And I want 18/18 for the Aleph J.

Does each pair go to one rail? With the 2 lines being used for a single PSU set?

So with the one toroid, 2 rectifier setup, are the AC pairs hooked up with the rectifier sets in parallel? With the same AC pair hooked up to both PSU sets?

Sorry for the lack of knowledge, the kits I have built had this figured out already.
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Old 5th August 2013, 02:34 AM   #27
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Connect one winding to each rectifier board. By two AC output pairs I presume that you mean four wires, not four sets of windings.

Do you have 14V windings for 18VDC or 18 VAC windings for ~24VDC rails?
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Old 5th August 2013, 11:07 AM   #28
Bones13 is online now Bones13  United States
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I have not chosen a transformer yet, rather I am still researching.

By pairs, I am referring to a twisted pair AC set, so 4 actual wires as output from the transformer.

As I understand it, I need 18 VAC outputs (x2) for 24 volt rails for the Aleph J.
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Old 5th August 2013, 11:48 AM   #29
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Yes, 18 VAC x 2 will get you 24 VDC.
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Old 8th August 2013, 09:53 PM   #30
mattmcl is offline mattmcl  United States
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I could use some help with parts selection. I'm building a dual mono Honey Badger with two 45v transfos. That means 63v on the rails. Would these be suitable diodes?
FES8GT-E3/45GI-ND

Also, I'm having a heck of a time figuring the correct values for the snubber caps (CX1, CX2, CS1, CS2) and resistors (RS1, RS2). The referenced article makes my head spin. Any help here would be greatly appreciated.
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