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Old 10th January 2001, 02:42 PM   #1
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Hi to everyone !
After reading a lot from the forums and studying alot of designs I fell upon the Aleph 3 service manual in the pass site http://www.passlabs.com. It has exactly what I was looking for. A single ended class a design. You get more power then Zen amp, you can have balanced input and itīs easy to change the power output. Just perfect for me. There is a big BUT like allways. DIYers know this part. The output transistors must be changed because TO3 package mosfets are slowly getting rare to find and expensive do to new hexfet plastic ones and there is the need of a new PCB since there is no design avalaible.
I am thinking of using for the output the IRF240 or IRF250 transistors or maybe the plastic isolated ones IRFP240 and IRFP250.
The rest of the circuit is normal and easy to understand.
This amp gives 30 watts rms but can be changed to give more like the bigger models and itīs power disipation is rather good for a class a design.
It uses a balanced single ended input with low power hexfets like the balanced line preamp from pass and a power follower in the output in single ended class a looks like the Zen amp but isnīt. It has no capacitor in series with the signal in the output.
If anybody likes a new project like this and has ideas please post.
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Old 10th January 2001, 04:39 PM   #2
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Default Me too

I have looked at that too. I am building the A-40 but the Aleph looks like a great project. And I had the same concerns as you. Let me know what you find.
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Old 10th January 2001, 07:58 PM   #3
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Talking Aleph Project

Hi,

I was looking at either building the Hoffman balanced, single-ended 30w amp from Audio Electronics Aug 1998 #4 issue or the Aleph 3 for it's obvious advantages.

In the Aleph 3, there is a slight difference in the constant current source from one channel to the other, e.i. R-29 in the left side says 619 ohms, but for the right it's 523 ohms. Also, C-1 is on different sides of Q-3, depending which schmatic you are viewing. Why? Does it have to do with the mirror image of the board? I don't understand why 2 channels of the same amp have different values or why the schematic is drawn different for each channel. Am I making sense?

Would you consider building a regulated stage for the input section? Or is it enough to have the constant current?

I think building the Aleph 3 would be awesome! I couldn't afford to buy even a used one right now.

Let us know how you do with this project.
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Old 10th January 2001, 08:11 PM   #4
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Wink Hexfets for Aleph 3

To-3's dissipate heat the best because of the metal can, the To-247 come in second I think because of it's size. TO-220 comes in third. Another advantage to the TO-247 is that you can screw it to the heatsink without using an isolator for the screw. The case of the TO-247 is plastic all the way throught the hole and even to a degree the rear is plastic, but the rest is metal, so an isolator must be used for affixing the TO-247 to the heat sink.

I'm using the TO-247, in this manner, for my ZEN amp.
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Old 10th January 2001, 10:51 PM   #5
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Hi I am back !
Happy this project is interesting to a lot of people.
I have some replies for some people who took time to post some replies.

doktor : The A40 is a classic design I think and fully tested after so many years. I know a lot of people are very happy using this amp.
Itīs a push-pull class A design right ?
I think thatīs the best you can make for high power and low heat in class A.
Whatīs kind of transistor are you using in the output ?
Good luck.

vdi_nenna : I havenīt seen the Hoffman amp. Is it posted somewhere online ? I am interested in seeing the design.
For the Aleph 3 I was going to start from the electronic design from the manual so I donīt realy know what parts are in the pcb layout.
I am going to use probably the IRF9610 in TO220 package as input gain devices and IRF240 or 250 for output. They are TO247 package but there are 2 kinds. IRF240 with metal back and IRFP240 with full plastick case for full isolation.
I know a lot of companies use them for amps so they dont have problems.

bye for now
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Old 11th January 2001, 12:42 AM   #6
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Lightbulb A-40 and Aleph 4

The output trans on the A-40 are Darlingtons...I think. They are tough to get and kind of expensive $8-9 bucks each. This is when I first looked at the design several years ago.

In one of the letter in Audio Electronics Magazine, a substitute was requested from a reader. It was just this past year. If you don't subscribe to A.E., now AudioXpress, you should. It's monthly now, not bi-monthly. Anyway, if you want to know the subs for the output trans for the A-40, let me know.

Did I say Aleph 3? I meant 4.

Fully plastic cases, huh?

The Hoffman amp was just a schematic in an issue. I don't know if Mr. Hoffman has a web site, but I'm sure that he posted on this site. On this forum page, look under "Convergent". He's always looking for Schematics. That's how I found him...in AudioXpress' Want ads looking for schematics. His email should be under his profile tag.

It's so simple, that I might still try it anyway. You could easily hard wire it in a couple of days if you know what you're doing. Ask him about any changes. Because there was a misprint or 2 in the power supply description. It was not drawn, just stated.

Hope this helps and let us know what you find.
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Old 11th January 2001, 01:24 AM   #7
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well all the amps in the aleph series use exactly the same topology so it doesnīt really matter what model we are talking about. The only thing that changes is the output stage and how many fets form it.
I just took a look again at the A40 pages and yeah it says special darlington transistors with low resistance.
I donīt have a clue about similar ones. Maybe you can get some help from Pass.
Yeah it is so simple to make.
I will try to find the Hoffman scheamtic.
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Old 11th January 2001, 02:22 AM   #8
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Default check out this web site

http://www.institute.uni-bremen.de/~...eph/aleph.html

this guy actually built the aleph 3 looks good too.
Actually I would be interested in subs for the A-40 output they are darlingotns. Thanks
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Old 11th January 2001, 02:25 AM   #9
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Thumbs up Oh Cool !!!

Hey thanks a lot for that link I am checking it out in a
few. If I find something similar will post.
Thanks again
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Old 11th January 2001, 04:15 AM   #10
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Wink A-40 substitute output transistors

Dok, I'll have that sub. for the A-40's output for you tomorrow.

That guy's Aleph 3 was nuts! Did you see those heatsinks! Where do people get this stuff?

Prom, if you can't find the the Hoffman amp schematic, I'll copy it and email it to you in a few days, then let me know what you think.

Vince
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