Pass aleph 3 project

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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 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 it´s 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 it´s 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 isn´t. 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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Aleph Project


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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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.
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.
It´s a push-pull class A design right ?
I think that´s the best you can make for high power and low heat in class A.
What´s kind of transistor are you using in the output ?
Good luck.

vdi_nenna : I haven´t 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 don´t 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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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 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.
well all the amps in the aleph series use exactly the same topology so it doesn´t 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 don´t 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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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.

Wow !
Yeah it looks good. I don´t know thow if putting everything on the bottom of the box to cool is a good idea. It would be better i think on the heatsinks directly.
Anyway it does look cool. I have never seen heatsinks like that anywhere.
I can´t find the Hoffman schematic anywhere. I don´t think he is a registered member here.
If it´s easy to send a pic of it thanks.
(btw. I am not in a hurry I will be away a few days).
I've also seen the Aleph 3 service manual for a few months. I believe that from the circuit, the Aleph 3 is not featured with balanced input and the first -stage is the normal differential amplifer, similar but not exactly the balanced line stage (Super symmetric without the folded cascoded..see Pass's patent page).
The Aleph 3 is simply the Zen amp augmented with
1) differential input stage (probably to isolate output from input in the feedback loop and thus allow high input impedance and lower output impedance than the Zen)
2) 2 output sections in parallel for higher current drive
Probably some more that I don't see.
A good amp to try to make, however.Thanks for the generousity of Pass Labs.
You can modify it to have balanced input like the rest of the aleph amps because they all share the same design.
The output isn´t a Zen because the Zen has gain and the output section of the aleph is a power follower.
Apart from that the aleph has no change in phase.
The pair in the input is better the balanced line stage because of the current source. Apart from that it has the same function.
btw does anybody have a real schematic of the super symmetry circuit. I have seen the patent posted but it would be more usefull to see the real thing in practice.
Thank for your reply.
the link

Refering to the link. I think he says somewhere on the web page the case is a 3phase motor controller case. Very good idea anyone with a friend in an industrial/electrical job??
I think if you look closely you will see the fets are mounted on the sides of the heatsinks.
I was also wondering about any patents and rights etc when looking at building the Aleph. But wouldn't this only apply if you were sell the amp. As to make money off some elses ideas?? What do you guys think?

VDI_Nenna The subs for the A-40 outputs I have heard about so far are MJ11016, MJ11015 let me know if you find anything different. So far I have PCB's etched and some components mounted. Still waiting for a shipment from DigiKey (2 dats late) BTW I posted looking for Silver Micas a while back they can be found at the Digi web site it seems not everything is listed in the catolgue.
Wow that´s why the case looks strange...
Oh yeah you are right the transistors ARE on the heatsink.
I was not paying attention to all the pics in the site. I think the case is only two parts that you screw together.
There is no problem to make an amp like aleph with a few mods. It´s just for DIY or else Pass wouldnt publish it.
The main reason he published the service manual is because they stop producing the aleph series since they have the x series with new circuits and the parts for the aleph wont be around long or too expensive to buy.
Are the mj´s for the A40 expensive ?
Cost for the MJ's

The suppliers I have found for the MJ output devices seem to run $9-12 for the MJ11015 and $7-9 for the MJ11016.
Web-Tronics has them at and you can also find them at DC Kits or ACK Electronics

I'm in the process of sourcing the components for the Pass a40, but probably won't build it for a while yet - I have some other open projects that I need to finish that aren't as much fun...
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The Aleph 3 is single ended, but the 4 is both balanced and single. It's also 100w into 8 ohms. From what I could see, the schematic is more clear in the Aleph 4. It shows the intersections of connections. I need that to be able to build it correctly. The 3 doesn't have this.

Dok, I'll get the A-40 subs. tonight. But what you have sounds simular. I'll check anyway.
An implementation of super symmetry is in the SOZ circuit and the Balanced Line Stage projects, as well as X series of Pass Labs amp and some Aleph preamp (Aleph P 1.0 and 1.7 ... service manuals are on the web as well).
The major different that see (although not fully analyze yet) between Balanced Line Stage circuit and normal differential amp are
1) the coupling resistor between the two MOSFET source pins
2) the separate current sources for positive and negative sides.
So the Balanced line stage looks more like two single-ended connected to each other via the coupling resistor, rather than the differential amp. The Aleph 3 input is, however, exactly a normal diffential amp because it has a common current source connected to both the source pins of the two MOSFETs. According to Pass's patent page on super symmetric topology, the coupling device plays the major role in sharing the distortion to be approxiamately the same on both positive and negative sides, thereby cancelling each other out at the output.
The output stage of the Aleph is similar to a Zen, it is NOT a power follower.

It is non-inverting because it has 2 stages with both inverting, hence net result is non-inverting.

I guess a good starting point for DIY is to make first following the Aleph schematics. Later changes can be adopted to see how these can improve the sound.
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