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Old 15th December 2001, 11:50 PM   #1
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Default Aleph 2 (& others) as a project

First, the acknowledgements:
--I'd like to thank Nelson Pass of Pass Labs for making this circuit available to the DIY community. This is his circuit (all right...I modified it a bit, but it's still his). If you build this for profit, bad things will happen to you. <i>Bad</i> things.
--I'd also like to thank Geoff Moss for his efforts in translating this circuit board into a GIF file suitable for posting here. (I believe that he now hates the Winboard software fully as much as I do--you ought to see some of the things he says now that he's had to deal with that confounded program.)
--The artwork is mine. Any mistakes (don't start carping about the differences between this and the Aleph 2 schematic until I get a chance to explain) are mine, not Nelson's. Got it? License is hereby granted to individuals to make boards for their personal use (nonprofit), subject to any limitations Nelson might choose to impose. It's his circuit--his rights supercede mine by a country mile. Whatever he says, goes.
And that's the way it should be.

This is the board I use. It works. However, it is different from the stock Aleph 2 in a couple of ways (in fact, for convenience, let's call this an Aleph 2.60). Please note the following:
1) I chose to incorporate the input resistor network from the Volksamp Aleph 60 in order to bring up the input impedance.
2) Once I did that, it threw off the numbering system for the parts. I elected to simply keep going with the 60 numbering system.
3) C9 (Aleph 2 nomenclature--it's C18 on the 60) has been returned to the emitter of Q5, the way it is on the 60. I had a reason for doing this, but as it's been over a year since I did the layout, I've forgotten why. Oh, well. Nelson will probably say that it degrades the sound to do that, so I'll end up with egg on my face. (Honestly, I don't think it's going to change much--it's just there to quiet the juice going into Q5. It boils down to which side of the current sensing array you're connecting it to, and as that's on the order of .17 ohms, it's going to be a pretty small difference.)
4) I made a place on the circuit board for C6 (Aleph 2 nomenclature), but I've never put it in. The 60 doesn't have it. If you want to put it in, there's a space. When in doubt, flip a coin.
5) Parts values, by and large, are the Aleph 2 values, due to the higher rail voltage. If, for instance, you use 4.75K for R13, you'll be driving Z5 harder. If you use a 1/2W part, it can take it, but there's no need to put that much current through it as the gate of Q3 draws next to nothing, current-wise.
6) For the power LED, I chose to use two resistors fed from each rail. This will ensure that both rails discharge on turnoff. In other words, they're doing double duty as bleeder resistors.
So much for the changes to the circuit.
Why did I lay it out the way I did? Why didn't I put the output current sensing array (R22-27) on the output boards? Why do I use two identical output boards?
In a word...flexibility. Use one output board for the output devices, and another for the current sources. For those of us who do not have ready access to heatsinks, it's easiest to have the current sources and the output devices in separate banks (and these, in turn, separate from the front end), so as to be able to make use of whatever surplus heatsinks come our way. I use this circuit in a water-cooled system (see elsewhere for details), but most of you will not. You'll be at the mercy of the stereo gods when it comes to heatsinks. This should give you (and me) latitude when it comes to trying to fit this circuit into large chunks of finned aluminum, then trying to cram transformers and caps in and around the circuit.
There's also the aspect that I wanted this circuit to be able to cover more than one Aleph model. Want a 1.2? Use four output boards. Want a 4 or a 2? Use a pair. Want a 5? Only populate every other slot in each board. The only requirement is that you use at least one of the end positions, because that's where I've set up the sense connections coming from the source resistors. One source resistor on each bank will need to connect back to Q4 (for the output devices) or Q5 (for the current sources). Note also that the output boards are symmetrical end-for-end (electrically speaking). You can put your hookups at either end. This gives you maximum freedom in physical layout.
Although I haven't sat down and gone through the other schematics part by part, these boards should come pretty close to working for the other Pass/Volksamp Aleph models. For sure, the outputs will work. The front end board should do so with minimal modification.
The images are component side views.
The front end board is 4.2 x 3.6"
The output board(s) are 1.3 x 6"

(There's more to be explained and uploaded. There will be stuffing guides and parts lists, etc. Geoff and I are flogging this along as quickly as we can, and we're both already cross-eyed from staring at our screens for hours on end. I owe the man a beer or two for this... N.B.: I'm also working [albeit slowly] on a dedicated board for the 3. Or maybe I'll just go ahead and make it a 30. We'll see. Be patient.)

Grey
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Old 16th December 2001, 05:12 AM   #2
grataku is offline grataku  United States
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Grey and Geoff,
thank you very much for the work you are doing here!
The layout looks great, too.
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Old 16th December 2001, 05:38 AM   #3
mlloyd1 is offline mlloyd1  United States
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Grey:

Thanks for sharing. Very nice layout. I think I'll try it myself.

Michael
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Old 16th December 2001, 06:05 PM   #4
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Okay, round two...
I'm short on time (again), so I'll drop these in without comment except to note that the optional ground strip across the middle is just that--optional. If you want, you can hook it up directly to whatever you use for your grounding point. I put it there on the off chance that it might help shield the incoming signal via the 221 ohm gate resistors in case of oscillation.
I've never used it. Never needed it.
And again, my thanks to Geoff for the translation into GIF format...

Grey
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Old 16th December 2001, 06:09 PM   #5
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The output board artwork:
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File Type: gif alephbk.gif (2.7 KB, 5311 views)
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Old 16th December 2001, 10:46 PM   #6
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This is a good example of civilized communication on 21st century.
Bravo.
We all appreciate this.
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Old 17th December 2001, 12:30 AM   #7
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A couple of quick notes:
--I designed the output boards for MOSFETs with the GDS configuration. I used IRF644s (the TO-220 case version of the MOSFET Nelson was using. Most of you will probably want to use a TO-247 case, due to higher heat dissipation capabilities...unless you want to go water-cooled, use fans, or use really large convective heatsinks. I believe all the most likely candidates are GDS. If you want to use something else, it shouldn't be all that difficult to rework the board layout.
--The tab goes towards the nearer edge of the circuit board (but I trust that you could have figured that part out for yourselves...)
I'm still working on the stuffing diagram for the front end board. I hope to finish it late tonight or tomorrow, at which point I'll squirt it across the Atlantic to Geoff for conversion. As soon as it's done, I'll get it posted and you folks will have a complete set of board layouts.

Grey
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Old 17th December 2001, 03:39 AM   #8
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Thumbs up To Grey and Geoff.....

A BIG thank you for the great work......!!!
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Old 18th December 2001, 05:38 AM   #9
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The stuffing diagram for the front end board:
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File Type: gif alephfrs.gif (35.0 KB, 4972 views)
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Old 18th December 2001, 05:40 AM   #10
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The stuffing diagram for the output board(s):
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File Type: gif alephbks.gif (16.5 KB, 4673 views)
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