Aleph 2 (& others) as a project

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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.)



  • alephfr.gif
    6.6 KB · Views: 5,709
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...

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.

More notes:
--There are five Zener diodes in the front end. Please observe that the anode (the end without the stripe) is marked "A." Yes, I suppose I could have done a "C" (or "K") for cathode on the other end, but I trust that you folks can live with it.
--Heatsinks for the front end differential are mounted thus:
Q1's heatsink mounts "normally," i.e. the fins project towards the input hookups, cupping the device itself.
Q2's heatsink is mounted "backwards," i.e. the fins point back away from the device towards the rail hookups.
--There are three electrolytics on the front end board. Note the plus signs.
--I'll work up a tidy parts list after I've had some sleep.
--Folks, look this stuff over. If anything isn't clear, ask. As I told Geoff, I'm so used to the layout that I tend to take things for granted. I tried to look at the boards with fresh eyes, but there's no guarantee that I've made it properly clear.
Oh, Geoff, thanks again for the conversions from pseudo-BRD to GIF.
Goodnight, folks...

Check the art carefully to make sure that it will work for a 30--I haven't checked how suitable it is for other Aleph models. Note that I made no provision for R1 & R8. I matched my front end devices instead. If you want, there's no reason you couldn't tag them in underneath the board.
If you mean specifications like distortion and such, no. One, I'm not set up for it. Two, they don't correlate to sound quality. Three, at the time I was just glad to see that everything worked properly (circuit boards okay, no wiring errors, water-cooling sufficient, etc.). It did meet power into 8 ohms, though.

Grey: Thanks for sharing your work! I have a more general question for you (or anyone else). What effect does increasing the input impedance have in terms of matching to other equipment and/or output level of the amp? I think I remember reading something to the effect of increasing the input impedance makes the amp more sensitive to lower level input signals (higher output with lower input)... Is this correct?

Thanks for the help!
There are good reasons, both pro and con, for various levels of input impedance. I chose to use the higher Zin because I'm running a quad-amped system and it would allow me the option of using a simple cap into the Aleph as a first order crossover. Not that you can't use a cap at a lower Zin, but then the cap has to be bigger, and it's easier (and lots cheaper) to find small values of polystyrene/polypropylene/Teflon/etc. than it is to find larger ones.
Now, as far as gain (sensitivity) goes, the resistor that sets the Zin for a device forms a voltage divider with the plate/collector/drain or cathode/emitter/source (for a follower) of the previous stage. The higher the Zin of the second stage, the more voltage develops across that part of the divider. In tube circuits, it's not uncommon to see grid resistors of 1-2M, although 100-500k is more usual. Solid state impedances tend to be an order of magnitude lower. It takes a fair jump in Zin to make a difference, though, once you get above a certain point.
For what it's worth, I seem to recall measuring the gain of the 2.60 at one point and finding that it was spot-on for a 2, in spite of having the 60 input network.

Good luck.
You might have just saved me the trouble of doing another layout for the small amp...and anyone who saves me time (which I'm perpetually short of) is my best buddy for the day.
Note that a couple of the traces shifted over by miniscule amounts during the conversion process. (Not Geoff's fault--there are just too many links in the chain of programs between my doing the art and the final GIF.) Watch the clearance where some of the traces sneak between two pads. At the comparatively low voltages that we're talking about it shouldn't be a problem, but if your PCB process will allow you the luxury, you might want to touch up those clearances, just for cosmetic purposes if nothing else.
If we can discover a program that will do a good job of exporting an image, we won't have to fight this battle in the future; but Paul's got a separate thread going for that.

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.