| GRollins |
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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| grataku |
Grey and Geoff,
thank you very much for the work you are doing here!
The layout looks great, too. |
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| mlloyd1 |
Grey:
Thanks for sharing. Very nice layout. I think I'll try it myself.
Michael |
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| GRollins |
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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| GRollins |
| The output board artwork: |
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| Ioannis |
This is a good example of civilized communication on 21st century.
Bravo.
We all appreciate this. |
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| GRollins |
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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| cp642 |
| A BIG thank you for the great work......!!! |
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| GRollins |
| The stuffing diagram for the front end board: |
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| GRollins |
| The stuffing diagram for the output board(s): |
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| GRollins |
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...
Grey |
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| Freddie |
Thanks for the PCB layout... I will start to build an Aleph 30 this weekend.
/Freddie |
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| hifi |
have you done any meassurments on those boards?....or i mean on the amp when it is finished...just want to compare numbers with the original aleph ;-)
/micke |
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| GRollins |
Freddie,
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.
Micke,
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 |
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| Eric |
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!
Eric |
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| Nelson Pass |
I don't think that's correct, but if you are willing to
forego balanced operation, you can have an
arbitrarily high input impedance on the positive
input. 1 Meg would not be out of the question :) |
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| Freddie |
Grey,
I've checked the art. The front end of the Aleph 30 is the same as the 60... So the layout will work good.. A few resistors with different values that's all.
I'm going to start building the front end on friday
/Freddie |
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| GRollins |
Eric,
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.
Grey |
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| GRollins |
Freddie,
Cool.
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.
Grey |
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| Eric |
| Nelson and Grey: Thank you for your quick replies! Nelson, thank you again for your willingness to share your work with us! |
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| Freddie |
| Here comes the Aleph 30 output board. |
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| Freddie |
| Here comes the stuffing diagram |
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| Freddie |
Here comes the stuffing diagram.
Remember to scale the layout to correct size!
/Freddie |
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| Freddie |
Here comes layout for the Aleph 30 output stage. Use this one if you have mosfets with TOP3 (TO247) package for example IRFP240. The layout posted above is for TO-220.
/Freddie
(I just did some changes to the layout, the holes were too big) |
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| wuffwaff |
Grey,
I just finished making the layout for my Aleph 5 using yours as a starting point (thank you very much). I opted for double sided prints with a ground plane (saves etching fluid.........), using one eurocard (100x160mm) for two front end boards and one eurocard for four output boards. The advantage with euroboards is that you can get them with a thicker copper layer (70 mu).
Thereīs one thing I didnīt understand in your layout, the "from output devices (CS sence)" is used twice. Why didnīt you connect the emitter from Q5 with "from output devices" on the print itself?
And another question: Whatīs the advantage of R0? Itīs used with the 60 but not with the Aleph 5 or 4.
william |
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| GRollins |
William,
Since you're using a double-sided board, you can run the emitter of Q5 on the other side of the board. I set myself the task of making a single-sided Aleph board. I have nothing against double-sided PC boards, and in fact usually keep some around, but I found that I didn't really need it for this project.
If you think you see a way to sneak a trace from the emitter of Q5 around to the top of the resistor array, by all means do so. However, if you're using a double-sided board, a larger board, or run a connection to the interior of the board (instead of connecting at the edge), you've changed the rules of the game.
To me, doing a PCB layout is like assembling a jigsaw puzzle. I don't have any fancy software; I do the layouts by hand, trying several different versions, then keeping the best portions of each. It's a nice mental challenge. My goals are:
--No interior connections.
--Keep connections to as few edges of the board as possible. This isn't really strictly necessary, but it makes service easier if you can unbolt the board and get underneath while it's still connected. In this case, I managed to keep connections down to three sides, one side exclusively inputs, with no high current wires nearby.
--Keep signal traces as short as possible.
--Keep the overall board as compact as possible, while allowing for heat dissipation. I cut my boards to size on a band saw. If you want to use a larger board, then other options might present themselves.
--Use as few layers as possible.
--No jumpers allowed.
--To the extent possible, keep components lined up. This is purely esthetic--it makes my eyes happy to see nice orderly rows like that. I was particularly smug when I managed to get that long row together across the middle of the board. Not that it matters to anyone but me. Bear in mind that at the time that I did the layout, I hadn't really considered that anyone else would ever see the layout but me. As far as I knew, there were only two homebrew Alephs in the world, mine and Mark Finnis's. It never entered my mind that there would be so many other folks who would take on the building of an Aleph, or that I would be posting my layout online. I just did as neat a layout as I could imagine and went on from there.
Note that large regulated power supplies generally run an output and a separate voltage sense. The sense connection is connected to the load with a light gauge wire, as there's no current draw to speak of and hence no voltage drop across the wire. In this manner the sense/feedback circuit within the power supply is able to get an accurate reading of what's going on at the load without having to worry about heavy losses across the output cable.
That's similar to what I did with the Aleph layout. A fairly heavy wire (I forget what I used, 12 ga. maybe? doesn't really matter, it's only about 2" long) for the actual output, and a much smaller wire (about 20 or 22 ga.) for the sense.
The purpose of R0 (along with R1 & R8, which I opted not to use) has been covered before. R0 is there to keep ground loops from forming. You can omit it and jumper straight to ground if you like.
Grey |
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| Jmertz |
First off, I would like to thank everyone who has contributed to this forum. I recently joined and have enjoyed reading everyone's posts. I was wondering if anyone could lead me to the schematic for the board layout that is posted on this thread. I have all the schematics from the passdiy website (aleph 2, 3, 4, 5) but can't seem to get all the reference designators to match with the layout that is posted. I see mentions of the volksamp schematics, are those available?? I and a co-worker of mine are in the process of planning the construction of two aleph4 amplifiers and may be interested in using this layout. Also, I missed the explaination of why R0 (R1, R8?) helps with ground loops. Can anyone help me with this? I do not see how an additional resistor from R4 and R5 to ground can help. aren't they already tied to ground? Thanks for your help.
Jake |
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| GRollins |
Jake,
The Aleph amplifiers began life as a product in the Pass Labs lineup, lived a long (by audio standards) and fruitful life, then passed into the great listening room in the sky.
But...
The stereo gods had mercy and, due to the great diligence and valor shown during their first life, granted the Alephs a second life under the moniker Volksamp (www.volksamp.com). Two circuits were chosen for this special priviledge, the Aleph 2 and the Aleph 3.
However, both were returned to life with some differences. Lower bias current in the output stages--this so that the smaller heatsinks would not be overburdened--and a bit of a re-fiddled front end.
After rolling the bones and swirling tea leaves, I decided to use portions of the newer front end design, but mostly the older circuit of the Aleph 2. After adding the resistors for the front end, the resistor numbering became problematic, so I simply defaulted to the Volksamp numbering scheme for the rest of the parts. This should all become somewhat clearer when you look at the Aleph 60 schematic.
There's a thread somewhere back in the Pass Labs forum where Nelson addressed the R0, R1, and R8 issue. None of them are necessary. R0, as stated above, is for ground loop prevention. R1 & R8 are for DC balance and CMRR, and are selected to match the transistors that are actually in the circuit.
Grey |
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| blschuler |
Hi folks, I'm the new guy. An Aleph 4 is my first and only electronics project. I'd like to participate in this forum by shareing my subjective conclusions as they relate to the value of R13.
When I first completed my Aleph the sound albiet good was not quite the warm and romantic sound I was expecting. I trusted my subjective conclusions enough to decide an some aspect(s) of my version was not up to factory par.
I read the A75 articles on the Passlabs site and drew the conclusion the 1 watt zener I was using for Z9 should have been a 1/2 watt type and perhaps 4 ma of current through it wasn't enough to keep it quiet. I didn't have any 1/2 watt zeners around so I played with the value of R1. With R1 changed from 10K to 6.8K the sound was now darker and less hard, a decided improvement.
I bought some 1/2 zeners and replaced the 1 watt types at the same time returning R13 to it's orginal 10K value. The sound is better yet, now possessing a wounderful black ambience. For the purposes of experimentation I retried the 6.8K resistors and found I prefered this over the original configuration, yet another small step in the warm/romantic direction. I suggest you try it for your self.
I should also mention I am using tantalum caps on the neg input and maybe they contribute some hardness to the sound. I haven't tried anything else and will gladly entertain suggestions!
I don't want to come across arogent by deviating from Nelson's fantastic design. I don't claim this slight change to be a general improvement, I simply found a way to satisfy my own subjective taste within my given stereo set up . In other words be nice to the new guy! :)
Brett |
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| Nelson Pass |
Just a postscript on the fate of the Aleph design. We
have re-acquired the Aleph for the purpose of integrating
it into the XA products at Pass Labs, and I intend to put
newer Alephs onto the market in something resembling
the original and current circuit.
The Volksamp Alephs are terrific products; in my opinion
better performing than the originals, but they have only
enjoyed lackluster sales, and that is, of course, not
acceptable. |
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| Jmertz |
Thanks Grey,
That clears up that part. I reviewed the volksamp schematic and some things do not make sense to me:
1) I do not see any dominant pole compensation capacitor. Is this circuit stable without it?
(the other Aleph amps have 680pF or .001)
2) I see that C18 is supposed to get rid of supply ripple, but why isn't it just returned to ground instead of Q5 emitter?? Doesn't the noise go straight through C18 onto the outut rail? I do not see the logic behind this.
3) Also, I have seen C21 from collector to base(Q5) and sometimes from collector to emitter(Q5), what's up with that??
4) one other observation, no thermister in the transformer primary, is inrush current not important anymore??
later
Jake
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| scrazy |
Shall we build the Aleph first stage using this frontend PCB then make sure the first stage works fine and maybe using for matching first stage MOSFET?
How should I measure the input stage's DC offset ?
thanks a lot! |
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| panos29 |
PCBs for aleph30 and aleph L
Dear fellow Aleph DIYers, after a popular demand about my aleph PCBs published on Passdiy.com, I decided to publish my designs in jpg format for easy printing .
However I will only do so if if Mr. Nelson Pass grant me the permission to do so.
Note though that these are just scans of my prints as my pcb editor do not output any kind of popular format (the editor i use is board maker by Tsien Labs). However although scans are not perfect, the prints are o.k for fabrication of the pcb. I also include the stuffing diagram in two versions (mask1 & mask2). The parts numbering system is the one used in aleph30.
Moreover, I also made a pcb for the aleph L but i will only publish it after the kind permission of Mr Nelson Pass.
Once more I would like to thank Him personally for being our source of information and knowledge.
Panos |
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| GRollins |
Jake,
1) Stability is a relative term. The Mini-A sitting next to me was behaving poorly. I moved the wire for the negative rail. It became meek and mild-mannered. I haven't had any problems with the Aleph 2.60 circuits.
2) Q5 rides up and down with the output waveform. If you tie C18 to ground, you'll be getting the output waveform across it. Besides, if you think about it, the output rail is a (fairly) low Z path to ground, anyway.
3) Gremlins.
4) Thermistors aren't necessarily called for in the Great Scheme Of Things. If you want a thermistor, put one in. There have been zillions of amps built without them, and will be zillions more before all is said and done. There's a tremendous amount of latitude involved in building circuits. Far more than many people realize. Many part values are chosen because the part happened to be next to one's elbow at the moment when the need arose and it worked. Those who live by numbers, slavishly calculating each and every part to nine decimal places, fail to see the forest--they're too busy counting trees. True, there are numbers that must be adhered to: Don't exceed the ratings of a part, for instance. But people who get flustered over the difference betweent 100,000uF and 120,000uF in the power supply because the formulas tell them that 100,000uF is 'enough' are missing the point.
If you build it, the music will come.
scrazy,
I matched parts out of circuit. If you want to do so in situ, by all means do, but it will save time if you at least rough them in so that you have similar devices grouped together. You could, I suppose, wire up the front end differential by itself and test it. Make sure that Q2's gate is grounded so that it doesn't flop around like a dead fish and cause problems. However, the front end is such a simple thing that there's not much that can go wrong unless you put in one of the MOSFETs backwards.
You wouldn't do that, would you?
DC offset is measured at the output. I'd use a load resistor.
Grey |
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| scrazy |
thanks Grey
Is there "High Resolution" PCB layout image avaliable?
Because "Low Resolution" image's qualtiy is not very good when using them for printing...
As I remember you using IVEX for PCB design, maybe I could using your IVEX pcb files convert to higher resolution image suitable for printing?
thanks again...;) |
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| GRollins |
The file format that Ivex uses won't upload, as it's BRD, whereas the upload function here only allows GIF, JPG, etc. I'll ponder on this a bit and see what I can come up with. Don't expect instant results, as Geoff and I hammered on this for a week just to get this far.
The long term solution, I fear, will be to recreate the board layout by hand in CIRCAD--which does export BMP files--but that's going to be a real nuisance. Needs to be done, however, as I want that Ivex software off of my computer ASAP.
Grey |
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| promitheus |
It would be very helpfull if you could get the pcbīs in better print quality. I canīt really use the jpg pic of the pcb. It doenīt really look good in real size.
Please post new pics when possible.
Greetings Promitheus |
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| GRollins |
Guys, I'll do what I can, but I've got a virus rampaging through my PC at the moment--kinda like Godzilla tearing into Tokyo--I'll be lucky if I get out of this in one piece.
My stories are my highest priority, gotta rescue them first. I'll try to save the board files and stuff, of course, but those will have to wait their turn...
Grey |
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| Geoff |
Grey
Don't worry about the .brd files, I've still got a copy of them.
Geoff |
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| Nelson Pass |
Panos,
Permission is, of course, granted.
np |
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| fcel |
Re: Building a stereo version of Aleph 2
First question & a lot of other questions to follow ....... for my beginning research into building this power amp.
1. Approximately how much does it cost to built it?
This is what I've read/know so far:
I've read that to get 12 sets of matched transistors, it's suggested (I believe) to buy 100 or 150 transistors .... it needs a lot of heat sinks .... requires decent size transformers and I suppose big capacitors, etc .....
Assuming that I'm going to order all the electrical parts thru the typical parts vendor like Digikey, Mouser, Avel-Lindberg, Par-Metal and none thru the "garage sale", how much approximately would be the cost? I know, I know, the heatsinks will be the major cost. How about a separate cost estimate for the heat sinks via the "proper channel - which means nice heat sink" and one via the 'surplus vendor shops - which means not so good looking heatsinks"? |
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| GRollins |
fcel,
It's been well over a year since I ordered parts and I never really did detailed accounting, but I believe that I spent around $5-600 (not including heat sinks) for enough parts to build two pairs of Aleph 2s. A large part of that was for 100 output devices. Others seem to have had far better luck than I did in getting matched sets out of smaller quantities of MOSFETs. Luck just isn't my strong suit. You could probably get away with ordering something like 30-50 devices and come up with sufficient matches.
Assuming that you're building a pair of 2s or a 60, you're looking for 4 sets of 6 output devices.
Grey |
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