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-   -   Aleph-X builder's thread. (http://www.diyaudio.com/forums/pass-labs/28336-aleph-x-builders-thread.html)

protos 16th February 2004 09:44 AM

Aleph-X builder's thread.
 
Following the highly succesful WIKI for Aleph-X boards and expecting that there will be hundreds of queries on construction, technical issues etc I propose the inauguration of this thread which should be useful to those interested.

Faber 16th February 2004 11:39 AM

As soon as I receive the boards, I will post the requests :-)

Bye!

hifiZen 16th February 2004 11:39 AM

Quote:

Originally posted by Mark A. Gulbrandsen
I am in the process of populating my first pcb and have a few questions about the board and component choice.


1. Is there any sonic difference between using the IRF9610 or the ZVP3310A devices? I have both so could go either way there.

2. What is the purose of the R48 and R49 position which is shown as a 0 ohm jumper in both locations? Why put space for a resistor if there is only a jumper there?

3. Is a half watt metal film for R-21 ok? Grey called for a 3 watt resistor in this location....

4. What is a good value to start at for C7,8,9,10 ? I don't want to oscillate when I run it up the first time....

5. I assume that it is ok to use the IRFP240 device in leiu of the 044?

Note that I am building this first unit to get used to and learn about this design. Its going to be built exactly as it is on the diagram.

Thanks in advance for any input you might shed on these questions.

Mark


Hi Mark, Let me answer some of your questions:

1. I haven't done that much testing yet. The ZVP3310A was suggested by another member as an improvement, and since it was easy to add a stuffing option for it, I did so (actually, grataku put it into the original layout). I built my prototype rev0.9 channel using it (with a small TO-92 clip-on heatsink) and it sounds fine. Using the Zetex part also left more 9610's to match pairs from.

2. R48 and R49 are indeed jumpers, though the option is there to add resistors if you like. R48 would basically function to soak up some excess voltage and reduce power dissipation in the current source FET (especially for higher rail voltages), and provide some measure of series parasitic capacitance reduction / isolation. You will have to balance this against the reduced DC voltage across the current source FET (think linearity), and decide for yourself how much resistance you want there. Starting with just a jumper is a perfectly fine choice though. R49 is there to allow some flexibility in wiring the input ground... you can jumper it or add some isolation resistance if you like. Again, your choice, and will depend on factors unique to your implementation.

3. Half watt should be fine, or you can just jumper it (I jumpered mine). R21 normally doesn't do anything... the only time it really matters is when the gate protection zeners D2-D5 are conducting. You've made me wonder, though, why Grey used 3W. Hmm.... can't remember... don't want to go digging through that mammoth thread... ;)

4. C7-C10 are at this point just vestigial footprints. I haven't heard of anyone needing to use them, so you can confidently omit them without harm, especially if you're sticking to the basic design without any drastic alterations. Of course, you should still check for oscillations anyway. I could have removed them from the board, but that would have driven up the order cost by incurring an NRE tooling charge.

5. 240 is fine. I believe numerous people have already built with those.

The most valuable piece of advice I have for you is match, match, match. The most important parts to match are: Q5<->Q7 (critical), Q2<->Q11, R6<->R41 (yes, you should try to match these... use a current source and a voltmeter to find their value), and R23<->R25. For other component hints, download the info package (there's a link to it from the order wiki), and read the notes in the BOM spreadsheet.



edit by pinkmouse: I have moved this over from the PCB thread as it is more relevant here, but be aware that the question this answers is not above, but below! ;)

Mark A. Gulbrandsen 16th February 2004 11:40 AM

Ok, I'll be first in line and move this post over here where it belongs.....

I am in the process of populating my first pcb and have a few questions about the board and component choice.


1. Is there any sonic difference between using the IRF9610 or the ZVP3310A devices? I have both so could go either way there.

2. What is the purose of the R48 and R49 position which is shown as a 0 ohm jumper in both locations? Why put space for a resistor if there is only a jumper there?

3. Is a half watt metal film for R-21 ok? Grey called for a 3 watt resistor in this location....

4. What is a good value to start at for C7,8,9,10 ? I don't want to oscillate when I run it up the first time....

5. I assume that it is ok to use the IRFP240 device in leiu of the 044?

Note that I am building this first unit to get used to and learn about this design. Its going to be built exactly as it is on the diagram.

Thanks in advance for any input you might shed on these questions.

Mark

Mark A. Gulbrandsen 17th February 2004 02:03 AM

Thanks for all the insight Chad!! Its much appreciated and you've answered allmy questions.

Mark

moe29 17th February 2004 02:50 AM

i know this is a stupid question, but...

do the back to back differential pair fets have to be electronically isolated?
if so, what's the process used for allowing them to share the same
heat sink.

grataku 17th February 2004 03:15 AM

no heatsink just a silpad and a nylon screw.

GRollins 17th February 2004 03:59 AM

The grounding resistor at the input was specified at 3W because I've seen some preposterous DC potentials in my time.
Half watt? Sure. Until the first time you have a "problem installation."

Grey

P.S.: As I recall, Nelson used a 3W also.

Taco 17th February 2004 06:15 AM

Hopefully there are more builders who report their results. From the previous group buy I haven't seen many finished projects.

protos 17th February 2004 10:12 AM

I am also wondering how many will be built in the end.But with over a thousand boards out there I estimate conservatively that if half those that ordered are serious then we have about 100 people that intend to build it in the near future.To be even more conservative I think about 40-50 Aleph-x's are going to be made at least.


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