Pcb For Aleph 5

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#21
fcel said:
Kristijan have shown -ve of C9 (220uf) connected to +ve output as per spec from the Pass Labs service manual. You have shown yours connected to the emitter of transistor MPSA18 as documented in the other thread.
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WARNING - Be very careful with Neslon's schematics!

The original circuit does not show C9- connected to the output, it connects to Q5e / C7 / Q18-20d / Rs of the current source / the infamous LED / R22-25.

Nelson's typography is "joins are shown as broken lines", however he disobeys this himself where C10-R19 crosses Q5b-R20, which is a join and should have been broken.

The circuit as shown, I believe, is correct.

Then BrianGT says:
How would one keep the Aleph 2 cool, with all of the mosfets so closely spaced together? That would mean that one heatsink would dissipate 300W. That seems pretty difficult, unless you are using active cooling.
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I too would be happier with greater spacing between the FETs, the center fellas are gonna have a hot time!

cheers, mark

PS: And I'm still not on a commission
 
#22
Mark,
You indicated the the original circuit does not show C9- connected to the output ............. but the latest circuit diagram from Pass Labs does shows C9- connected to the output as well as Kristijan circuit diagram in this thread. Is Nelson Pass aware that it's shown that way. As discussed in the other thread, Brian, Grey , Wayne and probably others do know what's the correct connection. I don't know how they know! Should it be corrected so that some other poor guy like me don't have to go through this exercise again? It has been discussed that it does not make any difference but I'm curious as to why it does not make any difference.
 
#24
..... but the latest circuit diagram from Pass Labs does shows C9- connected to the output as well as Kristijan circuit diagram in this thread.
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Given the circuit diagrams have changed over time, I went back and re-downloaded the PDF for the Aleph5.

This is PL33FE01 of 09/23/96.

I'm confused. I cannot see where you get a connection from C9- to the +Output. Again, it connects to the junction of the current source resistors/drain of the output FETs, immediately before the output resistor quadruplet - and to the emitter of Q5, as always. This is also how I read Kristijan's circuit diagram, BTW.

Can you e-mail me a copy of the diagram to which you are referring, or post it here.

cheers, mark
 
#25
Mark: I was talking about the Aleph 2 circuit diagram. If you look at the PDF file of Aleph 2 on Pass Labs web site, you'll see that C9- is connected to the + output. Same on Kristijan web site. I brought it up because even though it's shown that way, everybody seems to built it with C9- connected to the emitter of MPSA18 - just like in Aleph 4 or 5. And I was just questioning why and how they know. Brian said he asked Nelson already and the reply is connect C9- like in Aleph 4 or 5.
 
#26
Curiosity got the better of me .... I just went back and downloaded all of the service manuals.

Now ..... I'll grant you the Aleph2 diagram (PL30R0 - 12/1/96) does show C9- connected to the output!

Further to Brian's comment from NP, which side of a 0.08ohm resistor (0.047/6) you take this feedback is likely immaterial.

Sorry to be a "stick in the mud", but I get obsessional about some things 🙂

cheers, mark
 
#27
Amazing how when 2 people are looking at different things they see a different perspective .....

As Nelson says, from the circuit operation it would make no difference. All other circuits (A5,4,1.2) are the same so I would go with this, personally.

If you have made your PCBs as per the A2 then don't worry and just go ahead.

Nelson has had the odd problem with "borrowing" circuit diagrams, ie. instead of re-drawing the whole thing he starts with a "sister" circuit and amends the fine details ..... this was the genesis of the now infamous "x3" versus "x6" mishap in the A4 circuit. I ain't gonna pick on him too much for this 😉

cheers, mark
 
#31
Hello to everyone,


I received several e-Mails on C9 issue and it seems that some peoples are little confused.

The C9 issue is not that important like most people think and you shouldnt be bordered with that. The C9 can be connected on both ways stated in previous threads without any problem.
The only difference is in .47R/6 => 0.078 Ohms and in this case it will not make any difference.

Also, last year when I made my first PCBs prototypes, I was also wondering myself why Mr.Pass connected C9 in that way, then
I made several tests and measurements(q.current,power,distortion,freq.response) on both ways of connection, and results were identical.

There is no way for sonic difference, and after all the original Pass Labs Aleph 2 amplifiers used identical circuit diagram like it is originally posted by me,and that is the main reason why I lefted the circuit unchanged, like Mr.Pass originaly designed it.

For sonic difference you should be more worried about speaker quallity and sonic characteristics of your room and no for well proven and excellent sounding design, at least at my opinion.


Kristijan Kljucaric
 
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