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-   -   Aleph 30 Questions (http://www.diyaudio.com/forums/pass-labs/25273-aleph-30-questions.html)

PatekMan 3rd January 2004 07:32 PM

Aleph 30 Questions
 
Let me start off by saying I am building my first diy audio project, and part hunting has gone well and I am now just searching for a few quick answers before delving too deep into the project.

- On the schematic in the service manual (Aleph 30) what does the R1 * mean? Is this a pot?

- I will be doing separate power supplies (I have two small transformers [300VA]). Should I leave the two channels completely separate and only ground one to the chassis or ground both of them. I believe I read this forms a ground loop, but I need some expert advice. Also, in doing this would I tie the AC-earth to this same point on the chassis as one of the channels? Does this form a loop through two AC lines?

- Is it OK to use 2 x 50,000 uF caps per channel instead of the 2 x 30,000 worth on the original schematic? Its merely a matter of what I have access to.

- One last question sort of unrelated to those above. Would a Antique Sound Lab AQ2004 pre-amp match well to this amplifier? If not, are there any cheap tube pre-amps (< $400) that are a good match?

I apologize if any of these questions are repeated, I searched but was not wholly sure about any of them. I really appreciate any and all help.

Thanks.

Mark A. Gulbrandsen 3rd January 2004 10:47 PM

The more capacitance the better, put in all you can afford! Just be careful of the resultant turn on surge, it may need to be limited somewhat. Both my Mini Aleph and my 2's have 120,000 mfd per rail and I reccomend that much if you're going straight capacitors. The best scheme is a CLC type supply with a CRC type being next in line. However both mine are straight capacitor banks and the backgrond noise is about nil. when the 30 is done consider building an Aleph P or a BOZ balanced preamp to take advantage of the balanced input on the Aleph 30. You'd actually spend less money in the long run. Either the Aleph P or the BOZ are pretty hard to beat in the sound department.
As for grounding you'll find that both channels need to be grounded to the chassis. Use one per channel of the current limiting devices thats used by Pass in the Alephs to do this. This ought to eliminate any AC ground loops.

Mark

moe29 4th January 2004 01:34 AM

R1 and R8 are not essential if you match the front end devices
carefully, i believe they help with DC offset - someone correct me
if i'm wrong.

--------------


The balanced preamp on the PassDIY site is the BZLS
Balanced Zen Line Stage... great construction article - great pre.
Would be a great match for your Aleph 30.

it's also known as the BOSOZ.

The BOZ was the first preamp article to mate with the Zen Amp.

------------

I'd reccoment a CLC for your power supply if you're only going to
use 2 caps. Use a 2mH Inductor. I always reccomended a part
from MCM Electronics (mentioned in the SOZ article) but i just
looked at the MCM site and they say it is discontinued :(

Mark A. Gulbrandsen 4th January 2004 02:04 AM

Well, CRC would still be a decent choice and if he is on a budget then that is probably his best alternative. Really, alot of straight filtering works well too.

Mark

Dennis Hui 4th January 2004 02:08 AM

I built my A30 without R1 and R8 and it works fine.
I did match the IRF9610 devices though.

I used 2x62000uF per rail and the amp to me
is very quiet. You may want to look at the
Zen Variation part 4 article (fig 6) for a suggestion
on the power supply hookup.

Good luck with you project.

Dennis

PatekMan 4th January 2004 06:26 AM

Thank you
 
Thank you all for your timely responses. I guess I've still got some figuring out to do regarding the power supply. Thanks.

PatekMan 5th January 2004 07:38 PM

A few more questions ...
 
In regards to the schematic, is the r3, c11, and r6 the balanced input network? If so, removal should not effect normal signal. Am I correct in this regard?

Is it best to go with ceramic, tantalum, or other types for caps such as C8, C10, C9?

Maybe I am mistaken but the gnd's that are attached to r13 and speaker out are shown to go to gnd. would these go directly to chassis gnd or would they be connected to the other side of R0 before being connected to chassis ground. I noticed that R0 is not present in other Aleph schematics and this had me curious.

And as a response to the power supply replies I believe I will be just using caps, no CRC or CLC since my caps are so big it will just be one per rail. Should I use a bypass cap across each? This is not in the schematic, but I have seen it in other power supplies.

Also in the schematic are caps between the AC-input. What are these and are they necessary?

I think that is all for now, thanks for all your [everybody's] help.

PatekMan 7th January 2004 05:30 PM

Questions answered
 
I got most of my questions answered, but I am curious about the balanced inputs. I will only be using unbalanced inputs (RCA) so I was wondering if I can remove the balance input parts with no problem.

Are r3,r6,c11 only there for balanced inputs. In other words if I remove them will this effect the RCA inputs at all? I don't believe it will, but I'm curious.

Any help is appreciated, thanks.

Brent


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