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Old 21st January 2004, 05:04 PM   #1
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Default Commercial Aleph P question

hey, quick question.....

Attached is a picture from AudioGon.com of an Aleph P; http://cgi.audiogon.com/cgi-bin/cl.p...ran&1079430819

Am I looking at the attached picture correctly? This unit appears to have a source selector on the left, and seperate left and right manual volume controls in the center.

Questions:
*What is the panel control on the far right side?

*Also, why do the DIY projects use TO-220 IRF610 FETs and not the T0-3 IRF204/244 devices as pictured here in the commercial product?

Thanks,

-David
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Old 21st January 2004, 06:17 PM   #2
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Default Re: Commercial Aleph P question

Quote:
Originally posted by dw8083
hey, quick question.....

Attached is a picture from AudioGon.com of an Aleph P; http://cgi.audiogon.com/cgi-bin/cl.p...ran&1079430819

Am I looking at the attached picture correctly? This unit appears to have a source selector on the left, and seperate left and right manual volume controls in the center.

Questions:
*What is the panel control on the far right side?

*Also, why do the DIY projects use TO-220 IRF610 FETs and not the T0-3 IRF204/244 devices as pictured here in the commercial product?

Thanks,

-David
If you look on the Pass Labs site:
http://www.passlabs.com/aleph.htm
you will see 2 versions of the unit, under the service manual category. From looking at the picture, I am pretty sure that is r1.0 version seen in the first service manual. The circuitry for the first unit is quite a bit different from the second version.

I believe you are right about the source selection being on the left, given the appearance of the switch and the service manual. SW101 in the service manual, I assume.

I am assuming the middle two are pots used for controlling the left and right channel gain, and correspond to the pot in the middle of the gain stage (P101)

The volume is controlled with a 6-bit relay ladder, as the service manual shows, with an ADC (ADC0804) managing them. I am pretty sure the control on the right is the potentiometer which controls the adc, which in turn controls the relays to set the volume. (P1 is the component designation for the pot)

I would guess that the at the time of the design, the to-3 devices were on hand, as it appears that the p1.7 model switched to to-220, based on looking at the pcb overlay pictured in the second service manual. The P1.7 also switched over to a microcontroller, providing the means for more features.

--
Brian
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Old 21st January 2004, 07:00 PM   #3
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It's interesting the choice between the big devices like an
IRF244 vs something smaller and faster like an IRF610.

First, having a lower source impedance and more bias on the
TO-3 devices helps even things up, but still they have a sound
of their own. I could never make up my mind which I liked
better, but I think in the end most people preferred the
smaller devices due to the slight spectral shift toward a
brighter sound.
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Old 22nd January 2004, 10:16 AM   #4
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Hello Mr Pass,

in the photo of the Aleph P V1.O I see 7 relays on the output volume control. In the service manual there are only 6, why?
Another question, in the same photo I see too 3 trimpot but on the manual I haven't locate. There is another version of the 1.0 ?

Thank you and sorry for my bad, bad, bad english!!
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Old 22nd January 2004, 12:22 PM   #5
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Having built both versions I must say the diffrance in character of the sound is quite big.Both sound very good but I like my Aleph P 1.0 a lot!
It probably has it's own sound but I just love it.

Looking into service manuals I figured that Aleph P 1.7 is pretty much a balanced version of Aleph L with added CCS on negative side of the circuit.

Mr Pass,is there any way to try more bias in Aleph P 1.0?
Maybe it will sound better...I have all four gain devices mounted on a small heatsink and it barely gets warm.

Bartek
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Old 22nd January 2004, 12:35 PM   #6
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Quote:
Originally posted by Nelson Pass
It's interesting the choice between the big devices like an
IRF244 vs something smaller and faster like an IRF610.

First, having a lower source impedance and more bias on the
TO-3 devices helps even things up, but still they have a sound
of their own. I could never make up my mind which I liked
better, but I think in the end most people preferred the
smaller devices due to the slight spectral shift toward a
brighter sound.
Nelson,
Would it be the best of both worlds if you used something at the input to buffer the bigger devices? I am assuming that the darker sound is the result of more gate capacitance. I guess if it was better, you would have done it already, but I thought I'd ask anyway.
Steve
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