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Old 21st February 2005, 05:40 AM   #1
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Default Nelson Pass diy pre-amps-best??

All,

I am intrigued by the following Pass products seem to have and would be very interested in building an excellent (read best bang for buck) pre-amp. However, I notice that there are several designs out there (BOZ, etc).

Which offers the best audio performance, which is the most rewarding? If possible, I would like to have a balanced input pre-amp, although outputs must be single-ended. I do not need to switch between different sources, only 1 source-CD!

I use a non-inverted gainclone and Royd doublet speakers.

Thanks for any advice
Ryan
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Old 21st February 2005, 06:06 AM   #2
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I think the Aleph P 1.7 is the best. I built one and love it. I also built mine with one output and input. A PC board is available from Kristijan Kljucaric . I also have a spreadsheet with all of the parts I used, where I ordered them from, the manufacturer and their cost, if you are interested. I used the some of the better parts available (Holco Resistors, Blackgate Caps, DACT Attenuators, Plitron Toroidal, Cardas RCA's, Vampire XLR's etc) but the preamp can be built with generic parts with excellent results.
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Old 21st February 2005, 06:58 AM   #3
Variac is offline Variac  United States
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Solely from reading at this site, I would say the order is


1. P1.7
2. Bride of Son of Zen (also called Pass balanced preamp I think)
3. Bride of Zen
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Old 21st February 2005, 07:09 AM   #4
acaudio is offline acaudio  Germany
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I like my P1.7 too.

See here: Aleph P1.7 first pictures

Adam
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Old 21st February 2005, 04:51 PM   #5
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Hi,

you could also try the X-BOSOZ with or without current source.

BTW can anybody explain to me how the Aleph P1.7 current sources work? I looked at the service manual but somehow donīt understand the way the upper and lower current sources work togheter.

William
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Old 21st February 2005, 09:39 PM   #6
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I asked the same question a while back and Nelson gave a great answer for newbies trying to determine which model to build.

"BSOZ and Aleph P are largely the same preamp. I recommend
BSOZ due to its greater simplicity. You don't want to tackle the
attenuator of the P as a novice."

He also said that the BOSOZ sounds better then the Bride of Zen, even in unbalanced mode.

Here's the thread, it's worth a read:
Best Pre-amp to build for a new DIYer?

Here's another interesting thread on BOSOZ parts selection thoughts:
Best BOSOZ preamp parts selection thoughts

I built the BOSOZ with the parts as listed in Nelson's build guide, and the sound is astounding. Blew away my Rotel 980 premap. I would use a single transformer rather than 2 as originally specified. AvelLindburg has a 55+55 120VA model they sell for a really great price. This one works well.

Good luck,

-David
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Old 23rd February 2005, 06:35 AM   #7
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Hi William,
referring to a single side of the preamplifier, and consider only the bias operation: so no signal applied, and both halves of the circuits are at the same potential.
The upper CS (Q15) set the drain current to about 30mA (Q11 junction voltage, 0.66V across R44, 22.1 Ohm).
The lower CS forces the drain current to about 20mA, so we have about 10mA (the remainder) across the paralleled resistors R53 and R56.
Since both sides of the circuits are considered to be in the same bias point, Q16 and Q19 sources are at the same potential, so no current can flow through R51.
The equivalent value is about 3.2 KOhms, so the voltage across them is about 32V, and so the Q15 (and Q18) drain bias point.

Best regards
Marcello
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Old 23rd February 2005, 09:01 AM   #8
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Thanks Tortello,

figured out the 30mA and 20mA part but didnīt know why those 4k75 and 10k were there.


Thanks again,

William
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Old 23rd February 2005, 09:31 AM   #9
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That is how I liked them:

1. Alpeh P 1.7/ Aleph P 1.0 (prefer 1.0 becouse of it's sound signature).
2. Aleph L (all the time active version, didn't quite liked the second one).
3. BLS
4. Bride of Zen

I built all of them using 95% the same parts. I always used 5K ladder type attenuator at the output.
As I said in another thread the diffrance between BLS and Aleph P 1.0 is huge to me. I don't know why, the circuits seems similar, but to me Aleph P outperform BLS in every single aspect, especially soundstaging, detail and smoothness.No matter balanced or unbalanced. But it's just me and my point of view.
I think Aleph P 1.7 is more neutral than P 1.0, which I think has it's own signature, but I like it.

Bartek

By the way the coupling caps are very important as they can make or break the sound of these preamps. Don't expect spectacular results from Wima's ort cheap polypropylenes like SCR or similar.
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Old 23rd February 2005, 06:00 PM   #10
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The Bride of Zen is my least favorite of the group sonically,
although it is also the simplest.

It is a 2nd harmonic circuit, and the others are 3rd - Isn't that
interesting?

One of these days I'm going to write up something about the
sound of 2nd vs 3rd, as I've been able to perform some
experiments which go apple-to-apple as much as possible
with this, and I find that a very high percentage of people
prefer the 3rd harmonic character of a balanced circuit, even
though most of them also profess a preference for 2nd
harmonic.

If you want to try this for yourself, just bridge a pair of original
Zen amps.

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