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Old 19th May 2007, 07:26 AM   #1
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Cool Designing Passive preamp

Due to the release of a transformer based passive preamp, some people in my local community are interested in passive preamp. A few of them seems to interested in my set up too:

Aleph L + Aleph 3 + Thiels 1.5

Since Aleph L is no longer in production, they cannot buy it now.
They urge me to tell them the design and specification of the combo.
So that they can diy it.

Specifically, I would like to seek help in the following:

1. Since impedance varies with volume in passive pre (right? I am not an expert.), what's the impact on sound? How can we alleviate its effect? Does the resistance value of attenuator important?

2. How can we match the input impedance and output impedance of a preamp [Aleph L: input imp=20Kohm, output imp.=250ohm]?

3. How can we choose the input impedance of the power amp?
Specifically, what value of input cap. is good for a power amp using with a passive preamp? [it seems that Aleph 3 is Direct coupple. Does it mean no input cap.?]

4. I have been puzzled for a decade why Papa designed a passive preamp for Aleph 3 whose gain is only 20dB? [Is cost only the concern here?] Will it compromise the dynamics?

Thanks Papa, I love this combo very much. Passive pre, Single end, Class A & non-NF design help me enjoy the beauty of pure music.
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Old 19th May 2007, 08:36 PM   #2
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I'm not clear on what you're asking. Are you under the impression that the Aleph L is a passive preamp? It's not.

Grey
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Old 20th May 2007, 01:08 AM   #3
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Send a message via MSN to tze-hao yen
he drink too much
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Old 21st May 2007, 12:51 PM   #4
h_a is offline h_a  Europe
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As you know the Aleph L 1.2 was up to a certain attenuator position a completely passive preamp.

Cheers, Hannes
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Old 21st May 2007, 03:05 PM   #5
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Assuming that B&W_arthur is asking something about the Aleph preamp, as opposed to a "normal" passive preamp, I'm assuming that he anticipates needing gain at least some of the time. Since there's no way to get gain out of a passive preamp (unless you want to get into transformers--something that is alien to the Aleph series), we're led to the idea that B&W_arthur wants an active preamp.
Yes, the L does tend to invite a semantic argument, but until it's clearer what he wants, I'm left guessing that he's needing gain, hence an active preamp, which is what the MOSFET is in the Aleph to provide.

Grey
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Old 21st May 2007, 03:41 PM   #6
Vix is offline Vix  Yugoslavia
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OT question.....

Did anyone compare the sound of Aleph L (first variation- either 12 or 18 DB gain) with Bride of Zen? How would you describe the difference?

B&W_arthur, if you need a "passive" pre, just build a buffer, either a mosfet one, like in ZEN V4, or, better yet, use a Jfet, like in a "Buffer for Blues"...

Vix
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Old 21st May 2007, 04:55 PM   #7
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Quote:
Originally posted by Vix

Did anyone compare the sound of Aleph L (first variation- either 12 or 18 DB gain) with Bride of Zen
They are quite similar.

Referencing the later Aleph L, at the unity gain position of the
volume control, the preamp was a straight through, and I would
consider it passive below that point. Above unity, the output
looked at a divider between input and the output of an active
section. I thought it worked splendidly, but it did not seem to
catch the imagination of the audiophile community as much as
I would have expected.

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Old 21st May 2007, 05:00 PM   #8
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Pesky customers. They never react the way they're supposed to.

Grey
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Old 21st May 2007, 05:06 PM   #9
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Quote:
Originally posted by GRollins
Pesky customers. They never react the way they're supposed to.
I've learned not to rely too much on my market simulation software.

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Old 21st May 2007, 05:13 PM   #10
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mr pass you forgot that some one is a heavely drinker stereophile
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