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Old 17th September 2003, 02:38 PM   #1
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Location: Copenhagen
Default Pre-Amp Pass Aleph L


I have an Aleph L pre-amp (latest model) and it is quite nice.
BUT it is playing to loud, even at the first click on the attenuator.

What is the best way to fix this problem ?

Thank you
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Old 17th September 2003, 08:14 PM   #2
Hans B is offline Hans B  Denmark
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Join Date: Feb 2003
Location: Aalborg, Denmark
Hi Mikael

Pass aleph L should have a dipswitch located somewhere inside on the PCB - this dipswitch can switch the gain between 0 and 17dB - please see the service manual at passlabs - It explains it quite well (better than I).

The manual can be found here:

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Old 17th September 2003, 08:19 PM   #3
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Probably L-Pad at the output that will attenuate a couple db.The latest is the one that to some point works as passive,yes?
I built the two versions of L preamp some time ago and I remember I liked the first (always active) more although the diffrance wasn't that big.Also the first version had the possibility of changing the gain (0,6,12 and 18db) by simple changing the diffrent resistor at the input.Also I've noticed thet Aleph L set for 6db gain had more gain that BLS set to 12db gain.I hope this helps a bit
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Old 17th September 2003, 08:25 PM   #4
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Hi Hans,

Thank you, but I'm afraid the I've got the rev. 1.2 model with 17 db gain and it is not ajustable with a dipswitch.

Best regards
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Old 18th September 2003, 09:16 PM   #5
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Join Date: Feb 2001
Location: Columbia, SC
The easiest way to do it would be to put a voltage divider at the input. The exact values aren't critical. If you were to wire two 47.5k resistors in series, put one end to ground, the other end to the input jack, and take your signal from the mid-point, it would cut your input by 6 dB. Probably not enough reduction to do the job, but you get the idea.
Note that this will effect your Zin a bit (lower it), but it's a lot easier than replacing all the resistors in the volume control, plus it's something you can take out later if you want to.

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Old 18th September 2003, 10:10 PM   #6
Apogee is offline Apogee  United States
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Location: Tacoma, WA
Newby question here...

Why the divider rather than just a high quality resistor in line with the input?

By referencing to ground isn't there a possibility of injecting noise at the input of the amp? (I know the ground is supposed to be quiet but I also know lots of other appliances creating noise of all legs of the power supply....)


"If I had my life to live over again, I would have made a rule to read some poetry and listen to some music at least once a week." - Charles Darwin
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