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Aleph P 1.7 Volumecontrol Output-imendance question
Aleph P 1.7 Volumecontrol Output-imendance question
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Old 26th February 2014, 05:32 AM   #21
generg is offline generg  Germany
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Aleph P 1.7 Volumecontrol Output-imendance question
Sorry the data are for the Aleph P, the predecessor of Aleph P1.7 ..... :-(
I forget this sometimes.
The topology is different. The volume controller data might be the same.
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Old 9th July 2018, 03:05 PM   #22
sarathssca is offline sarathssca  India
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Quote:
Originally Posted by AudioSan View Post
don't put the attenuator before the aleph. that will result in a noisy preamp. there is a reason that it is behind
In pass B1 buffer preamp and in majority of cases we have the attenuator before the preamp and then followed by the main power amp.
(ie. source ---> attenuator ---> preamp --->power amp)

What is the reason for having volume control / attenuator after the preamp here?
(ie. source ---> preamp ---> attenuator ---> power amp)
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Old 9th July 2018, 06:21 PM   #23
Nelson Pass is offline Nelson Pass  United States
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Aleph P 1.7 Volumecontrol Output-imendance question
Here is the schematic of the output shunt resistor network.
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File Type: gif ALEPH P 17 SERV 007.gif (54.3 KB, 158 views)
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Old 9th July 2018, 06:40 PM   #24
sarathssca is offline sarathssca  India
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Quote:
Originally Posted by Nelson Pass View Post
Here is the schematic of the output shunt resistor network.
Hi mr. Pass

Thanks for the schematic of the attenuator ..
Could you please give some info regarding its placement , ie. Between the source and preamp or between preamp and power amp .. or it doesn't matter in either case ?
On b1 the volume potentiometer is between source and preamp buffer and in aleph preamp it's between the preamp and power amp ..
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Old 9th July 2018, 06:56 PM   #25
Zen Mod is online now Zen Mod  Serbia
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Aleph P 1.7 Volumecontrol Output-imendance question
P1.7 - attenuator is in after electronic gain stage , meaning on output of preamp itself

besides taking my words as true ........ you can see XLRs on right end of picture

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Old 10th July 2018, 01:45 AM   #26
sarathssca is offline sarathssca  India
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Just wanted to understand what is the reason for putting the attenuator at the end of the preamp instead of at the beginning of the preamp as we more often see, for example in pass b1 preamp .. could you please give some info regarding this ..
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Old 10th July 2018, 05:21 AM   #27
AudioSan is offline AudioSan  Norway
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Quote:
Originally Posted by sarathssca View Post
Just wanted to understand what is the reason for putting the attenuator at the end of the preamp instead of at the beginning of the preamp as we more often see, for example in pass b1 preamp .. could you please give some info regarding this ..
The answer is in the line you quoted from me. Aleph P1.7 have some noise.
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Old 11th July 2018, 07:42 PM   #28
koja is offline koja  Canada
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I think Papa just wanted to take advantage of Aleph P being able to drive any load so he stuck a 1kOhm attenuator behind it, so any noise contributed by the preamp itself also gets attenuated (a purist approach I guess). since that brings the output impedance up shorter leads (up to 3 feet) to the following amp stage are recommended.

Aleph P itself does not like a hot input and there are attenuating resistors with dip switch settings at the input to drop the level if necessary.
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Old 12th July 2018, 05:04 AM   #29
PRR is online now PRR  United States
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Quote:
Originally Posted by sarathssca View Post
...what is the reason for putting the attenuator at the end of the preamp instead of at the beginning of the preamp as we more often see....
From the now-secret Service Manual:

The volume control system ... ... to achieve good common mode rejection performance, the output attenuation must be matched far more precisely than can be accomplished with potentiometers, and so relays and precision resistors are used.

Yes, this is "different". Mr Pass is known for re-thinking conventional methods. We normally pot first then line-amp, so we won't overload the line-amp.

Pass was working with BIG devices at high voltage. Overload won't happen.

These devices "may" have more hiss than conventional designs (I am not an expert on this). Pot first puts turned-down signals close to hiss. Bringing signal in un-reduced gives best signal/hiss ratio.

We don't normally pot after the line amp (though I know a few which pot before and after, much $$$). With conventional line amps this is a waste of line-amp output, and also messes with the impedance at a point which may be driving long cables. But again Pass was working with BIG devices idling at high power, and these conventional trade-offs were re-thought.

It looks fine to me. Not the thriftiest music-box around, but sometimes that is not the point, the music is.
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Old 12th July 2018, 05:58 PM   #30
Nelson Pass is offline Nelson Pass  United States
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Aleph P 1.7 Volumecontrol Output-imendance question
Worth noting, there were additional gain controls via pots between the
Sources of the Mosfets, degenerating the gain, and were used as balance
controls. In spite of better numbers with maximum degeneration, most
users preferred a high gain setting, even if it meant running the output
volume control low.
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