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Old 14th March 2015, 02:17 PM   #1
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Default 1'ST edition Aleph P

These question may very well be left for the factory but since this is Saturday and my Aleph P arrived last night I thought I would start here.

I purchased a Aleph P serial #003 and upon first listen there was noise almost like a ground loop or improperly grounded circuit. No hum. Also I was getting two sources playing at once. I pulled the top and found the two wires that would I believe to connect to the center pins of the RCA's right next in line from the output jacks off and hanging (damn FEDEX). One other wierd thing is that someone apparently wanted two sets of outputs so they wired jumpers from the output jacks to the same center pins of the input jacks that had the wires that came off. *** That is why I had two sources playing at once. **** I will fix this.

The only manual for the P on the pass website is for the revised version and some changes were made.

This preamp has way too much gain for me, too much to be able to be use. The later revision has changes made to the Master volume control to allow it to be set in a number of positions (5 normal and 5 positions that are -12db down.) Then the separate right and left controls do the fine tuning. My preamp has a more conventional ladder volume control. The separate volume controls for L & R are a 1K conductive plastic pot.

If I need more attenuation can I use a higher value pot in its place, or add a resistor in line?
Walt

Last edited by waltroman; 14th March 2015 at 02:19 PM.
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Old 14th March 2015, 09:56 PM   #2
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this one ?

increase R115 to decrease gain
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File Type: pdf Aleph P.pdf (67.1 KB, 102 views)
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Old 14th March 2015, 10:53 PM   #3
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Much thanks, will have a good look see tomorrow. If I want to drop 6db whay would a good value be? 1K to 2K?

Walt
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Old 14th March 2015, 11:04 PM   #4
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I'm lazy for calc now ......... but let try with some simple crude logic

gain span is from 8 to 14db , with max to min value of P101

considering its value is 1K ,gain change is 6db .......... try to increase R115 exactly for 1K .... to 1K5 (1K6 more common value , also good)
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Old 14th March 2015, 11:17 PM   #5
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Thanks again.
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Old 14th March 2015, 11:23 PM   #6
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ya owe us some porn
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Old 15th March 2015, 03:17 AM   #7
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Just finished up with a rough week, off tomorrow, maybe pics then. I have never done pics here, should be able to figure it out. Spent a few hours listening and the preamp is awesome.
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Old 18th March 2015, 10:58 AM   #8
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I have been on the phone with the techs at Pass. The more I look at my copy of the P it does not match what became the first production units. I asked about increasing the value of R115 or changing the pots to 1.5K or 2.0K units they indicated that higher resistance would allow higher noise. They offered a better way would be to jumper a 1k resistor across two 750 ohm 3 Watt resistors except I cannot find any 750 ohm 3 watt resistors. Do not know how to copy the pdf to here.

Every schematic I have seen is loaded with 1uf and 10uf caps and none here. I am not sure if this preamp is cap coupled unless it uses one of those large 1000uf caps. This may have been one of the original prototypes.
Any idea the location of resistor R115? Should it be one of the 3 watt resistors?

Here is a the ad where I bought the preamp. It has a pic of the inside. Clicky to expand the pics.
Pass Labs Aleph P Preamp Non remote version - Audio Asylum Trader

Last edited by waltroman; 18th March 2015 at 11:08 AM.
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Old 18th March 2015, 12:01 PM   #9
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there must be some miscommunication - I can't see how increasing amount of source degeneration can increase noise

however , it seems that is early specimen (Ser. No. 003) , mosfets (IRF240) as active elements and bipolars (MJE) in PSU reg role

it's probably time for Papa to chime in ....... but - if schematic is in any way similar to one we have , you can make this :
look at picture I attached , and two red arrows ; desolder one red wire from right pot , solder 1K resistor (small one of 250mW is good enough ) to pot lug , solder wire to free end of resistor .

do the same on other pot with white wire

regarding output caps ..... I'm not seeing any other than big honking electrolytics ...... but that's separate issue ( bypass them or not , recap entire thingie or not)
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Old 18th March 2015, 01:13 PM   #10
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I remember some amps (from other "factories" ) made with lesser hardware .....
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