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hags 26th September 2007 03:03 PM

Aleph P 1.7 questions
I have ordered diy boards for the Aleph P1.7. I'm not too familiar with it but have built the BOSOZ and it looks familiar.
I have been pouring through threads at diyaudio/passlabs for descriptions/manuals for this project. Some comments interest me and I thought I'd ask.
This is a high current source with high output impedance which can drive a short circuit.
I am aware of the recommended potentiometer for volume control at the output, would(n't) the circuit benefit from a set voltage divider at the output rather than a variable resistance? Is there some optimum value or does it matter? Certainly there would be less interaction with the next stage.
Secondly, I have seen it mentioned that there should be pots at the input to avoid overloading the mosfets. Is this a real concern? What is overload, 2 volts, 10 volts? Again, would the circuit benefit from a set voltage divider rather than a variable resistance?

Stefanoo 27th September 2007 06:12 AM

2 Attachment(s)
if you post here your email adress i can send you the service manual for the Aleph P 1.7, in case you don't have it.
Anyways, the orginal project, by Nelson Pass, states that there is a stepped shunt type attenuator placed at the output of the preamplifier.
You can eather use the value that Nelson used on the project or you can make one larger and therefore finer by calculating the appropriate values.

Here a link on the forum that talks about this issue:

Speaking of aleph p thought, I still didn't want to post it till it wasn't completely finished and extensivetly tested.....but i can't resist to show you guys my it is.......

(I will attach a couple of pics of one channell of the Aleph P 1.7 .......obviously not all the components are on it... :) )

Stefanoo 27th September 2007 06:14 AM

2 Attachment(s)
and here is another one....

this is a double side board.
Onn the bottom layer i have routed just the power supply and few signals (only higher and less delicate signals).

gaborbela 21st October 2008 08:58 AM

I need some help with my Aleph 1.7 preamp
I would like to ask for help with my Aleph 1.7 preamp .
There are 4 switch were the signal enter I don't know what to do with them .
I want to use the amplifier in a balanced mode , balanced in , balanced out .
No SE at all .
Would you please someone inform me which switch have to be on or of out of the 4.
I purchased my PC board from Kristijan from Croatia .
I afraid to power up the preamp until I don't know what is the purpose those 4 switches .
My email address
May be the service manual has some comment on these topic or please someone just explain it to me .
We also can see those switches on the schematic .
Thanks for the help .

Stefanoo 21st October 2008 01:35 PM

Hi Gaborbela,

nothing to be afraid of if parts are accurately mounted just test power supply first and then power the main board up without too much pain.

The 4 switches you see at the input are used to set the gain of the preamplifier nothing else.

You have the main active gain control which is represented by the 2K variable resistor
You also have the output volume control to passively adjust the output level
In order to maximize noise performance just keep in mind that you should set the active gain as high as possible (reasonably) to be able to work with the few first steps of the output attenuator and also accomplish a lower output impedance.

For SE configuration you short the -out and -in to GND.
Conversely for Balance configuration just properly hook a canon connector and there you go!

That's all folks.

Have fun with your project.

gaborbela 21st October 2008 05:54 PM


Tnank you very much .

Greetings .

Stefanoo 21st October 2008 09:44 PM

if you have any other doubts, feel free to ask and we will try answer you.

have fun.

gaborbela 21st October 2008 11:16 PM

I do have one question , do I put the volume control of the output of the preamp like at the BOZ . Or I can use the volume control between the DAC and the preamp.
Which choice would be better .
Thanks for your answer .
Greetings from Toronto

Stefanoo 22nd October 2008 07:54 AM

you can do both ways, but the best is to adjust the volume at the output.
That would lower the noise of your system.

If you do choose this way, i suggest you to find a suitable value for the main gain (the 2K trim pot) and replace it with an equivalent good metal film resistor.

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