Aleph P1.7 "the design starts here"

[Stefanoo]

Hope somebody will be interested to make this Nelson Pass 's preamplifier.
The opinion on the sound'quality, in comparison with the model L, are in disagreement.
I read that sombody preferes the P version sombody else the L version.

Accordingly to Nelson, the P version, would offer a better performances in noise terms and in dynicamc.

Anyways i finally decided to start to build this version but without the remote control, the only preamplifier.

I have to thank first Nelson Pass that allows us to use his projects to have fun and build something that actually sounds good.
Second i have to thank the guys here on the forum that were willing to share the service manual of the preamp and alwais willing to be supportive.


Anyways....i hope that somebody will like the idea of building this pre "with me" and work this out with me.


Anyways......



Here the first results that i got from the simulations ... i have some doubts..


Best,
Stefano

[Stefanoo]

the power supply simulation.
In green the output and in red the output from the 2 capacitors.

This result shows that the rising time is about 12seconds, as it can be seen.

Is it not too much...is there anything wrong with this result?

is this fact an issue?

[Stefanoo]

Now the simulations on the main board.


I have big problem to figure this out and i'll explain why.


On the service manual, in the main schematic, the connection are not marked with a point, as it should be, and so it's not so easy to understand if, when a net crosses another net, if actually it connects with it or not.
So, for instance, the input (i'm now referring to the inverting input, but everything is mirroarably to the not inverting input) would seem to go solely to the 10k input resistor R6.

But in this configuration i obtained, by visualizing on pspice, wrong output...at least what it looked to me.

So i had to connect that net that crosses the input and connects R61 and R69 to the input.
With this configuration i obtained results that i will post and that at least make sense to me.

Please, tell me if i'm doing wrong by connecting the input to R69 and R61.

[Stefanoo]

This first simulation involves the output potentiometer on the main board.

I made a parametric simulation in order to check the value of the output for the following values of the potentiometer:

61.9, 249 and 8.6K.


The input, as it can be seen, is a 4V pk-pk sinusoid.
The output is around 4mV for 8.6k.


Is it normal that have a so small output swing compared with the input?

shouldn't be the output signal bigger than the input?
(output almoust 1000times smaller than the input)

Moreover, on te original schematic there is the 2K trimmer with the "rightgain" label.
When i try to vary its value, i don't obtain any variation on the output swing signal.
Is it normal?

[ilimzn]

Perhaps posting this on the Pass sub-forum would be a good idea... the moderator might move it there.

[Stefanoo]

The simulation for different input value

i obtain distortion for over 7volt Pk-Pk on the input and les than 800mV.

Is it normal that the preamplifier destorces under 800mv input signal?

[Stefanoo]

NOOOOOO i made a mistake....ehehehe....i thought i was on the Pass Forum......

if the moderator can close this post i will open another on the other forum....


sorryyyy!!

[Stefanoo]

since i can't edit the first post anymore and delete the 3d, i ask to the moderator if he can do this for me..sine i have already opened this 3d on the Nelson Pass's forum!?

Thanks a lot.

[analog_sa]

Is it not too much...is there anything wrong with this result?

Nothing wrong. What do you expect with such a big cap on the gate? It is a slow-start feature.

I have big problem to figure this out and i'll explain why. On the service manual, in the main schematic, the connection are not marked with a point, as it should be, and so it's not so easy to understand if, when a net crosses another net, if actually it connects with it or not.

Just a basic understanding of how semiconductor circuits work should clear the big problem

[bscally]

this is a good place to start.

This discussion may be better places on the Pass Labs board.