Aleph P1.7 "the design starts here"

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Stefanoo

Stefanoo

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Joined 2006
#1
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
 
#2
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?
 

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#3
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.
 
#4
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?
 

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#5
I simulate the circuit for different values of the input.

I obtained distortion for the inpunt signal over this range:

up 7volt Pk-Pk and down to 800mV pk-to-pk
(as it can be seen on theattached pictures).

Is it normal that the preamplifier already distorces for an input of 800mV?

How much is suppose to be the input signal range and the output swing?
 
#9
Thanks for the link, but it referes to the Aleph3 's schematic , but it's good to know that i wasn't the only one have a problem with the connections on the schematic, since they are not marked off.

Anyways, I hope somebodyelse, also, will take part at prject and maybe will help me out with this issues.


Best,
Stefano.
 
#12
May i recommend a basic electronics course like "The Art of Electronics"? Mosfets, differential amps, CCSs - it's all there.

Once you understand the basics you'll be able to get excellent value out of simulations.

Do you understand how the "potentiometer" in P works?
 
#13
Stefanoo said:
Thanks for the link, but it referes to the Aleph3 's schematic...
Click to expand...

Nelson is consistent in his style. All his schematics are drawn the same. There's no law that says that schematics must be drawn one way or another. It used to be common to draw little arcs where a wire would jump over another without connecting. These days, that's out of fashion. In ten years it may come back. Who knows? Sit down, look at the schematic, and ask yourself,"Is it reasonable that there might--or might not--be a connection here?"
This seems to me to be an instance of trying too hard. There's making a valid attempt to understand the circuit, and there's obsessing. My suggestion is to build the circuit, then study the real thing in action while listening to music. The circuit isn't that complicated. Just build it.
Charlie Papazian has an expression for beer makers: "Relax, have a homebrew." You could do worse than to adopt a similarly relaxed approach to electronics. Shaky, fearful hands are apt to get shocked. Relaxed, steady hands don't bump into things that go zap.
Oh, and I second analog_sa's recommendation to get a good electronics book.

Grey
 
#14
Stefanoo, the link regarding point#5, as grey said is really all you need to remember. However, if you are simulating in Pspice, are you using Orcad? Capture or scheamtics?
If your using Capture you can copy and paste into MSPaint and save as a .png file and post what you have here. Then we could easily comment on any necessary corrections.
If your using schematics, I have no idea how to get your file into a format you can post here. It has been done though, I just don't know how???
Taking a look at the original schematic however, I see only 1 possible mistake. The line from R46 and R61 does not connect to the output or the input on it's way to Q12 and Q13, Hope that helped 😀 😀 😀
Another thing I noticed, your sim results window seems to have poor resolution. Is that due to your setup? Like "print step" and "step ceiling" settings???
 
#15
i use capture, so thanks for the advice on how to post it here.
I'm going to post the schematic now.

You told me that the line from R46 and R61 does not connect to the output or the input on it's way to Q12 and Q13, but if i don't connect that line to the output i receve error on the bias point calculation.


I don't know if anybody can help me to find the mistake on the schematic that i have drawn.

And, moreover, where can i set the resolution on pspice?

Thanks a lot.
 
#17
as i said, if i don't connect the input with that line that crosses the input and output, i get errors on the pspice analysis.

If i connect it, instead, on the analysis results, i get a normal output wave form but i have the issue of a big attenuation and distortion for a 1v pk-pk input signal, which i think it's not correct to have distiortion at that high value of the input signal.

How much is the output of the aleph p preamp suppose to be?
Since it's an active pre, i guess it should have a gain, but from the simulation it has an attenuation of about 1000!!!
 
#19
Ok, i understood.

The problem is that if i don't connect in that way, the simulator gives me erros and it's no any longer possible to simulate the project.

Here i 've attached the schematich (with capture) and the simulation profiles.
I had to change the extention because i don't have winzip.
I used winrar to compress the files.
So, in case you download it, you have to remember to rename it as .rar and uncompress it with winrar.


If you have capture and pspice, please try to open it.

I don't really know the reason of why i get that error not connecting R6 and R22 (the way that is supposed to be)


Thank in advance
 

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#20
I complete the set of my simulations by attaching the frequency response.

The behaviour looks very strange to me.

Now i've stopped my monologue....hope that somebody will be willing to help me with this and comment this post.


I take this project as something fun and something where i can improve and build my kwnoldge on simulators cicuit design, layout..and so on.
It's very important for me that the most experienced guys here on the forum help me with this....so i hope you guys will be willing to hlp a noobies as me.
i would appreciate it very much.



Thanks iin advance for your support.


Best,
Stefano.
 

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