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-   -   Semisouth Aleph J? (http://www.diyaudio.com/forums/pass-labs/176857-semisouth-aleph-j.html)

buzzforb 8th November 2010 12:27 PM

Semisouth Aleph J?
 
I have been reading here, there, and everywhere about the different Pass amps that have been made. I have many questions which is evidenced by my random scatter-brained post. MY question for this thread concerns the possibilty of substituting the Semisouth power J-Fet's in the Aleph J layout. THis uninformed question is based on the firstwatt articles including specifically the Sweet Spot. I am a newb, but have plenty of time to ask questions :devily: while simultaneously trying to figure out what the hell i am talking about. If this is doable, i will probably go ahead and buy the pcb's from Peter if they are still available. MY thinking is that this amp would be similar to the J2. I would just do the F5, which is a much easier build according to most, but i have limited funds and think, at least for now, this is what i want.

Nelson Pass 8th November 2010 03:01 PM

It's a pretty similar topology, but the details of biasing the
dual input pairs and the top side output current source are
different.

Specifically, I use a mu follower circuit to due what used to
be the "Aleph" portion, as the lower threshold voltages of the
power Jfets do not allow high enough Vce voltage for the
bipolar control transistors to have as good performance.

:cool:

Bill Fuss 8th November 2010 03:20 PM

How about just replacing the signal fets with the SemiS and leaving the 240s in the current source? Then use the appropriate resistor value to supply the gate. Sounds easy enough, but woud it make a significant sonic improvement?

buzzforb 8th November 2010 05:18 PM

I would think..:scratch2: that i stand to gain very little if anything by replacing one set of fets with another. I have found a simplified version of the mu follower typology. I will see if i can work with that. THe output seems familiar so i will have to go back over the various articles and schematics and see what i can find. This is like treasure hunting and I am a pirate with two eye patches.:Pirate:

Bill Fuss 8th November 2010 06:19 PM

I would not make that assumption. The Master is always looking for better semiconductors.

Zen Mod 8th November 2010 06:38 PM

I made my Babelfish J2 ;

but I have o intention to go in public with even poor Babelfish version of Papa's current product

boyz - please go with that in closed circles

Bill Fuss 8th November 2010 06:56 PM

I was looking for Papa's opinion. I'm trying to help with options for Buzz. A J2 would be a big bite for a newbie.

buzzforb 8th November 2010 07:55 PM

Forgive me, if in my ignorance I have crossed a line. I can assure everyone that I don't know my mosfet head from my jfet *** (as if that's not already evident). If I am pushing too far into something it is out of ignorance. I believe Bill recognizes this and is trying to steer me in the proper direction. Papa is just too damn kind (thankfully so) and as always offers a small morsel to try to assist others in doing what he loves. For me, the thing the makes Mr. Nelson unique is not his mastery of electronic circuits, but rather his willingness to generously share something that he could keep all to himself. Even IF i had the ability to do him harm, I would not. Now that we have cleared that up, will somebody please tell me why this amp is smoking :scratch:

Zen Mod 8th November 2010 08:15 PM

dunno - maybe I'm wrong generally ........ but that's what I think is fair

buzzforb 8th November 2010 09:56 PM

Guess this means i am back to the F5.


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