Path: utzoo!mnetor!uunet!mcvax!philmds!leffe!janpo
From: janpo@leffe.UUCP (janpo)
Newsgroups: sci.electronics
Subject: Re: Posted schematics
Message-ID: <53@leffe.UUCP>
Date: 6 Apr 88 08:33:15 GMT
References: <1961@mips.mips.COM>
Reply-To: janpo@leffe.UUCP (Jan Postma)
Organization: Philips I&E DTS Eindhoven
Lines: 61
Keywords: Mark-Levinson audio preamp JC-2, non-graphics
Summary: Minor mistakes in JC-2 preamp description?

In article <1961@mips.mips.COM> mark@mips.COM (Mark G. Johnson) writes:
>! ##########################################################################
>! Mark Levinson audio preamplifier model JC-2
>!	Phono amp section (including RIAA equalization)
>!
>! here is the active amplifier circuit; feedback network comes last
>!	positive input = node 10, negative input = node 20, output = node 50
>!	system ground = node 0
>!
  {Part of description deleted}
>!
>! Second stage: fully complementary push-pull w/ differential inputs
>R31a     31     80     249
>R31b     31     80     249			! Note: 2 R's in parallel (!!)
>Q32P   C=32   B=22   E=31   PNP    TYPE=2N4403	! Motorola bipolar PNP
>Q33P   C=33   B=21   E=31   PNP    TYPE=2N4403
>Q32N   C=32   B=32   E=34   NPN    TYPE=2N4401	! Motorola bipolar NPN
>Q33N   C=33   B=32   E=34   NPN    TYPE=2N4403
                        ^^
>R34a     34     90     249
>R34b     34     90     249			! 2 more R's in parallel
          ^^                                    ^^^^^^^^^^^^^^^^^^^^^^^^
Realy? According to me Q32N and Q33N represent a current mirror. Because
of a mismatch between the two transistors, each transistor requires an
emitter resistor to compensate for this mismatch. Thus:

 Q32N   C=31   B=32   E=34   NPN   ....
 Q33N   C=33   B=32   E=99   NPN   ....
 R34a     34     90     249
 R34b     99     90     249

 { Again, part of description deleted }

>! RIAA equalization curve (2 pole, one zero)
>R63a     50     63     50K
>C62a     50     62     0.06U			! (micro)Farads
>C62b     62     63     0.02U
>R62      62     63     3.75K
                 ^^
The RIAA network will be connected between the push-pull output stage 
(Node 50) and the negative input terminal of the diff amp (Node 20), I
assume. Consequently, node 63 should have been 20 I think. Right? 

>!
>! that's all
>---------------------------- 
> -Mark Johnson	*** DISCLAIMER: Any opinions above are personal. ***	
> UUCP: {decvax,ucbvax,ihnp4}!decwrl!mips!mark   TEL: 408-991-0208
> US mail: MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086

Unless the two minor mistakes, I managed to draw the circuit diagram
within a quarter of an hour. Although not very well suited for
processing by a computer, this way of sending schematics works fine.
At least that's my opinion.

BTW, Mark, do you have any other Mark Levinson or High-End diagrams :-)? 
I know it's quite a lot of work to post them but if you like to post
them, I would be very gratefull. Maybe you did it already in rec.audio
but that's a newsgroup we don't have here :-(.

Jan Postma