Mark Levinson JC-2 revised schematic
Mark G. Johnson
stage of the Mark Levinson audio preamp model JC-2, Jan Postma found
a typographical error: I incorrectly typed `63' when I should have
typed `20'. The schematic as originally presented was missing a
"solder dot" connecting the two together --- this shows that
proofreading errors can occur with text as well as with drawn figures.
A corrected revision in included below.
The JC-2 circuit (designed by John Curl) is rather interesting in its
biasing of differential BJT pairs. The original posting _was_ correct
in that regard: the emitters of the diff pairs ARE directly connected
together, and then tied to the rails (supplies) by a resistor. In both
cases this resistor is actually implemented as two 249 ohm resistors
wired in parallel. Jan points out that this unusual for the NPN current
mirror. It *is* unusual but this is what's in the Mark Levinson preamp.
Finally, Jan writes:
> BTW, Mark, do you have any other Mark Levinson or High-End
> diagrams :-)?
The answer is, yes, and I'll try to post them between now and Tax Day.
! ##########################################################################
! ########## REVISION 2: corrects a typo. Node 63 == node 20
!
! 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
!
! Power Supplies & local bypass capacitors
Vplus 80 0 13.0 ! Volts
Vneg 90 0 -13.0 ! Volts
C80 80 0 4.7U ! (micro)Farads
C90 90 0 4.7U ! (micro)Farads
!
! Input differential amp with resistor loads (lowest possible noise)
J10 D=21 G=10 S=23 Nch TYPE=E110 ! Siliconix N-channel JFET
J20 D=22 G=20 S=23 Nch TYPE=E110
R21 21 80 100.0 ! Ohms
R22 22 80 100.0
! Tail current source for input diff amp
J23 D=23 G=25 S=24 Nch TYPE=E110
R24 24 90 249
R25 25 80 27.4K ! (Kilo)Ohms
R23 25 90 10K
C25 25 90 10.0U
!
! 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=2N4401
R34a 34 90 249
R34b 34 90 249 ! 2 more R's in parallel
! stabilization network (NOT the RIAA phono equalization)
C33 32 0 39P ! (pico)Farads
C35 21 35 220P
R35 35 33 10.0
!
! Output stage: complementary parallel-JFET push-pull (!!)
J41 D=80 G=33 S=41 Nch TYPE=E212 ! Siliconix N-channel JFET
J42 D=80 G=33 S=42 Nch TYPE=E212
R41 41 43 60.4
R42 42 43 60.4
J45 D=90 G=33 S=45 Pch TYPE=E175 ! Siliconix P-channel JFET
J46 D=90 G=33 S=46 Pch TYPE=E175
R45 45 44 60.4
R46 46 44 60.4
! 100 ohm trimpot, adjust for zero volts DC output
R50a 43 50 49.0
R50b 44 50 51.0
!
!
! Now the overall topology in which the active amplifier is embedded
! Phono input = node 1, phono output (to selector switch) = node 70
!
!
! input network (to provide correct RC load on phono cartridge)
R10b 1 10 100.0 ! Ohms
R10c 10 0 49.2K ! (Kilo)Ohms
C10b 10 0 50P ! (pico)Farads
!
! RIAA equalization curve (2 pole, one zero)
R63a 50 20 50K
C62a 50 62 0.06U ! (micro)Farads
C62b 62 20 0.02U
R62 62 20 3.75K
! low frequency pole
R64 20 64 110.0
C64 64 0 1000U ! (micro)Farads
! high frequency pole
R61 60 61 10.0
C61 61 0 470P
!
! output network (connects phono amp to selector switch)
C60 50 60 2.0U ! hi quality polypropylene
R60 60 0 51.1K
R70 60 70 60.0
!
!
! that's all
--
-Mark Johnson *** DISCLAIMER: Any opinions above are personal. ***
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