So if I understood you correctly whenever the equalizers are plugged in (in my case D5 equalizers) then all the signal goes through D5 and the JC-1SM is out of the circuit, and the signal is amplified by setting up the switch rockets in the d5 (or A type) modules.
So I'm guessing were I to use an external step up transformer then I should remove the equalizers entirely (A type, D5, D6, etc)
No, excuse me for being vague maybe. If the D equalizers are in, so are the JC-1-SM. If the A-equalizers are in, the JC-1-SM is out of the signal path, even if it happens to be installed in the ML-1. There are connections on the D cards not present on A that takes care of this. I shall try to finish my sketches soon. In the meantime, Mark Levinson Vintage Audio Gear also has some indicative sketches. The Levinson papers (in an earlier post in this thread) does not show exactly which components are on the equalizers, on the main board, or on the JC-1-SM.
I have some NOS, unpopulated phono boards for the ML-1. See the attached pics
What I believe are the MM cards (single sided) have a ML #30-0001-00; the part number of the MC cards (double sided) is #30-0003-00. Also have some double sided, blank boards (no part number) of what I believe were the line driver cards. $20 each plus shipping if you're interested.
As you probably know, the original circuitry in the potted modules was designed by John Curl and built by Dick Burwen (in Massachusetts). As sales increased, production was later brought in-house. Burwen continued to make similar (don't believe identical-as they used an IC) modules and there is some info on them on the Burwen website. These modules were also used in the ML LNP-2 and the original Curl circuits are shown in contemporary Audio Amateur Magazine. After John's "falling out" with Levinson, Tom Coelangelo redesigned them and I believe the "newer" circuits are what's shown on the referenced ML site. The plug-in-pin "form factors" for the two different amplifier modules were also made by other companies and used in many mixing consoles.
Other pic shows some reverse engineering work we did on a few -1's.
Charles
What I believe are the MM cards (single sided) have a ML #30-0001-00; the part number of the MC cards (double sided) is #30-0003-00. Also have some double sided, blank boards (no part number) of what I believe were the line driver cards. $20 each plus shipping if you're interested.
As you probably know, the original circuitry in the potted modules was designed by John Curl and built by Dick Burwen (in Massachusetts). As sales increased, production was later brought in-house. Burwen continued to make similar (don't believe identical-as they used an IC) modules and there is some info on them on the Burwen website. These modules were also used in the ML LNP-2 and the original Curl circuits are shown in contemporary Audio Amateur Magazine. After John's "falling out" with Levinson, Tom Coelangelo redesigned them and I believe the "newer" circuits are what's shown on the referenced ML site. The plug-in-pin "form factors" for the two different amplifier modules were also made by other companies and used in many mixing consoles.
Other pic shows some reverse engineering work we did on a few -1's.
Charles
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No problem, now I understand it better though. I guess what you explain here for the ML-1 works in the same way for the JC-2, since they are quite identical except for the power supply (from what I know).
Module pins we used are Mill-Max, available at Mouser and likely elsewhere.
Sockets: 0314-0-15-15-34-27-10-0
Pins: If the daughter board module is mounted upside down (component side down), like the original Levinson modules, you need 1” length: 3106-2-00-21-00-00-08-0
If the daughter board module is mounted component side up, then 1/2” tall pins (which we used) will work: 3104-2-00-15-00-00-08-0
Sockets: 0314-0-15-15-34-27-10-0
Pins: If the daughter board module is mounted upside down (component side down), like the original Levinson modules, you need 1” length: 3106-2-00-21-00-00-08-0
If the daughter board module is mounted component side up, then 1/2” tall pins (which we used) will work: 3104-2-00-15-00-00-08-0
Dear Charles, Do you still have these PCB's? I need 2 pairs for the phono section and 1 pait for line. I looked at your schematics but for me too vague to read properly so a schematic to these boards are welcome too. Please let me know how to acquire, thank you so much.
Greteings,
MarioGert, Netherlands
Most likely the line amp modules lose their lifes after so many years. Check you preamp with CD or Tuner input. If this fails too then you need line Amps.
Originals not available or second hand old ones too for way too much money.
I had the same problem and we got through the schematics provided and the necessary original parts and built line modules.
If you need these, contact me as we have a few pairs in stock. Glad to send you a pic if you like.
Greetings
Mariogert
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Hello Georg, long time since this thread was last used, I hope you are well
Returning to use this preamp now I find myself with no MC, and only MM cartridges
For use with MM type, should I remove the 2 D modules and the JC-1SM module and leave put only the two Class A Phono Preamplifier modules?
Thanks!
Hi Landon,
only the two Class A Phono Preamplifier modules would not be enough unfortunately, the RIAA equalization would be missing. From the attached LevinsonJC-2reviewAudioApril1976.pdf :
D. Moving-Coil Phono: 60 dB gain at 1 kHz. Uses JC-1SM pre-
preamp with phono amplifiers. Uses D or D1 equalizers.
That is what you currently have and is the configuration for MC. (phono_jc1_2.jpg)
A. Normal Phono: 32.5 dB gain at 1 kHz. Uses system A plug-in
equalizers and is for regular magnetic cartridges.
That is what would be needed for MM - D equalizer and JC-1SM removed, but an A equalizer board (e.g. an A4E) added. (phono_a4e.jpg)
Sometimes such EQ boards are offered on ebay but at rather "fantastic" prices, buying a MC cartridge is a cheaper option. A DIY version should be possible and not too expensive.
only the two Class A Phono Preamplifier modules would not be enough unfortunately, the RIAA equalization would be missing. From the attached LevinsonJC-2reviewAudioApril1976.pdf :
D. Moving-Coil Phono: 60 dB gain at 1 kHz. Uses JC-1SM pre-
preamp with phono amplifiers. Uses D or D1 equalizers.
That is what you currently have and is the configuration for MC. (phono_jc1_2.jpg)
A. Normal Phono: 32.5 dB gain at 1 kHz. Uses system A plug-in
equalizers and is for regular magnetic cartridges.
That is what would be needed for MM - D equalizer and JC-1SM removed, but an A equalizer board (e.g. an A4E) added. (phono_a4e.jpg)
Sometimes such EQ boards are offered on ebay but at rather "fantastic" prices, buying a MC cartridge is a cheaper option. A DIY version should be possible and not too expensive.
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Hello!! Thank you very much for the thorough explanation !
So it seems I need a pair of those A4E, and as you mention items like those tend to be crazy expensive. A DIY sounds better, question is who on earth makes those haha
Thank you very much