Jeff Rowland Coherence 1 - Schematic for the Modules wanted - diyAudio
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Old 30th October 2013, 10:03 PM   #1
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Default Jeff Rowland Coherence 1 - Schematic for the Modules wanted

This Thread exist already and is closed:
Jeff Rowland Coherence One Schematic

I want to have the schematics of this discrete jFET operational amplifiers:
1) Phono Amp Low Level
2) Phono Amp High Level
3) LINE AMP INVERTING
4) Line Amp NON inverting

Who can help?
The modules are similar to those from JC-2 (John Curl, Mark Levinson)
http://www.hifido.co.jp/KWmark+8/G01...2874-41444-50/

Last edited by tiefbassuebertr; 30th October 2013 at 10:09 PM.
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Old 26th November 2013, 05:06 PM   #2
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Default Questions to the Operational Amplifiers used for Offset Servos

A friend of me purchased two preamplifier devices of this model.
he send me an inside image from both devices - go to the attached pics.
I miss the operational amplifier ICs (DIP-8) - instead this I discover only the 8-pin sockets without the ICs - except by the second device - there are two OP-Amps in the area for the inverting line amps.

according the simplified schematics there are drawed offset servo OP-Amps for each module (four/each channel).

Follow question rises up:
In which cases are the offset servos in use and in which cases
they are dispensable?

Thank you for advices.

P.S.
To the same model there are also this thread:
JRDG Coherence One Series I & II powersupply

Last edited by tiefbassuebertr; 26th November 2013 at 05:12 PM.
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Old 26th November 2013, 05:25 PM   #3
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Sorry, cannot really help but fwiw i once deconstructed a similar module. Took me a few days and wasn't any fun. And in the end - where there should have been a zero feedback circuit - 4 cheap opamps were found and nothing else worth concealing.

I wouldn't be too surprised if under the epoxy lies one of John Curl's circuits.
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Old 27th November 2013, 01:24 AM   #4
ramallo is offline ramallo  Europe
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I couldn't get all the schematic, I got all except the modules (by the moment) ( If I'll can get it I publish it for sure ).

I have a question: have you any offset on the output?, my unit have 5 volts and I couldn't find the failure
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Last edited by ramallo; 27th November 2013 at 01:27 AM.
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Old 27th November 2013, 03:06 AM   #5
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Quote:
Originally Posted by tiefbassuebertr View Post
In which cases are the offset servos in use and in which cases they are dispensable?
That was one of the highlights of the improved Coherence One, no DC-servos, the transimpy circuit of the Series II modules could do without.
(LNRDS and Stereoplay had articles on the JRDG Coherence One SII, omission of the servo was mentioned in one of them)

Coherence One 1st series has a 411 crud for every module installed.
All series II versions have empty opamp sockets. In case a module turned stray dog as it became older, an opamp could be installed as service patch.

Last version of the SII had no DIP8 sockets soldered to the main board at all, empty landing pads.
Jeff likely figured he could kill two birds with one stone : save a buck, and possibly sell an extra gain module. There's economics for ya !
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Old 27th November 2013, 04:52 PM   #6
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Quote:
Originally Posted by tiefbassuebertr View Post
This Thread exist already and is closed:
Jeff Rowland Coherence One Schematic

I want to have the schematics of this discrete jFET operational amplifiers:
1) Phono Amp Low Level
2) Phono Amp High Level
3) LINE AMP INVERTING
4) Line Amp NON inverting

Who can help?
The modules are similar to those from JC-2 (John Curl, Mark Levinson)
JC-2(220V╗┼══í╦ Mark Levinson HiFi-Do McIntosh/JBL/audio-technica/Jeff Rowland/Accuphase
Sent ramallo a while ago an article [pdf] on it. One page shows schematics with some detail. I'll send if you like to have it.
Best regards.
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Old 28th November 2013, 10:47 AM   #7
gk7 is offline gk7
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Quote:
Originally Posted by tiefbassuebertr View Post
...
The modules are similar to those from JC-2 (John Curl, Mark Levinson)...
The only similarity is that they are potted. Anything else (size, pinout, look and
most likely the circuit too) are different.
I dont think John Curl has ever worked for Jeff Rowland.
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Old 28th November 2013, 02:31 PM   #8
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Quote:
Originally Posted by Antoinel View Post
Sent ramallo a while ago an article [pdf] on it. One page shows schematics with some detail. I'll send if you like to have it.
Best regards.
Good idea - thank you.
my email address: kirschner-hifi@tiefbasswiedergabe.de
Quote:
Originally Posted by ramallo View Post
I couldn't get all the schematic, I got all except the modules (by the moment) ( If I'll can get it I publish it for sure ).
I have a question: have you any offset on the output?, my unit have 5 volts and I couldn't find the failure
I haven't measure offsets, because the devices showed in post #2 I will get next year at the earliest. At which modules you have the mentioned offset with 5VDC ?
Quote:
Originally Posted by jacco vermeulen View Post
That was one of the highlights of the improved Coherence One, no DC-servos, the transimpy circuit of the Series II modules could do without.
(LNRDS and Stereoplay had articles on the JRDG Coherence One SII, omission of the servo was mentioned in one of them)

Coherence One 1st series has a 411 crud for every module installed.
All series II versions have empty opamp sockets. In case a module turned stray dog as it became older, an opamp could be installed as service patch.

Last version of the SII had no DIP8 sockets soldered to the main board at all, empty landing pads.
Jeff likely figured he could kill two birds with one stone : save a buck, and possibly sell an extra gain module. There's economics for ya !
Thank you for your explanations. Just for such cases a detailled schematic, documentation and Service-Manual is
indispensable. Unfortunately it isn't available, maybe therefore because it don't exist in the wished kind as by the most typical small high end audio companies usual.
The schematic, I did have in the mean time, is a disaster concerning the clarity. No component values and no internal circuit diagram from the modules. Thus no circuit description resp. understanding possible.
I think "411" means the LF411
http://www.ti.com/lit/gpn/lf411-n
The abbreviation "LNRDS" I had never heard before

Last edited by tiefbassuebertr; 28th November 2013 at 02:48 PM.
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Old 28th November 2013, 03:16 PM   #9
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La Nouvelle Revue Du Son (in France, it's common to abbreviate it to NRDS)
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Old 28th November 2013, 04:13 PM   #10
dadod is offline dadod  Croatia
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Quote:
Originally Posted by jacco vermeulen View Post
La Nouvelle Revue Du Son (in France, it's common to abbreviate it to NRDS)
Jacco, did you used that signature before? I used that sentence in one my answer, in other thread,recently.
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