Conrad Johnson MV75 "update circuit drawing" - diyAudio
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Old 15th October 2012, 06:57 PM   #1
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Default Conrad Johnson MV75 "update circuit drawing"

Hi,
Anyone who know whether the shown CJ MV75 drawing is correct ? Please find the "new" updated drawing at :

https://picasaweb.google.com/1031761...02912673127378

The Conrad Johnson equipment/amplifiers of any kind is very difficult to find in Europe. The possibility to build a clone seems to be one way to learn more about these great amplifiers. Any help with the CJ MV75 circuit would be highly appreciated.

regards.
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Old 15th October 2012, 08:10 PM   #2
SY is offline SY  United States
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It looks like most of the CJ amps I've worked on- later ones inserted a cathode follower between the input voltage amplifier and the phase splitter. It's basically the same circuit that Mullard and Eico used in the '50s and '60s, though Mullard used a pentode for the voltage amp and Eico used a 12AX7.
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Old 15th October 2012, 08:13 PM   #3
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Drawing seem to be correct.
BTW, it is absolutely typical triode pre-driver -> long tail phase splitter -> UL push pull topology. You can take vintage Revox, Sansui, or countless similar schematics as a basis of your own build.
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Old 15th October 2012, 10:05 PM   #4
dgta is offline dgta  United States
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The schematic posted contains errors, and they appear to be deliberate.
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Old 15th October 2012, 10:27 PM   #5
Cassiel is offline Cassiel  Libya
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I contacted CJ via email and they sent me the requested schematic the next day. Not the one you're looking for, just saying you could try to do the same.

Quote:
BTW, it is absolutely typical triode pre-driver -> long tail phase splitter -> UL push pull topology.
A very common circuit, however the power supply is not that common. And it has huge transformers. Those two things make the difference.
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Old 16th October 2012, 05:14 AM   #6
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Quote:
Originally Posted by dgta View Post
The schematic posted contains errors, and they appear to be deliberate.
Yes, thank you! Tell me where you have found the errors? Thats why I asked the forum!
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Old 16th October 2012, 05:15 AM   #7
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Quote:
Originally Posted by Cassiel View Post
I contacted CJ via email and they sent me the requested schematic the next day. Not the one you're looking for, just saying you could try to do the same.

Ok, good idea. I shall try to write to CJ.

rgds
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Old 16th October 2012, 06:02 AM   #8
dgta is offline dgta  United States
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Quote:
Originally Posted by Leakstereo20 View Post
Tell me where you have found the errors? Thats why I asked the forum!
The biasing of both the first and second stages is improper. I can't tell you what the "correct" version would be, since I don't know their intended operating points.
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Old 16th October 2012, 10:42 AM   #9
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Quote:
Originally Posted by dgta View Post
The biasing of both the first and second stages is improper. I can't tell you what the "correct" version would be, since I don't know their intended operating points.
Since you don't know their intended operating points, how could you then state that the biasing of the first and second stages is improper?
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Old 16th October 2012, 12:51 PM   #10
SY is offline SY  United States
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Quote:
Originally Posted by dgta View Post
The biasing of both the first and second stages is improper. I can't tell you what the "correct" version would be, since I don't know their intended operating points.
The 90K9 looks like a misprint (or I didn't read it correctly). 90R9 would be more appropriate.
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