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Old 10th June 2008, 06:33 AM   #1
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Default Marantz 7 Preamp

My Marantz 7 clone preamp sounds very good in the high and low frequency range, but the vocal sounds thin. How do I improve on the midrange?
Thanks

AudioHifi
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Old 10th June 2008, 01:16 PM   #2
kmtang is offline kmtang  Canada
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Default Modified Marantz 7 line amp

HI,

You may change the last buffer tube with 12AU7 for better vocal with the following changes in cathode resistors:-

680 ohm => 2K ohm

27K ohm => 15K ohm

What type of coupling capacitors are used in yours?? I am using Jensen copper-in-oil. They sound very nice and sweet indeed.


Johnny
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Old 12th June 2008, 02:58 AM   #3
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Hi Johnny

Thanks for your suggestions. I have already repalced the buffer tube with 12AU7 (Phillips JAN) but did not change any resistors
Coupling caps are all Sprague.
What should be the value of the output cap?
Some DIYers use as high as 5uf although the original schematic is only about 0.22uf

Thanks

Audiohifi
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Old 9th July 2009, 11:15 PM   #4
Jempie is offline Jempie  Indonesia
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tell me more about this preamp
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Old 10th July 2009, 01:33 AM   #5
shyeung is offline shyeung  Hong Kong
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Is it worth to clone a M7?

Any better circuit out there?

What supply circuit would better the M7 circuit?

Thanks
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Old 10th July 2009, 07:33 AM   #6
Jempie is offline Jempie  Indonesia
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Do you have a picture of this amp or a link
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Old 10th July 2009, 10:46 AM   #7
SY is offline SY  United States
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Quote:
Originally posted by shyeung
Is it worth to clone a M7?

Any better circuit out there?

No, unless what you really want is an M7. There are many, many far better preamp circuits out there- there has been some progress since mass market designs of 50 years ago. For a start, read the preamp book from Allen Wright and, of course, Morgan Jones's "Valve Amplifiers" for both insights as to how to make a first-rate preamp and the reasons that designs like the M7 fall short.
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Old 10th July 2009, 07:49 PM   #8
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Default I agree with SY.

Much water has run over the dam since a Marantz 7 was designed. It's all 12ax7. The cathode follower output stages are way too slow, and newer designs with alternative tubes such as a 6GK5, 6ER5, 7308 and active CCS and sinks are much more the order of the day. Ray
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Old 11th July 2009, 04:53 PM   #9
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Quote:
Originally posted by SY

the reasons that designs like the M7 fall short.
I have none of these books. Can you please outline what exactly is wrong with design of M7?
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Old 11th July 2009, 06:14 PM   #10
SY is offline SY  United States
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Get the books. It will take far more typing and explanation than is worthwhile here- those authors covered the ground thoroughly, and if you're interested in tube design, they are must-haves.
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