Marantz 7 Preamp

Audiohifi · 10th June 2008, 07:33 AM

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

kmtang · 10th June 2008, 02:16 PM

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

Audiohifi · 12th June 2008, 03:58 AM

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

Jempie · 10th July 2009, 12:15 AM

tell me more about this preamp

shyeung · 10th July 2009, 02:33 AM

Is it worth to clone a M7?

Any better circuit out there?

What supply circuit would better the M7 circuit?

Thanks

Jempie · 10th July 2009, 08:33 AM

Do you have a picture of this amp or a link

SY · 10th July 2009, 11:46 AM

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.

grhughes · 10th July 2009, 08:49 PM

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

LinuksGuru · 11th July 2009, 05:53 PM

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?

SY · 11th July 2009, 07:14 PM

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.

10th June 2008, 07:33 AM	#1
Audiohifi diyAudio Member Join Date: Apr 2005 Location: Singapore	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

10th June 2008, 02:16 PM	#2
kmtang diyAudio Member Join Date: Nov 2004 Location: Vancouver	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

10th July 2009, 08:49 PM	#8
grhughes diyAudio Member Join Date: Mar 2005 Location: Cubicle Sweet Cubicle, SW, MO, USA	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 __________________ "The gift of imagination is the gift of the gods imparted to a few for which they receive innumerable kicks in the a$$ their entire life." Le Corbusier (Edward Jenneret)

11th July 2009, 07:14 PM	#10
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	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. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

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12th June 2008, 03:58 AM	#3
Audiohifi diyAudio Member Join Date: Apr 2005 Location: Singapore	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

10th July 2009, 12:15 AM	#4
Jempie diyAudio Member Join Date: Jan 2008	tell me more about this preamp

10th July 2009, 02:33 AM	#5
shyeung diyAudio Member Join Date: Feb 2006 Location: Hong Kong	Is it worth to clone a M7? Any better circuit out there? What supply circuit would better the M7 circuit? Thanks

10th July 2009, 08:33 AM	#6
Jempie diyAudio Member Join Date: Jan 2008	Do you have a picture of this amp or a link

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