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I found a very interesting article about simplified Marantz line amplifier.
https://ttradio.net/clone-marantz-7-m7-line-amp/
Here is what my friend simplified based on the Marantz 7 diagram, so which one should I go for? The one from ttradio or one from my friend?
Please advice!!
Follow Ups:
I found a place who offers constant current source.
Here what he said:
"You could use a CCS on the plate of the first 12AX7 section, and also on the cathode of the 12AU7 cathode follower without disrupting anything. Not so clear on the second 12AX7 section - it may have some effect on the EQ. Probably not a huge change though?.......it would work there. The JFET version with low current is best for the 12AX7, since it only is running 1-2 mA typically."
Any thoughts 🤔
Can I use CCS loaded the ECC83 in this line section? This means both 270K and 100K would be replaced by CCS.
The B+ should be higher.
My friend has just shared a circuit for his Marantz 7's phono section project.
I will follow this, once I complete the line section, I'll come to that later.
I could never get past the mountain of coupling and cathode bypass caps in this design. That's why I built my own based on the RCA. No cathode caps and only two for coupling. I would also never use a 12AX7 for output duty, especially in a standalone preamp. It's simply too limited. Not trying to rain on this parade, but I do think the best years of this product are behind it.
I take a look into the most earliest Marantz preamp, the audio Consolette, its phono section seems less complex.
My friend told me it sounds better than the 7 by comparison.
What do you think 🤔
Firstly, thanks to all comments!!
Secondly, I high recommended inmates who are inbterested in Marantz parts swapping. Here you go.
I go therough the line section so far, and will study about the phono section.
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-1/
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-2/
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-3/
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-4/
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-5/
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-6/
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-7/
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-8/
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-9/
https://jeffsplace.positive-feedback.com/a-guest-article-from-mr-shirokazu-yazaki-my-adventure-with-my-old-marantz-model-7-part-10/8/
The articles give me a very good idea and direction how to deal with the Marantz 7. Even though I'm doing differently as I have read ythe following suggestions by someone posted on diyaduio.com
"Marantz 7C
The Marantz 7C and McIntosh C22 are in my opinion totally over rated preamplifiers.
Firstly their RIAA sections are both AC coupled from 1st to 2nd tubes.
Secondly their EQ is active and driven by poorly designed cathode followers.
Thirdly the choice of tubes (ECC83) is certianly not the best.
Fourth the quality of the rotary switches is not good at all.
The power supplies are wimpy and not well designed but in that era this was par for the course.
Of course in their defense the available parts in the 50's and 60's was quite poor compared to what we have today.
We have restored many of these with great results.
Replace every single passive part.
Hard wire the RIAA parts.
Add a constant current source to the cathode followers
Completely upgrade the power supply with electronic regulation and better DC on the filaments.
Modify so that all switches do not carry audio signals but only DC to control high quality relays for all audio switching.
Modify the high level stage to be DC coupledand replace the balance control with a passive type centre tap to ground and the volume control with a blue velvet type wired either conventionally or in shunt mode.
Add in a cc source for the final cathode follower (7C and C22)
Remove the output level pot on the C22 as it simply adds more colouration."
I think this circuit can be improved in a number of ways.
First there really needs to be a grid stopping resistor at the input of the first tube. Probably about 4.75K. It would not be a bad idea to have a second stopping resistor at the grid of the second tube as well.
The coupling cap arrangement between the second and third tubes is a bit clumsy.
The second tube could be direct-coupled to the third tube, eliminating two 1M resistors and a 0.01uf coupling cap.
The coupling cap at the output of the second tube (0.22uf) could then feed just the feedback and nothing else.
I would increase the value of the output coupling cap to about 2uf. The 100K output load is a bit low if a 0.47uf cap is to be used since many amps have an input impedance about the same. That would put the cutoff at slightly less than 7Hz, which is a bit high if you want to avoid phase shift in the bass region.
The larger you make that cap the more the power supply must be stable otherwise with certain amps you'll get a low frequency instability. You may have to increase the value of the cathode resistor of the 3rd tube a bit to deal with the increased Voltage drop across it. 33K might do just fine.
Dear Ralph,
Sounds great! Let me talk toy tech whether it is possible to make any change as he already started the work.
Thanks 😊
They are the same except for the volume pot value and the second stage's coupling cap value.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Look again - all four(!) of the coupling caps are much larger capacitance in the TTradio circuit.I assume that the smaller caps are what the original M7 used, and the larger caps reflect a more modern design goal. Do you want it to sound like the original, or "improved"?
Edits: 02/03/25
Only the midrange that is closed to the original and the other area I tried to improve. I'll see.
I have the unit here and it is a clone Marantz 7 and extremely well built, and it come with tube regulation with 6J1 and 6V6.
What I'm going to do is adding 2 x Salas SSHV2 after the tube regulation for circuit, and my friend order for me, and now on the waiting list. I retain all small caps except the output I will use 0.47uf.
Those 0.01uf I will try the Super Mica that mentioned in the positive feedback articles.
I have some Sprague orange drop PS series 0.22uf that I bought to refurbish my vintage collections (Pilot, Heathkit, Fisher and few others) 2 decades ago.
22AWG Jupiter cloth tinned wire will be used for signal.
I don't know what would it sound like, and I might try to do some treat and see.
Thanks for you guys helps!!
PS. I try to keep all values small instead using large cap.
I guess I'm getting sloppy.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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