Anyone made a DIY Marantz 7/7C?

The cut down version schematic sounds about ideal, IMHO.

You can make it sound really good by carefully choosing your parts and by using point to point wiring instead of a PCB, for instance.

The Guitar amp guys still sell nice black phenolic tag boards with silver plated turrets, just like Marantz used. Great for a DIY project...

Imagine this carefully laid out on a nice enclosure with a thick brushed front panel. You'll have a killer preamp!
 
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I have both of those schematics, along with a scan of the complete Marantz 7 manual that I snagged from the web (if I find a tube schematic or manual, I download and save it). The first one is a scan of the original Marantz schematic. One thing to keep in mind is that the hand-drawn version on the right is only half of the circuit, the other one shows both sides. The "full" version also looks a lot more complex because of those odd tone controls that used the discrete-resistor switches instead of pots. I wouldn't have a clue where to start looking for those, but it wouldn't be too hard to bread-board something together with regular rotary switches. It also wouldn't be that hard to add a "tone defeat" switch to bypass them alltogether. Personally, I've found that I like having tone controls when listening to the radio, around here I think the broadcast engineers are all tone-deaf. When listening to recorded media, I usually use the tone defeat on my KR-9400.

As far as a chassis goes, I got a funky 60s Heathkit cabinet for some sort of ham radio equipment with some junk at an auction. It's been almost entirely gutted, but it would be very easy to install a silk-screened aluminum plate face in place of the current Heathkit face.

One thing I need to find are good 9-pin sockets. All of the small sockets in the two Lowrey organs I gutted were the thin "wafer" type that everyone says are junk. My Heathkit O-scope has very nice, thick plastic 9-pin sockets that look ideal...but I'm not gutting it. ;)

Of course, if I do this and get it working, the next step would be deciding on an amplifier to clone (or amplifiers, in the case of monoblocks). I have a ton of schematics from Marantz, McIntosh, and others. Decisions, decisions.
 
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I've been studying this project (along with trying to get the Victor receiver running right), and so far I've come up with one issue that I'm not sure how to overcome - some of the switches are rather unusual in the full version of the circuit. OK, most of them are unusual. The high and low pass filter switches, the phono equalization switch and most of all the stereo mode switch all seem to have contact properties beyond the standard "on/off/on" type of switch. The tape monitor seems to be a fairly standard "on/on" design, at least. So far I've only been able to come up with two solutions:
1) Use standard switches and jumper across them to simulate the original structure. This would require the use of diodes to keep current from flowing where it shouldn't, which might have an effect on sound.
2) Breadboard circuits with duplicates of certain circuit sections. I probably wouldn't have to use diodes, but there would be a lot of unnecessary duplication of circuitry.

I'd far prefer to find some switches at least similar to the design of the originals. I'm going to dig around on Mouser's website to see if they have anything.
 
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Sorry for bumping this one back up, but those stepped pots are available on ebay. Type in "Stepped Attenuator" for a 10K version and "Step Attenuator" for a 100k version. This seller also sells preamp kits which are apparently derived from the 7C, Kinda eyeballing it.
 
LinuxGuru said:
Hi, Sam! Did you find any substitute for 7C tone control rotary switch?
Click to expand...

Been busy and haven't had much time to think about it, unfortunately. The Heathkit cabinet I want to use is blocking my garage screen door, and even that hasn't motivated me much lately.

Mattwizz3 said:
Sorry for bumping this one back up, but those stepped pots are available on ebay. Type in "Stepped Attenuator" for a 10K version and "Step Attenuator" for a 100k version. This seller also sells preamp kits which are apparently derived from the 7C, Kinda eyeballing it.
Click to expand...

Great info! I'll definitely be looking into that. I had planned to find some switches and bread-board the circuitry, but a two-layer 10-position rotary switch isn't easy to find.
 
My replica

I just finished my own Marantz-7-Clone

The faceplate is an original 7c and from ebay. The Chassis is a
replica sold on ebay too. The Wood-Cabinet is also from ebay made in
china. The black knobs with the switches are parts from a Telecaster
guitar amp always awailable on ebay. Tube are NOS JAN Philips. I used
some bumble-bee caps I purchased last year and 2 original Vitamin-Q
in the phono stage. For the other coupling caps I used russian
oil-paper types, that sound great. I used them before in my Mullard
5-10 project. The original selenium rectifiers on ebay are far too
expensive, so I bought a full wave selenium rectifier from Siemens on
ebay for the HT and I use a standard rectifier for the heaters. I
don't know the sound of an original Marantz 7, but I am very pleased
with the sound of my replica.

own-front.jpg

own-back.jpg
 
Those bumblebee caps are considered notorious junk in some relms of antique electronics. My Citation I is also full of the things therefore it should sell for a sound similar to a 7C?

No doubt they'll be coming out of the citation in favor of a more reliable cap.

Steve
 
Not all bumblebees are created equal. Marantz specified mylar types in critical circuit areas. They look identical to the more mundane paper type on the outside.

Also, the circuit of the 7C is much more accurate and the signal path is cleaner than other period preamps.

The Citation seems overly complex to me.

By the way, excellent job on your replica teddyboy!
Post nudies if you can. :thmbsp:
 
Gut Shots! Super Kewl, I thought about using a 7C shell for a build. Just a very nice way to use what you can find.:thmbsp:
 
Open mouth insert foot. Didn't know they were Mylars :).


crooner said:
Not all bumblebees are created equal. Marantz specified mylar types in critical circuit areas. They look identical to the more mundane paper type on the outside.

Also, the circuit of the 7C is much more accurate and the signal path is cleaner than other period preamps.

The Citation seems overly complex to me.

By the way, excellent job on your replica teddyboy!
Post nudies if you can. :thmbsp:
Click to expand...
 
I was actually considering buying a 7C-inspired half-kit from a gentleman in Canada, consisting of a preamp board and a power supply. I guess I have more research to do on which preamp to get. At this point it may be quicker/easier to just upgrade my PAS-2.
 
There's also a theory that the legendary designers of the day took leakage into consideration when developing their circuits. This is because it was very hard (and expensive!) to find caps that did not leak (even a little), when new. So some leakage was allowed in the design, and it could still meet spec.
 
Has anybody actually built one of the rep kits available?

Plenty around now so I'm curious if anybody can offer real world feedback on them.
 
I would like to build a true 7C kit, like the 7K that was released by Marantz Japan in 1979. Now that would be a blast!
The Chinese now have the capability of recreating such a kit if they wanted to...
 
Ive seen a few kits that look decent. Most are just the line stage circuit or the phono circuit. A couple had both combined. All had the extra inputs, filters, tape loops, tone controls, ect. removed. Since I don't use tone controls much I have thought about building one of the stripped down clones with the phono stage.
 
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