Undoing the **WORST** DIY mod ever... Update: Audio Classics to the rescue!*

Discussion in 'Audio Hardware' started by Joel Cairo, Apr 20, 2017.

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  1. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon
    WARNING - There are pics... viewer discretion is advised.

    After you get over the raw shock of seeing them (and it may take it a bit), please give me your best advice as to how to restore this poor Frankenstein-ed thing back to health.

    Here we go--

    Marantz 7C - Pic 1.jpg Marantz 7C - Pic 2.jpg Marantz 7C - Pic 3.jpg Marantz 7C - Pic 4.jpg
    Yes, someone actually converted a Model 7 tube preamp to solid state. Boggles the mind, doesn't it?

    I got it from a very reputable dealer who gave full disclosure (in fact, I asked permission to use their pictures to start this thread, which they graciously granted).

    Here's their description:

    "Welcome to the strangest Marantz 7 tube preamp [we've] ever owned. Apparently the original owner thought solid state was the 'wave of the future' and installed a separate solid state circuit so this preamp has Tube and Transistor outputs. The phono stage is all tube. Treble, bass and several other functions bypassed."

    As to the price, it was much cheaper than the going market price for a fully original unit, but still was over $1,000.00... it **is** a Model 7 after all! (Well, at least partially...!)

    So I'm hoping at least some of the missing parts can be salvaged from other Marantz units of the period-- I'm thinking of the missing knobs/pots, etc... the missing circuit board may be a lot tougher to come by...

    So-- now that the initial shock is over, what are the most obvious parts that I'll need to procure to get this little gal back to her original condition...? Any suggestions...?

    Thanks for any help you can give...!!!

    - Kevin
     
    McLover and hi_watt like this.
  2. TheVU

    TheVU Forum Resident

    Well, they bypassed the tone circuit.
    I guess you've got that going for you.
    Which is nice.

    Edit: I thought that was Echo's photo work!!!
    I'm sure you talked with Kurt about unfrankensteining it.
     
  3. stereoguy

    stereoguy Its Gotta Be True Stereo!

    Location:
    NYC
    I dunno. Sometimes you just have to give up....i think this might be one of those times.
     
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  4. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon

    It is, and I did. He said that I should listen to it first, because he though it sounded OK... but I don't think I have the heart to plug it in as it is...

    Doesn't the Model 7 have a "drop out" tone circuit? (when the knobs are at 12:00, they drop out?)

    - Kevin
     
  5. crooner

    crooner Tube Marantzed

    Wow. That's some interesting mod!
    And I'm sure it can be reversed but not without some work involved. Or at least a stock Marantz 7 on hand to replicate the wiring!

    The unit looks good cosmetically and apparently only one small extra hole has been drilled in the back panel so that's a definite plus!

    The innards look a little messy but I've seen worse. This is definitely a great candidate for a complete rebuild. Perhaps using the famed Arizona "Cactus" Caps, Schottky diodes and other modern goodies.

    This looks like the work of an engineer/experimenter. He should have worked from scratch instead of butchering a classic!
     
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  6. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon
    Or someone who's got a lot of clear pictures of the inside of a stock (or reasonably stock ) Model 7 that they'd be willing to provide as a guide...

    Well I know this is where the hornet's nest gets stirred up, but I'm definitely of two minds about this. Part of me says "vintage parts for the absolutely authentic sound", but the other part of me says "it'll be a helluva lot easier to assemble the needed values using modern-day caps & resistors". I'm fairly sure that Terry DeWick would recommend Nichicon QXs or Illinois caps to replace the missing bumble bees (He used Nichicons to replace the bad bumble bee caps in my old 8B, and it really didn't affect the "voicing" of the amp). I've got the parts list, but what are the modern-day equivalents of the various caps & resistors used in the Model 7?

    Word.

    - Kevin

    PS - Here are more pictures of the inside of the amp (top side)-- this guy looks to have added quite a bit...
    Marantz 7c top_1 SMALL.jpg Marantz 7c top_4 SMALL.jpg Marantz 7c top_6 SMALL.jpg Marantz 7c top_7 SMALL.jpg Marantz 7c top_8 SMALL.jpg
     
  7. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon
    And some inside, from underneath...

    Marantz 7c underneath_1 SMALL.jpg Marantz 7c underneath_2 SMALL.jpg Marantz 7c underneath_3 SMALL.jpg

    Definitely gonna need some help. :D

    - Kevin
     
  8. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon
    So, folks have been curious about an update--

    I've removed about 4 pounds of extra components (actually true...!) from the unit, and stripped it out to this:

    Marantz 7c - empty SMALL.jpg

    And I've obtained a "donor" 7T which has yielded amazing replacement parts... but I have a question about the caps and resistors that wrap around the treble control. I've figured out the replacements that I need to order for every position but one-- it's position 8 on the 7T control, circled on the wiring diagram below:

    Marantz 7T - treble control components circled SMALL.jpg

    As you can see, this actually does exist on the 7T version, as pictured and circled below:

    Marantz 7T treble control circled SMALL.jpg

    My question is-- does this wiring exist on the original Model 7 treble control? I think the cap is supposed to be a 1,000 pf ceramic capacitor (500 V)... but if so, what are the values for the two resistors (which I assume are 1/2 Watt, 10% carbon comps)?

    Can anyone with the proper knowledge take a look, and let me know?

    Thanks!

    - Kevin
     
    timind likes this.
  9. Mark broadhead

    Mark broadhead Forum Resident

    Location:
    Newcastle England
    Have you tried Diyaudio.com ? Im thinking you're more likely to find a solution there.
     
  10. Litejazz53

    Litejazz53 Perfect Sound Through Crystal Clear Digital

    Hi Kevin:

    I would not have touched that with a 40' pole, because I do not have the skills to rebuild the pre-amplifier to it's original build, as I'm sure the majority of audio folks on this site don't have those skills, if they do, hopefully they will chime right in. You either have the electronics background or the purchase was just too much for you to pass up, however, I can assure you, if you don't know and understand circuits and EVERYTHING there is to know about that unit from old diagrams, detailed diagrams showing component values, etc, you have taken on something that is just far beyond reasonable to even attempt. All of these brilliant people who upgrade components like Sony SACD players, say the 5400 or the Oppo 105 Blu-ray players could "possibly" attack this project if you threw several thousand at it, but even they would have to refer back to the original, detailed schematic of the Marantz piece and travel the electrical patch to each point to make sure the correct value component is reinserted in the circuit. You see, you don't know what values this very tech savvy man compromised by changing the entire design of the piece, and the way it is now, it might be a transistor abortion, because the entire design was not intended to be transistors. You have tackled something that is far beyond what most people would even consider.

    If it were me, and I had that piece, I would contact Marantz and going over everything with them and simply ask them if they have some people on the side that have been with the company many years, that might can guide you, heck, you might get very lucky and find someone that knows old circuits like the back of his hand, much like putting together a cross word puzzle, and he would love the opportunity to reassemble that pre-amp. You could call some of these shops that do these upgrades and pick their brains. If however you are brilliant enough to undo what has been done, get those schematics and HAVE AT IT! Good luck with this project and please post how this all turns out. Best suggestion, call the dealer, find the guy who actually did the change over and get him to change it back, Yes! :righton:
     
    Last edited: Jun 14, 2017
    shadowhillway likes this.
  11. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon
    Update, October 2018:

    Well, I knew I was in **way** over my abilites-- and the folks I talked to about taking on the job simply felt they couldn't put the time in to do the restoration work properly, so things looked pretty bleak for this little lady...

    Until I talked with Ryan at Audio Classics-- it seems they have a gentlemen there named George, who a) can accomplish magical things with old tube equipment and b) loves classic Marantz components. Put the two together, and it appears that this little girl will actually get to sing again.

    So, she's on the way to Vestal... and we'll see how she comes back. I've encouraged Ryan to snap a few pics while George is in the process, so hopefully, we'll have some updates as the work progresses...

    I'm very glad to see this happening-- this little lady deserves a better fate than being pieced out for spare parts!

    - Kevin
     
  12. BIGGER Dave

    BIGGER Dave Forum Resident

    I’m not seeing that one small extra hole. If you’re referring to the hole to the right of the line cord and fuse holder, that’s stock and is normally occupied by a Philips head screw.
     
  13. TarnishedEars

    TarnishedEars Forum Resident

    Location:
    The Seattle area
    I used to do some pretty extreme mods back in the 80s when you could get gear like Dynacos for nearly free. But I'm glad to say that I never butchered one of these units! And the last thing that I ever would have done would have been to convert one of these to SS.

    Fortunately I confined most of my butchery to Dynacos, which were great platforms for modding back when they were plentiful and cheap. But doing this kind of thing today makes no sense anymore since such gear is no longer plentiful nor cheap.
     
    Last edited: Oct 20, 2018
    crooner and McLover like this.
  14. crooner

    crooner Tube Marantzed

    Look closer:

    [​IMG]
     
  15. crooner

    crooner Tube Marantzed

    I hope Audio Classics is able to wire this back to stock at a reasonable price. The wiring to the switches is very complex and appears to have been completely stripped by the modder. Wiring up a new tube bed is a piece a cake compared to that...
     
  16. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon
    Yeah, the one small hole thing was a definite stroke of luck... particularly considering how much extra circuitry he'd put inside the chassis.

    Another exceedingly lucky thing? It doesn't really show at first glance, but the holes in the faceplate where the missing Bass and Treble controls used to be were being utilized as plug inputs (phone jacks, I think)... and he didn't have to drill out the holes to enlarge them.

    What a head shaker...!

    - Kevin
     
    Agitater likes this.
  17. crooner

    crooner Tube Marantzed

    Yeah that's very odd to use the front panel bass and treble control openings for phone jacks.
    I wonder what kind mad scientist this was. Perhaps AP Van Meter or Bob Carver himself back in their experimental days?
     
  18. Removing the tube gainstage in a unit and replacing it with transistors was a source of pride in the 60's and 70's. I remember hearing talk about this from my father's fellow musician/studio friends.

    Read about recording Crimson and Clover. That's what the engineer did to the Pultec EQ's; he gutted the tubes and replaced them with SS :yikes:

    Goto the section about Allegro Sound Studios, 2nd paragraph.

    Tommy James & The Shondells ‘Crimson & Clover’ | Classic Tracks
     
  19. BIGGER Dave

    BIGGER Dave Forum Resident

    Ah, yes. You’re correct. I was looking for a hole, not a screwhead.
     
  20. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon
    I **know** that's the punchline to some joke I heard in college... :D

    - Kevin
     
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  21. TarnishedEars

    TarnishedEars Forum Resident

    Location:
    The Seattle area
    Unfortunately I suspect that this unit is going to cost more than it is worth (or than it will be worth) to get it back into something approaching stock condition. It is going to take a LOT of work to restore this unit.
     
    crooner likes this.
  22. allied333

    allied333 Audiophile

    Location:
    nowhere
    What a jerk!
     
  23. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon
    "We do these things not because they are easy, but because they are hard."

    And sometimes, because it's just the right thing to do...

    -Kevin
     
  24. crooner

    crooner Tube Marantzed

    I have always been wanting to build a complete Marantz 7 from scratch. I almost pulled the trigger at one of those reproduction chassis available a few years ago on eBay. But the thought of having to wire up the complex front panel switching somehow put me off. These things are known to become unstable if the wire looms are not sized or oriented properly.

    If I were ever to wire one, I'd have an original on hand just to copy every wire on it.

    Or.... somehow get the assembly manual from the elusive Marantz 7K kit from 1979. It's in Japanese, but the pictorials should be easy enough to follow...

    [​IMG]
     
    Last edited: Oct 22, 2018
  25. Joel Cairo

    Joel Cairo Video Gort / Paiute Warrior Staff Thread Starter

    Location:
    Portland, Oregon
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