Doc modding Marantz imperial 7

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Latteman
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Re: Doc modding Marantz imperial 7

Unread post by Latteman »

Yep- “routering” is an art
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Not much progress here but thinking and chin scratching :think:

I have rescued these 35cm circular discs which were the seats on a couple of breakfast bar stools - long since rusted. The finest fake wood :grin:

Image

I keep getting these fancy ideas which turn out to be really expensive so I am making an effort to try and use stuff I already have round and about. So I will try and use these as the bases of my speakers. They are 5cm wider diameter than the steel spheres so should be ideal.

I was toying with the idea of making the tubular upright from rings cut out of baltic birch ply in a translam construction. However, have you seen the price of baltic birch these days ? In fact have you seen the price of anything lately ? Fook me, as a farmer from Yorkshire I have nearly had a heart attack.

So out goes that idea, I won't be buying any baltic birch. So for the upright I was going to go with a length of 110mm pvc underground drainage pipe which I also happen to have plenty of :grin: Doesn't ring like metal, is strong in cylindrical form and is super light. Will need painting. Can be filled if need be and I might have a cunning idea on that front. The wiring will be passing through this pipe on it's way to the steel sphere.

Latest mock up

Image

I will be having a circle of wood between the two steel hemispheres. Only about19mm in thickness and will have holes cut through it to join the two hemispheres together. It is there to stop the steel hemispheres chattering against each other and when the two halves are clamped in tension against it it should stop any tendency for the steel to ring.

This wooden divider was going to be baltic birch but as I am no longer getting any of that it will be some of the finest chipboard that I have to hand :grin: It's lack of strength doesn't matter in this application.

I was going to make a wooden hoop adaptor for the driver to sit in but that idea has been relegated. It will now be of 3mm steel but carefully welded inside the sphere. All will become clear in due course. I was thinking of epoxy gluing a nut on the back of the driver's magnet which a very long threaded rod would screw into. This would go all the way through the sphere, cylindrical leg and wooden base. When tightened up with a nut under the base this should exert enough clamping force to keep the whole thing together and I won't even need any fasteners to attach the driver.

More soon.....
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Fretless (Fri Jan 07, 2022 9:35 am)
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Toontrev
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Re: Doc modding Marantz imperial 7

Unread post by Toontrev »

So pleased this thread is back up and running, its my internet favorite. Never miss a post!
Keep up the good work Stu.
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karatestu (Fri Jan 07, 2022 6:52 am)

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Re: Doc modding Marantz imperial 7

Unread post by Vinyl-ant »

Cut soil pipe to length, 2 mdf caps with a 12mm hole in the centre, bit of m12 studding through the hole, drop the pipe over the studding so its down the centre, fill with concrete, put top cap on, m12 nuts on either end done up tight to keep it all together, wait to set, remove nuts and end covers, cut soil pipe off, presto, a tower with a thread to bolt a top and bottom onto.

Paint concrete stand tower bright purple
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Re: Doc modding Marantz imperial 7

Unread post by antonio66 »

You're a genius Ant, painting it bright purple will improve the sound quality no end :lol:

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Re: Doc modding Marantz imperial 7

Unread post by Vinyl-ant »

Peter belt said so.
You need to put a picture of the stand in the freezer for it to work properly though
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Latteman (Fri Jan 07, 2022 10:02 am) • karatestu (Fri Jan 07, 2022 10:26 am)
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I guess I can try different uprights but there is a trade off I believe. Heavy versus light. Many people including Savvy prefer light to heavy. I have not done any real comparisons. If I was to go with a solid upright I would probably use the solid 70mm brass bar I have although concrete would probably ring less but won't look as good. If it was solid I can't route the cables up it unless there was a channel through it.

I was leaning towards the 110mm drainage pipe because it is light. But there is the fact that I must keep the centre of gravity low so they don't get knocked over by the ankle biters. I had the idea of putting some brass bar inside the pvc pipe which only contacts the base and not the walls of the pipe.

The 3mm steel sphere whilst being extremely stiff does not weigh as much as you might think. It doesn't weigh anymore than a wooden cube of the same volume especially if said cube is steel lined. A sphere uses the lowest amount of surface area for a given volume compared to any other shape. I am very wary about making these things super heavy and squeezing the life out of the music.
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

Unread post by Latteman »

I think u may need to live with them a while and get a characteristic feeling before finalising the support, room, record storage and equipment meant my speakers sit atop 2 12” record cubes- so a heavy large support- speaker base is directly onto the top cube and each cube is separated by cone spikes- bottom cube on the washing machine anti vibration pads. Seems to work for me. I did try to hide the cables - zip tied to speaker support but just let them find their own way now- not pretty but ok
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karatestu (Fri Jan 07, 2022 11:55 am)
Analogue Source -
Diy Turntable ,- Thorens Td321 donor
Diy tonearm- Well Tempered clone,
Benz Micro Ace L
Hitachi HT-660. Ortofon Vito mc
Nva Phono 1 MC board
Digital Sources- MF M1 Clic, Diy IDE cdp, iPhone 6s.
Amplification 2x Nva A20; A30 mk2; AP10H; Khozmo passive pre
Speakers- Diy full omni bipolar 8”/6.5” & R. Allan CB4; Ls5/3
Dc blocker to Nva mini BMU

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Yeah, suck it and see is the obvious way to go about this. I don't want to spend forever trying different stand materials as this speaker saga has taken long enough already.

I am keen to have a mix of materials in these speakers. In my tiny brain I think this will possibly help to average the sound out so nothing dominates and shouts this is a metal or wood or plastic speaker. As the stands are actually going to be part of the speaker and all compressed together with a long threaded bolt then these can help mix up the type of materials used.

I have steel obviously provided by the two hemispheres. I don't want any more steel in the mix. I have wood (fake chipboard wood :grin: ) for the base and the divider between the two steel hemispheres. That chipboard will be light. I was going to mount the driver in wood but that is going to be hard to accomplish because there is only a 17.5mm wide ring required and I am trying to make the interface between the driver and enclosure as smooth and rounded as possible whist still being strong.

The single cylindrical leg will provide the plastic in the mix but I may have to cleverly add weight inside it - possibly without touching the pipe walls unless I find it needs damping. The tweeter sphere is currently plastic and I am unsure if I will be sticking with that or getting some 15cm steel spheres. I like the idea of it being plastic as it keeps the weight down , is easy to work with and adds a bit more plastic into the mix of materials. The tweeter sphere doesn't have to be especially stiff as it is only handling high frequencies but a steel tweeter sphere may be superior when you look at it in it's role as a diffuser for the mid bass. Maybe the stiffness of steel would be better for that ?
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

If you are in a situation where the speaker enclosure is too big ( can't happen very often) for the driver then how do you deal with this. J expect most would put a load of bracing in and kill two birds with one stone. I have heard of bricks and such things put inside.

I was going to put sand inside which should damp resonance by converting it to heat when the particles move against each other. For some reason I have been thinking about what would happen if I put 20mm gravel inside. There would be substantial voids between pieces and I wonder what that would do to the back sound wave and what frequencies would it affect (if any).
DIY inspired by Richard "The Doc" Dunn RIP

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