some Meltrope questions

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Inigo
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Re: some Meltrope questions

Post by Inigo »

In my experimental Exhibition, the rattle came clearly from too loose balls. I pressed the screws and springs a bit more and the rattle disappeared. Yet this must be fine tuned, for excessive pressure dampens the treble too much. The other irritant factor is the tubbyness of the sound, not noticeable with acoustic recordings, but most conspicuous when playing electricals. For these, I find to sound better the unmodified Exhibition, but using soft needles of the Recoton or Laubscher type (those with thick shank but a much finer point). Fibres make electricals sound good too.
In all, I believe that I went too far in relaxing the pressure on the diaphragm, for this also increases the thickness of the air chamber behind the diaphragm. I find this to be the main cause of the tubby sound. It must also be better tuned.
And yet I have to try a metal diaphragm, in the EMG fashion... Yet to be done.
EDITED the underlined passages.
Last edited by Inigo on Mon Oct 31, 2022 2:31 pm, edited 1 time in total.
Inigo

anchorman
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Re: some Meltrope questions

Post by anchorman »

Interesting, and thanks for the pictures! I have definitely not seen the full range of what EMG had on offer! Some of the mass produced items I’ve seen are simply marginal in the implementation of what otherwise might be a sound design. Some things don’t lend themselves to sloppy manufacturing and loose tolerances!

leels1
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Re: some Meltrope questions

Post by leels1 »

Inigo wrote: Mon Oct 31, 2022 8:54 am In my experimental Exhibition, the rattle came clearly from too loose balls. I pressed the screws and springs a bit more and the rattle disappeared. Yet this must be fine tuned, for excessive pressure dampens the treble too much. The other irritant factor is the tubbyness of the sound, not noticeable with acoustic recordings, but most conspicuous when playing electricals. For these, I find to sound better the unmodified Exhibition, but using soft needles of the Recoton or Laubscher type (those with thick shank but a much finer point). Fibres make electricals sound good too.
In all, I believe that I went too far in relaxing the pressure on the diaphragm, for this also increases the thickness of the air chamber behind the diaphragm. I find this to be the main cause of the tubby sound. It must also be better tuned.
And yet I have to try a metal diaphragm, in the EMG fashion... Yet to be done.
EDITED the underlined passages.
Have you tried fabricating an aluminium one?

I too have found that tubby sound, it’s not too bad, but I think maybe it’s the gaskets I’ve used- too thick maybe and too much pressure when the back is on?

More experimenting needed.

leels1
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Re: some Meltrope questions

Post by leels1 »

anchorman wrote: Mon Oct 31, 2022 1:03 pm Interesting, and thanks for the pictures! I have definitely not seen the full range of what EMG had on offer! Some of the mass produced items I’ve seen are simply marginal in the implementation of what otherwise might be a sound design. Some things don’t lend themselves to sloppy manufacturing and loose tolerances!
There’s some surprising soundboxes out there that perform well but seem less well known. “The Lenthall” for example is great.

anchorman
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Re: some Meltrope questions

Post by anchorman »

Steve wrote: Sat Feb 19, 2022 8:48 am
epigramophone wrote: Sat Feb 19, 2022 6:22 am Great care must be taken when removing the original HMV rubber isolator. The backs of late No.4 and all No.5a/5b soundboxes are pot metal and easily broken, so much so that UK dealer John Sleep www.windupgram.co.uk has had replica backs manufactured in modern light alloy.
But these are not identical to the originals and in my opinion miss the whole point of the original design entirely with their mistakenly manufactured solid collar backs which do not have any space inside for the rubber isolators at all, meaning there is a full mechanical fix and continuous contact between the tonearm and soundbox. A complete failure to understand the purpose of isolating the motor vibrations from the soundbox and unwanted resonances from colouring the sound waves emitting from the diaphragm.
The motor doesn’t do much to make noise even on a rigidly mounted soundbox. Ive got to study the “formulas” again and learn a bit more of how those equivalent circuits work to describe what’s happening as various parts of a soundbox are changed. Ahmed made some videos he sent to me showing one of his EMG or expert soundboxes with the ordinary rubber mount that is available and a softer one that he made, and it was astounding how much difference it made to have a more elastic connection between the tone arm and the soundbox. but you need a horn that can reproduce the bass notes for it to matter much. I don’t think you’d ever tell the difference on the majority of machines (portables) that normally have a number 4 or 5 soundbox. I’ve 3D printed backs that had a solid connection to the tone arm, and they worked surprisingly well. I imagine John Sleep’s aluminium backs for the number 4 perform fine for most people’s use on HMV 101’s.

anchorman
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Re: some Meltrope questions

Post by anchorman »

Since this is a thread about meltropes, I thought I’d ask if anyone has tips for replacing the rubber gaskets in a meltrope II?

I just got one, and that needs doing, along with needing new rubber isolator. Maybe I need to look at it again in the morning with fresh eyes, but it’s not obvious to me how it comes apart.

anchorman
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Re: some Meltrope questions

Post by anchorman »

IainW wrote: Fri Oct 28, 2022 4:35 am Another question for Meltrope type soundbox fittings can anyone confirm if the thread form for the back collar on Meltrope / EMG / Expert etc soundboxes are BSB 26TPI or something else? The answer probably lies in the forum somewhere but I have not managed to find it.
Iain
I can confirm that the threads are 60 degree on both meltrope II and III. I don't have the means at the moment to measure the minor diameter of them except by measuring inside the nut, though could probably find a way using digital photography, and normalizing the outer diameter to some enlarged measurement, and do the maths to get what the minor diameter is. I took close up pictures of the threads as close to perpendicular as I could, then enlarged the picture and overlayed both a 60° and 55° profile in a drawing program. Closest thing to a proper shadowgraph that I can manage at the moment...

The larger meltrope threads are 1.25" o.d. x 24 tpi, the i.d of the nut is 1.204"

the smaller threads on the meltrope II are 1.060" o.d. x 32 tpi the i.d. of the nut is 1.03"

best way to reproduce the soundbox threads in the home shop is to cut to size to and test with an existing nut (if making the soundbox) or soundbox (if making a nut).

anchorman
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Re: some Meltrope questions

Post by anchorman »

The diaphragm on the Meltrope II is 0.005" thick, 1.9" in diameter. Since I have this one i just got apart now, I will be making a die set to reproduce the diaphragm at some point.

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