Meltrope III Diaphragm attachment to needle bar

[contessa]

Ah, many thanks. The reason I asked to see both sides is because we have an ongoing and unsolved mystery regarding some of these (later ?) diaphragms which have an extra section with annular rings on the reverse side. If you would like to look at the following thread you can see what I am talking about (scroll down on page 3):

viewtopic.php?f=11&t=33157&hilit=Meltrope&start=20

So, the diaphragm with the added section therefore has four parts---one large and one small with annular rings and one "spider" or "dished washer" on either side. They were pressed and then riveted together. To date, nobody has quite been able to explain why they did this or what the effects might be. Additionally, it is unknown whether or not any form of glue or anti-rattle material was interposed. From investigations to date it would appear that they were just pressed and riveted---job done !

Looking at the photos, yours does not seem to be in this category and should, therefore, only have three parts.

It is too bad that whether adhesives were used or not is unknown.

However, if these still sound nice without any, it shouldn't matter anyway!

[HMV130]

Thank you for providing us with more pictures.

Please consider what Emgcr kindly specified - I also agree that it appears that the diaphragm of your soundbox has three elements rather than four (so no "spider" element is involved).

Being assembled by pressing it is almost impossible to address such damage properly. The good thing is that one of the two rivets is still attached to the stylus bar (I tried once to glue the stylusbar directly to the diaphragm but I noticed a crtitcal lack of rigidity in the center area).

In this case an acceptable result can be obtained by carefully glueing first the rivet to the stylus bar thus stabilising the two pieces. Then it is possible to glue the rivet to the diaphragm.
If you are going to do so I would suggest you place the diagram in the soundbox first and then use as reference the two ball bearings in the bottom section of the body of the soundbox so the stylus bar will be properly aligned.

[HMV130]

[...] To date, nobody has quite been able to explain why they did this or what the effects might be. [...]

I started to believe that this component might have been introduced to increase the surface area through which vibrations are transmitter to the entire diaphragm. The immediate effect could be that the diaphragm itself, being more rigid at its center, is more prone to act like a piston in relation to air-chamber . Of course this is just speculation.

[contessa]

Thank you for providing us with more pictures.

Please consider what Emgcr kindly specified - I also agree that it appears that the diaphragm of your soundbox has three elements rather than four (so no "spider" element is involved).

Being assembled by pressing it is almost impossible to address such damage properly. The good thing is that one of the two rivets is still attached to the stylus bar (I tried once to glue the stylusbar directly to the diaphragm but I noticed a crtitcal lack of rigidity in the center area).

In this case an acceptable result can be obtained by carefully glueing first the rivet to the stylus bar thus stabilising the two pieces. Then it is possible to glue the rivet to the diaphragm. If you are going to do so I would suggest you to place the diagram in the soundbox first and then use as reference the two ball bearings in the bottom section of the body of the soundbox so the stylus bar will be properly aligned.

I assume that what I have been referring to as 'spiders', are actually called 'washers', or 'rivets'?

My plan is to replicate another rivet by cutting down a sheet of alumnium, skewing the rivets, with the diaphragm between them, on the fulcrum. Just as it was originally made. However, of course, the end of the fulcrum would be fixed by epoxy or other adhesives instead of being metal-pressed.

If somebody should attempt a similar repair, the rivet, when measured with my caliper, turns out to be 0.1mm in thickness, 8mm in diamter (please note that my measurements could be imprecise.).

[HMV130]

Thank you for providing us with more pictures.

Please consider what Emgcr kindly specified - I also agree that it appears that the diaphragm of your soundbox has three elements rather than four (so no "spider" element is involved).

Being assembled by pressing it is almost impossible to address such damage properly. The good thing is that one of the two rivets is still attached to the stylus bar (I tried once to glue the stylusbar directly to the diaphragm but I noticed a crtitcal lack of rigidity in the center area).

In this case an acceptable result can be obtained by carefully glueing first the rivet to the stylus bar thus stabilising the two pieces. Then it is possible to glue the rivet to the diaphragm. If you are going to do so I would suggest you to place the diagram in the soundbox first and then use as reference the two ball bearings in the bottom section of the body of the soundbox so the stylus bar will be properly aligned.

I assume that what I have been referring to as 'spiders', are actually called 'washers', or 'rivets'?

My plan is to replicate another rivet by cutting down a sheet of alumnium, skewing the rivets, with the diaphragm between them, on the fulcrum. Just as it was originally made. However, of course, the end of the fulcrum would be fixed by epoxy or other adhesives instead of being metal-pressed.

If somebody should attempt a similar repair, the rivet, when measured with my caliper, turns out to be 0.1mm in thickness, 8mm in diamter (please note that my measurements could be imprecise.).

As specified it appears that there is no spider (fourth element) in your soundbox. With rivet I refer to the piece shown in the picture 20201123_223641.jpg (the piece that it is still attached to the stylus bar).

In any case I look forward to seeing the final result! Good luck

[contessa]

Thank you for providing us with more pictures.

Please consider what Emgcr kindly specified - I also agree that it appears that the diaphragm of your soundbox has three elements rather than four (so no "spider" element is involved).

Being assembled by pressing it is almost impossible to address such damage properly. The good thing is that one of the two rivets is still attached to the stylus bar (I tried once to glue the stylusbar directly to the diaphragm but I noticed a crtitcal lack of rigidity in the center area).

In this case an acceptable result can be obtained by carefully glueing first the rivet to the stylus bar thus stabilising the two pieces. Then it is possible to glue the rivet to the diaphragm. If you are going to do so I would suggest you to place the diagram in the soundbox first and then use as reference the two ball bearings in the bottom section of the body of the soundbox so the stylus bar will be properly aligned.

I assume that what I have been referring to as 'spiders', are actually called 'washers', or 'rivets'?

My plan is to replicate another rivet by cutting down a sheet of alumnium, skewing the rivets, with the diaphragm between them, on the fulcrum. Just as it was originally made. However, of course, the end of the fulcrum would be fixed by epoxy or other adhesives instead of being metal-pressed.

If somebody should attempt a similar repair, the rivet, when measured with my caliper, turns out to be 0.1mm in thickness, 8mm in diamter (please note that my measurements could be imprecise.).

As specified it appears that there is no spider (fourth element) in your soundbox. With rivet I refer to the piece shown in the picture 20201123_223641.jpg (the piece that it is still attached to the stylus bar).

In any case I look forward to seeing the final result! Good luck

Yes, that was what I had intended to say.

Have a good day

[emgcr]

[...] To date, nobody has quite been able to explain why they did this or what the effects might be. [...]

I started to believe that this component might have been introduced to increase the surface area through which vibrations are transmitter to the entire diaphragm. The immediate effect could be that the diaphragm itself, being more rigid at its center, is more prone to act like a piston in relation to air-chamber . Of course this is just speculation.

Yes, it is hard to know isn't it ? In general, my experience is that highly flexible diaphragms result in better all-round reproduction. It would seem that, by adding a further component, greater stiffness would result. Might this not produce in a smaller diaphragm movement and a lesser piston effect ? However, the Meltrope engineers seem to disagree or they would not have gone to so much trouble ? By the time they introduced this modification they had been producing soundboxes for some years so must have had a great body of evidence and experience to draw on. What a shame their empirical findings no longer exist---as far as we know !

[chunnybh]

I started to believe that this component might have been introduced to increase the surface area through which vibrations are transmitter to the entire diaphragm. The immediate effect could be that the diaphragm itself, being more rigid at its center, is more prone to act like a piston in relation to air-chamber . Of course this is just speculation.

I agree with you.

Regarding the Meltrope III, if the diaphragm is still attached to the stylus bar, leave it alone. If it's still attached but spins on the bar, glue it either with shellac or even superglue so it does not spin.
Once the diaphragm is removed from the stylus bar, in my opinion it's a dud. I have never managed to successfully put that back together again.

I believe that secure pressed rivet method of the Meltrope is just one of the design features that gives it it's brilliant sound. It was probably done to save on cost.
I’ve often heard “I found a good Meltrope, it’s a keeper”. I have bought several Meltrope III’s and found the diaphragm damaged. It’s difficult to see with the cover plate hiding the diaphragm. Looking inside at the back of the rivet will usually indicate if the diaphragm is damaged. If it’s not perfect, it’s damaged.

The Meltrope III was often found on portables. It was relatively cheap and could fit on most tonearms. But one drop on a record or even a skid would ruin the diaphragm. Compare that to an HMV 5 soundbox with its pivoting stylus bar with no lateral movement allowed. You really need a lid drop to damage it. That could very well be the reason for the cup washers on the Meltrope and also the extra rings added to later Meltropes. Strengthen the center of the diaphragm reducing the chance of damage.

I was well impressed with the article by Peter Heath “The Mechanics of Soundboxes”. His conclusion that the compliance of the diaphragm is the major factor in the purity of reproduction had me thinking that the major drawback of EMG and Expert soundboxes is the diaphragm. That tiny screw used to fix the diaphragm to the stylus bar just seems inadequate to move the whole diaphragm. A spider or even cupped washers would be something to experiment with.

[Henry]

I was well impressed with the article by Peter Heath “The Mechanics of Soundboxes”. His conclusion that the compliance of the diaphragm is the major factor in the purity of reproduction had me thinking that the major drawback of EMG and Expert soundboxes is the diaphragm. That tiny screw used to fix the diaphragm to the stylus bar just seems inadequate to move the whole diaphragm. A spider or even cupped washers would be something to experiment with.

My experience with the Exhibition sbx confirms this statement; i.e., when I rebuilt it, I inadvertently melted a larger ring of beeswax around the diaphragm screw than I intended. The result was a big improvement compared to the previous small melt. The increase surface area and mass of the larger blob of beeswax evidently transmits more efficiently the vibrations of the stylus and stylus bar. By analogy, a spider on an aluminum diaphragm performs the same function as the beeswax on the mica diaphragm. That's my best guess, anyway.

(Of course, beeswax also functions to seal the hole where the tiny screw passes through the diaphragm.)

[chunnybh]

My experience with the Exhibition sbx confirms this statement; i.e., when I rebuilt it, I inadvertently melted a larger ring of beeswax around the diaphragm screw than I intended. The result was a big improvement compared to the previous small melt. The increase surface area and mass of the larger blob of beeswax evidently transmits more efficiently the vibrations of the stylus and stylus bar. By analogy, a spider on an aluminum diaphragm performs the same function as the beeswax on the mica diaphragm. That's my best guess, anyway.

That totally makes sense to me. Instead of soft bees wax I have been using Chinese red wax for letter seals. It dries to a brittle finish and the reproduction is much improved. You need to heat up the stylus bar with the soldering iron before applying the red wax, otherwise the brittle wax falls off after a few months.