some Meltrope questions

[leels1]

Following the comment re attaching the needle bar to the diaphragm, this example when I got it had a piece of flat metal acting as the diaphragm for some reason.

I had an old screw connecting needle bar so cut the old non screw end of the Meltrope needle bar off and soldered the screw fit on.

Not sure if the metal washers add any value acoustically, or if they were there as part of the original way of fixing to the diaphragm, but I added one either side just in case. It MAY help the piston action of the diaphragm providing an element of extra rigidity to the centre or not.

This also has a new made diaphragm and sounds pretty good (I’ve found that all Meltrope IIs sound slightly difference anyway).

[Inigo]

Nice! You could share some videos of it playing...
My last experiment with an Exhibition was to modify again the suspension, using its own springs in a different position, so they press the fulcrum plate against the knife points. I mounted them on the external screws in reverse, using their cups and holes to retain a bearing ball in each side against the fulcrum plate. Adding some rubber washers to the screws, in the EMG fashion, you can regulate the pressure exerted by the balls. It's the same parts, adding the washers and the balls only. This, together with a glass diaphragm, mounted in new soft rubber gaskets, and the back mounted loose, to exert but a soft pressure on the diaphragm edge, made it all the conversion.
Some photos attached.
Sounds well, isn't it? So believed I.
But it performed not at all well. I couldn't avoid the balls to rattle in loud passages, and I didn't find a difference in sound. I get tired and abandoned the idea.
Certainly, I only tested it on the short conical horn of an HMV tabletop old style no 3 (European counterpart of the Victrola VI) and I still must try in on an orthophonic machine... although I doubt it can compete with a Meltrope, or a good HMV no4 or 5a.

[epigramophone]

What a great thing would have been to make new backs for hmv soundboxes, providing them with the Meltrope adjustable system for the collar...

Someone has already had a similar idea and has made this : https://www.ebay.co.uk/itm/334600637506 :

[Inigo]

I've just tested my experimental Exhibition on the HMV 127. With acoustics sounds very good. With electrical records, it has more bass and volume overall, but sounds tubby, not as open as the Meltrope.

[leels1]

Nice! You could share some videos of it playing...
My last experiment with an Exhibition was to modify again the suspension, using its own springs in a different position, so they press the fulcrum plate against the knife points. I mounted them on the external screws in reverse, using their cups and holes to retain a bearing ball in each side against the fulcrum plate. Adding some rubber washers to the screws, in the EMG fashion, you can regulate the pressure exerted by the balls. It's the same parts, adding the washers and the balls only. This, together with a glass diaphragm, mounted in new soft rubber gaskets, and the back mounted loose, to exert but a soft pressure on the diaphragm edge, made it all the conversion.
Some photos attached.
Sounds well, isn't it? So believed I.
But it performed not at all well. I couldn't avoid the balls to rattle in loud passages, and I didn't find a difference in sound. I get tired and abandoned the idea.
Certainly, I only tested it on the short conical horn of an HMV tabletop old style no 3 (European counterpart of the Victrola VI) and I still must try in on an orthophonic machine... although I doubt it can compete with a Meltrope, or a good HMV no4 or 5a.

What a great idea. Though I think the original exhibition springs are very rigid which perhaps doesn’t allow the needle bar to move correctly in this configuration?

Have you eliminated any side to side movement of the needle bar? I had to do the screws up quite tight to stop this.

Also wonder if the diaphragm just can’t cope as it doesn’t have the piston action in the same way as with a ridged aluminium diaphragm.

Lastly, the size of the exhibition doesn’t allow as much diaphragm movement given it’s small. Arguably the size of the Meltrope and HMV 5s (probably the 4 too) allows this greater movement and gives a better sound.

I’ll get some videos posted soon!

[leels1]

What a great thing would have been to make new backs for hmv soundboxes, providing them with the Meltrope adjustable system for the collar...

Someone has already had a similar idea and has made this : https://www.ebay.co.uk/itm/334600637506 :

That’s the one I quoted in the other post. I think a change of the diaphragm to an alu with some small central ridges would have been a good mod to add too.

[anchorman]

I think the issue with side to side movement is why EMG and expert used steel points rather than the knife edge Victor used on the exhibitions. My one day plans to make a soundbox of that style include using small tungsten carbide points set into the body of the reproducer to act as fulcrums for the needle bar. Done right into appropriately shaped indents in the needle bar, it ought to hold correctly with little pressure and not be too inclined to rattle about.

[anchorman]

Also, regarding the needle bar diaphragm fixing screw, I think reducing the weight there is probably helpful for reducing the force needed for the needle to move the diaphragm. whatever washers are involved ought to be as small and light as possible. It seems like the whole needle and diaphragm assembly ought to be as light as possible within reason.

[leels1]

I think the issue with side to side movement is why EMG and expert used steel points rather than the knife edge Victor used on the exhibitions. My one day plans to make a soundbox of that style include using small tungsten carbide points set into the body of the reproducer to act as fulcrums for the needle bar. Done right into appropriately shaped indents in the needle bar, it ought to hold correctly with little pressure and not be too inclined to rattle about.

The EMG soundbox I have is more or less the same as an Exhibition, well, a brass fronted one anyway. I think it’s quite early though. It’s definitely EMG as the backplate has EMG engraved on it but it’s obscured by the diaphragm. I’m starting to think it was a conversion from a mica diaphragm.

It has the knife edges but there is no lateral movement. There are however two grooves where the spring tips sit on the bottom of the needle bar.

It does sound quite good but again the small diameter does I think mean it doesn’t perform as well as it could.

[emgcr]

The common EMG design does not have lateral constraint on the needle holder platform--merely the two knife edges locating in two fine grooves. This is not generally a problem and works very well. However, some did have just one groove and one point to completely eliminate the possibility of sideways movement. Personally, I prefer the two groove design which affords more tuning options.