WANTED: Replacement HMV 5A / 5B backs

[Inigo]

Yet I've had only three of these soundboxes, all mazak backplates, and except for a broken connector neck (easily repairable) I've had not problems with them. One of them I polished a bit, for it seemed to get jammed onto the front ring, that had to be cut and then resoldered to make it fit again. But since then it works marvelously... See this video... Don't trust your neck! It loaded sidewise and I cannot rotate it straight!
https://youtu.be/dWRWC8RaDOA
Others in my channel are also recorded with these soundboxes... They perform very well!

[soundgen]

Brass back taken

[Elias Dee]

https://www.windupgram.co.uk/replacemen ... und-boxes/

"The shortcoming with these replacement backs is the absence of the place to fit the rubber ring. When connected directly to the arm, the compliance provided by the rubber ring is lost, creating a high load on the record groove (and increased wear), as well as eliminating the acoustic damping provided by the rubber ring. I have experienced the beneficial effects of the rubber ring everytime I replaced a hardened one with a new ring. The acoustic effect is clearly noticeable, as well as the reduction in record wear."

I disagree entirely with this comment. I have two HMV 5a sound boxes, one with a replacement backplate and one with the original backplate. They sound identical. The rubber ring (with a brass ring inside it) was to ensure a tight fit and it makes no difference at all to the sound. There is no mechanical reason that it would. With regards to the weight the original back plate is much heavier and creates much more wear and drag. The replacement aluminium one is very light and as a result produces far less wear and drag (the turntable revolves for longer ) I am very glad I bought one of these back plates. Unfortunately they are now sold out and no more will be made due to the high cost of making them.

[JerryVan]

https://www.windupgram.co.uk/replacemen ... und-boxes/

"The shortcoming with these replacement backs is the absence of the place to fit the rubber ring. When connected directly to the arm, the compliance provided by the rubber ring is lost, creating a high load on the record groove (and increased wear), as well as eliminating the acoustic damping provided by the rubber ring. I have experienced the beneficial effects of the rubber ring everytime I replaced a hardened one with a new ring. The acoustic effect is clearly noticeable, as well as the reduction in record wear."

I disagree entirely with this comment. I have two HMV 5a sound boxes, one with a replacement backplate and one with the original backplate. They sound identical. The rubber ring (with a brass ring inside it) was to ensure a tight fit and it makes no difference at all to the sound. There is no mechanical reason that it would. With regards to the weight the original back plate is much heavier and creates much more wear and drag. The replacement aluminium one is very light and as a result produces far less wear and drag (the turntable revolves for longer ) I am very glad I bought one of these back plates. Unfortunately they are now sold out and no more will be made due to the high cost of making them.

Believe it or not, there are a lot of extremely knowledgeable people here, with decades of experience, that really do know what they're talking about. You however, are new to the forum, (welcome), so for now, I'm going to take their advice on the question of the rubber isolators.

[gramophone-georg]

It is not about sound. It's about record wear. Without the softening/ damping action of a pliable isolator, the needles wear the records excessively. Here's a test- with a fresh steel needle play a clean record. After it plays, rub the needle tip with your finger or a white cloth and see if there is black residue.

[Inigo]

And not only that... The whole orthophonic sound system design was conceived as a complex network of masses and mechanical impedances whose sizes and compliances were selected to comply with compromised requirements, all it driven to obtain the best power transfer from three record groove to the air vibration, in the chosen frequency range. The suppression of such an important compliance as the rubber neck which couples the soundbox mass to the tonearm mass maybe can not be noticed by a standard ear, but no doubt it impacts on the designed transmission of power, impairing it.
The needle vibration ascends by the needlebar to the spider, but the bar is supported on the soundbox, and at the support pivots there is an equivalent reaction force exerted on the entire soundbox body. The vibration communicated to the entire soundbox at the needlebar support point has an enormous back reaction in the soundbox entire mass, which is coupled through the compliance of the rubber neck to the tonearm mass. Also at the diaphragm edge, supported on the soundbox body, there is another reaction force. These forces tend to vibrate the entire soundbox and tonearm. No doubt that the masses of tonearm and soundbox being so large, make them act as a sort of 'force sump' for that part of the circuit, but the compliance of the rubber neck is needed to isolate both masses one from the other, to control the reaction as desired by the designers, especially when one considers the enormous differences of this reaction at the lower and higher frequencies.
To modify the compliance and mass of that part is like changing the chokea and condensers on the earth line of a radio circuit. It still can sound well, but undoubtedly the original design is changed and something is lost. To do it intentionally, with perfect knowledge of the original and the altered values of these components, under an engineered design, on order to obtain a desired effect, can be done in pursue of improvement or changes of these frequency response, etc etc.
But I don't believe that the design of that new aluminium backplate, with an important reduction of compliance and mass, was something performed by Percy Wilson, Davey, or any of the usual experts... It seems to be just a casualty and an ignorant oversimplification of the design. It's like going back to the trial-and-error gramophone design of the past, spoiling the design of the WE men that invented such a marvel. They took the old experimental design and improved it by these delicate changes of impedances and masses, and they got an enormous well-engineered response. The drastic replacement of these parts by such different ones is the destruction of these engineering efforts.

In the other hand, that is just what I'm trying to do with my experiments with the exhibition soundboxes... I have no doubt why I don't obtain a satisfactory sound! although in truth it isn't the same case, for there is not such an engineered background in this case, but a refined and carefully developed trial and error process, and no more than experimental work.

[Steve]

It's about BOTH the sound reproduction quality AND record wear. Both aspects would be heavily compromised by these aluminium backs irrespective of the lighter weight of the modern back.

Carlos is absolutely correct to identify the huge improvement in sound quality when a soft compressible, but tightly sealing isolator is fitted to the back-plate.

The fact that an important detail like this was omitted by the originator of the modern manufactured backs does not really surprise me as many items he has sold have been quite obviously incorrect or poorly "restored" with replacement ill-fitting parts.

[Elias Dee]

"Believe it or not, there are a lot of extremely knowledgeable people here, with decades of experience, that really do know what they're talking about. You however, are new to the forum, (welcome), so for now, I'm going to take their advice on the question of the rubber isolators. "

Believe it or not you have no idea who I am or what I know. Whilst I understand the theories on here it falls into the realms of expensive Hi Fi cables i.e. unproven audiophile anxiety. I don't believe given the huge weight of an HMV 5a, the factors of mass and friction, the very inflexible rubber and the tiny movements of the needle that it makes any difference to either the wear on the record or the sound quality and neither do I believe back in the day that they had the scientific equipment to even test such a theory. Until I see any kind of detailed scientific analysis of this subject involving microscopes and detailed audio and mechanical measurements I'll stick to my theory that it makes zero difference. True audiophiles by the way would never play a 78 with a steel needle and would use a microscope to match the stylus to the original cutting lathe ! (I know because I was involved in 78 digital restoration)

[Steve]

"Believe it or not, there are a lot of extremely knowledgeable people here, with decades of experience, that really do know what they're talking about. You however, are new to the forum, (welcome), so for now, I'm going to take their advice on the question of the rubber isolators. "

Believe it or not you have no idea who I am or what I know. Whilst I understand the theories on here it falls into the realms of expensive Hi Fi cables i.e. unproven audiophile anxiety. I don't believe given the huge weight of an HMV 5a, the factors of mass and friction, the very inflexible rubber and the tiny movements of the needle that it makes any difference to either the wear on the record or the sound quality and neither do I believe back in the day that they had the scientific equipment to even test such a theory. Until I see any kind of detailed scientific analysis of this subject involving microscopes and detailed audio and mechanical measurements I'll stick to my theory that it makes zero difference. True audiophiles by the way would never play a 78 with a steel needle and would use a microscope to match the stylus to the original cutting lathe ! (I know because I was involved in 78 digital restoration)

Believe it not, you don't actually need a digital recorder, microscope or any level of anxiety to hear the difference. Admittedly, you ideally need two ears, both working well.

I have noticed the clearly superior sound available when I've swapped out the rock hard rubber isolators from the backs of Paillard No. 8's or "Concert" types - often found on high quality Decca machines. With a soft pliable isolator, well-fitted to ensure no air leaks, the sound improves in clarity, volume and bass. Coincidence? I'm doubting it.

[Elias Dee]

Ah the old "golden ears" argument used on many audiophile forums. I can hear no difference between a 5a with the new plate vs one with the old so we'll have to agree to disagree.