Diaphragm protection insurance.

[emgcr]

One of the big problems with ancient acoustic gramophones where automatic mechanical stops are not present has to do with the variable nature of “run-out” grooves---or sometimes lack thereof at the end of the recordings---particularly on older discs. How many precious soundbox diaphragms have been destroyed when the needle fails to stop at the end of the grooves and either collides with the motor spindle or disappears off the left-hand edge of the turntable ? An occupational hazard perhaps and one which forces us all to be physically present, alert and ready for action when the music/speech finishes.

I had such a disaster recently (driver error, inserting the needle to insufficient depth in an attempt to reduce volume !) which has prompted me into a project I have been meaning to carry out for many years but never quite got around to. In this case we are talking EMG where the tonearm parking position is on the “wrong” side of the turntable which reduces the options as to how to construct an easily operated and effective stop. One possibility used by friends is to sit a movable weight on the deck-board and, although this is very effective, the weight has to be moved or removed before the tonearm can be parked on its cradle. I have always imagined a simple spring-loaded post sunk into the deck-board capable of being depressed out of the tonearm’s way or of rising up as an effective barrier. The problem has been how to construct the mechanism to achieve this goal easily.

I recently came across a brilliant potential solution in the form of a bathroom “pop-up” plug now being manufactured in their millions. They are cheap---perhaps five dollars or less. It is the main brass core of the design which is relevant to this ambition and the stainless steel basket and actual plug top can be unscrewed and discarded. The remaining “click-clack” mechanism is very clever, employing four channels in a vee configuration which have ever decreasing floor heights which are tracked by a round-nosed stainless steel pin held in position with a small “key ring”. The central spring-loaded plunger can be depressed by the finger or thumb and the new lower position held until another press allows the original height to be regained. To retain this core, it is necessary to make a lower flanged holder (aluminium in this case) into which the mechanism can be screwed (M16 X 1.5) which, in turn, is wood-screwed to the underside of the deck-board. The top of the plunger is threaded (M8 X 1.25) and can be used to attach a nickel-plated extension rod passing through a similarly-plated brass top-hat guide screwed to the top of the deck-board---see photos.

The final debate is exactly where to place the stop. There seem to be two options. The first would be to arrest the tonearm’s motion somewhere within the run-out grooves but such would necessarily mean forcing the needle to jump track at the end of every record putting unwanted strain on the needle and diaphragm. Additionally, label diameters and therefore run-out groove positions, vary so catering for all eventualities is almost impossible. The second option is to arrest progress somewhere within the label area even though the comparatively rough surface of the paper produces more friction and unwanted resistance than the shellac surface---but only for the occasion when failure has already occurred rather than for every record. Once again, the fact of varying label diameters points to the desirability of choosing a position well within the circumference of the smallest label size---often HMV. The photo shows a suitable position still well removed from the danger of the motor spindle or crossing to the other side of the disc.

I can well understand many owners perhaps not wanting to drill a hole in original wood but, in this case, the deck-board is a replacement. The system works well.

[Orchorsol]

A superb solution Graham, ingenious and beautifully executed!

I too live in fear of a soundbox pile-up. I've had one catastrophic one, and I don't want another!

Just in case any of our TMF brethren can't see much of a problem here - this is a much greater risk of us EMG and Expert enthusiasts due to the highly developed tonearm geometry resulting in a necessarily large overhang, plus the diaphragms were also highly developed and are irreplaceable (or at least, there are no replacements that perform anything like as well). Although most of us set our EMGs up with dynamic levelling to ensure minimal force in either direction (skate or anti-skate in modern hi-fi turntable terms), by the time one gets into the runout areas the inward force is increasing rapidly. As we discover to our soundboxes' peril, some records have improperly formed locked grooves (either not fully joined up, or shallow).

For years now I've used a large weight (with felt feet) on the motorboard, but as you say, I can't park the tonearm on its rest without removing the weight, and I habitually don't - but this leaves a slight risk of damaging the tonearm when closing the lid.

As an alternative, I recently bought a cheap secondhand pack of those appalling drinks coasters made from cut-down 78s to place on top of the record being played - but the force of the needle hitting the edge and/or riding against it in the event of a runaway could be a problem and needs more thought...

Huge thanks for sharing this Graham. My only concern with it is the obvious one of drilling into an original motorboard, but on the other hand, the beautiful construction and the thought that EMG/Expert themselves would undoubtedly have provided such a solution themselves (had it not been so easy and routine back in the day to replace a diaphragm and rebuild and tune a soundbox) almost gets me there... Are you going to go into production?

[epigramophone]

A simple and elegant solution. I would expect no less from Graham.

I have always assumed that EMG and Expert never fitted any form of autobrake as such mechanisms can impose drag on the tonearm. The amount of drag may be very small, but EMG and Expert tonearms move so freely on their bearings that any drag would be noticeable.

As the owner of an electrically motored Expert, I have often wondered whether the turntable could be automatically stopped electrically without drag, but since my electrical knowledge does not extend much beyond wiring a 13 amp plug I leave this possibility for others to explore.

As for records throwing soundboxes about, among the worst offenders are some WW1 era German pressings which have very short and abrupt run out grooves.

[Curt A]

Nice solution... thinking outside of the box. Compared to a damaged diaphragm or reproducer, a hole in the motor board seems worthwhile, especially since the whole assembly looks like it could be original...

..."among the worst offenders are some WW1 era German pressings which have very short and abrupt run out grooves."
Another example of German espionage at work...

[phonosandradios]

I recently bought a cheap secondhand pack of those appalling drinks coasters made from cut-down 78s

Oh no! I always wondered who bought those At least you didn't buy them "new".

[emgcr]

As the owner of an electrically motored Expert, I have often wondered whether the turntable could be automatically stopped electrically without drag, but since my electrical knowledge does not extend much beyond wiring a 13 amp plug I leave this possibility for others to explore.

If you happen to be using Garrard or wish to replace with such, here is an orginal solution which could work for you with very little drag (depending upon where the lever is set), in this case driven by a Type ED motor via belt, but the electrically-operated auto-stop mechanism is a generic "bolt-on" addition for all their steel deck-plates and can be fitted where appropriate for the tonearm arc. One might have to replace the vertical operating post with something longer to engage with the Expert tonearm depending upon specific geometry. The top of the operating arm in this photo is two inches from the steel deck-plate which itself has a height of about a quarter of an inch.

[physicist]

As the owner of an electrically motored Expert, I have often wondered whether the turntable could be automatically stopped electrically without drag, but since my electrical knowledge does not extend much beyond wiring a 13 amp plug I leave this possibility for others to explore.

As another owner of an electrically motored Expert (the image on the left is a bit of a giveaway), this has set me thinking....

It would be easy (and relatively non-invasive ) to set up an optical detector and a light beam where the tone arm breaks (or, with a tiny mirror, makes) the light path when you want the motor to stop.

Access to the tone arm rest could then be unrestricted and there would be no drag on the tone arm.

If the detector switches off the mains power with a relay, the motor would run down over a few seconds.
If active braking is desired, a more complex arragement would be necessary to apply a DC voltage to the motor coils for a short time to actively slow the motor.

[emgcr]

My only concern with it is the obvious one of drilling into an original motorboard, but on the other hand, the beautiful construction and the thought that EMG/Expert would undoubtedly have provided such a solution themselves (had it not been so easy and routine back in the day to replace a diaphragm and rebuild and tune a soundbox) almost gets me there... Are you going to go into production?

Ah ! I was waiting for that one ! The problem is that although the "click-clack" mechanism is very cheap, making the rest is not. For instance, just the polishing and nickel plating amounted to £40 plus the cost and time of delivering to and collecting from the platers. It took me two days to think about, design and make the bits from scrap steel and brass and I had the already nickel-plated screws in stock from other EMG work. Of course, now having a finished product to copy would greatly reduce the timescale and therefore cost so I shall have to think further. I suppose if there were to be considerable orders the project might be worthwhile---not that I am trying to make money---quite the opposite in fact but there are so many other projects demanding time and resources !

One final thought is that every order would have to be accompanied by a measurement specific to the gramophone to which it is to be attached---distance between underside of tonearm to top of deck-board. Every item would have to be bespoke as clearances are tight due to the short operating compass (8.5mm---0.335"). Also, it would probably be a necessary idea to buy a few hundred brass mechanisms as spares to allow for possible future failures when mass production may have ended. The units are well-built but everything wears out eventually.

[CarlosV]

I utilize a simpler but effective solution: a label protector from an old record cleaning machine. The record cleaner is long gone, but the protector got a new application. It is very light, made of hollow plastic with a rubber bottom, and acts as a stop against jettisoned tonearms. See the photo below:

[Orchorsol]

My only concern with it is the obvious one of drilling into an original motorboard, but on the other hand, the beautiful construction and the thought that EMG/Expert would undoubtedly have provided such a solution themselves (had it not been so easy and routine back in the day to replace a diaphragm and rebuild and tune a soundbox) almost gets me there... Are you going to go into production?

Ah ! I was waiting for that one ! The problem is that although the "click-clack" mechanism is very cheap, making the rest is not. For instance, just the polishing and nickel plating amounted to £40 plus the cost and time of delivering to and collecting from the platers. It took me two days to think about, design and make the bits from scrap steel and brass and I had the already nickel-plated screws in stock from other EMG work. Of course, now having a finished product to copy would greatly reduce the timescale and therefore cost so I shall have to think further. I suppose if there were to be considerable orders the project might be worthwhile---not that I am trying to make money---quite the opposite in fact but there are so many other projects demanding time and resources !

One final thought is that every order would have to be accompanied by a measurement specific to the gramophone to which it is to be attached---distance between underside of tonearm to top of deck-board. Every item would have to be bespoke as clearances are tight due to the short operating compass (8.5mm---0.335"). Also, it would probably be a necessary idea to buy a few hundred brass mechanisms as spares to allow for possible future failures when mass production may have ended. The units are well-built but everything wears out eventually.

Thoughts both salutary and sobering, many thanks Graham!