Dec 032013
 

This may only be of a niche interest to a tiny minority of readers. However there is some interest in using these professional cartridges in domestic audio systems where the tonearm uses the widespread and conventional SME/EIA bayonet fixing [1].

Introduction

First of all it has to be understood that EMT cartridges were specifically designed to be used in a professional environment, especially that of broadcast studios. A prime consideration (apart from sound quality) was one of consistency and uniformity. EMT developed their own pick-up arm: first the curved 12″ arm, the 997 (known as “the Banana”), then later the cranked 9″ arm, the 929. Whilst these are made to a high standard, there is nothing about them that later arms such as the SME, Ortofon, Fidelity Research or Jelco, couldn’t match. Rather it was the fitting of the arm to the deck that was important, simplifying the installation of the cartridge: once fitted, with the cartridge/headshell mass balanced out and the recommended tracking force and bias set up, the VTA and overhang were automatically correct for the cartridge. Such was the unit-to-unit consistency of the EMT cartridges that in the unlikely event of a cartridge failure, a replacement could be fitted in seconds without having to re-adjust VTA, overhang, azimuth or bias – an important requirement in the broadcast environment, where ‘down time’ is to be avoided.

To achieve these ends EMT ended up with a cartridge/headshell design unlike most of its contemporaries. Not only was the headshell quite short (i.e. the distance between the stylus and bayonet fitting connector flange), the contact arrangement was unique and could only be mated with EMT’s own arms, that were also designed so as to provide correct overhang: there being no adjustment for overhang within the headshell. The contact arrangement was similar to the now standard SME/EIA arrangement of four spring-loaded plungers that mate with four corresponding contact ‘pips’ on the connector stub, save for one very important difference: the disposition of the contacts was rotated through 45° compared to current use. That is, the contacts have a ‘diamond’ rather than the usual ‘square’ arrangement. This is often referred to as the ‘Neumann’ configuration, since Neumann supplied EMT with their DST61 and DST62 cartridges after Ortofon ceased supply. It has been said that EMT deliberately retained this contact scheme so as to prevent, in the words of EMT, “sublimation” of the cartridge from the original deck and arm to the pickup arm of an enthusiastic employee!


Left: EMT TSD cartridge. Right: Photo showing the unique contact arrangement EMT used for their cartridges.
Photo: eBay

There is one other minor difference between the coupling arrangements of EMT cartridges and those of other headshells: the alignment spigot points downwards, rather than upwards. This is largely unimportant, as most, if not all arms with a bayonet fitting have two diametrically opposed alignment slots.

Comparison of the contact arrangement used by EMT (left) with that used by SME/EIA (right)
Photo: BDH

So to the actual use of EMT TSD cartridges in non-EMT arms:

There are three ways in which one can use an EMT cartridge design on a different arm. These are:

1 Use the EMT XSD design. This uses a modified design of headshell having an extended length bayonet stub (hence the ‘X’ in the designation), solving two problems at once: when fitted to say an SME arm, the overhang is close to optimum and the contact arrangements are as standard. Even the alignment spigot follows the usual convention of pointing upward. Clearly this is the best and most obvious path to follow, however the original EMT company is no longer in business and such modified cartridges are now hard to find. EMT cartridges are still available from the ressurected EMT company [6], however the XSD version is no longer made.

2 Strip the generator out of the EMT headshell and fit it to one of your choice. Recommended for those who have doubts about the resonant properties of EMT’s headshell and who also have the necessary skill, dexterity and patience to perform such a piece of surgery. The naked moving-coil generator is particularly vulnerable to damage, especially the very fine lead out wires from the coils. Such an operation is not for the faint-hearted!

If one is suitably adventurous enough, the generator could be installed in a ‘headshell-less’ or fixed headshell arm design such as the Breuer, Hadcock, Infinity ‘Black Widow’ or Graham designs. However the compliance of the EMT design is a moderate 12 cu, so lightweight arms are not necessarily desirable.

3 Use an adapter with a conventional EMT TSD design. This method requires further explanation.

Mechanical

The adapter is made by Ortofon and is designated APJ-1. Ortofon make this adapter, not for use with EMT cartridges but for use with their own C-type cartridges. These cartridges, made by Ortofon in the days before they introduced the longer ‘whale’- shaped headshell familiar to SPU users, use a short headshell designed to mate with the Ortofon RMA 229 and RF229 arms (supplied to EMT and fitted to the 927 and 930 turntables, before EMT came up with their own designs in 1951). The Ortofon C-type cartridges are now back in production again and Ortofon have made an adaptor so as to allow their use with conventional current pick-up arms. What this adaptor does is to extend the length of the bayonet stub by 21.5mm, so that the stylus to bayonet flange distance is the same as that of the SPU series. The adaptor thus consists of a short stub with a four-pole female bayonet connector at one end (to mate with the cartridge) and a four-pole male bayonet connector at the other (to mate with that of the arm).

The contact arrangements on the new Ortofon C-type cartridges follows the modern convention, however if the adapter is opened up by loosening a socket-headed grub screw, a second grub screw is revealed that allows the contacts at the female end of the adaptor to be rotated 45° with respect to the keyway, as appropriate for EMT designs. It is absolutely vital that the female contacts are rotated 45° clockwise as viewed from the front of the adapter, otherwise the two cartridge outputs (L and R) not only will be transposed but the left-hand channel will be out of phase with the right-hand channel.

  

Left: Ortofon APJ-1 adapter. Centre: Adapter opened up to show inner grub screw, allowing contacts to be rotated relative to the keyway. Right: Contacts rotated 45° clockwise as viewed from the front.
Photos :BDH

Now this might appear to solve matters completely, but it’s not quite so straightforward as that. First of all, the Ortofon adapter increases the length of the headshell stub by 21.5mm, whereas the EMT XSD headshell stub is 19.0mm longer than that of the EMT TSD. This 2.5mm difference in length implies a similar increase in arm effective length and overhang [2].

Top: EMT TSD cartridge with Ortofon AJP-1 adapter, overall stub length 21.5mm. Bottom: EMT XSD cartridge, overall stub length 19.0mm.
Photo: BDH

In many arms the adjustment for overhang is made in the headshell. This cannot be done for the EMT/adapter arrangement. One is obliged to use an arm that employs a slotted keyway-style arm base, such as an SME. Even then this change might lie outside the compass of adjustment (± 12.7mm) if the arm base is not positioned optimally relative to the turntable centre. For example, if the turntable used is the Thorens 124, it might be necessary to change the arm board for one where the SME arm base slot is cut on a near radius, further away from the centre, and even then the arm base will have to be positioned as far back as possible, achieving correct overhang but preventing the shielding can to be fitted. Fortunately no hum problems are likely to occur.

The EMT TSD/Ortofon adapter combination weighs 24.2g, compared with 21.0g for the EMT XSD. When mounted in SME arms the arm cartridge resonant frequencies are 8.3Hz for the 3009/II arm, 8.7Hz for the 3009 Improved (this combination needs the 1902/HWR counterweight) and 8.1Hz when used in the 3012 pick-up arm. These figures become 8.8Hz, 9.3Hz and 8.5Hz respectively for the EMT XSD [3]. All of these figures are slightly on the low side, however there shouldn’t be any problems experienced with turntable isolation and feedback. If the damping dashpot is fitted to the SME arm, these resonant requencies will be raised by about 1.5Hz, placing them closer to the recommended 10Hz as well as reducing the Q-factor at resonance.

Given the small increase in effective length (230.92mm) and slight decrease in offset angle (21.76º) [2], it is clear that the arm/cartridge combination cannot be set up so as to minimise the tracking error angle, and hence distortion, at both the Stevenson null-points [4]. The best option is to use the new values of effective length and offset angle to determine new null-points, fixing one of them at the inner null-point of 60.325mm, allowing the use of the alignment protractor supplied by SME. If this is done the overhang is calculated to be 15mm, requiring the arm base to be moved back by 2.94mm. The two null-points are at 60.325 and 110.95mm. The maximum second harmonic distortion will occur at a radius of 78mm (0.63%) and at the outer groove radius of 146.05mm (0.95%). Again the re-adjustment of arm base by 2.94mm ought to lie within the compass of the SME sliding bedplate, provided the arm base slot has been cut according to the mounting template provided by SME.

The second consideration when using the Ortofon adapter concerns the precise electrical connection of the cartridge coils to the arm leads.

Electrical

As has been mentioned the contact arrangement on the EMT cartridges differ from convention. The contacts are arranged in a diamond shape: the two vertical contacts connect to the left-hand channel, with the lower contact connecting to the screen, and the two horizontal contacts connect to the right-hand channel, with the right hand contact (when looking into the bayonet socket) connected to the corresponding screen. On conventional headshells, when looking into the bayonet socket, the two contacts on the left connect to the left-hand channel and those on the right to the right-hand channel. In both, the lower contacts connect to the screen of the arm lead out cables.

Now when the Ortofon adapter is fitted, with the female bayonet connector rotated by 45°, the two return connections (i.e. the screens) are transposed. What this means is that the return path for the left-hand channel is provided by the screen of the cable corresponding to the right-hand channel and vice versa. Under most situations this will not cause any problems as the screens of the two cables are connected together at the pre-amp or SUT. If however, the arm is wired in a balanced configuration, no end of problems will arise since the two coils are now effectively connected in series and in phase, giving a monophonic signal only!

It has been mentioned that the female contacts must be rotated by 45° in a clockwise direction as seen from the front of the female socket. If the contacts are rotated in an anti-clockwise sense, the two channels will not only be interchanged they will also be out of phase with one another (the right-hand channel will be polarity inverted). And if the signal leads are connected to balanced inputs, the two channel outputs outputs will effectively cancel.

As commented above, the transposition of the return conductors ought not to cause any problems, but to be absolutely assured of this then one can rewire the arm base. Again in most cases the arm in use is likely to be one of the SME Series I or II arms, since these have both a bayonet coupling as well as a sliding bedplate to adjust stylus overhang. In this case the SME arm is likely to be fitted with a 4-way Belling&Lee ‘Unitor’ socket for the signal connections. An adaptor can be made using a pair (one male and one female) of these connectors wired so as to correct the transposed return signal connections. An example of such an adapter is shown below. It is fitted between the current arm socket and the signal lead plug. The SME shielding can will just about cover the adaptor.

  

Left: Adaptor used to transpose the return signal conductors. Centre: Adaptor fitted between SME arm base and signal-lead connector. Right: SME arm base screening can fitted.
Photos: BDH

Summary

The best option is to use an EMT XSD-15, having the extended headshell stub. These are no longer in production, though used samples occasionally appear on internet auction sites.

Failing that, the next best option is to remove the generator from the EMT headshell and re-mount the generator in a headshell of your choice. This requires a fair amount of skill, dexterity and patience if the generator is not to be damaged: the coil lead-out wires are very fine and particularly vulnerable.

The third option is to use a modified Ortofon AJP-1 adapter as described. This is not a perfect solution; it allows mechanical and electrical connection, but the geometry is not optimum and the effect of the transposition of the return signal paths needs to be carefully considered. To be absolutely sure, the wiring of the arm base would need to be changed, or if an early version of an SME arm is used, a suitable adapter made up. Furthermore the AJP-1 adapters are not exactly cheap to obtain.

It might reasonably be asked if it is worthwhile to go to all the trouble of the third option, given the compromises made and less-than-optimum configuration. This is a question that only a listener can answer, however the incentive is that EMT TSD-15 cartridges are still available [6] for a reasonable price and are considered by many to be “up there with the best”. The small errors in cartridge/arm geometry will not be audible. And the EMT cartridge has a very healthy output (0.75mV at 5cm/sec), so making little demand on either SUTs or headamps.

Notes

[1] The current standard bayonet and contact arrangement was invented by Ortofon and was first adopted by SME. Owing to the widespread popularity of the SME design, the bayonet fitting is now generally known as the SME or SME/EIA bayonet. SME have always denied any claim to its design, correctly pointing out that credit for the design is due to Ortofon.

[2] Since the overhang cannot be achieved at the headshell, an arm having an adjustable sliding bedplate must be used. This limits the choice of arms to those made by SME: the 3009/S2; the 3009/S2 (improved) and the 3012, as well as the newer 3009R; 3010R; 3012R and the latest M2-12R.

In the case of the 3009, which has an effective length of 228.6mm and offset angle of 22° [3], the increase of 2.5mm in the headshell stub length translates to an increase in the effective length to 230.92mm (that is, an increase of 2.32mm) and a very small decrease in offset angle to 21.77°.

The geometry of SME 3009 was designed to follow Stevenson’s prescription for minimising tracking error [4]. For this the overhang is calculated to be 16mm. (SME appear to have miscalculated both the value of overhang (SME value 15.6mm), as well as the offset angle (which should be 22.82°)) With an effective arm length of 230.92mm, the correct overhang according to Stevenson is 15.82mm [4]. To accommodate the increase in overhang of 0.22mm, as well as the increased effective length, the mounting distance (arm pivot to turntable spigot) needs to be increased to 215.12mm. Compared with the SME arm mounting distance of 213mm, this means the arm needs to be moved back 2.12mm. This ought to lie easily within the adjustment range of the SME sliding bedplate (± 12.7mm), provided the arm base slot has been cut according to the mounting template provided by SME. If the arm is set up this way, the two null points will be at 69.02mm and at 102.25mm. The maximum second harmonic distortion will occur at 60.325mm (0.66%) and at 146.05mm (1.07%), that is at the start and finish of a typical 12″ LP [5].

A better option is to fix the inner null-point at 60.325mm, and recalculate [4] the overhang, given an effective length of 230.92mm and offset angle of 21.76º. The overhang is calculated to be 15mm, placing the second outer null-point at 110.95mm. With this overhang value, the arm base needs to be moved back (away from the turntable spindle ) by 2.94mm. The maximum second harmonic distortion occurs at a radius of 78mm (0.63%) and at the outer groove radius of 146.05mm (0.95%) [5].

Similar calculations can be performed for the 3009/S2 (improved) and for the 3012 arms, as well as for the ‘Revised’ (suffix ‘R’) models.

If the SME model M2 –12R is used, the bedplate adjustment range is reduced to ± 12.0mm.

[3] http://www.vinylengine.com/tonearm_database.php

[4] http://theartofsound.net/forum/showt…earm-alignment

[5] Second harmonic distortion as a function of disc radius, given the arm/cartridge geometry may be calculated using the following spreadsheet: http://www7a.biglobe.ne.jp/~yosh/armtrack.xls

[6] New samples of TSD style cartridges are available from:

 

 

 

Barry Hunt 

 

© Text Copyright and all photos 2013 Barry Hunt, except where noted and the Copyright there belongs with the named party. 

NB No part or portion of this article may be reproduced or quoted without written permission, failure to do so may result in legal proceedings.

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