Being reminded once again of the Decca ‘magic’ – the Decca Mk. VI cartridge revisited.
Having been granted a special exeat from the Alan Dowker Blumlein retirement home for distinguished audio components, the Decca cartridge was allowed out for good behaviour. I was interested in re-visiting the Decca design and the following notes and observations apply to my sample of a Decca Mk. VI (also known as the Decca ‘Gold’).
However, before I go into the details of installation, operation and audition of the cartridge, it is perhaps useful to describe the background and thinking of the engineers at Decca who designed the Decca cartridges, since these are unlike any other fixed coil dynamic cartridge. And because of that, are unique in the way they are installed and operated.
This report is very lengthy. I would advise readers go and make themselves a pot of coffee, to keep awake!
Background and history
In some respects the Decca cartridges are just like other fixed coil dynamic designs: a varying magnetic flux caused by the motion of the stylus is intercepted by a set of coils which convert the change of flux to an electrical voltage. Deccas could thus be described as variable reluctance (moving iron) cartridges. What makes Deccas unique is the virtual absence of a cantilever. Engineers at Decca’s research department were of the opinion that the modulation of the record groove read by the stylus needs to be converted into an electrical signal as soon as possible, otherwise owing to the less than infinitely rigid cantilever, information would be lost. Decca’s engineers called this undesirable loss ‘cantilever haze’. The operation of the Decca cartridge is best understood with reference to the following diagram:
(Diagram taken from Decca publicity material)
The iron cantilever passes through a toroidal magnet and coil, to detect the lateral motion and above that are two coaxial magnet and coil assemblies, to detect vertical motion. Clearly the cantilever has a greater stiffness in the longitudinal mode (as used in this situation) than it has in flexural mode (as used by all other cartridges using a conventional cantilever). Decca called this arrangement ‘positive scanning’. The three coils (two vertical and one lateral) are connected as a sum and difference ‘Y’ configuration – necessitating only three connections. The mechanical arrangement meant that the cartridge was not only sensitive to the lateral ‘side-to-side’ motion of the grove modulation, but also to any ‘fore – aft’ motion as well. This latter motion would be caused by the motion of the record underneath the stylus and would cause the stylus to collapse. To prevent this, a tie back cord is fitted, as shown.
Decca marketed these cartridges as the Decca ffss pickup (ffss stood for full frequency stereophonic sound). It was also referred to as a ‘head’, since Decca, like EMI and Ferranti, were of the opinion that the cartridge and arm should be designed as a single entity. This meant that the early pickups could only be fitted to Decca’s own arms. By the time of the Mk. IV edition however, Decca did offer versions that could either be fitted to Decca arms or to arms with the usual ½” screw fixings.
The Decca ffss cartridges were very well received, not only in the UK but in the US as well; with most users commenting on the excellent ‘attack’, dynamics, transparency and on the sense of ‘air’ surrounding the performers.
Despite the performance potential, the Decca design did create problems that were addressed and somewhat ameliorated in the Mk. V and later designs. Owing to the close proximity of both the lateral sensing coil and magnet, problems could be caused with the use of steel platter turntables. At worse, the magnetic attraction to the steel platters in use at that time upset the vertical tracking force. Again the close proximity of the lateral coil meant that stray hum fields from the turntable motor, or elsewhere, would be picked up, and these would be indistinguishable from the modulated field created by the stylus. To reduce these problems Decca improved the magnetic circuit (thereby reducing the susceptibility to hum pick up) and employed a new, more powerful, magnetic material (which allowed a reduction in the overall mass of the design). These improvements culminated in the Mk. V design, marketed as the Decca ‘London’ cartridge.
As part of the weight relieving process and to exclude stray hum fields, the Mk. V generator was enclosed in a thin, resonant, metal housing. This, in itself, can cause problems, as does the retention of the three-connector system. The general level of workmanship of these cartridges was poor to say the least; so poor that hand-selected samples were reserved for export. The housing of the Mk. Vs for the home market were coloured blue (and hence are also known as the Decca ‘Blue’), whereas those selected for export were coloured grey (hence the ‘Grey’, or ‘Export’). Later versions followed: a carefully built, so-called ‘improved’ model, the ‘Maroon’ (also known as the Decca ‘Plum’), retaining the 15μm spherical tipped stylus and the Decca Mk. VI fitted with a 15μm x 7.5μm elliptical stylus. This latter cartridge (variously known as the Decca London Elliptical or, on account of the colour, simply known as the Decca ‘Gold’) is the version under discussion here. (I have seen reference to a Decca ‘Black’, but know nothing about it. If any readers know of this, I would be very interested to learn more.)
Finally, one other aspect dictated by the unique design of Decca cartridges is the fact that they do not have user-replaceable styli – like moving coil cartridges, they have to be returned to the manufacture for stylus renewal. Decca countered criticism of this by pointing out that any user-replaceable stylus cannot be located with sufficient precision without the necessary tools that only the manufacturer would possess. A useful benefit was that whilst re-tipping, Decca would check all the internal parts and guarantee a performance as good as a new cartridge.
Installation and set-up
As can be appreciated from the above description of the operating principles of the Decca cartridge, they are not easy to install. First of all, in having two different generator mechanisms for horizontal (lateral) and vertical groove modulation, all Decca cartridges have separate and different compliance figures for these stylus motions. This in turn means that all pivoted pick up arms will, when used with a Decca cartridge, display two separate LF resonance frequencies. Furthermore, the compliance figures are pitifully low: 7.5cu vertical, 15cu lateral for the Gold. These are most likely static compliances so the dynamic values at 10Hz will be about half these values.
Both the Mk V and VI cartridges are designed to be used either with Decca arms or in arms that use ½” spaced screw fixings. When used with an early Decca arm the cartridge simply slides over the end of the arm, with the three spring contacts of the cartridge connecting with three contact pips at the end of the arm. When used in an SME arm or similar, Decca supply a plastic mounting bracket that slides into the end of the cartridge connecting the cartridge contacts to three pins, as well as providing the correct geometry for fitting into a headshell. The fit between this bracket and the cartridge itself is none too rigid, and in the days where rigidity was deemed paramount, this arrangement came in for much criticism. To provide an alternative mounting arrangement and to do something about the suspected resonant behaviour of the thin metal housing, GB, manufacturer of the highly regarded Zeta arm, produced a clamp or mounting block in which the Decca cartridge could be fitted. (Apparently the Decca cartridge was used extensively during the development of the Zeta arm.) I used such a mounting block. The photo below shows the cartridge in the GB mounting block fitted into a Jelco EIA bayonet fitting headshell.
The cartridge, mounting block and headshell weigh 22.2g – towards the upper limit of counterbalance of the SME arm, as this photo shows.
I applied the suggested tracking force of 1.5g as recommended by Decca. I see no advantage in going for lower playing weights. Using too low a tracking force causes more record damage, than is caused by using too much.
Having balanced the arm in both planes and applied the correct playing weight, the cartridge azimuth has to be checked. I use a mirror to do this – obsessive users will need to use a double beam oscilloscope and a mono LP. Both the Jelco headshell and the SME arm have provision for azimuth adjustment. I used that on the SME arm rather than that on the headshell for the sake of expediency.
I found a bias setting of 0.75g was sufficient – half that of the playing weight.
Vertical tracking angle is a parameter that can obsess some people even to the extent of adjusting for each and every record! I’m happy to go along with the advice of the arm manufacturer (both Decca and SME) and arrange matters so that the arm is exactly parallel with the surface of the record. VTA is not the easiest of things to set up on the older SME arms; the newer ones are much better in that regard. Under these conditions the azimuth adjustment on the Jelco headshell is well clear of the record surface, whereas the underside of the cartridge is only about 1mm clear; your records will need to be flat, only the mildest of warp can be tolerated without the cartridge grounding.
We now come to the most difficult, exasperating and time consuming part of the set up – that of adjusting for minimum tracking error. The Jelco headshell is slotted so as to adjust for the correct stylus to arm pivot distance, commensurate with minimum deviation from true parallel tracking. I used the two-point alignment protractor provided by SME. And this is where the fun started. I found that when I tightened the second nut, the whole cartridge/GB block would slew or yaw slightly. This happened every time, no matter how careful I was. In the end I got around the problem by fitting two hard plastic washers under the nuts. To give you an idea of how time consuming all this was: I can tell you that it took about ten minutes to fit the cartridge and GB block into the headshell; and over an hour to set the arm up!
Now having such a low compliance means that a lot of energy is extracted from the grooves, only a small fraction of which is converted into the electrical signal, the rest is ducted into the arm either to be absorbed in the arm, or near the pivot. As will become clear the cartridge arm resonant frequencies are on the high side, so I used an SME 3009/II arm fitted with the FD200 silicone fluid damping dashpot. With the possible exception of linear tracking arms, Deccas benefit from some form of damping at or near the arm pivot. In the case of unipivot designs this is usually the case. I used the lightest damping, provided by using the black coloured paddle. Calculated LF resonance frequencies are 10.7Hz lateral, 15.2Hz vertical: on the high side suggesting that perhaps an additional mass of 12g might be beneficial.
As mentioned earlier the Deccas use a three-wire system, so what do you do with the fourth lead in the headshell? Depending on the amplifier, one can both ignore, and not fit the fourth wire (either the blue or green coloured return) or these two returns can be strapped together in the headshell. This is what I did, as can (just) be seen in the photo below. Doing such may actually create a hum loop – strictly speaking it did in my case, as the Quad 33 uses DIN connectors, with common signal returns. However in my system the hum was drastically reduced to near inaudible levels: and then only heard when a record was not being played and the volume turned up to maximum. Systems vary, so a certain amount of experimentation is required.
Decca recommend a load impedance of 50kΩ. This is more or less the standard 47kΩ of most MM phono stages. I used a Quad 33 preamp, which offers an impedance of 68kΩ. It has been claimed by some that Deccas prefer looking into lower load impedances; indeed on a friend’s system, I found that 33kΩ seemed better. However in my system I found there was no audible change in varying the load impedance over the range 22kΩ to 68kΩ. I therefore left the load impedance at 68kΩ.
It is also claimed that the Decca is immune to additional capacitance. Most MM cartridges benefit from some additional capacitance to resonate with the coil inductance and reduce the HF rise. Usually this extra capacitance is 200-500pF. I did indeed found that adding capacitance around this value made no difference to the treble. To remove the treble ‘sting’ however, I found that it was necessary to add an enormous amount of capacitance: up to 10nF (= 10,000pF). The coil inductance of the Decca is 560mH, no different to most MM cartridges. Yes I know, I’ve done the sums and it doesn’t make any sense – but without it I found the Decca tiring to listen to. Deccas of this period displayed enormous sample-to-sample variation, especially in regard to the treble peak around 8kHz. My preference for a large amount of capacitive loading could well only apply to my sample.
So that is the installation and set up of the Decca Gold. You may feel that I have belaboured the installation but the Decca is unique and demands careful set. Owing to the very short cantilever, tracking error, azimuth and VTA are all critical and if not set up properly will severely compromise both the performance and tracking ability.
Well after the protracted and detailed description of the installation, you are all no doubt champing at the bit to know what it sounds like; assuming that you haven’t fallen asleep reading this. The short answer is “absolutely marvellous”. All that Decca magic is there: jaw-dropping attack; transparency; detail and a sense of ‘presence’ that is uncanny. If I had to sum up the Decca in one word it would be: ‘exciting’.
Now I have experienced all this before. However, then, the ‘edge of your seat’ excitement was tempered by the feeling that the Decca was just on the verge of misbehaving and the whole system would fall over. The constant clash of excitement and apprehension was just too much and ultimately was a fatiguing experience – I couldn’t put up with it for too long.
This time, possibly through taking greater care in set up and in trying to optimise the operating conditions, I experienced none of these difficulties. Unlike some other cartridges, that are very good on resolution, attack and detail, the Decca doesn’t draw attention to itself –“Hey listen to me”, rather it’s more of a case of “Hey listen to this”. It has been stated elsewhere that if you think your system sounds good when heard from an adjoining room, then it is good. Several times when I was in the kitchen with the joining door open, I would think “This sound good, what am I doing here? I’m going through to listen to it properly”.
Quite simply I’ve never had so much fun playing records; in fact CDs have barely had a look in. I just wanted to hear what my records sounded like with the Decca – leading to many sessions lasting through to the early hours of the morning.
The percussive attack on instruments such as the piano or snare drum, cymbals and other percussive instruments just has to be heard to be believed. I will cite one example the Curzon version of Grieg’s Piano Concerto (Decca SXL 2173). This is an excellent recording and always sounds good. Playing it with the Decca just gave me goose bumps and on reaching the finale, I was emotionally exhausted!
This is probably a good place to dismiss some of the myths surrounding the Decca. It has been claimed that the Decca sound best only when playing Decca recordings. Not so, I played recordings by most of the major companies: Philips, DGG, CBS, EMI, Verve, Blue Note, Atlantic, Mercury, as well as quite a few minor labels. They were all able to display the Decca ‘magic’.
Second, using a Decca will wear out or damage your records. Sadly, this myth continues to be promulgated by the publisher of a popular audio magazine. If any record wear did occur, the cartridge must have been poorly set up, and maybe tracked with insufficient tracking force.
It is also claimed by some that the Deccas are unreliable, leading to the sarcastic saying that if you like using Deccas you should own three: one in use, one being repaired and the third in the post! I don’t know anyone who uses a Decca who has experienced this.
So is the Decca the “best thing since sliced bread”? No, of course not – the Decca displays some noticeable shortcomings. The most obvious is a compression of depth, most likely due to poor crosstalk at high frequencies, although the width of the soundstage is acceptably wide. Bass, whilst not being bloated, is not particularly taut or firm. There are some practical aspects to bear in mind: the Decca is totally unforgiving of poor or worn recordings. Your records must flat; even if the warp will clear the base of the cartridge, warp wow is quite disturbing and sounds unpleasant. Furthermore, the very small clearance between the cartridge and the record means that records must be clean and any fluff cleared from the stylus after playing each side.
Despite all this, the performance of the Decca over the wonderfully flat mid-range along with the astounding attack, detail, dynamics and display of presence mitigates its shortcomings.
Will I be listening to nothing else from now on? Again no, I do like my EMT, Ortofon and Denon cartridges, and whilst they do not have the sheer presence of the Decca, or have such amazing speed and fast attack, they are more authoritative. I suspect they are also tonally more accurate. However such is the enjoyment brought about by a well set up Decca cartridge, that I am tempted to have one in permanent use attached to a second turntable
If all this has whetted your appetite to try a Decca – I’ve saved the best news for last. Following the sale of Decca to Sony/Polydor, Racal, owners of Decca closed down the Special Products Division where the Deccas were made. The rights to manufacture of the Decca cartridge were sold to Peter Wright and Brian Smith of Presence Audio and are now marketed under the ‘London’ name. These new Deccas, whilst being considerably more expensive, are now housed in a non-resonant machined aluminium block, enjoy a much greater standard of workmanship, display far less sample-to-sample variation and employ the standard 4-wire connection.
Decca Mk.VI cartridge (aka. Decca ‘Gold) fitted into a GB mounting block/clamp and mounted in a Jelco EIA bayonet fitting headshell.
Arm: SME3009/II with FD200 silicone fluid damping dashpot fitted. Black coloured damping paddle used.
Turntable: Thorens TD124/II in self-designed rigid open frame plinth.
Standard SME phono terminated leads connecting to a self-made resistance and capacitance loading switch box. Self-made low-noise microphone cables connect between the switch box and the preamplifier.
Preamplifier: Quad 33 (unmodified)
Power amplifier: Quad 405 (heavily modified)
Speakers: Quad 57 electrostatics.
Review product source….. reviewers own item.
London (Decca) distributor http://www.presenceaudio.com/
© Text and photos Copyright 2010 Barry Hunt
NB No part or portion of this article may be reproduced or quoted without written permission.