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Thread: Compatibility of Fidelity Research headshell & Decca

  1. #1
    Join Date: Feb 2013

    Location: North Yorkshire

    Posts: 129
    I'm Mark.

    Default Compatibility of Fidelity Research headshell & Decca

    Folks,
    Pardon my ignorance and hope you can offer some guidance as to a potential 'period' headshell that I am considering.

    I have an Ortofon AS212 tonearm equipped with a Decca Blue, atop a Thorens TD 124. It is equipped with the bog standard AS212 headshell which is quite light and not an ideal match for the Decca mounting block. Despite this, I have had it in use for several years and feel the time is right for making some improvements in the compatibility of the headshell.
    My problem is one of aesthetics (being an un-repentant design snob !!) - and I feel the replacement headshell needs to be in keeping with the arm and TT.
    The best look would be an Ortofon SPU ..... which may be possible, but in my ignorance I don't know if a Decca can be coupled into a SPU type headshell.

    Hence I'm leaning towards a Fidelity Research - such as the FR S/5 or perhaps FR S/2, which I assume may be easier to combine.

    I guess some people will have tried such combinations (if they are possible) and I hoped to glean advice as to pitfalls or good matches to prevent me making some incompatible/rash choices.
    Much appreciate any comments, so long as they ain't rude !

    Cheers.

  2. #2
    Join Date: Jan 2009

    Location: Essex

    Posts: 31,853
    I'm openingabottleofwine.

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    Hello Mark,

    Whilst I have no direct experience of running a Decca Blue cartridge fitted into a Fidelity Research headshell, I do have a lot of experience using several Decca designs (SC4E, Mk.V (Blue) and Mk.VI (gold)) fitted to SME arms with heavier non-SME headshells, mounted on Thorens 124/II turntables.

    To be able to help you, we have to see how compatible the Decca Blue is with your Ortofon AS212 arm. The range of cartridge masses that can be accommodated and the effective arm mass can be obtained from the published specification for the arm:





    The mass of the Decca Blue is 6.7g, well within the compass of the 5 - 12g range of the arm.

    The effective arm mass is more difficult to ascertain. It will depend to a certain extent on the mass of the cartridge which it counterbalances; a heavy cartridge requires the counterweight to be positioned further away from the pivot, thus increasing the rotational moment of inertia and hence effective mass. If we assume the effective mass is proportional to the mass of the cartridge counterbalanced, we see that 6.7g is about a quarter of the counterbalance range, so the effective mass might be about a quarter of its range, that is 13.5g. Thus the total mass is 21.2g.

    The next problem lies with the Decca cartridge itself. The compliance in the lateral plane is different (higher) than that for the vertical plane. Furthermore both published figures are static compliances, so need to be halved to be appropriate around 10Hz. Thus the vertical compliance is ~ 7.5cu and the lateral compliance is about 50% higer at 11.25cu.

    Based on all these figures, and the assumptions made, the calculated resonant frequencies are 12.6Hz for lateral movement and 10.3Hz for vertical movement. These calculated figures are only a guide, but suggest the Decca Blue will not misbehave in the Ortofon arm.

    You suspect the Ortofon headshell may be too light for the Decca. Deccas do like a rigid headshell, so it might be your suspicion is lack of rigidity, rather than mass, though the two are related.

    My experience of fitting the Decca Blue into heavier headshells has been with an EMT headshell:



    and with the Decca Blue mounted in the GB mounting block and fitted to a rigid headshell I bought from Ebay and whose make I don't know:


    (This shows a Decca Gold fitted but I have used the same setup with the Blue.)

    In all cased with the SME 3009/II arm the Deccas have behaved perfectly.

    Regarding the use of Fidelity Research headshells, in order to chose the most appropriate type you will need to unplug your Ortofon headshell (with the Decca still fitted) and weigh it. Subtract 6.7g to account for the cartridge mass and that will be the weight of the headshell.

    The Fidelity Research headshell options to choose from are:

    FR S/2 10.2g
    FR S/3 20.2g
    FR S/4 14.2g
    FR S/5 18.3g

    You may find some of these for sale on eBay, but they are now rare and won't be cheap. Good Luck.
    Barry

  3. #3
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 99,005
    I'm Grant.

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    great answer barry
    Regards,
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  4. #4
    Join Date: Feb 2013

    Location: North Yorkshire

    Posts: 129
    I'm Mark.

    Default

    Thanks for your reply Barry. As Grant says - Great answer.
    I haven't come across the GB mounting block and that certainly looks more rigid than the block which the Decca is currently fitted into and may be something for me to consider.

    I'll take the headshell off and weigh that, so I can see what I'm dealing with.

    Although I am using the "wedge" shaped Ortofon headshell (as shown in the manual you kindly scanned) I had to remove the straight, semi-circular fingerlift as the fixing of that compromised the Decca mounting block. I utilise a propreitary fingerlift that bolts through & fixes above. Although it works - it does look a dog's breakfast.

    I will also search out a photo of the present arrangement - for you to have a laugh at !

    Regards,

    Mark.

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