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set up of 12" Jelco

The old ADC magnesium headshells are the best I've ever come across if a light headshell is what's required. Light at about 7g and very rigid. I wouldn't have said it was much better than the Sumiko 12g headshell which is I think the same as the stock Jelco, but it is 5g lighter. As has been said, which is better (lighter or heavier) is entirely down to which provides the best match when taking the mass of the cartridge, eff. Mass of the arm and cart compliance into account. Rigidity is important though and obviously harder to achieve with a lighter shell without recourse to smart use of design and materials. If you plan to run different carts, it may be best to have several different weight's of headshell in the armoury. ADC headshells come up reasonably regularly on eBay (I'm bidding on one myself right now, so hands off ;) ). Ortofon currently do a headshell which is about as good and about the same weight that has a couple of additional weights to fine tune ... But it's a bit too funky looking for the retro look most of these arms have. No doubt it appeals to DJs :) it is a good alternative though.

The counterweight is part of the effective mass equation yes, but it isn't necessarily the case that a heavier one ups the effective mass. A heavier counterweight, all else being equal will sit closer to the pivot, which has the effect of lowering eff. Mass, so the Lord giveth and the Lord taketh away.

Glad you sorted the issue out anyway. Spindle to pivot isn't something that needs to be set in stone. Alignment can be achieved so long as it's not more out than the headshell slots will allow. Just be aware that you really need to use a two point protactor unless you are 101% sure it's spot on. Arm specific 1 point protractors rely on the absolute accuracy of the spindle to pivot distance, 2 point ones don't.
 
It's brought my attention to two issues.

There are people (not using bouncy decks) who assert that you can increase the effective mass (as a result lowering the arm cartridge resonance frequency) with good results. A more 'planted' sound. OTOH I was once warned by a tonearm manufacturer that doing this with high compliance cartridges might result in a premature failure of the cartridge suspension even if VTF was to spec. Also as Uncle Ants has noted elsewhere some of the Denon compliance specs are somewhat misleading and I gather some cartridge manufactures give compliance figures taken at differing frequencies.

A couple of friends report good results with various wooden headshells. Whether these address resonance issues arising from the SME/bayonet style headshell coupling by introducing a degree of lossiness I don't know. More experimentation needed there.


Its funny how things go around. The likes of SME, Alphason and Rega with their one piece armtubes had seemingly put detachable headshells to bed. Measurements suggest they were probably right. However, there is fun & flexibility in being able to change cartridges so easily and in being able to 'shape' the result a little.
 
pure sound said:
There are people (not using bouncy decks) who assert that you can increase the effective mass (as a result lowering the arm cartridge resonance frequency) with good results. A more 'planted' sound. OTOH I was once warned by a tonearm manufacturer that doing this with high compliance cartridges might result in a premature failure of the cartridge suspension even if VTF was to spec.
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Could be.

I have an OM cart fitted to a 12g Sumiko headshell that I use on a Rega R200 which is quite heavy for playing Mono vinyl (the total effective mass withy the cart is something like 27g) . The D25M mono stylus is low compliance (7cu), tracks heavy (3g), works fine and sounds good - resonance is about 11 to 12 Hz.

However if I fit a high compliance stereo tip like a 5e or a 30 (25cu) to it the resonance goes way down to around 4 or 5 Hz. When you drop the needle to the record or if there is even a slight warp or ripple in the vinyl, the whole thing wobbles visibly and alarmingly. That can't be doing the suspension any favours ... though it doesn't seem to actually mistrack, it doesn't sound all that great either, but that's a matter of taste I guess :)

The 103 behaved better the more mass you added. Working the figures back from a measured resonance using a test record and an arm of known mass suggested the compliance figure is about 10cu rather than the 5cu normally quoted (they measure it at 100Hz - which explains the discrepency) assuming my test record was reasonably accurate.

So it's more compliant than a lot of people assume, but that's pretty stiff all the same - you could go as high as 45g effective mass with the cart before running the resonance below 8Hz and it certainly sounded more solid the more mass you added. I took it as far as 35g all in and it sounded better than at lower masses. I think you would have to have an arm with a mass of well over 75g (which is just silly) to get the resonance as low as that Ortofon and I have a feeling it might just jump out of the groove or gouge lumps out of it rather than play it - I don't think it would be a smart plan.
 
On the subject of 12" Jelco arms, what is the wise opinion on the use of damping oil?

I have just bought another SP10 so my beloved beech plinthed Lenco G99 will be comming to market very soon.
 
Looks nice Alan. Someone posted somewhere else but it escapes me, that for filling in mix some of the sawdust with pva and use that. I've just done a plinth for a friend with cheap ply like you have and that's what I used to fill it. My ply was even cheaper than yours too. I found two sheets of 20mil in the skip at work so they went straight in the back of the van :)
 
Interesting that the carts sit far back with correct pivot to spindle.
I am using a SPU Silver Meister cart / headshell at the mo' so obviously no adjustment that end:), on my homebuild 12" Schick alike or my modded PL-71 arm for 12" wand...
I have found that moving the arm about 1.5 - 2.5mm further than the quoted spindle to pivot distances for the wands gives perfect alignment and sound - well hehe very very good sound anyway.

Now moving the cart far back in the headshell is different to moving the entire arm out. You are shortening the arc whilst I am retaining the arc but moving out the point at which the headshell aligns with the protractor (essentially moving the protractor round a bit more line up perfectly.

Several arm pivot to spindle distances I have seen quoted are 1.5 -2mm nearer than the going best rec for a SPU.

If you can try moving your distance out a bit and listening again.

Do you find the 12" calmer, better detail on bass and cymbals?

How about midrange - I find several 12" loose some emotion = too calm and have played around to find the current best effort. Others I've listened to include the seemingly mighty SMEv12 (nice but light for a SPU Royal N.

Pics of 'long PL-71'


 
That is a sweet looking arm Speedy!

I have been considering a 12" Jelco for a while now, but the whole question of resonance and effective mass has prevented me from doing so. While I have a DL-102 for mono duties that would work well with it, my main cart is a Benz S-Low Wood. It has a compliance of 15 x10-6cm/Dyne and would like an arm lighter than 20g. Is there any way to "lighen" an arms eff mass?
 
gortnipper said:
That is a sweet looking arm Speedy!

I have been considering a 12" Jelco for a while now, but the whole question of resonance and effective mass has prevented me from doing so. While I have a DL-102 for mono duties that would work well with it, my main cart is a Benz S-Low Wood. It has a compliance of 15 x10-6cm/Dyne and would like an arm lighter than 20g. Is there any way to "lighen" an arms eff mass?
Click to expand...

I guess by drilling holes on the underside you could lighten it and change the resonance characteristic.
Could also use a thinner SS tubing (SME used 9.5mm OD, 8.5mm ID, so 1mm thick) Could also use an aluminium or mag alloy tube - the possibilities are endless - problem is is which one will sound right for the cart. Walking the trodden path is the cheapest...
 
Chops54 said:
That arm looks very nice indeed Steve. I particularly like the shape of the arm mounting board :)
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That's a Coco-san production that is - I helped him cut and tap it (mostly use of my workshop and pillar drill as he's a very competent DIY'er or course) - gunmetal alloy. Did not know when doing it, that he would later on sell me the deck:))

If I ever decide what arm is a keeper I will get another piece and have a nice clean look to it.
 
That tube must be very light then. I made a 12" arm using an old Project arm as the base and I used 12mm aluminium tube but it's 1mm wall so a bit heavy. I drilled the underside to take some weight off but I feel it could do to lose a few grams more. I've searched everywhere for 12mm od with .5 mm wall without any joy.
 
I would not say it was very light when compared with the 9" tube it replaced. From the results I am getting it is about right for the SPU.
You can over mass things and the results are not good.
 
gortnipper said:
That is a sweet looking arm Speedy!

I have been considering a 12" Jelco for a while now, but the whole question of resonance and effective mass has prevented me from doing so. While I have a DL-102 for mono duties that would work well with it, my main cart is a Benz S-Low Wood. It has a compliance of 15 x10-6cm/Dyne and would like an arm lighter than 20g. Is there any way to "lighen" an arms eff mass?
Click to expand...

In the specific case of the Jelco the easiest way would be to use a lighter headshell than stock. Using an ADC as mentioned earlier in the thread will immediately drop the mass by 5g without drilling holes in the arm.
 
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