replacing tonearm with different effective length tonearm

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cytovette
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replacing tonearm with different effective length tonearm

Post by cytovette » 21 Aug 2019 14:43

I was thinking of eventually putting a Jelco tonearm on my Technics 1200. I was wondering how closely the new tonearm effective length should match the original tonearm.

The effective length for the stock Technics tonearm is 230mm. Can you go longer? If so how much longer before problems develop?

Thanks,

David

nat
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Re: replacing tonearm with different effective length tonearm

Post by nat » 21 Aug 2019 23:41

What do you mean by problems? Conceivably you could put any length arm on some sort of outrigger bolted on the back. Would looking terrible, upsetting the suspension, requiring the removal of the dustcover, and not necessarily sounding any better be problems?
I realize that this sounds sarcastic, but I don't mean it to be simply ranking on you. If the arm is giving you trouble (which can happen if the headshell contacts get pitted, or the wiring goes bad, or the bearings are damaged) then replacing it might make sense since the replacement arms from Technics either are no longer available or have jumped greatly in price.
But it you are just looking for better sound, you might stop and consider if a theoretically better arm jimmied into a table made for a specific arm is likely to actually sound meaningfully better. How will you fit the arm to the plinth? Will it be rigid enough to allow the arm to sound better than the Technics arm? The existing arm isn't the best arm in the world, but it is quite good, and allows VTF adjustment easily, which is a big plus for how an arm sounds. And it is designed for the whole system, in a table that was in production long enough for multiple improvements. So it is possible that a better arm will sound worse than the original arm in a table designed to work with it.

Woodbrains
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Re: replacing tonearm with different effective length tonearm

Post by Woodbrains » 22 Aug 2019 00:00

Hello,

It is there spindle to pivot that is important. If you have to keep the S2P distance the same as the Technics, then the effective length of the tonearm should be the same as the Technics, also. If you can alter the S2P distance, by using an alternative arm mounting board, then you can potentially use a tonearm that has a different effective length.

If your Technics arm is in good condition, perhaps fitting a KAB fluid damper might be a more significant modification.

Mike.

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Re: replacing tonearm with different effective length tonearm

Post by Hugo » 22 Aug 2019 06:55

Woodbrains wrote:
22 Aug 2019 00:00
Hello,

It is there spindle to pivot that is important. If you have to keep the S2P distance the same as the Technics, then the effective length of the tonearm should be the same as the Technics, also. If you can alter the S2P distance, by using an alternative arm mounting board, then you can potentially use a tonearm that has a different effective length.

If your Technics arm is in good condition, perhaps fitting a KAB fluid damper might be a more significant modification.

Mike.
Headshell offset also comes into the equation, so it's not just a matter of effective length. If the replacement arm can be mounted at the maker's stated spindle-pivot distance, then all will be well.

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Re: replacing tonearm with different effective length tonearm

Post by Solist » 22 Aug 2019 09:42

As everyone already pointed out, it is the STP distance the main thing to get right. You could in theory be slightly off with the STP and then compensate by adjusting the cartridge in the headshell slots, but I would really avoid doing that. There is no point going beyond 11 inches. And even that is a stretch. The longer then tonearm, the harder it is to keep it from resonating. 9 inches is a common size, everyone seems to be happy with it.

For that money, I would rather look for a nice cartridge, than putting another tonearm on the 1200. Or just buy another turntable.

cytovette
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Re: replacing tonearm with different effective length tonearm

Post by cytovette » 22 Aug 2019 13:18

Woodbrains wrote:
22 Aug 2019 00:00
Hello,

It is there spindle to pivot that is important. If you have to keep the S2P distance the same as the Technics, then the effective length of the tonearm should be the same as the Technics, also. If you can alter the S2P distance, by using an alternative arm mounting board, then you can potentially use a tonearm that has a different effective length.

If your Technics arm is in good condition, perhaps fitting a KAB fluid damper might be a more significant modification.

Mike.
That is what I was thinking. If I use an arm with 237mm EL I will need an armboard that lets me back up the pivot 7mm.

I not so much looking for better sound as looking ahead. My Technics 1200 was a dj deck at one time and I have had problems with the bearings, I was able to adjust them to fix the problem but figure I will eventually need a new arm. The Technics arms are pricey now so I will just go with a different type.

I have already modified the heck out of this deck, replaced the arm tube with carbon fiber, external power supply, rca jacks, fluid damper, sorbothane feet.

I worked as an electronics tech in the 70s, still am a CET I guess, and enjoy working on my gear just as much as listening to it. So I will use any excuse to diy something.

I even thought about building a tonearm with this
https://rover.ebay.com/rover/0/0/0?mpre ... 1378499741

Thanks for the replies:-)

Woodbrains
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Re: replacing tonearm with different effective length tonearm

Post by Woodbrains » 22 Aug 2019 14:34

cytovette wrote:
22 Aug 2019 13:18
Woodbrains wrote:
22 Aug 2019 00:00
Hello,

It is there spindle to pivot that is important. If you have to keep the S2P distance the same as the Technics, then the effective length of the tonearm should be the same as the Technics, also. If you can alter the S2P distance, by using an alternative arm mounting board, then you can potentially use a tonearm that has a different effective length.

If your Technics arm is in good condition, perhaps fitting a KAB fluid damper might be a more significant modification.

Mike.
That is what I was thinking. If I use an arm with 237mm EL I will need an armboard that lets me back up the pivot 7mm.

I not so much looking for better sound as looking ahead. My Technics 1200 was a dj deck at one time and I have had problems with the bearings, I was able to adjust them to fix the problem but figure I will eventually need a new arm. The Technics arms are pricey now so I will just go with a different type.

I have already modified the heck out of this deck, replaced the arm tube with carbon fiber, external power supply, rca jacks, fluid damper, sorbothane feet.

I worked as an electronics tech in the 70s, still am a CET I guess, and enjoy working on my gear just as much as listening to it. So I will use any excuse to diy something.

I even thought about building a tonearm with this
https://rover.ebay.com/rover/0/0/0?mpre ... 1378499741

Thanks for the replies:-)
Hello,

Like I said, don't worry about the EL of the Jelco. (Or whatever arm you are looking at) Find out what its pivot to spindle distance is, fit the arm into the technics table, with an armboard if necessary, at that dimension and it will be correct for that tonearms EL.

For example, a Rega P2D distance is 222mm. If you set the arm at that, it will work exactly how it is intended. IIRC, a Rega effective length is 238mm.

If you try to fit an arm based on its EL you will run into problems. If the Jelco's EL is 7mm longer than the Technics, moving it 7mm further away (from what exactly?) will not put it back to where the Technics (stylus) was. As another poster said, the arm offset comes into play too. If you just concentrate on S2P distance, all will be fine.

Mike.

cytovette
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Re: replacing tonearm with different effective length tonearm

Post by cytovette » 22 Aug 2019 14:52

I was referencing the EL because that and the overhang are usally what is specked. If that is the case I will subtract the overhang from the EL to get the P2S.

Woodbrains
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Re: replacing tonearm with different effective length tonearm

Post by Woodbrains » 22 Aug 2019 15:08

cytovette wrote:
22 Aug 2019 14:52
I was referencing the EL because that and the overhang are usally what is specked. If that is the case I will subtract the overhang from the EL to get the P2S.
Hello,

No, it is a different dimension entirely. A tonearm will have this information on its spec sheet. S2P distance is from the platter spindle centre point, to the tonearm pivot centre point. I have a Jelco 850S tonearm. It has a S2P distance of 214mm. ( I might be misremembering, I don't have the info to hand). It was supplied with a template that fits over the platter spindle, and has a pinhole at the S2P distance, which is used as a centre for drilling the hole for the bearing pillar. It is the only dimension required for mounting the arm, so much so, I can't actually recall the EL! The EL is useful for aligning the cart, but not for fitting the arm.

Mike.

cytovette
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Re: replacing tonearm with different effective length tonearm

Post by cytovette » 22 Aug 2019 16:00

I understand on but every spec sheet that I have seen the EL minus the overhang was always identical to the S2P. So if you have don't have the P2S but have the other two dimensions you can "back figure " the P2S.

I completely get what you are saying though. I need to have the P2S for the new tonearm AND the ability to mount it at that distance.

Thanks
David

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Re: replacing tonearm with different effective length tonearm

Post by sturgus » 27 Aug 2019 04:07

cytovette wrote:
21 Aug 2019 14:43
I was thinking of eventually putting a Jelco tonearm on my Technics 1200. I was wondering how closely the new tonearm effective length should match the original tonearm.

The effective length for the stock Technics tonearm is 230mm. Can you go longer? If so how much longer before problems develop?

Thanks,

David
David, you can get arm boards for your 1200 off the Bay. Many are drilled for different arms. I know you can get them for Jelco, Rega, and SME. They run around $70 or $80 bucks. You might also want to look at the Audiomods arm website they make one for the 1200 also. Good luck!

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