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Adding tonearm to turntable

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Adding tonearm to turntable

Postby edgarryan » 11 Apr 2011 03:02

Are there any rules when it comes to adding a second tonearm to a turntable? I have a spare Pioneer PL-12D tonearm that I would like to add to my turntable, once I've had a new plinth made for it. The effective length of this tonearm is 221 mm. How far away from the platter should I position the pivot of the tonearm? Thanks.
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Postby Jim Leach » 11 Apr 2011 14:20

Use the alignment protractors we have here and determine the mounting distance (spindle center to mount pivot center) and mount it there.

Once the correct distance, finish up with a proper set-up and you will be on your way!
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Postby zharca » 12 Apr 2011 00:43

221mm is quite short, the mounting distance comes out at a touch over 202mm.
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Postby Jim Leach » 12 Apr 2011 14:33

That IS short- 8.7"!

Tracking distortion will be higher than normal; a 'short' arm is 9" long...

Unless the other arm is a 12" I would go for a longer arm as a second arm.

(Maybe with a mono cartridge it would be acceptable if that is the plan...)
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Postby edgarryan » 13 Apr 2011 14:18

Hmmm, if it is short, how come the Pioneer turntable where this tonearm came from is quite highly regarded? I'm planning to install this in a pull-out Garrard AT6.
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Postby LPfan » 13 Apr 2011 14:58

You shall need to do away with the spring suspension of the chassis and mount it directly to the plinth to ensure correct working of the second tonearm.

Regards,

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Postby edgarryan » 13 Apr 2011 15:36

That is exactly what I plan to do, but how far from the platter should the pivot of the tonearm be?
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Postby rorenoren » 13 Apr 2011 16:06

Hi,

why not just measure the original mounting distance on the PL12D?
The guys at Pioneer (or CEC/Jelco) will have known the perfect mounting distance for that arm.

Regards, Jens
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Postby Jim Leach » 25 Apr 2011 19:40

Using our handy-dandy calculator here at VinylEngine, I calculated this (you have to choose the alignment you will run with first):

parameter:
pivot to spindle (mm)

Stevenson
204.347

Baerwald
202.144

Löfgren B
201.607
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Postby cats squirrel » 25 Apr 2011 20:26

are you sure that the 221mm is not the spindle to pivot distance?
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Second Arm

Postby josephazannieri » 25 Apr 2011 21:31

Yo edgarryan:

I have a second arm on my Garrard 301. The second arm, a Thorens TP13A, mounts at 215.6 mm and the primary arm, a Grace G707, mounts at 222 mm. 222 is 8.74 inches and 215.6 mm is 8.48 inches. Remember, there is about 15 mm of overhang on Grace, and about 18 mm of overhang on Thorens, so effective length of Grace arm is 237 mm or 9.33 inches and effective length of Thorens arm is about the same, 233.6 mm or 9.19 inches. "Effective length" includes the overhang. 202 mm mounting distance seems short, unless arm is really short. That's a little less than 8 inches mounting distance.

I agree with rorenoren. Measure the mounting distance, spindle to center of mounting hole for your added arm in its current location and use that as your distance. Using a figure cobbled in from formula may not give correct distance. You may be able to cheat a little by using the "effective length" from arm pivot to stylus and subtract the overhang.

You need to consider some things when mounting a second arm. First, second arm should be accessible. It's not easy to figure this out, as you can see from my 2 arm rig. Also, LPfan is right. You may have to take springs out from under turntable, and tie turntable right to new plinth, since the second arm must not be allowed to change its distance from spindle as turntable goes up and down on springs. This will induce distortion, and maybe speed irregularities. Didn't have to worry about this on Garrard because it bolts directly to plinth.

You will also need to consider grounding on second arm, My experience was that I had huge hum until I made sure that the right and left channel grounds were isolated from each other and also isolated from turntable chassis ground, which came in on a separate wire. I also had to be sure that all chassis ground wires and cartridge grounds were isolated from each other till they got to preamp control unit chassis and connected up there.

I designed an isolated ground switch that I used to stack both arms on one input, (2nd input on my Hafler preamp takes a Thorens TT with a Linn arm) and it works well. It has become a somewhat popular item on VE. I will send pix and a circuit diagram for the switch if you want it, but you will have to PM me with your Email address because VE will not accept PDFs or pictures from my computer. Also if you want pix of 2-arm Garrrard, say so and I will send them too.

And good luck from the old guy with too many arms,

Joe Z.
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Postby Jim Leach » 25 Apr 2011 21:54

You can fudge it; however it would be better to measure accurately, and determine the alignment you prefer to use for the new arm first- and then mount it at the correct spindle to pivot distance. That will make life easier.

Actually, if you make an adjustable arm board (or mount) you can then tweak it all you want... Might be a good idea since you have to make the mount anyway... The numbers I posted (assuming your effective length is accurate) give you the upper and lower distance ranges so you know how much adjustment you need in your mount.

Thinking about it, that would be the way to go for sure.
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Postby pogo » 25 Apr 2011 22:19

Jim Leach wrote:You can fudge it; however it would be better to measure accurately, and determine the alignment you prefer to use for the new arm first- and then mount it at the correct spindle to pivot distance. That will make life easier.

Actually, if you make an adjustable arm board (or mount) you can then tweak it all you want... Might be a good idea since you have to make the mount anyway... The numbers I posted (assuming your effective length is accurate) give you the upper and lower distance ranges so you know how much adjustment you need in your mount.

Thinking about it, that would be the way to go for sure.


I'd shoot for Baerwald -- although the DB doesn't list offset angle for the 12D, it looks like Pioneer favors 25 degrees which in this case would be near perfect for Baerwald.
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