tigerwoodKhorns Posted June 25, 2009 Share Posted June 25, 2009 I am making some armboards for a Technics SL 1200 to mount a Jelco 750 and another for an SME IV arm. The Jelco arm is a Sumiko Premere MMT. Its spindle to pivot distance is listed at 221.7 mm. 1/10th of a mm is a precision that I cannot ever achieve. I will be using a CNC machine, but it even has a kerf of 0.30 and is only a accurate as my drawings, which are from hand measurements off of the turntable. I am asuming that I need to download the templates off the internet, print and check for accuracy. Then make a blank armboard and install, mark it with the template, measure again, change the CAD drawing, then cut a new armboard with the mounting holes. Anyway, in a nutshell, are they serious? 1/10th of a MM? Most armboards are made of wood and you are not going to get that accurate. How accurate do I need to be? Please no "as accurate as possible" responses. This is an engineering issue and there is always a range. Quote Link to comment Share on other sites More sharing options...
Coytee Posted June 25, 2009 Share Posted June 25, 2009 Just yesterday I removed the armboard from a Thorens 121. I was looking to remove the arm from the board so I turned it over and looked at the little locking washer they attach them with (not sure what it's actually called) I didn't take it off but it would seem to me the opening of the hole would have SOME variation relative to the diamater of the tonearm base? In other words, given that I have NOT taken it off yet, I would expect the arm to move around in the hole just a little bit? Surely it's not a machined tight fit like a piston with ring, inside an engine cylinder? I'm with you that there should be a range (note, I'm refraining from saying as accurate as possible []) I can try to remove it later today and see if it wiggles in the mounting hole? I'd have no way to measure the wiggle with any accuracy. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted June 25, 2009 Share Posted June 25, 2009 some wiggle but not as much wiggle as you would think? I know I know, not what you wanted to hear. [8-)] Very valid question sir. Quote Link to comment Share on other sites More sharing options...
tigerwoodKhorns Posted June 25, 2009 Author Share Posted June 25, 2009 Thanks guys. The SME and Jelco arms both attach with bases that are bolted to the arm board. So the base that is part of the tonearm will provide some lash or play. The SME is spot on and build quality is like nothing that I have ever seen in a tonearm. The Jelco is a very solid arm and uses a set screw so there is a tiny variation when the screw is set. The issue is this. My measurement from the spindle to the pivot is difficult to make. I tried it with a tape measurer last night and it was not happening. However, I found a solution. I am just going to make a jig on the CNC machine and use that to locate the pivot point. If anyone is interested, ToneAudio.com will have a new issue out on Sunday where they test the much hated (at least there) Technics SL1200 with an SME 309 arm using a SoundHiFi arm plate. They loved the setup and claim that it will run with tables in the $3000 range. FWIW, they do tend to be pretty down to Earth. Here is the link to SoundHiFi: http://www.soundhifi.com/sl1200/index.htm It looks like they make a really high quality product but their armboards are about $175 shipped to the US. The way that I see it, the Jelco 750, which can be had for $600 with wiring brand new from AudioDragon on Audiogon, with a Denon 160 or 103 (no extra weight needed) on a Technics table should be a winning combination. The other Jeclo arm, the 250, is only $300 plus $100 for wiring. Is there any interest in these base plates? I may do a larger run because the setup time is the same. I am also working on a cost effective power supply mod. Quote Link to comment Share on other sites More sharing options...
Islander Posted June 25, 2009 Share Posted June 25, 2009 I'm not sure you need that much precision. Origin Live is a UK firm that sells lots of turntable modification parts and accessories. Here are their instructions for fitting one of their tonearms or a Rega tonearm, where plus or minus 3mm seems to be acceptable:armboards & mounting position It is certainly possible to fit the Origin Live and Rega tone arm to any deck but sometimes you may either have to modify your existing armboard or acquire a new one - (see a dealer for the second option). The tone arms require a singe hole in the armboard or plinth - 24mm or 25mm in diameter to fit into. Once the arm is inserted through this hole it is then secured by a large nut which clamps it onto the underside of the board . The distance from centre of arm hole to centre of platter spindle needs to be 223mm plus or minus 3mm. The arms can rotate to be fixed at any angle . The length of the arm from its mounting hole center to the cartridge end of the arm is 245mm. The arm overhang to the rear is 50mm to the end of the counterweight stub. As for the SL-1200, Hi-Fi World, a British audio magazine, did some mods on one last year and found it was the listening near equal of some pretty pricy belt drive decks. They also carry a DJ armboard for Sl-1200s for 39 Euros, which doesn't seem too expensive. Info here: http://www.tonearm.co.uk/dj-technics-arm.htm Quote Link to comment Share on other sites More sharing options...
tigerwoodKhorns Posted June 25, 2009 Author Share Posted June 25, 2009 Thanks, The 3 MM spec is interesting. I did nto think that getting to 1/10th of a MM was reasonable. Quote Link to comment Share on other sites More sharing options...
thebes Posted June 25, 2009 Share Posted June 25, 2009 This would probably work. Drill out the set screw holes for a new armboard. Install armboard. Take a length of thin wood, a wooden yarstick would most certainly do, drill one hole the exact width of the spindle. Measure your 227.1mm from the center of that hole. Drive a one inch nail through this piece of wood at the arm side measuring point. Place wood over spindle. Place the nail over a newly made and installed armboard. Lightly tap nail. This will give you your center point. Drill out the hole in armboard and remount. Just in case you are interested 227.1mm is 8.9409 inches. I don't trust those furrin measurements, so I'd probably use inches.[] Quote Link to comment Share on other sites More sharing options...
bliss53 Posted June 25, 2009 Share Posted June 25, 2009 It seems to me that the pivot distance can be off a couple of 10ths of a MM. I think that there is a small tolerance built in because the the overhang and lateral tracking angle adjustments have the effect of truing up the pivot distance for your particular cartridge. Quote Link to comment Share on other sites More sharing options...
Islander Posted June 25, 2009 Share Posted June 25, 2009 Have you been in touch with KAB USA? They seem to know an awful lot about SL-1200s, so it might be worth consulting them about your deck. KAB USA: http://www.kabusa.com/frameset.htm?/ They have lots of info, precision-prepped SL-1200s, SL-1200s that play at 78rpm, custom hardwood bases in a choice of woods, etc., etc. Quote Link to comment Share on other sites More sharing options...
seti Posted June 25, 2009 Share Posted June 25, 2009 It looks like they make a really high quality product but their armboards are about $175 shipped to the US. The way that I see it, the Jelco 750, which can be had for $600 with wiring brand new from AudioDragon on Audiogon, with a Denon 160 or 103 (no extra weight needed) on a Technics table should be a winning combination. The other Jeclo arm, the 250, is only $300 plus $100 for wiring Did you get the 12 inch Jelco 750 arm? That is what I have settled on for my Garrard 301 and I'm also going to use the Denon 103. How can you argue with a product that has been in constant production almost as long as the mighty Khorn. I just noticed that there is a 12 inch ortofon which is a very hot rodded Jelco 750 for $3K. At least we know it has good bones : ) I'll be very interested in your opinion when you get them spinning. Quote Link to comment Share on other sites More sharing options...
joessportster Posted June 25, 2009 Share Posted June 25, 2009 i have mounted several tonearms, and made a few armboards here at home the mount hole does need to be close however not dead accurate, as you will end up adjusting overhang of the cartridge using one of the many different protractors / tools, and this will make up for minute differences Joe Quote Link to comment Share on other sites More sharing options...
russ69 Posted June 25, 2009 Share Posted June 25, 2009 I'm not a TT expert but I'm good with geometric problems. The fact is that the tone arm is only tracking true at one point on the record, the rest of the time it's not quite true (tangent) to the groove. It's all a bit of Kentucky windage so to speak. I think reasonably close is good enough. The "experts" might have you align the cart using an scope and watch the trace from a test record but I'm not sure I can hear the difference. Thanx, Russ Quote Link to comment Share on other sites More sharing options...
Islander Posted June 25, 2009 Share Posted June 25, 2009 The fact is that the tone arm is only tracking true at one point on the record, the rest of the time it's not quite true (tangent) to the groove. I think the geometry is set up so that the stylus tracks true at 2 points on the record. Quote Link to comment Share on other sites More sharing options...
tigerwoodKhorns Posted June 26, 2009 Author Share Posted June 26, 2009 Guys, Thanks for the responses. I am going to cut a jig from plexiglass on the CNC machine with holes for each of the different arms. I have the geometry thing down and can locate the center. KAB has a lot of upgrades but he likes the stock tonearm. KAB is too expensive too. By the time you have you SL all decked out, you can have $1500 to $2000 in the table and arm. The mod that I am doing is not something that he does. This is a second table and I just want to try these two arms out on it. I figure that I should make some extra plates while I am at it. Here is another quesion for this project for the power suply mod that I am doing. I need an electrical plug or quick disconnect that will handle 5 wires. Where can I get one of these? I think they are called DIN plugs. Quote Link to comment Share on other sites More sharing options...
thebes Posted June 26, 2009 Share Posted June 26, 2009 Ask Fini. This Spring he built cables for 3 of us for use on Ortofon arms using Din plugs. He'll also provide pictures of the construction. Quote Link to comment Share on other sites More sharing options...
bliss53 Posted June 26, 2009 Share Posted June 26, 2009 Guys, Thanks for the responses. I am going to cut a jig from plexiglass on the CNC machine with holes for each of the different arms. I have the geometry thing down and can locate the center. KAB has a lot of upgrades but he likes the stock tonearm. KAB is too expensive too. By the time you have you SL all decked out, you can have $1500 to $2000 in the table and arm. The mod that I am doing is not something that he does. This is a second table and I just want to try these two arms out on it. I figure that I should make some extra plates while I am at it. Here is another question for this project for the power supply mod that I am doing. I need an electrical plug or quick disconnect that will handle 5 wires. Where can I get one of these? I think they are called DIN plugs. Check out http://www.vinylengine.com/library.shtml. You can print out a template for the 2 alignment points geometry. If you end up making a plexiglass one that is the same thickness as standard vinyl record, let me know and I will buy one. I used a friends that had a very slight engraved hatch at the two points for the stylus to rest in. Not so deep as to rip the stylus off. It also had a mirrored section adhered under the clear plastic to aid in alignment. I think is was made back in the 70's and I have been looking for one ever since. Quote Link to comment Share on other sites More sharing options...
tigerwoodKhorns Posted June 26, 2009 Author Share Posted June 26, 2009 I should have been more specific. I need to make a jig for setting the pivot of the arm, not the cart alighment, I tried to get the jig from Vinylengine and teh one for the Jelco is not to scale so I hav ethe measurement, just no template. For the electrical connections, I need them for an external power supply, not the arm cable. I have 5 wires, three thick ones (maybe 18 ga) and two small ones (20 something ga), so two plugs will work. If I cannot find anything, I will just use a barrier strip. Quote Link to comment Share on other sites More sharing options...
seti Posted June 26, 2009 Share Posted June 26, 2009 I should have been more specific. I need to make a jig for setting the pivot of the arm, not the cart alighment, I tried to get the jig from Vinylengine and teh one for the Jelco is not to scale so I hav ethe measurement, just no template. For the electrical connections, I need them for an external power supply, not the arm cable. I have 5 wires, three thick ones (maybe 18 ga) and two small ones (20 something ga), so two plugs will work. If I cannot find anything, I will just use a barrier strip. Email Jelco mail@jelco-ichikawa.co.jp and see if they can send you what you need. Just tell them the exact model number. Quote Link to comment Share on other sites More sharing options...
doctorcilantro Posted June 29, 2009 Share Posted June 29, 2009 My experience with a Bix and MG-1 was that the moutning template for MG1 offerredquite a bit of wiggle room. Maybe because the other parts on the tonearm could compensate. 1/10 of a mm doesn't sound right at all to me. DC Quote Link to comment Share on other sites More sharing options...
nu2toobs Posted July 9, 2009 Share Posted July 9, 2009 Chris, I have a plexiglass template that came with my Jelco, if you need to borrow it. Quote Link to comment Share on other sites More sharing options...
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