Omegaspeedy Posted September 11, 2010 Posted September 11, 2010 Owen and other TT guys in the know:), I have a few questions regarding setting up my home made wooden 12" arm. 1) Can I use a standard Baerwald calculator to set up the two null points (66 and 120.9mm) being a 12" arm. May seem like a stupid question but I'm not sure and want to get the geometry correct. 2) I haven't drilled the head shell mounting screws yet. What should the offset angle be. (longitudinal axis of cart to longitudinal axis of tonearm)? Note it is a straight arm. Distance from stylus to pivot = 12". 3) The pivot is approx 12mm above the estimated stylus position in the horizontal position. Will this induce distortion that will be notable? This design is fully adjustable and I intend to add an arm holder and anti skid once I have set the geometry up. The wood came off an old gymnastic spring board and is light, hard and very slightly springy though not notable over this length. The spring board dated back to the 1940-50's and is very stable and dry. It is lovely to work with and all the machining was done today with a router. I hope its got the resonance characteristics that make an arm sound good. I have no idea how to find its natural resonance frequency though but guess it should be somewhere about 350hz? Sorry for all the photo's this weekend, this vinyl stuff has me very excited especially when it sounds so bloody good and engaging:) I never had this when I had my last TT as it didn't tick the boxes for me, but this one.....roll on!
Owen Y Posted September 11, 2010 Posted September 11, 2010 omegaspeedy;132754 wrote: Owen and other TT guys in the know:), I have a few questions regarding setting up my home made wooden 12" arm. Looks super! You used big equipment spikes? 1) Can I use a standard Baerwald calculator to set up the two null points (66 and 120.9mm) being a 12" arm. Yes, same for any length pivoted arm. 2) I haven't drilled the head shell mounting screws yet. What should the offset angle be. (longitudinal axis of cart to longitudinal axis of tonearm)? Note it is a straight arm. Distance from stylus to pivot = 12". for an arm of Effective Length say 305mm...for Baerwald Alignment, Offset Angle should be 17.8mm (allow some angular adjustment, via slots or hole tolerance), Overhang 13.35mm / Pivot-Spindle 291.6mm. 3) The pivot is approx 12mm above the estimated stylus position in the horizontal position. Will this induce distortion that will be notable? This is difficult to answer. You will see that the SME pivot is above the stylus level. Theoretically, when the stylus moves up & down, lowest tracing error/distortion is when the vert arc pivot is at same level as stylus...but the angular difference is small. OTOH, stylus tracing takes place at a miniscule scale & this sort of thing could have significance. I need to think on this Q a bit more sorry. Check out the unique RS Labs Tonearm, which clearly does not adhere to this thinking!... http://www.enjoythemusic.com/magazine/equipment/0701/rslabs.htm
Owen Y Posted September 11, 2010 Posted September 11, 2010 How have you 'engineered' what appears to be a unipivot bearing...ie the 'thrust pad'.
Owen Y Posted September 11, 2010 Posted September 11, 2010 Also, try to arrange your wire routing to minimises drag/friction against arm free movement. One way, in principle, of doing this is to have the arm wire exiting the tonearm wand at or very near the arm pivot. The wire may also not have the benefit of shielding by a metal armtube - whether this becomes an issue is system dependent.
Omegaspeedy Posted September 11, 2010 Author Posted September 11, 2010 Cheers Owen, always great info! Yes the pivot point and weights are Hasaudio heavy equipment spikes as you've spotted:). The thrust bearing setup uses a brass screw against the point of the spike. If it works out as I hope, I'll drill the head of the Phillips brass screw to bring it to a good point. At the moment it is sitting on the four surfaces around a Phillips star head. Not bad but a continuous radius would be better. Depending on the amount of roll adjustment available (I've use an asymmetric spacer between the arm and the counter weight so rotation positions C of G differently!!), I might have to add horizontal out riggers with small counter weights. Hopefully not though. The slot you see on the under side finishes very close to the pivot and I have yet to drill the exit hole for the wire to exit from the top of the arm to RCA's. Hopefully this will reduce drag some what. Thanks again for the info Owen, I'll get down to it tomorrow and see if I can get it up and running. Cheers James.
Papa Hemi Posted September 11, 2010 Posted September 11, 2010 Great work - a unipivot! Are you satisfied with the thrust pad / bearing surface? Re anti-skate and tone-arm wiring, you may be able to address these issues together. I have seen, and done it myself on LAUDy, where you exit the cable just forward of the pivot. Arrange the cable in a way that it provides antiskate as the arm moves/arcs toward centre. It is an effective solution in that it adjustable and undo-able. keep up the great work - I'd love to get a hold of some of that spring board.
Owen Y Posted September 11, 2010 Posted September 11, 2010 Originally when Dave W made the bearing for my unipivot, he used a ball point pen ball tip, bearing into the recessed head of a socket head hex screw. Here is a plan view of my arm (originally 250mm length) showing main outriggers at the bearing boss. You can see that the cartr offset tends to tilt the arm azimuth to one side - this can be addressed by adding a weight on the spindle side, in a number of ways. I added the headshell outriggers, which dble as a handy finger lift. (This was copied from a Hadcock arm mod idea published in HiFi World mag You will find that a 12" arm needs much more counterweight, esp if you want to keep the latter close to arm pivot as poss, to minimise bending in the tonearm beam. Attached files
Omegaspeedy Posted September 11, 2010 Author Posted September 11, 2010 Papa Hemi Great work - a unipivot! Are you satisfied with the thrust pad / bearing surface? Hi Papa, I'll need to run it and see but if all is well and if so, i'll drill the brass Phillips screw head to a point. This will make it a permanent fixture of the arm as I won't be able to unscrew it. I've got a bit left over, enough to make a 12" arm. PM me your address:)
Omegaspeedy Posted September 11, 2010 Author Posted September 11, 2010 Awesome Owen, that is a true bit of engineering! Are you still using it now? Those little out riggers might be needed based on the offset angle of 17.8. The cart will cause an imbalance that will need sorting out. Maybe using an imbalance to my advantage by adding one out rigger to compensate the cart angle with enough adjustment to roll both ways? I need to mount the cart and see what will be required.
Papa Hemi Posted September 11, 2010 Posted September 11, 2010 " I need to mount the cart and see what will be required." Nothing that can't be sacrificed for the greater good I hope.
Owen Y Posted September 11, 2010 Posted September 11, 2010 Yes, still using the arm - now experimentally extended to 12", but there will be no going back I think. The h'shell o'riggers do not help the azimuth imbalance, unless the LHS one is made heavier. Additionally these wts add to the h'shell mass to be counterbalanced. However in the published article, there was a contention that it assisted stability of a unipivot. You will find that the unpivot has NO stability until it hits the groove. The bearing boss theaded o'riggers are the ones that affect the azimuth. However, although the amount of imbalance is small, esp when the stylus hits the groove. I think many unipivots don't bother.
Papa Hemi Posted September 11, 2010 Posted September 11, 2010 mine wobbles a bit when I put it in the groove. But it soon settles down. Only two or three wobbles, or periods. A sort of yaw really, but quickly damped. To the relief of all.
Omegaspeedy Posted September 12, 2010 Author Posted September 12, 2010 Ok guys, sounds like stability settles as you've mentioned so I won't worry too much at the moment. I found great use for Apple the I-touch today. You have to take your hat off to Apple because they do some things right:). The supplied ear phones use wire in them that is so fine, flexible and colour coded that I couldn't resist cutting them up to use as makeshift tone arm cable (until I pick up the silver, sorry Harvey, I'll get in touch soon). It is as thin as a pin!! Owen, that 17.8 is spot on. The alignment works great at 66/120.9mm. I salvaged some tone arm pin sockets from the monitor plug on the back of an old computer. they slide on beautifully. I'll solder them up tomorrow. The pic show the arm with rubber bands holding up the wire and these will be remove once I figure out how to hold up the wire in the slot.
Owen Y Posted September 12, 2010 Posted September 12, 2010 omegaspeedy;132871 wrote: I salvaged some tone arm pin sockets from the monitor plug on the back of an old computer. they slide on beautifully. I'll solder them up tomorrow. Please elaborate...where will these pin sockets be installed, sounds a good idea...ahhhh, I see, as the cartridge 'clips'. The pic show the arm with rubber bands holding up the wire and these will be remove once I figure out how to hold up the wire in the slot. There's always Blutak
Omegaspeedy Posted September 12, 2010 Author Posted September 12, 2010 Hi Owen, I meant cartridge clips:) and the solder won't go near the cart. I'll solder the arm wire to the clips. Blutac sounds good. On closer inspection of the wire, I don't understand how it is insulated. It seems to be fine multi strand copper surrounding a fabric inner? When it was insulated prior to removal from the outer cable, the wires were all bunched together, touching (left and right + and - channels). Could they be lacked? Not sure how well they will solder but will experiment first.
Owen Y Posted September 12, 2010 Posted September 12, 2010 Try to pre-tin the wires - if you can do that, attaching the clips should be plain sailing. If you have some sm size heatshrink, some short lengths (8-10mm) at the clip solder junction can act as strain relief (& addit insulation). Not sure about the nature of these wires, they may be coated wire...in which case heated solder should strip it.
Omegaspeedy Posted September 12, 2010 Author Posted September 12, 2010 Owen Y;132874 wrote: Try to pre-tin the wires - if you can do that, attaching the clips should be plain sailing. If you have some sm size heatshrink, some short lengths (8-10mm) at the clip solder junction can act as strain relief (& addit insulation). Not sure about the nature of these wires, they may be coated wire...in which case heated solder should strip it. Thanks Owen, I tell you how I get on tomorrow. Fingers crossed it works out.
Owen Y Posted September 12, 2010 Posted September 12, 2010 Use min heat where poss...thin wires & the insulation is prob not made for soldering.
Omegaspeedy Posted September 13, 2010 Author Posted September 13, 2010 Owen, they soldered up very well. Nice to work with too and I can recommend I-touch head phone cable. MUSIC!, a bit more noise, and could be the cable I borrowed today off Neil, will do a cross check with the other cable I have but all and all it sounds great! Tracking seems good as you've said, sits well once in the groove. To finish up..... 1) I need to make a lifter as it is a bit tricky to set going. 2) Final sanding and oiling of wand and base support. 3) Drill brass bearing to a point and lube. 4) tidy up RCA mount that the tonearm wires connect to. 5) Remove rubber bands and support tonearm wires. If noise is still a problem, how do you earth a wooden wand? Cart body to Earth RCA?
Owen Y Posted September 13, 2010 Posted September 13, 2010 I found that twisting unshielded arm wires helps to reduce hum. No need to separately earth cartr body or 'ground' the wood tonearm. Edit: Beaut arm rest! Maybe lacquer the wood to 'stiffen it? Or just stick w the magic Danish Oil, which has been successful to date!
Omegaspeedy Posted September 13, 2010 Author Posted September 13, 2010 Thanks Owen i'll give it a go.....
ilikecrumpets Posted September 13, 2010 Posted September 13, 2010 That looks amazing James! How difficult would it be to drill a centre hole through the arm tube for the cable?
Omegaspeedy Posted September 13, 2010 Author Posted September 13, 2010 Pretty difficult as it's 12 inches long but I have machined a 5mm slot along the bottom which will conceal the wires but I may have to hang them up with bluetac. Cheers James
Papa Hemi Posted September 13, 2010 Posted September 13, 2010 Certainly looking good! That wire looks to be the trick, as do the recycled cartridge tags. Another option for holding cable in place could be the trusty old glue gun.
Omegaspeedy Posted September 13, 2010 Author Posted September 13, 2010 Papa Hemi;132920 wrote: Certainly looking good! That wire looks to be the trick, as do the recycled cartridge tags. Another option for holding cable in place could be the trusty old glue gun. Yes papa, I was thinking that except a small pool of pva in three points. If I re-wired the arm, I could dig it out without damage to the slot.
Recommended Posts