Over the last month or so, I've put together a rim drive TT that doesn't use an idler wheel - the motor connects with the subplatter through a pliable wheel made of high density closed cell foam. Restoring a Rek-O-Kut L-34 made me a rim drive convert and I started playing with the idea of a DIY version. I borrowed the soft wheel idea from the Weathers TTs and the subplatter drive from a BSR. The motor is from a BIC and the platter assembly from an AR. I tried every variation of hard mount/suspended mount I could think of and wound up hard mounting the motor and putting the platter assembly on rubber cushions. It's very quiet that way. It's 33 1/3 only and the speed is adjusted by moving the wheel relative to the rim which effectively changes the wheel diameter. Once speed is set, it's stable.
The TT definitely has rim drive characteristics, including visceral bass and crisp attack. It's been in the system for the last few nights and I'm really enjoying the music I'm getting from it.
The TT definitely has rim drive characteristics, including visceral bass and crisp attack. It's been in the system for the last few nights and I'm really enjoying the music I'm getting from it.
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great looking build Doug. Thanks for posting about the soft drive system which seems like a very good idea. Did you experiment with different density foams or any open cell foams? I suppose open cell foam which would be dense enough may be difficult to source. I find your ideas and builds very inspirational. Best regards Moray James.
To adjust speed for 45 or 78 could you simply give the motor an LM317 PSU and use a pot to replace the set resistor in the LM317 circuit? This way you could adjust speed at least until you find out the three settings you need for 33, 45 and 78 then replace the pot with 3 resistors and a switch.
Thanks, Moray
I had the high density closed cell foam around from other projects and got lucky when it worked as well as it did. I think open cell would just be too flabby and might deteriorate too quickly. I'm working on molding silicone wheels. The first results are promising, but the diameter has to be more precise than with foam and I haven't quite figured out how to do that yet.
I had the high density closed cell foam around from other projects and got lucky when it worked as well as it did. I think open cell would just be too flabby and might deteriorate too quickly. I'm working on molding silicone wheels. The first results are promising, but the diameter has to be more precise than with foam and I haven't quite figured out how to do that yet.
There is some stuff sold at home depot that you use to mix with fiberglass. It hardens pretty quickly. I'll go out to the garage and check the name in a second. Anyway, I would pour this stuff in a cardboard box and then put your correctly sized wheel in the liquid. The wheel would be made of silcone because silicone comes out of this easily. Then when it hardens you have a great mold to pour silicone into.
Heading to garage...well, surprise.. its called fiberglass resin.
I usually make a mold out of silicone and then pour this stuff in it to get a resin positive but you could do the reverse, using the hardened resin as a mold for the silicone.
Heading to garage...well, surprise.. its called fiberglass resin.
I usually make a mold out of silicone and then pour this stuff in it to get a resin positive but you could do the reverse, using the hardened resin as a mold for the silicone.
udailey,
The motor is AC synchronous so it's frequency controlled, but with a DC motor, your suggestion would solve two or three considerations at once. For this motor, I could make three wheels of different diameters and just slide them on and off, which with this TT would be fairly easy, but I only play LPs.
Your suggestion of making a precise model of the wheel and then making a mold is a good one. I've been coming at it from the other direction by making a close approximate mold and relying on the squish factor of the silicone to compensate.
The motor is AC synchronous so it's frequency controlled, but with a DC motor, your suggestion would solve two or three considerations at once. For this motor, I could make three wheels of different diameters and just slide them on and off, which with this TT would be fairly easy, but I only play LPs.
Your suggestion of making a precise model of the wheel and then making a mold is a good one. I've been coming at it from the other direction by making a close approximate mold and relying on the squish factor of the silicone to compensate.
Impressive but the sub chassis should be turned around and that cut off leg extended and the tonearm located to it. This will keep the platter and arm association rigid whilst the whole of the sub chassis can be compliantly mounted to the plinth and hence decoupled somewhat from the motor.
a few comments...
dtut,
I'll think you will find out that the table may be improved using an idler to further isolate the motor from the platter. I've also contemplated using a direct rim drive. The biggest hassle is getting the speed correct.
dtut,
I'll think you will find out that the table may be improved using an idler to further isolate the motor from the platter. I've also contemplated using a direct rim drive. The biggest hassle is getting the speed correct.
Simon, Thanks for your response. I considered reattaching the cutoff sub-chassis arm and aligning the sub-chassis the way you suggest, but I wanted as much unencumbered real estate as possible in that corner so I could mount tonearms of different lengths. If someone wanted to try this TT and wanted to use the correct length tonearm, I would recommend giving your idea a try. What I didn't think of is that, because it's been cut, the sub-chassis arm length could be adjusted to accommodate different arms. If this TT goes to version lll, I'll try that.
Stew, Thanks for your response. This TT was originally built as a "what if . . ." project just to see if I could design and build a working direct rim drive model. The fact that, to me at least, it works very well is a happy bonus and means I'm reluctant to add the complication of an idler. If you're at all tempted by the direct rim drive idea, I seriously recommend giving it a try - if not this design, then whatever you come up with. By using a 300 rpm synchronous motor, I was able to deal with the speed problem fairly quickly once I found a that closed cell foam worked as a tire. I've been following the recent posts to your "219" thread and it occurred to me that the 219 would be a great arm for this TT.
I finally figured out how to mold a correct sized silicone tire and mounted it last night. In some mechanical ways, it's an improvement over the closed cell foam, but I'm not sure it sounds better.
Stew, Thanks for your response. This TT was originally built as a "what if . . ." project just to see if I could design and build a working direct rim drive model. The fact that, to me at least, it works very well is a happy bonus and means I'm reluctant to add the complication of an idler. If you're at all tempted by the direct rim drive idea, I seriously recommend giving it a try - if not this design, then whatever you come up with. By using a 300 rpm synchronous motor, I was able to deal with the speed problem fairly quickly once I found a that closed cell foam worked as a tire. I've been following the recent posts to your "219" thread and it occurred to me that the 219 would be a great arm for this TT.
I finally figured out how to mold a correct sized silicone tire and mounted it last night. In some mechanical ways, it's an improvement over the closed cell foam, but I'm not sure it sounds better.
Personally I like the idea of a non suspended idler/rim drive. There are other means to deal with unwanted resonances. I know the comments regarding the rigidity of the platter bearing and the tonearm, but using a movable tonearm base hasn't had any apparent negative effect on any of my tonearm builds.
I am most fond of the "K.I.S.S." principle or "do the basics brilliantly" thought regarding any audio piece. To me the simplicity and the purity of the engineering shines through. Simply elegant. Einstein had it right: "Everything should be made as simple as possible, but not simpler" (nor more complicated I think).
The "219" is a perfect match, as it is SO easy to do without full machining capabilities. Some care must be taken (mostly drilling the arrow shaft as it is very hard, and very brittle which can throw small metal spurs straight into your eyes.
But certainly easier to reproduce if needing more than one.
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