Any electronics buffs in the house to help with turntable project?

I purchased a Technics SL-6 turntable. Turns out a part was bad on the tonearm. I ordered a replacement, that came with the same plastic part "split." Thirty year old unit, perhaps a weakness in that part, I decided to cut my losses and get a different turntable (a 25-YO Technics linear model).

BUT, I was thinking maybe I'd scavenge the motor + platter from the SL-6 and make a plinth, and add a tonearm (eBay) and basically make my own turntable.

I did a little probing with my meter and found the 6-pin wire carried +12v on pins 2 and 6. Pin 1 was common. So I cut the end off a wall wart and wired it to the motor's board just like that. I wasn't expecting it to spin when I powered it up, and it didn't. But it didn't smoke, either.

I found that adding a jumper between 4 and 5, that the turntable spins up and runs very close to 33-1/3. I note that the service manual shows I can adjust the speeds using VR201 (45-RPM) and VR202 (33-1/2). I'm assuming my variance from 33-1/3 is due to my switching wall wart? For the record, I believe I'm slow by about 4%.

If I use a jumper between 3 and 5, the platter spins very fast. A jumper between 3 and 4 and it doesn't spin at all. And again, a jumper between 4 and 5 and I get approx. 33-1/3.

Would it be possible for anyone to look at the schematic in the service manual and tell me if there would be a way to get 45-RPM, or if I'm even on the right track?

The schematic shows 5v near the start/stop as well as speed selection areas, so I'm sort of wondering whether I should be tying 4+5 to get the 33-1/3. Maybe I need a DC-DC controller to give me 5V and then use that as the input to the motor telling it what I need it to do?

Link to service manual:

http://www.jpthien.com/temp/technics_sl-6_service_manual.pdf

 

I figured it out, I now have 33 and 45-RPM working.

I have a CNC router so will start contemplating my plinth.

I guess all that is left will be determining what to use for a tonearm, and the geometry of arm to platter.

Anyone have any links to guidelines on arm/platter geometry?

 

Sorry, no idea whatsoever.

 

Check out audiokarma.org when you get a chance.

 

I think for most regular arms the distance from the spindle to the pivot of the arm should be 21.5cm but don't quote me on that as I could be wrong.

 

I think pivot to spindle distance is determined by the arm you're using.

TONEARMS of JELCO ICHIKAWA JEWEL

A feickert protractor would be a easy way to find the center of the pivot to spindle distance.

Dr.Feickert :: Protactor

All advice offered by me is strictly amateur.

 

Thanks guys.

Any idea of tonearm height relative to platter?

 

Thanks, I posted over there.

 

As said, the only measurement is from the spindle to the center of the tonearm post.

You'll need to buy an arm that allows VTA changes

 

This sounds like an interesting project. Do you intend to use the motor control electronics in your build? I would.

 

Absolutely, there is no other way to do it, these motors are magnetically driven.

That is what appealed to me about these turntables to begin with.

 

Looked at tons of tonearms on eBay during breaks today.

On the one hand, $400 for a used SME tonearm seems reasonable. OTOH, I don't know what kind of shape the bearing(s) will be in, etc.

Is a decent-quality tonearm with integrated cuing lift, rest, reasonable RCA interface, removable head shell, all for $100 too much to ask?

 

You could look for something like a non-working Sony PS-x50, 60, or 70 with the Sony PUA-7 arm. It has what you're looking for in an arm.

 

Okay thanks, added to my remembered searches on eBay.

 

This is not very scientific as I haven't even measured it but when you have an average cartridge installed and you placed the stylus on the platter plus record. The lower edge of the arm -which should be about parallel to the platter- should end up being about +/- 10mm or 9mm) away from the platter, record included.

 

So while I've been looking for an economical tonearm solution, I decided to try a little experiment.

I had also been looking at DIY tonearms and tried to make half a gimbal using some material I scrounged up from the junk drawer and parts cabinet.

The "hinge" is made from two steel ball bearings pushed into the "arm," and two cup-type set screws.

Resistance is higher than I'd like. I'm not sure if a different size ball bearing or set screw would help. If the ball is riding on the edge of the cup, resistance might be higher.

I can see the advantage of the Schroeder tonearm where resistance is concerned, but I have a workable tonearm solution on the way (a gentleman from diyAudio is sending me a tonearm harvested from an old Gemini turntable) so I'll likely just wait for that now.

But I figured I'd post some pics for fun.

 

Had some time today, did some more work on my tonearm.

Once I had the up/down resolved, I moved onto the spinny aspect.

These are just test pieces, or a proof of concept.

It occurs to me that I'm going to need a used cartridge that is both inexpensive and fairly durable, when I get to the testing phase. Any suggestions?



http://www.jpthien.com/temp/IMG_5095.MOV
http://www.jpthien.com/temp/IMG_5098.MOV

The two links above are movies showing the degree of resistance.

 

Moved onto a unipivot concept for my arm.

Waiting for parts from McMaster. Need a threaded rod-end to handle the counterweight. Also ordered aluminum as well as stainless spacers, to replace the plastic ones. I ordered two different lengths of spacers, so I can build a 1-1/2" or 2" tall pivot assembly. The two different height possibilities, with the two different material (aluminum,stainless) weights, should allow me to adjust the response of the arm quite a bit.

The arm is CNC cut maple for now. I'm using the SME V measurements, so pivot to stylus is 233.15mm and offset angle is 23.635-degrees. The slots in the top of the wand will allow me to secure the wiring (I'll use wraps of colored crochet thread my wife has).

If this works, I will consider getting some other materials for arms and the pivot bottom plate, like carbon fiber or different types of wood.

The threaded rod-end will (hopefully) allow me to adjust azimuth by adjusting the counterweight slightly left/right. The center hole of the rod end is 1/4", I couldn't find anything from materials on-hand or the hardware store to emulate this very well. Once I get it, I'll be able to squeeze that rod end between two spacers and then adjust left/right fairly (hopefully) easily. It seems to work with the eye bolt.

I wish I lived close to a McMaster, the will-call desk folks would know me by name.

 

BTW, I need a non-working 1/2" cartridge for testing purposes, and some screws and nuts for it.

If anyone has a non-working 1/2" cartridge that doesn't work that they'd donate to the cause, especially if you have some screws and nuts, I'd be very grateful. My "headshell" is 3/16" thick right now, so the screws would have to be long enough to get through that, plus the cartridge.

Yes I have considered getting one on eBay but by the time I do a no-stylus cartridge + screws I'm at $30 - 40 dollars, and I'm not even sure I'm going to be able to make all this balance at this point.