Adding a pitch control

[adnick]

So the idler mechanism looks a lot like the other Russco’s, for instance the fine adjustment on the Studio Pro is in that slot next to the selection lever, must be one somewhere on yours….

 

[Old Jazz Guy]

There are only 2 places with what I'd call adjustments capability:

A small screw beside each speed slot...



and a nut on the gearshift lever.



Neither option seems to be anything more than an adjustment for pressure of the idler wheel on the drive shaft of the motor. And none of them seem to be convenient...

 

[adnick]

^^^ Those on the side are it for each speed, depending on the idler, you can probably get +/- 1rpm, (maybe more) from speed selected without any noise degradation.

Andy

 

[adnick]

One note: The speed adjustment will be less going up from each target speed, for instance from 33&1/3 it’s not going to adjust as much up as down…

 

[Old Jazz Guy]

OK, good to know. I also hear that they are used more for precise calibration rather than coarser pitch adjustment.

Oh and by the way, I installed my new felt today! Not bad for a first try I think!

 

[adnick]

Looks really good

 

[Old Jazz Guy]

Thank you. The hardest part was cutting the outside edge - it's not perfect by any means...

I need to make a spindle jig to mount my rotary cutter on, and see if I can make that edge a bit cleaner.

I bought 2 full yards of felt, so I can try a few more times to get it right.

 

[Old Jazz Guy]

One note: The speed adjustment will be less going up from each target speed, for instance from 33&1/3 it’s not going to adjust as much up as down…

Yes - as a musician I understand that - pitch is math - frequency doubles or halves per octave as you go up or down - the frequency of the note G at 200 Hz for example - the next G an octave down is only 100 Hz, but the next octave UP is 400 Hz. I assume the relation to adjusting platter speed to vary pitch the same amount in either direction must be similar, in that to lower pitch the platter needs only to slow down 1/2 as much as would be required to raise the pitch a similar interval.

12 semitones per octave means that 1 tone is roughly 8.3 percent, but the numbers in decrease are actually halved, and the numbers in increase are doubled... I think ... lol... exponents at work here.

I know that Dual turntables vary their pitch controls in the order of 10% + or - , so they don't go as sharp as they go flat...

 

[hirscwi]

The circuit in the link you sent might work, I didn't dive into it in detail. I have used a couple of the 555 IC and don't find them to be very suitable for this purpose. In addition to something to generate the sine wave of correct frequency (and being able to vary that frequency), you'll need to amplify it back to 120 VAC with sufficient wattage. I'd go with something proven and designed for turntables. I can point you to a couple threads on DIYAudio if you're interested.

That motor will require at least 40 watts to drive it - bigger than any I've seen before. I'm not aware of any commercial controller that will drive it.

It will be a great table when you're finished and well worth the effort to restore it. Before you go too deep into a motor controller, I'd replace the run cap and clean up the bearings. then give ti a listen. The pitch may not bother you and I suspect the speed will be very constant ( low W&F).

Be sure to allow some ventilation when you build your new plinth.

 

[hirscwi]

Sorry, I missed some of the posts. I agree that the setscrews on the side of each speed are adjustments for pitch. May obviate the need for any controller.

Also, it's probably worth having Terry replace the rubber on the idler.

 

[Old Jazz Guy]

The circuit in the link you sent might work, I didn't dive into it in detail. I have used a couple of the 555 IC and don't find them to be very suitable for this purpose. In addition to something to generate the sine wave of correct frequency (and being able to vary that frequency), you'll need to amplify it back to 120 VAC with sufficient wattage. I'd go with something proven and designed for turntables. I can point you to a couple threads on DIYAudio if you're interested.

That motor will require at least 40 watts to drive it - bigger than any I've seen before. I'm not aware of any commercial controller that will drive it.

It will be a great table when you're finished and well worth the effort to restore it. Before you go too deep into a motor controller, I'd replace the run cap and clean up the bearings. then give ti a listen. The pitch may not bother you and I suspect the speed will be very constant ( low W&F).

Be sure to allow some ventilation when you build your new plinth.

I agree that the setscrews on the side of each speed are adjustments for pitch. May obviate the need for any controller.
Also, it's probably worth having Terry replace the rubber on the idler.

Thanks. My new plinth will have venting on each side but one, where there will be a storage drawer.

I intend to clean up the bearing, and replace the caps before putting the machine into service. The drive idler is nice and soft, and makes no noise whatsoever that I can hear so I don't believe it's time to change it yet. It may have been done before I came into possession, but I don't know for sure.

The link I sent you has been pooh-poohed by a local guru who's opinion I trust implicitly, so I figure knowing that along with your concerns it's likely not something I will pursue. However, I am interested in exploring the DIYAudio threads you speak of. Links to those would be appreciated. The set screws are just for fine calibration I believe, but I will see what they do. If they're just for very fine tuning, then I will be using a strobe etc. to ensure they're set, and then leaving them alone. If I do wind up creating any kind of stand alone pitch control it will need to function in the order of 10% + or - to be worthwhile. It's fun to try to figure it all out, but if it can't be done right, and affordably, then it may simply turn out to be a lost cause!

Cheers!

 

[Fishead]

@Fishead - I'm interested in this device you speak of. Is there a link to the actual product you have that you can post here? I'd really appreciate it. I have been warned that such devices need to be designed to work safely when handling fairly high current levels for these heavy and powerful turntable motors.

I don't think the Project Speed Box S would work for you, sorry.....for reasons that others have mentioned, speed appears not to be controlled via AC power. You can see what I was talking about here:

https://www.musicdirect.com/analog-accessories/pro-ject-speed-box-s

No longer available, but you can find one on the big auction site. Again, I don't think this is what you are looking for. There are others as well, my Wave Mechanic being one such, but nothing that appears suited to your situation.

 

[Old Jazz Guy]

@Fishead Right. I'm learning as we go here... and from what I've learned, if it's not a variable frequency drive, it won't work. Even with a variable frequency drive, I have to be watchful of motor overheating when slowing pitch down much more than 1 or 2 % according to some I've talked to.

Thanks for your help all the same! If you think of anything else, let me know.

 

[muchachos]

This is a great project. What a monster of a find.

Anyone have an appropriate QRK nameplate for sale?

Last things first, eh? There is an auction site user, 'audiotagsiowa', who sells lots of vintage aluminum name badges. I've picked up Garrard and Empire labels from him which were quite well done for about $12 CAD shipped. I think he does custom jobs too as he is happy to add to his offerings.

 

[Old Jazz Guy]

@muchachos thank you - I'm excited to get this thing living again, and thank you as well for the info re audiotagsiowa - I'll search it up.

 

[Old Jazz Guy]

I'm in the process of test mounting a GE VRII in one of the head shells for the Rek-O-Kut Micropoise, and discovered in the other headshell a Pickering V15 AME1.

I have no idea what size the stylus is, and I can only assume the cartridge works (until I actually test it), and of course I assume that the stylus that came with it is garbage but I was happy to find that my spare Stanton N400 V3 series stylii plug right in! Yay!!

Pickering V15 with stylus that came with it:



Pickering cartridge with the Stanton stylus



Second headshell with what I believe is an NOS GE VRII and I have had in my stash for years...





Rek-O-Kut Micropoise S320(?) Transcription length tonearm.



I'm going to give the tonearm and the head shells a nice clean and polish once I've checked it everything and see that everything works.

I'm having fun!

 

[gadget73]

Here's a somewhat out of the box way of doing it. This idea stolen directly from @SteveJewels and his turntable build. Further details can probably be found somewhere on here of exactly what he used.

If you take an accurate and stable sine wave generator and feed it through a sufficiently stout power amplifier you now have a single phase variable frequency supply. Tweak the frequency, change the speed. Amp needs to be able to chug out a good 100+ volts RMS at sufficient current to run this motor, so we're not talking about weenie amps here, and the generator needs to be at least as accurate as the line frequency otherwise your speed regulation is going to be worse than factory spec.

 

[Old Jazz Guy]

Yes I had heard about that. Not the road I wanted to go down but thank you for the suggestion!

I am thinking more and more that this is simply not something that's going to be feasible for me unfortunately.

 

[gadget73]

sometimes the best solution to a problem is to do nothing. Maybe pick up something like a Lenco if you need to play some stuff with really wonky speed variations.

 

[hirscwi]

@Fishead Right. I'm learning as we go here... and from what I've learned, if it's not a variable frequency drive, it won't work. Even with a variable frequency drive, I have to be watchful of motor overheating when slowing pitch down much more than 1 or 2 % according to some I've talked to.

Thanks for your help all the same! If you think of anything else, let me know.

I don't believe this is true with the right controller. You'll have a wide range of speeds - from at least 33 to 78 with the same motor and the proper controller.