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Adding a pitch control

Old Jazz Guy

Old Jazz Guy

New Member
Hey all - so I have determined that my old no-name transcription turntable actually is a QRK Model 17. I am in the process of sprucing it up with a good servicing, a nice Rek-O-Kut Micropoise transcription arm, new felt and a custom plinth. This thing is massive - and HEAVY!!

My question to you all is:

I wish to add a pitch control - and how would I do that?

I have a similar vintage Garrard 4HF with a pitch knob, and I wonder if I find a junker could I wire in the pitch control to the QRK? Fortunately, there's already a 1/2" hole in the QRK's chassis where someone drilled for an additional tonearm or a light, but nothing is there now, so it's the perfect place to add a pitch knob.

The other thing I need is a QRK name plate if anyone has...

Cheers all!
 
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Hi OJG, and welcome to AK!

This may not be what you are after, but a suggestion nonetheless.....I have an external power supply that provides the function of regulating the voltage to the motor. It also came with a fancy remote that allows me to see the speed by pointing it at a strobe disc on the platter but it's really just fluff IMHO. The system is extremely accurate and maintains the voltage, no matter what is coming in from the wall, so very consistent. There are a number of such units available so you can do some poking around until you find what suits your needs. I think Project makes one.....

Good luck and happy listening! Very cool that you are resurrecting that veteran!
 
The voltage is not what controls the rotational speed on most QRK tables. They typically use some version of AC synchronous motor. The rotational speed of that type of motor is controlled by the frequency supplied, not the voltage. A picture of the motor would help. There are several motor controllers that will work but most commercial ones will not have enough output wattage to operate the commercial motor on a QRK. There are several DIY options that work beautifully and allow tweaking of the frequency fed to the motor (and hence fine-tuning of the rotational speed. Plus some of the QRK tables do have a mechanical pitch adjustment.
 
Thanks!

It's a Bodine motor about the size of a large grapefruit - massive. If there was a pitch control on this machine it has been removed, but I'm not sure if there ever was one. I will update this thread with a picture of the turntable guts... if there is a DIY option that is affordable and effective, and can be installed with just a knob showing, that would be perfect. Stand by and I'll post a pic soon.
 
Very impressive table, love it…..As already stated, voltage +/- 10 as an example, has no effect on the speed but ROK called the idler adjustment something like “fine speed control” , but your not changing the motor rpm when doing this adjustment.

This is completely different than say my Thorens TD124 which has actual pitch control….

Have a TR43H and TR12H and a Russco Studio Pro all which require idler adjustment to get stable precise speed….

The knob in the photo has small set screws on each side of the chrome flange that functions as idler pressure adjustment(s) which allows one to set the “speed” minutely…

6E73E4B2-9DE5-4213-8F1A-E62BD32BC1DD.jpeg

VR
Andy
 
Interesting - an entirely mechanical adjustment. I assume that the idler drive has to be pliable enough for it to work well, and that the motor is strong enough to overcome any additional strain created by increases in pressure.
 
If you need more range, then you can modify the motor for a tapered spindle and figure some mechanical method of moving the idler up and down relative to the motor to change the speed. Probably easier said than done though.
 
Agreed - that would be the more user-friendly and available at the moment option, but it would likely be more challenging to design and install. I'm looking for an electrical version... going out to take pictures shortly for @hirscwi and see what he says...
 
It does, but that's not the point for me. Often I find that older records and even some new ones are not mastered at the right speed, so if you play them at 33, 45 or 78 as required, they're playing either sharp or flat to the correct pitch. As a musician and record producer blessed/cursed with what's known as Perfect Pitch, I like to be able to adjust the speed to the actual correct RPMs. :yikes: :blah: :)
 
Here are pics of the electrical workings, and the motor plate.

I assume the can at the top of the picture below is the device that regulates the current to the motor, and allows it to run at a constant speed without fluctuating due to voltage from the wall.

The AC power cord is currently not attached to the bus bar - the white piece of tape and the connector to its left are where the AC cord connect.

20220319_121250.jpg

Here is the motor plate:

20220319_121312.jpg
 
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So - I have been told that the thing I called a can is actually one of two capacitors - an anti spark or click suppressor (when turning the turntable on), and the other is for starting the motor up and getting the heavy platter turning quickly.

Regardless I'm still interested in some of the DYI options available to me for adding a pitch control.
 
The can capacitor shown does NOT regulate voltage (caps don't do that). What the cap does is to create a second phase sine wave for the motor at about 90 degrees offset from the first. The motor could be 2 or 3 phase - I can't tell from photo. The only way to regulate the rotational speed of this motor is to vary the frequency fed to it (unless there's a mechanical pitch control that is not shown in the partial photos - I seem to recall that the QRKs I've worked on had a pitch control but could be wrong). The type of controllers I mentioned will work but they will definitely need to be robust - I can't read the Ampere rating on the motor so I don't know the wattage needed but I'd guess at least 25W - maybe more. Doable, but not cheap.

I would replace the capacitor regardless of what you do. It's a "Motor Run" cap. You can get film caps for about $5. It appears that you need a 3.75mfd cap for this motor. That's not a size that's made but you can combine a 3mfd (e.g. Kemet C274ACF4300WA0J0 with a .75mfd cap (e.g. CDE 754MABA01KHL). These must be in PARALLEL. Whatever you do, bu sure they are MOTOR RUN caps.

By the way, that's one large motor. I have a deck with an Ashland 1/100 HP motor and it's wonderful. Yours is 1/75HP so 33% larger.
 
Fishead said:
Hi OJG, and welcome to AK!

This may not be what you are after, but a suggestion nonetheless.....I have an external power supply that provides the function of regulating the voltage to the motor. It also came with a fancy remote that allows me to see the speed by pointing it at a strobe disc on the platter but it's really just fluff IMHO. The system is extremely accurate and maintains the voltage, no matter what is coming in from the wall, so very consistent. There are a number of such units available so you can do some poking around until you find what suits your needs. I think Project makes one.....

Good luck and happy listening! Very cool that you are resurrecting that veteran!
Click to expand...

@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.
 
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hirscwi said:
The can capacitor shown does NOT regulate voltage (caps don't do that). What the cap does is to create a second phase sine wave for the motor at about 90 degrees offset from the first. The motor could be 2 or 3 phase - I can't tell from photo. The only way to regulate the rotational speed of this motor is to vary the frequency fed to it (unless there's a mechanical pitch control that is not shown in the partial photos - I seem to recall that the QRKs I've worked on had a pitch control but could be wrong). The type of controllers I mentioned will work but they will definitely need to be robust - I can't read the Ampere rating on the motor so I don't know the wattage needed but I'd guess at least 25W - maybe more. Doable, but not cheap.

I would replace the capacitor regardless of what you do. It's a "Motor Run" cap. You can get film caps for about $5. It appears that you need a 3.75mfd cap for this motor. That's not a size that's made but you can combine a 3mfd (e.g. Kemet C274ACF4300WA0J0 with a .75mfd cap (e.g. CDE 754MABA01KHL). These must be in PARALLEL. Whatever you do, bu sure they are MOTOR RUN caps.

By the way, that's one large motor. I have a deck with an Ashland 1/100 HP motor and it's wonderful. Yours is 1/75HP so 33% larger.
Click to expand...

Yes, you are entirely right - I've been talking to a local electronic radio repair guy who's familiar with these kinds of things, and he said exactly the same things you did and taught me some stuff at the same time.

Thanks for the further insight!
 
The larger cap is definitely NOT an anti-spark cap. It is a motor run as just mentioned. These are specifically designed to have mains voltage across them at all times. Do not replace with any other type of cap.

The small grey box with red and black wires to it could be a spark suppressor. Can't tell from photo. Such a cap is usually in the range of .01 to .47mfd and is X-Y rated (i.e. safe to put across mains). It is connected directly across the switch and help to reduce arching which ruins the switch contacts. Do not replace a spark cap with anything but X or Y or X-Y rated cap or you can have a problem.
 
For those wanting more general pictures:
20220320_142900_001.jpg 20220320_142815.jpg

I am doing new felt today or tomorrow, and building a custom plinth over the bext while.

Anyone have an appropriate QRK nameplate for sale?
 
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