Help with using a pwm controller in a turntable

[tonyser]

Hello all,. New to the forum and electronics generally.
Got a few questions about adding variable pitch ( pwm controller ) to a PT01 scratch portable turntable - more info on turntable here : http://www.numark.com/product/pt01-scratch

first question .The pwm controller I'm planning on using is this one. http://www.ebay.co.uk/itm/1-8V-3-5-...145301?hash=item2cb240b1d5:g:0d0AAOSw44BYKWUc
1) Is this suitable ? , the motor in the turntable is 6v
2)What's the best way to wire it. I'm thinking of comming off the voltage regultor 9v stepping it down to 6v maybe using LM2596 Step Down Voltage Regulator or something similar ? or There is a usb 5v power point , maybe I could use that?
3) These methods bypass the on board pitch selector 33/45/78 rpm . How could I wire it so I keep the rpm selector as a option along with variable pitch controller.
Thanks for any help with these questions.

 

[Nigel Goodwin]

It depends entirely on how it originally works, historically most cheap turntables used little DC motors with the speed controller an integral part of it, so probably wouldn't work if fed PWM.

Assuming there are separate adjustments for speed control? (usually preset resistors), simply replace the 78 one with a pot you can easily adjust - no need for PWM.

 

[ChrisP58]

One thing I'd be concerned with would be electrical noise.

Phono preamps are pretty sensitive to noise. And cheap PWM motor speed controls can be very noisy.

 

[dr pepper]

You could just replace all the speed control circuitry with the ebay device, and use a stroboscope disc and just draw lines on the pot scale where 33/45 revs are, if absolute accuracy isnt required this oughta work.
I'd be looking at the pwm controller and finding out what freq it runs at, you'd want it to be well above audio or else you'll hear a whine from the speakers, and even this might not be great if your feeding very high power amps with this thing.

 

[tonyser]

Thanks to everyone for your input . You have all offerd great solutions . As I said I'm new to electronics so I have a question.
To use your suggesion Nigel would I just remove the 78 trim pot and replace it with a linear pot of the same value or higher ?. The 78 pot says 101 , so I'm thinking its a 100 Ohms pot. I'll test it when I remove it .

If its a 100 Ohms trim pot what value standard linear pot would I repace it with ?
Heres a pic of the trimmers that control the pitch.

I've ordered the pwm controller , as soon as it arrives I'll be able to try other suggestions to find best solution. cheers

 

[Nigel Goodwin]

Notice that the 33/45 pots look to be 105, so that might be a better bet for a wide range control.

I would suggest setting it to 45 (or 33) and seeing how wide a range of control the existing preset gives you - and try the same with the 78 preset as well.

It might be as easy as replacing the 78 preset with a larger value pot.