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I need a circuit that 'buffers' voltage applied to an electric motor to slow down its movements. For a record player.

I'm looking to build a circuit that slows the voltage spike sent to an electric motor. Something that would progressively apply power and progressively power down.It's for a linear turntable. The tone-arm is belt-driven by an electric motor. The issue is, the motor moves so suddenly that it creates an audible 'thump' in the speakers from the quick movement. Would a capacitor in parallel do this?

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rickharris5 years ago
A soft start

Is the motor DC?

Is it speed controlled.

If this is a bought system i am surprised that there isn't a soft start on it.

Wouldn't it be easier to mute the speakers until the deck is up to speed?
CST10 (author)  rickharris5 years ago
This is not for the drive motor, this is for the DC motor that pulls the tone-arm across the record. It's an older TT
You did say that sorry I jumped to a conclusion.

IF the motor is DC and IF it only drives one way

You can try putting a fairly large capacitor in parallel with the motor - Make sure it is a high enough working voltage AND connected the right way round or electrolytics go Puff (or Bang).

Otherwise I think your back to muting the amp until things settle down.
CST10 (author)  rickharris5 years ago
The 'thump' happens everytime the motor moves the tone-arm.

Basically the tone-arm on a linear tracking turntable is two pieces. One is mounted to the chassis, rides along a track, and is moved by the motor. The other half, the half with the cart and needle, rides on the record, and tracks along. There's a contact switch between the two hales, when the needle and cart ride far enough along the record, the switch makes contact and the motor slides the main half along its track. It bumps a fraction of an inch every time, every few seconds.

The motor drives the tone-arm both ways across the record, it auto-returns.

I think we have got to the stage where it isn't possible to make further progress without actually being there and seeing/testing what is happening.

Sorry.
Trouble with that, without a current limiting resistor, something may go bang in the driver. With a current limiting resistor, it may stop the motor working properly.

The best way might be to concoct something with a voltage regulator, so the output impedance is very low all the time.
Good point. It' not going to be easy. I expect the motor voltage is reversible anyway.
We're in H bridge territory then
lemonie5 years ago
Is this something you are making or something that used to work-right but doesn't now?

L
A lot depends on the motor type used. I've never seen a DC motor turntable drive, unless its had some serious control gear to regulate the speed