Dual 510...spinning too fast


New member
Username: Pyrensyth

Post Number: 2
Registered: Jan-05
I recently bought a Dual 510 turntable. I live in Australia, I happen to know the the mains voltage is 242 volts or thereabouts (it fluctuates a little). The turntable is an American turntable, meaning that it runs of 110 Volts. It actually says on the back 110 to 125 volts. To use this turntable i had to buy a step down transformer. The Input written on the transformer was 230 to 240 volts, the output was supposed to be 115 Volts. No problem there right? Wrong...the turntable was turning too fast, about 35 RPM when it was meant to be turning at 33.

I figured this had something to do with the belt being worn, but it doesn't does it? Ultimately I came to the conclusion that the motor must be turning too fast, in which case the voltage must be too high. I checked the voltage coming from the Stepdown transformer...135 Volts, not good. I took the transformer back and got another one...similar, but a different brand. Same problem. I went back and bought a very expensive stepdown transformer ($100). I took it home and checked the output, 125 volts, (it said it would produce 115 volts but at least it was better than before.) I plugged the turntable in thinking that since the recommended voltage written on the back is 110 to 125, everything would be sweet. But no, the turntable still turns too fast (maybe not quite as fast as before, but still too fast). This has left me with a few questions that need to be answered...

1. Is it possible that its the belt, and a new belt will remedy the problem.
2. Is 125 Volts too much? Could this be the problem?
3. If it's neither the voltage nor the belt, what the hell is it?
4. Don't tell me about the problem with line frequencies with this turntable, I already know, the line frequency in Australia is 50 Hz so this shouldn't be the problem.

If you've gotten this far thanks for reading all this, I know it's alot, but this is really bugging me.

New member
Username: Pyrensyth

Post Number: 3
Registered: Jan-05
Oh wow, i just read that the strobe light relies on the line frequency to operate. The line frequency in Australia is 50 Hz, the turntable was designed to operate off 60 Hz. Meaning the strobe is flashing slightly too slow. Am i correct in thinking that this would show the turntable to be turning faster than it really is? If that's the case, the turntable may in fact be turning at the correct speed.

J. Vigne
Unregistered guest

You are correct, sir!


Unregistered guest
I just got a 510 with the same problem. I took it apart and it all looked okay. I think the motor may be messed up. I'm still looking into it. Does your pitch control work? If you find anything out, I'd appreciate an email or a posting with the solution.

Unregistered guest
Some turntables use a synchronous motor which synchronises itself to mains frequency (50 or 60Hz) Voltage variation makes less difference to this type of motor. Your Dual 510 actaully has an ASYCHRONOUS motor in it meaning that it doesn't matter about the frequency, but the voltage does. My turntable (bought in 1962) has a voltage selector allowing you to select 220-230V or 230-240V depending on voltage, there is a dropper resistor used so if you select 230-240V some of this voltage is dropped across the resistor so the motor turns steadily. An ASYNCH motor speed will change if the voltage varies between about +/-10V of the stated operating value. If the belt is slack, the turntable when first set turning will take time to reach optimum speed and will not have very much torque and speed will not be that constant. You can either change the belt or take the old one, and cut a small segment out of it then glue the ends back together with superglue.
Good Luck :-)

Unregistered guest
I'm not convinced that your problem has to do with the 230/110 voltage issue that has been discussed heavily in this thread. I live in the USA and have the same turntable with the same problem you have described. The slower speed seems to equate (roughly) to the higher speed, and when I move to the higher speed it really takes off. The belt is fine and the transport is working correctly, the motor is the only component that can account for the speed increase. I bought mine in the mid 70's so I not sure how my problem relates to your but I would sure like to find a solution.

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 3625
Registered: May-04

" the motor is the only component that can account for the speed increase."

Motor speed and the size of the pulley on the motor relative to the size of the sub-platter pulley. Most European tables that used a synchronous motor changed the pulley dimmension to acommodate the different voltage/cycles.


Unregistered guest
Voltage is not your problem. If you are simply connecting a multimeter to your outlet, you will read peak voltage. The actual voltage of the line will be higher than its rated voltage - aka RMS voltage. The first transformer you bought with an output of 135V, is actually more correct than the expensive one with and output of 125V. Your are however, correct in your assumption that the problem is the strobe. Listen to a CD of the same track that you are playing on the turntable. If they line up and end at the same time, your pitch is fine. Enjoy!

New member
Username: Ovenmaster

Post Number: 4
Registered: Apr-05
I tried replacing the belt on my Dual 1257. The correct thickness is 0.026" and it runs fine on 33, but won't change up to 45 because it's too flabby when it rides up against the shift fork. I replaced it with one that was 0.040" and no matter how far down I turned the pitch control, it ran way too fast on either speed. So now I need to find a belt that's the correct thickness as well as length. Belt thickness DOES matter!!

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