[davidb928]

I have a Denon 1200 turntable and lately, I'm having a hard time keeping the speed stable. On several different albums, the speed will be fine, and then all of a sudden it will either speed up or slow down noticeably, then return to normal speed/pitch.

I've tried to play with the speed adjustment dial, but the problem keeps coming back.

Turntable's been in storage for about 10 years, but was playing fine for about two weeks until this began to happen.

Only thing I can think that's changed is the use of a Hunt record cleaning brush. I've not been pushing down on the record while cleaning, but is it possible I (or one of my kids) could have inadvertently damaged the motor somehow?

I can bring the TT in to local audio shop, but really don't want to incur the minimum $125 charge just to have someone look at it, if there's some tweak I could try first.

Suggestions? Thanks!

System:
Adcom GTP 500II preamp/tuner
Adcom 535 power amp

[Wayner]

Is the table belt drive?

Wayner

[davidb928]

Nope—direct drive.

[davidb928]

Hmmm....Found this on www.kabusa.com...could it be the servo control on my TT is malfunctioning? (I'm fairly sure the Denon has servo-control; it was a highly rated table in its day.)

Speed Drift (Due To Static Stylus Drag)
In a freely rotating system like a turntable, any friction near the outside edge will try to slow the rotational speed. In drive systems without servo control, the turntable truly slows down the moment the stylus enters the groove, some as much as several percent. As the stylus moves towards the center or end of the record, the torque increases and the turntable regains most of its free rotating speed.
To avoid the affects of this static stylus drag, the drive system must have servo control.

[royphil345]

Servo tables prevent speed variations due to power fluctuations, but stylus drag can still be a problem. I've found that lower-end DC servo tables, both belt and direct drive, are about the worst as far as suffering from stylus drag. I'm sure higher-end tables with beefier servo motors are much better...

In order to prevent speed variations due to stylus drag, you'd need a motor large enough to be uneffected by it or a quartz-lock system. A servo table has no means of sensing the actual speed of the platter and making corrections. Servo just keeps the power supply to a DC motor stable.

The first things I'd suspect would be a dirty pitch pot or speed control switch... any power switch or internal switch that starts the platter spinning when the tonearm is moved over the record or is activated by a control lever, etc...  A shot or two of contact cleaner in these places might fix it right up. Make sure you get something safe for plastics and pots. A cleaner / lube would probably be best. Could just be a part has drifted out of spec (probably a capacitor) and needs to be replaced... In this case you would be correct about the servo system malfunctioning.

[toocool4]

Is there a pattern to when it speeds up and slows down, can you think of anything that is happening when the speed changes?

I don’t know if this applies but I have several Sony personal stereos my WM-DC2 speeds up or slows down if my mobile phone is in close proximity to the stereo. While in close proximity when the phone poles for signal or receive calls or text it affects the stereo. Could you have something in close proximity to your TT that interferes with the pitch?

Chris   

[TheChairGuy]

Hmmm....Found this on www.kabusa.com...could it be the servo control on my TT is malfunctioning? (I'm fairly sure the Denon has servo-control; it was a highly rated table in its day.)

Yeah, AC Servo, I believe.