Technics SL-1301 running 1% fast

Hello All,
I recently purchased a Technics SL-1301 with a jammed 45 selector switch that I managed to fix. While testing the turntable for any other issues I discovered the reference strobe app on my smart phone wasn’t synching with the turntable’s strobe which is supposed to be locked at 33.3333. rpm. I adjusted my phone strobe speed to 33.666 and it synced with my turntable strobe light. As it turns out this turntable doesn’t have pitch control pots. For further reference I played the same song from vinyl and an online steaming source. The vinyl slowly out paced the streaming source. I’m trying to figure out if a +1% drift is common for quartz locked turntables. I’ve read that the reference crystal frequency may drift over time, and this turntable is over 40 years old. Otherwise, the turntable runs great and holds steady with a surprising amount of drag. Any help is appreciated. Worst case scenario is I’ll have a little more free time from my vinyl ;).
 

Attachments

  • IMG_8744.jpg
    IMG_8744.jpg
    615.2 KB · Views: 132
Last edited:
IC201 pin 7 square wave should be 262.08kHz. 1% fast would be 264.7kHz, and of course would mean the crystal is running at 4.2352mHz instead of 4.1932mHz.

There's no adjustment for the oscillator on this model, so if it is off you'll need to either replace it or adjust the value of C226. The SP10-MK3 service manual, control circuit, IC202, gives some clues. I'm not sure adjusting that much is a good idea, but am too lazy to do the math.
 
I'd be inclined to print out a strobe disk and check the speed with a fluorescent or incandescent lamp. The apps available on smartphones are useful, but generally not accurate for speed.
As JP said above, its unlikely that the Xtal has drifted that much.
Even comparing songs from differing sources is only useful if you're sure they come from the same master.
 
I'd be inclined to print out a strobe disk and check the speed with a fluorescent or incandescent lamp. The apps available on smartphones are useful, but generally not accurate for speed.
As JP said above, its unlikely that the Xtal has drifted that much.
Even comparing songs from differing sources is only useful if you're sure they come from the same master.


Ralph's smart. :D


Those phone strobe "apps" are IMO worthless.
It seems people rely on their damn phones for everything these days.
And relying on something streamed over the internet is also questionable.


You're dealing with a 1970's, 1980's product, and should use the appropriate (era) tools for troubleshooting and calibration.
 
Thanks for the help and insight. Those crystals are hard to find. Thinking c226 is out of spec, but the tolerance in the manual is 10%. Anyway, I’m wrong. I can’t explain why the phone app is also wrong by 1%. I just checked twice with the good ole stop watch (on my smart phone) and counted the number of rotations at 33rpm for 6 minutes: 200. If there is a +1% increase the count would be ~202. Ugh sorry for the false alarm - I think this is lesson to forget the technology and enjoy the magic of music :))
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
But then you're only referencing it to mains frequency , whicn is up and down like a yoyo...

How much?

My experience, and the UK data cited here, says unless the grid is in crisis (Shoreham has gone off-line unexpectedly), the yoyo is under 0.1%, NOT 1%. And often visible on a strobe disk, as added wobble on top of the repeatable wobble from printing and platter errors.
 
I’m trying to figure out if a +1% drift is common for quartz locked turntables. I’ve read that the reference crystal frequency may drift over time, and this turntable is over 40 years old.


No, quartz is far more stable than that, drift is measured in parts per million, not percent.


The way to check the turntable is with a strobe - otherwise you are conflating the accuracy of the streamed version and the vinyl with what you are trying to measure (both sources may be out - they are not reliable references).


And if the turntable is out perhaps there's a speed adjustment control that just needs tweaking.
Is this video relevant? Fixing Unstable Speed on Technics Turntable - YouTube
 
IC201 pin 7 square wave should be 262.08kHz. 1% fast would be 264.7kHz, and of course would mean the crystal is running at 4.2352mHz instead of 4.1932mHz.

There's no adjustment for the oscillator on this model, so if it is off you'll need to either replace it or adjust the value of C226. The SP10-MK3 service manual, control circuit, IC202, gives some clues. I'm not sure adjusting that much is a good idea, but am too lazy to do the math.

Hi,

I found an apparent discrepancy in one of the crystal loading capacitors (C227 - 220pF vs 330pF) connected to IC201 pin 3. This could be a typo because I haven't been able to measure the value. I've attached screenshots of that section in SL-1301, SL-1401 and SL-1300MK2 (C205). Could the discrepancy account for a slight change in frequency? I recently replaced the electrolytic capacitors, diodes, and readjusted voltage, current and tracking with an oscilloscope. Now I am entertaining the idea of replacing some of the more essential ceramic capacitors (though I hear they rarely need replacing) when I stumbled on the discrepancy. I should add when I used the same phone strobe app on my sl-1700 (now sold) both strobes were spot on.
 

Attachments

  • SL-1301.jpg
    SL-1301.jpg
    124.4 KB · Views: 61
  • SL-1401.png
    SL-1401.png
    805.1 KB · Views: 56
  • SL-1300MK2.png
    SL-1300MK2.png
    615.2 KB · Views: 55
Probably a typo. Errors in their service manuals are rather common. Typically best to replace it with the value that came out - it’s stamped on the cap. That said, I wouldn’t bother.

Ok thanks for the response. Decided to experiment on my turntable with new MLCC capacitors from mouser. Will see if there’s any difference in waveform and frequency in 220 pF vs 330pF.