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Diagnosing / repairing infrequent turntable RPM variance, very brief & infrequent speed / pitch changes-Technics SL-B1
post Jan 23 2011, 23:58
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This Technics SL-B1 turntable - given by son - has very short (maybe 1 - 2 sec) & infrequent (1 or 2x / LP side??) changes in pitch - quite audible. It's one w/ a pitch / RPM adj wheel & strobe. Maybe this was a seriously cheap unit when new & basically P.O.C. No idea. Never had a pitch problem w/ the direct drive Dual that my son borrowed the cartridge from, but then, it wasn't decades old.

God knows how old this is (S.N. = 001 [kidding] - it's MS1116C161), & could be due to lubrication. Again, I'd expect it to occur more often.

The changes are over so quickly, can't look at the platter / strobe to see if shows anything changing. Have it hooked up to an UPS w/ AVR (automatic volt. regulator). Assuming that works, changes in speed shouldn't be due to voltage variations - but haven't checked voltage changes, much less monitored over 15 - 30 min period.

I believe it's belt driven (not had apart) & problem could be belt slipping, but I'd expect it to occur more often if it was. 99.9% of time, no audible pitch changes.

*** Have noticed the pitch adj (wheel) doesn't hold the speed constant. Could be # of reasons, incl. bad electronic components in rheostat. I used this type table in '70's, & most showed the markings fairly stable. Sure, there was slight variation back & forth, but not from markings dead still to moving at pretty good clip.

The strobe / markings on this Technics start to drift up / down from stationary, then maybe back to stationary for a few min. But I can't tell change in pitch when that happens. It's very touchy - a micro turn of the adj wheel may cause markings on platter to start spinning considerably. One's I used in '60's - '70's had much less sensitive adj wheels. ("You're livin' in the 60's, man!)

Haven't looked at the guts of adj wheel either - if it's mechanical variable rheostat or strictly electronic.
Any suggestions (toss it?)? Thanks.
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post Jan 25 2011, 01:50
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If it uses an idler pulley, then it's not direct drive, right?

Yes, that's not right, or, No, that's correct. My Dual is direct drive & uses an idler wheel (not pulley - I misspoke) that moves up / down tapered motor shaft to slightly change speed of idler wheel, which engages a flange on the platter. The motor shaft has 3 steps for 3 speeds & each one is tapered slightly.

Current problems aside, the Technics SL-B1 specs I found (who knows if they're correct) are a bit better in wow/ flutter & rumble than my Dual specs, even though the MSRP was much higher on the Dual. Some mfgs fudge their specs more than others, or may be I never had sensitive enough ears to detect differences. If I can't fix the Technics, I'll drag out the Dual.

Yes DVDdoug, I've seen that page several times - others will find it useful. I have several wave repair / noise editing prgms to occupy my time. They all have their pros / cons (what little I've used them). Nero 9 Wave Editor (& SoundTrax to record), Audacity (1.3.12b), Creative X-Fi Titanium's software pkg & Cool Edit 2.0 (last ver before Sony bought it & changed name).

Nero's a little light on explanation of what some settings do, but their auto declicker / decrackle / denoise (all separate w/ several settings on ea) work pretty good if fool w/ levels a bit. Not the most intuitive prgm I've ever used, but once learn it, works as advertised.

Audacity is a nice prgm. Like Nero, has way more than I'll ever use. Pretty good documentation - better than Nero's IMO. I like Audacity's equalizer a bit better & has record / play peak meters, even when have waveform windows fill entire screen. Many of its components are written by different people. I imagine it works well once learn it.

Creative's wave repair isn't bad, though I've not tested it on LPs. It's a little light in the loafers - but it is free. Haven't tried Cool Edit but lots of folks have used it for many yrs.
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Glenn Gundlach
post Jan 25 2011, 04:39
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You mis-understand the concept of 'direct drive'. Your 1218 uses an 1800 RPM (4 pole) synchronous motor with a conical pulley. The pitch control varies the height of the idler to change the 'gear ratio' and therefore the speed. Still, if the line frequency changed (it never does) the speed would change porportionally. My Dual 721 is a true direct drive table. The motor runs at 33 1/3 or 45 RPM without belts or idlers. The advantage is no vibration induced rumble. Direct drive speed is maintained with a servo system totally independent of line voltage or frequency. Some are crystal referenced but as Dr Richard Greiner, UW Madison electrical engineering professor in the '70s said, "it's an elegant solution to a non-existent problem".

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Posts in this topic
- Jenni28   Diagnosing / repairing infrequent turntable RPM variance   Jan 23 2011, 23:58
- - DVDdoug   That's a strange symptom. QUOTE It's ve...   Jan 24 2011, 20:15
- - Jenni28   Thanks. Yes, it's belt. Anyone know where I...   Jan 24 2011, 21:46
|- - DonP   QUOTE (Jenni28 @ Jan 24 2011, 15:46) You ...   Jan 24 2011, 23:05
- - DVDdoug   Another option is to transfer the cartridge to the...   Jan 24 2011, 23:35
- - Jenni28   QUOTE If it uses an idler pulley, then it's no...   Jan 25 2011, 01:50
|- - Glenn Gundlach   You mis-understand the concept of 'direct driv...   Jan 25 2011, 04:39
|- - DonP   QUOTE (Glenn Gundlach @ Jan 24 2011, 22:3...   Jan 25 2011, 13:41
|- - stephan_g   Old thread, I know. QUOTE (Glenn Gundlach @ J...   May 29 2011, 01:29
- - Jenni28   Glenn - I didn't misunderstand the direct driv...   Jan 25 2011, 17:25
|- - cliveb   Apologies for coming in late - I've been away ...   Jan 30 2011, 11:18
- - Jenni28   Thanks Clive, for the link. I wasn't familiar...   Jan 30 2011, 19:04
|- - eevan   QUOTE (Jenni28 @ Jan 30 2011, 19:04) You ...   Jan 30 2011, 21:04
|- - Jenni28   QUOTE (eevan @ Jan 30 2011, 14:04) Use a ...   Jan 31 2011, 15:29
|- - eevan   QUOTE (Jenni28 @ Jan 31 2011, 15:29) Whic...   Feb 1 2011, 22:42
- - Jenni28   Yes, eevan / Ivan, some persons from Europe someti...   Feb 2 2011, 02:49
- - Arnold B. Krueger   QUOTE (Jenni28 @ Jan 23 2011, 17:58) This...   Feb 2 2011, 13:42
|- - Glenn Gundlach   QUOTE (Arnold B. Krueger @ Feb 2 2011, 04...   May 29 2011, 05:46
- - Jenni28   Arnold, yeah, sounds like a grease spot on belt m...   Feb 2 2011, 18:03
- - Arnold B. Krueger   QUOTE (Jenni28 @ Feb 2 2011, 12:03) Arnol...   Feb 3 2011, 14:19

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