[78-L] TURNING THE TABLES, (was New Cheap Turntable)

[JD]

Date: Sun, 3 Jan 2010 14:31:28 -0800 (PST)
From: DAVID BURNHAM <burnhamd at rogers.com>
Subject: [78-L] TURNING THE TABLES,  (was  New Cheap Turntable
To: 78-L at 78online.com
Message-ID: <533444.43283.qm at web88104.mail.re2.yahoo.com>
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JD wrote:

>Let me add that I was using an excellent cartridge, properly mounted and that I'm experienced enough in audio and >music (a professional in both) to know what I'm doing and certainly what I'm hearing. 

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>From your credentials, I assume you would have recognized if this was the problem but the effect you were hearing >with your clarinet opening, (Rhapsody in Blue or Tchaikovsky's 5th?), sounds to me like acoustic feedback from the >speakers to the turntable.? If you have a good sub-woofer, very low frequencies, even sub-sonics, can travel >through your home's structure and you can easily see the tone-arm shaking and you will hear low frequency >modulation of the clarinet sound as well as a significant amount of rumble.? I also can't see a turntable designed >for the treatment it receives from disc-jockies being able to run smoothly with a high-compliance cartridge.

>db
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You assume correctly, David. It was certainly not acoustic feedback, there can be no doubt about that.  Recall that I played the same disc on my two other turntables and the reproduction was perfect. Additionally, the playback level (moderate to low) was nowhere near a level that would induce acoustic feedback.  I repeated this test several times.  BTW, it wasn't Gershwin or the Tchaikovsky 5th which starts with low clarinet and which effect might have gone unnoticed. I think I've identified the Lp. I just went through my few remaining Mercs and narrowed it down to SR 90132 (Side two): Bartok: Hungarian Sketches, Minneaplis S.O., Antal Dorati, conducting. It begins with clarinet over soft strings. Not quite the way I remember it but I'm sure that's the disc. 
Next case...
Jack

To reiterate, both my turntables have competently designed arms that perform as required and expected. Sadly, I can't say the same for the arm of the turntable in question. Sometime in the 70s or perhaps 80s I'd purchased a three speed DUAL turntable (model 608). It had variable speed, direct drive and a strobe. It might have been my ideal turntable except for the fact that certain aspects of its construction were somewhat flimsy  and the interchangeable cartridge mounts were problematic contact and hum-wise as many tend to be. But it did perform quite well despite the fact that the strobe indicated very slight (and inaudible) speed variation from the initial setting as it ran.  It did, however  have an interesting feature built into the arm's counterweight. It featured an ad adjustment for controlling arm resonace. I didn't give thnis much thought until I played Shure's ERA IV Audio Obstacle Course LP (TTR 115) on it. This is an LP sure to delight any turntable tinkerer.  The last band on side two is a tone arm resonance test. The same music is repeated several times, always at the same level but with a different subsonic frequency (4, 6, 8, 10 or 12 hertz) added each time. All went well until an offending frequency exited the arm. The arm then behaved as if it was trying to jump off the turntable. Adjustment of the resonace knob on the counterweight of the Dual proved its effectivness. It really worked. The purpose of this test on Shure's Lp  was to show the effectiveness of Sure's Dynamic Stabilizer on its V-15 IV cartridges. I had a couple, they were magnificent  and that feature really worked. . Apparently, arm resonance effects are real and can cause real problems under the wrong circumstances. Anyway, it's from this demonstration that I came to the conclusion that the problem with the new TT was that of arm resonance and not flutter or anything else. It's the only time I've ever knowingly encountered that symptom (other than the Dual-Shure demonstration) in a turntable. Next case...
Jack