STOP the TECHIE 1200 Ringing !
It has been some time since I did some real work on my techie 1200.I have some time now and have cleared 3 days from my Covid 19 lockdown schedule.
4yrs ago when I was working with some forum members on Bearings and Power Supplies I had noted that I must look at the techie Platter.
There were various posts on the forum re mods, expensive new replacments and a variety of aftermarket matts.
One worked through replacing the rubber damping on the platter underside to reduce the platter "ringing". Ringing being a common issue used often by the aftermarket dealers to sell their goodies or snake oil.
Never keen on modding anything unless for good reason I wanted to delve.
To date I have contented myself with a variety of matts, mainly DIY slicone based but did make a 4mm copper top plate.
My first look at my platters, one a MK2 deck the other a MK5, (I belive these are originals for the decks) got me thinking of how I could measure performance led me to thinking into how best to measure their performance.
I wanted to measure the resonance of a stock platter.
Resonance ( mechanical) is a vibration at a given frequency either unwanted ( Platter?) or wanted ( Tunning Fork)
I often describe a turntable and its immediate electronics (phono pre) as a vibration amplifier, so why not try using its vibration detector (pick up) and electronics to do just that under a controlled situation.
I had an old Shure pick up, a phono+pre amp and most importantly an oscilloscope so I could see whats going on. I am a great enthusiast of " seeing is believing" with all to do with audio--particularly turntables.
My first go at measuring the resonance of my platter was designed to rest the pick up needle on the edge of a platter with the platter supported in a bearing, the bearing held in a bench mounted vice. The only contact point for the platter was the bearing shaft.
The Shure M44 was connected to the phono pre input of a pre amp its output connected to an oscilloscope. A gentle tap on the platter outer are should show up any ringing or resonance on the scope display.
System gain was set and left untouched throughout, the only variable being the intensity if my "gentle tap". What I was looking for was not a "precise tap" as this was an exploratory excercise looking for comparisons. Primarily the level of ringing before considering any mods and the level after any mods were done.
The first photo show the basic meacuring set up. The Shure is fitted to an old techie arm and sitting over the TT spindle with height adjustment, clamped to the spindle when height was set. The platter was gently tapped and the resultant display on my Scope
[IMG][/IMG]
The second shows the scope display, a beautiful sine wave running at close to 250 HZ--- what a clean sinewave almost as good as a tuning fork.
[IMG][/IMG]
The issue associated with this resonance was to my mind the time it took to decay to zero from its start. On this platter it was close to 4 seconds - a long time
There clearly was an issue here that required attention.
My test set up also picked up any unwanted vibration from the workbench etc , and now that I had seen the level of this resonance I wanted to do many more tests with platters and their matts.
Changing matts etc on this platter would be a hassle realining it, so I had to think of a better test set up.
Back to the drawing board.
This will be a long post so ill do it it chapters
End of Chap1
Technics 1200 tweaked,Ianmac Bearing,DACT DIY Phono Pre, Belcanto CD-2, Engineered Switzerland DIY Renderer, Benchmark DAC2, Hypex NCore, ATC SCM40
2nd system --Engineered Switzerland DIY streamer, Sony CDP11,Topping D50 DAC, Hypex NCore. Kef 1point2 speakers. Ianmac Filters