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Acoustic feedback effect on turntable ...
I put a stationary record on the TT and lowered the stylus onto it. I then play Pink noise from the speakers, while recording the cartridge/pick-up signal. This is what I get
Turntable 1 Michell Gyro SE, SME V AT-OC9MLii at 59db gain /200 ohm. No platter mat used,
Then another TT Denon 51F with Shure V15 IV Jico SAS-B at 39db gain /47k added to the plot=blue curves
Let's see if we can tell much in a comparison using 30 second samples, they go by very quickly :) This subject came up in the new AT cartridge thread...
Acoustic feedback effect on turntable ...
I put a stationary record on the TT and lowered the stylus onto it. I then play Pink noise from the speakers, while recording the cartridge/pick-up signal. This is what I get
Turntable 1 Michell Gyro SE, SME V AT-OC9MLii at 59db gain /200 ohm. No platter mat used,
To find out what compliance / resonance is on a pickup, you need to know what the effective mass of your tonearm is, and what it is with the pickup installed. Usually you take the stated effective mass and add the pickup weight. But effective mass is not just effective mass, is the stated effective mass with the arm balanced with or without the pickup going to make a difference. So to nerd out a little about this, I played around with some math and statics and torque.
It turns out that if you add mass to a balanced arm, the arm must be rebalanced and that entails a change=INCREASE in the effective mass, and after a lot of tinkering and checking and some mistakes and finally correcting the mistake I come up with the following formula:
dEM= Increase in effective mass=CM1+(CM1^2+2*H*CM1)/W
Where:
CM1=PU mass or other change in weight
H= Effective mass of the headshell end of the arm, typically 90 to 95% of the stated effective mass
W= Mass of counterweight
Let's take an example with a stated effective mass of 10 grams and add a pickup of 10 g with screws and all, and a counterweight of two hundred grams (which is quite hefty=high end counterweight)
New effective mass is therefore not 10+10=20 but 10+10+1.45=21.45 grams or a full 3.6% lower resonance frequency, (possibly the same % effect on calculated compliance from test plate resonance Hz). If you have a lighter counterweight, for example 100 grams, the addition is twice as much, almost 3 grams. This may be an explanation for those wondering why the resonance frequency was lower than they thought…
For simplicity I assumed a static balanced arm, but with a static balanced arm the effective mass will be slightly less due to counterweight adjustment, can be calculated from static balance equation…that can amount to 0.2 to 0.3 grams …
There is indeed a lot to worry about regarding vinyl reproduction
I will, looks good enough to try it out, Canada was the closest to me and price seems right. I have to confess, btw - Stereophile had an article on the turntables Unitra makes.
Though in my defense, I didn't read the full piece but went to the Unitra website and looked at their products myself, instead.
Haven't found a dealer, from the website of Unitra - that ships the WT-2 or any products from them for that matter, to the US.
I sent an e-mail to Unitra to find out who would be willing to sell and ship. Will take a while longer than I thought, I guess - still on it, though.
Fisher MT-6330 turntable speed stability and internal pictures. Not serviced-, but not bad. in fact close to the spec of 0.035 DIN W&F.
(The visual trend and data is very similar to the new Denon 3000NE=
It is a good 70usd replacement for my 30usd Sony PS-212 as as kitchen bench TT to try out cartridges and stuff.
Next I will service the simple tings myself , clean pots and set speed control and motor DC bias according to service manual
The slow oscillations once per rev are maybe from too high servo gain, but servo gain is not adjustable as it is on the 6250 model
forums.stevehoffman.tv
thegrooveman.com
