Need some quick Technics help

[Marco]

Yup... Great advice there, Dave

Marco.

[Khom]

I did some measurements a few years ago, see picture. Checked hum when cartridge is over vinyl and on it, inner and outer groove. I was surprised by the second harmonic (100 Hz) and tried to lower it by removing upper part of transformer permalloy shield, but no luck. Obviously, it's mechanical hum. So, moving transformer into separate case is absolutely necessary action.

[Mike_New]

Interesting traces Valery, I like coloured wiggles!!
I notice that the "power ON in outer groove trace at 100Hz, which is further from the transformer; is somewhat higher than the
"power ON" inner groove which would be much closer to the transformer.
At 50Hz they are identical but slightly higher in amplitude. How would you explain this??
One possible analysis is that the platter is vibrating at the second harmonic due to bearing looseness allowing it to do so.
The outer edge of the platter would of course have a higher amplitude than the inner part.
What would happen if you put a heavy weight onto the centre??

[Khom]

Sorry for delay. I don't have suitable explanation for the same levels at 50 Hz. I can suspect only interference between waves coming through two ways for transformer vibration propagation. First: base -> main bearing -> spindle -> platter -> needle and second: base -> tonearm pivot -> tonearm tube -> cartridge. I'm not sure. Besides, it was a quick test and I could be wrong.

100 Hz can be explained by transformer coil vibration, because we have bridge rectifier and current consumption has the form of short and high amplitude currect pulses at 100 Hz. Additionally, it can be magnetostriction effects or transformer shield vibration.

When I got Techie I knew that transformer must be removed in short time and I didn't make detailed experiments. I just removed it and forgot.

[guardofmagog]

I did some measurements a few years ago, see picture. Checked hum when cartridge is over vinyl and on it, inner and outer groove. I was surprised by the second harmonic (100 Hz) and tried to lower it by removing upper part of transformer permalloy shield, but no luck. Obviously, it's mechanical hum. So, moving transformer into separate case is absolutely necessary action.

Back in 2009 there was a debate between two PSU manufacturer regarding this 100Hz issue. If I recall well, one was saying that it was the AC 50Hz harmonic (2 x 50Hz) and the other one was saying that it was the strobe light generating this. I tend to believe that it is the strobe light since the 100Hz tone was also apparent in USA where we use 60Hz. The harmonic should have been 120Hz right? KABUSA strobe disabler does remove this 100Hz tone.

[CageyH]

So does fitting an external PSU and having just the strobe on the switch.
That is the way I have mine connected, and without the platter dots, the strobe serves little purpose.

[guardofmagog]

So does fitting an external PSU and having just the strobe on the switch.
That is the way I have mine connected, and without the platter dots, the strobe serves little purpose.

Hi Kevin,

I don't know if your strobe switch is sufficiant to remove the 100hz tone, I am no expert but it seems a bit more complicated than that. Here's an insert of KABUSA.COM website explaining this issue. You can find this info in the What's new section at the end of the page. For the PSU and Strobe light disabler you can find information in the Everything Technics Starts Here section.

I'm sure it will be helpful,

Eric


Jan 4, 2009
SL-1200 Power Supply Controversy
Just as there was lots of criticism of the '1200 arms before they were rewired and fluid damped, now there seems to be a new focus on the 1200's internal voltage regulator: A textbook 3 transistor slow start circuit that maintains the operating voltage at 21VDC at a runnung current of 259mA. You know, I did all this research years ago, so when I first looked at this UK site's data, I thought they had something, but I have looked closer and can now comment more intelligently.

A UK website is showing 'scope photos suggesting that the load regulation of this circuit is somehow unacceptable. I feel I have to point out a big error with this conclusion. It's so obvious when you study the numbers: Their data is not the showing the motor current at all, it is showing the strobe lamp current! Just look at the repitition rate, it is symetrical 10ms(100hz). Motor currents pulse at a very slow rate(1.65 Hz). If the motor was pulsing at 100 hz, like their 'scope photo shows, the motor would be humming along at some 2,000 rpm(100/3x60)! And it can't be ripple from the main capacitor either for that waveform would not be symetrical like they show. It is so easy to mis read data when you are expecting a certain result in advance. We see this done with tonearm resonance flexure plots as well as harmonic distortion plots. It is always important to actually "run the numbers" to get the true impact. It also helps to know what you are looking at.
Installing an outboard PS after the internal regulator may reduce the strobe artifact, but disabling the strobe itself is a better solution for then, the noise source EMF no longer exists.

The internal regulator responds very well to motor load currents, but is not "fast" enough to completely extinguish the strobe lamp currents. However, note that it is doing quite a good job as the regulation is still only 0.05% of the 21VDC operating voltage. When I saw this in my own research, I saw a much more cost effective solution to it: our SX-1200 Strobe disabler circuit completely removes this artifact and EMF at a very low cost. Because while you may only see 10mV RMS on the 21V main rail, on the other side of an isolation resistor, you have 16VP-P which produces yet another EMF field. The only way to remove it is to disable the current path to the strobe LED's.

[CageyH]

From what I read in the above, disabling the strobe to reduce the noise is very similar to not turning it on?

[guardofmagog]

From what I read in the above, disabling the strobe to reduce the noise is very similar to not turning it on?

Sorry I can't help you on this. If you are worrying about it you may contact Kevin at KAB by email. I emailed him a few times on different products and he is very generous in providing information.

[Marco]

That's rather interesting, and I suspect that Kevin is right again (as usual)

The strobe light-disabler mod is one of those I chose to have carried out years ago, when I bought my SL-1210 from Kevin, and had it fully 'KAB modified'. I now feel vindicated in doing so, as indeed I do combining it with the use of a quality off-board PSU, although no longer one of Kevin's.

In any case, the strobe lamp no longer performs any useful function, once you've changed the platter!

Marco.