PDA

View Full Version : Interesting experiment



jantheman
10-05-2011, 13:00
Just for fun..like we do...I thought I would check the speed of my 1200 using a Keystrobe LED. With the slider set to 0, the 1200 is spot on using the 1200's own red LED and platter strobe marks but using the Keystrobe LED I have to set the slider to -1 to get a steady reading. However placing the Keystrobe disc (the Keystrobe comes in 2 parts, disc and LED transmitter) on and trying again with the Keystrobe LED and the disc I have to set the slider back to 0 to get a steady reading.
Sounds a bit wierd as I thought they would have both been calibrated for 50Hz. I'm assured that the Keystrobe is calibrated for 50Hz cos it has 2 sides to the disk 50 and 60 Hz so you can choose which to use.
Anyone have an explaination pls.....

Stratmangler
10-05-2011, 13:12
Could be that the mains frequency at the time you tested was up slightly.
The 50Hz nominal frequency we have in the UK is measured over a period of time and then averaged - there is some leeway for variation, but it's pretty tightly controlled.

Assuming that -1 is one down from 50Hz, ie 49Hz, I wouldn't worry about the discrepancy, as it will make no audible difference.

StanleyB
10-05-2011, 13:15
Assuming that -1 is one down from 50Hz, ie 49Hz, I wouldn't worry about the discrepancy, as it will make no audible difference.
If it was a DAC, 2% of jitter would be considered totally unacceptable.

MartinT
10-05-2011, 13:23
Could be that the mains frequency at the time you tested was up slightly.

The Technics is quartz locked and the keystrobe obviously has its own clock, so mains frequency doesn't come into it. I guess the keystrobe and disc have their own timing which doesn't match the Techie's own strobe.

You are safe to assume that the Techie's speed in the locked (detent) position is spot on, or you could get a Mike New platter with no strobe markings so that you don't have to worry any more ;)

Stratmangler
10-05-2011, 13:24
If it was a DAC, 2% of jitter would be considered totally unacceptable.

Aye, that's true enough.
Maybe Ray should complain to his electricity provider ;)

lurcher
10-05-2011, 13:34
If it was a DAC, 2% of jitter would be considered totally unacceptable.

Yep, but its not a DAC. Providing an AES clock supply to every house, and lamppost in the country, while allowing dozens of different clock sources across the entire UK to feed into the clock at the same time might show how tricky it is getting the mains frequency to a steady standard. It was never intended to be used as a timing standard. I suspect the only reason they try and avareage 50Hz is for the few remaining clocks using synchronous motors, and for those the spot frequency doesnt matter as long as it averages out over a 24 hour period.

A friend who works in the generating industry once described the fun it is starting up a supply and getting it syncronised with the 50hz grid before they can join it into the network. And then keeping the thing spinning at the right speed.

jantheman
10-05-2011, 13:35
Could be that the mains frequency at the time you tested was up slightly.
The 50Hz nominal frequency we have in the UK is measured over a period of time and then averaged - there is some leeway for variation, but it's pretty tightly controlled.

Assuming that -1 is one down from 50Hz, ie 49Hz, I wouldn't worry about the discrepancy, as it will make no audible difference.

Dont thnk so....using the platter markings and slider set at 0, when the reading is taken using the 1200 led its dead steady but using the Keystrobe led at the same time its not. Setting slider to -1 gets the keystrobe dead steady but then the 1200 led reading is off.
Using the keystrobe led together with its disk and the 1200 led against the platter marks (at the same time) they both read OK....
Do you see what I'm saying.....the 1200's led and platter marks and Keystrobe disk and LED used independently of each other (slider set at 0) both give a correct reading but try mixing the keystrobe led and the 1200 platter marks and you get a false reading....

shane
10-05-2011, 13:41
The Technics is quartz locked and the keystrobe obviously has its own clock, so mains frequency doesn't come into it. I guess the keystrobe and disc have their own timing which doesn't match the Techie's own strobe.

You are safe to assume that the Techie's speed in the locked (detent) position is spot on, or you could get a Mike New platter with no strobe markings so that you don't have to worry any more ;)

The Technics motor may be quartz-locked, but where does the illuminating LED get it's supply from? If it's from the same quartz reference as the motor, then it's pointless as an absolute reference. if it's from the mains, then it'll show you how far out the mains is. Ideally, it would have it's own quartz reference, but I bet it doesn't!

MartinT
10-05-2011, 14:05
The Technics motor may be quartz-locked, but where does the illuminating LED get it's supply from?

I'm pretty sure it comes from the same reference, so it's a cheat :)

pure sound
10-05-2011, 14:13
the Technics platter strobe markings are not for 50Hz.

Stratmangler
10-05-2011, 14:29
the Technics platter strobe markings are not for 50Hz.

I've just gone through the user manual, and not once is reference made to the strobe working at 50Hz.
In fact it can't be, because it also says that the third line down from the platter top indicates speed lock at true for both 33,1/3 and 45rpm.