Diy Strobe for measuring turntable speed accuracy.

by **Headshrinker** » 12 May 2009 10:30

Off course there's always the Velleman K2656 kit which is a universal crystal timebase (surprisingly similar to this one with selectable 50, 100, or 400 Hz output). I bought one years ago and have finally stuffed the board and soldered it all up. I plan on getting it up and running on the weekend (hopefully). Anyway, just thought I'd throw the suggestion out into cyberspace should anybody want an alternative etc.

Steph

by **rito25** » 20 May 2009 18:34

will the disks work under a compact florescent light?
and are the little dots supposed look like they aren't moving, or should they be blurry?

by **Headshrinker** » 21 May 2009 00:19

The lines on the strobe disc are supposed to stop and not creep in either direction. It's actually a sign of just how stable the power supply and motor are, as often there is a little bit of movement from side to side, as getting a riiple-free supply takes a fairly solid power supply, or ideally, a battery fed regulated DC supply. If the motor runs on AC then the best method is to generate a rock solid frequency like the better quality Linn supplies do. I built my DC supply with coke-can sized capacitors and a good quality regulator. At one stage I was even considering two stages of regulation, which would have probably been overkill, but possibly could have yielded an audible improvement (bass, soundstage). Turns out one stage was enough, but my power supply weight about 10 kilograms.

Flourescent light has a 100Hz or 120Hz frequency, depending on whether your supply is 50 or 60 Hz, respectively.

by **rito25** » 21 May 2009 02:11

So how do i tell if my turntable is going at the right speed?

by **Steerpike_jhb** » 21 May 2009 14:19

a 45rpm strobe disc that is accurate under 50Hz lighting. The closest you can get is 45.112rpm

Fascinating!! So would you offset the crystal to get it accurate??

I have recently learned that most discs are actually cut at 45.11, and not 45.00 - because the cutting lathes were mostly driven from synchronous motors.
So the 'error' in the strobe disc turns out to not be an error at all, because you dont want 45.00.

Quartz turntables that do exactly 45.00 are apparently wrong.

will the disks work under a compact florescent light?
and are the little dots supposed look like they aren't moving, or should they be blurry?

Generally CFL lamps don't work - they don't flash at mains frequency, they have their own oscillators inside.
The blurriness of the dots depends on the 'quality' of the strobe waveform. My DIY version gives significantly less blurry dots than a mains-powered neon or LED lamp, because the current pulse to my LED is very short.

So how do i tell if my turntable is going at the right speed?

The strobe ring appears to stand still, as if it were not rotating at all.

by **rito25** » 21 May 2009 14:23

So what kind of light source should I use?

by **Damien Taylor** » 21 May 2009 15:56

Either mains incandescent or the specially made strobe unit.

by **denti alligator** » 26 Sep 2009 19:47

I'm not able to create my own strobe. What's a good source for a cheap fluorescent or strobe light that will do the job?

by **Conrad Hoffman** » 27 Sep 2009 03:25

LED night lights don't have much filtering and will flicker at line frequency. The contrast of the pattern will be low, but they're quite usable if the room lights are low. IMO, you're way better off with a simple neon bulb and resistor. A neon bulb flashes on both positive and negative cycles, so you get a 120 Hz (USA) flash- what most strobe disks are optimized for, and what gives you the best contrast.

My alignment template program also prints nice strobe disks-
http://www.conradhoffman.com/chsw.htm

Best,
Conrad

by **Plattenbau** » 28 Nov 2009 18:09

Hello everybody,

the thread is kinda old, but maybe somebody could still help me out there with my problem.
I'am not a total newbie in electronics expecially when it comes to turntables. I own a record shop in germany and do repairs and refurbishes on turntables every now and then, with no major problems so far. However I can only build/repair basic electronic stuff since I don't have professional equippment and/or professional skills.
However... this little circuit is killing me, and before I waste another set of ICs I thought I try to ask the community first.

I etched six PCBs which come out very nice and clean and thought to build a prototype first - leaving the trimmer capacitator c1 out and using 22pf capacitators for c2,c3. I used just one LED, bridging the other 2 LED slots. In my second prototype I also used a bridge instead of a switch, since I don't had any left. I had to use substitutes for the ICs, since I haven't found the exact ones in germany. I asked in a lokal electronics shop, an they said it' fine (IC1 = hcf4060be, IC2 = hef4013bp). I made no further alterations than these to the circuit.
When I connect a batterie and pushing (or on the second pcd only connecting the batterie) the switch the light doesn't turn on, but the batterie gets pretty warm/hot... and so does IC2...

So if somebody is able to help me with that, I would appreciate it!

thanks a lot!

Dennis / Plattenbau Aachen

by **Steerpike_jhb** » 28 Nov 2009 18:37

There is an error on my PCB overlay diagram - I think it was mentioned in this thread a while back, the LED flat side should face away from the ICs.
The longer pin of the LED should be closest to (snip) the ICs.

This should not cause the serious overheating you describe though.

Try your circuit without the LEDs inserted, see if IC2 still gets hot.

The substitute chips you used are fine - no problem tere, BUT be aware that these chips are damagd by static electricity and handling in dry weather. They should have been sold to you in protective conductive tubes or the special black or pink bags.

by **Plattenbau** » 30 Nov 2009 10:36

Tried that - same thing!

The dealer is reliable. I ordered the first set of ICs online - I have the same problem with them. I'll pick up my camera from work today and post a picture - maybe that helps. If you have another idea till then, just let me know!

many thanks,
Dennis

by **MelodyMaster** » 30 Nov 2009 10:53

Steerpike_jhb wrote:Anyone tried viewing the strobe disc by the light of a television screen (conventional CRT type). That would be a very accurate 60Hz reference - IF it provides enough light. (0r 50Hz in europe/south africa)
(must be a real broadcast - although a DVD player ought to give a very good refence too).

That would be 59.97 Hertz, which is virtually the maximum allowed slowdown during peak power consumption periods in Canada. (The system runs fast overnight to catch up, average frequency over the full day must be exactly 60 Hz to several decimal places.)

Necromancy, heheh, I didn't see that it was the first page. That's valid info though...

by **Steerpike_jhb** » 01 Dec 2009 23:12

MelodyMaster wrote:That would be 59.97 Hertz, which is virtually the maximum allowed slowdown during peak power consumption periods in Canada. (The system runs fast overnight to catch up, average frequency over the full day must be exactly 60 Hz to several decimal places.)

D'OH! I forgot they changed the TV frame rate for colour, oops I mean 'color'. 59.94 Hz I believe. Still for PAL and SECAM countries, it is exactly 50.000Hz

I measured quite large instantaneous changes in mains frequency, which would have an impact on synchronous turntables, although would not show up at all in a daily average.
Such ac-mains frequency fluctuations would show up on a strobe disc illuminated by a tv set; even if the tv frequency is "off" by 0.1%, it remains rock-steady.