DIY TT: motor, motor PS, platter speed measurements - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 2nd October 2002, 01:49 AM   #1
dice45 is offline dice45  Germany
diyAudio Member
 
Join Date: Jan 2002
Location: Munich, Bavaria
Default DIY TT: motor, motor PS, platter speed measurements

All,

this thread is a split-off from the DIY TT thread and meant to harbour all discussions concerning
motor, motor PS, platter speed measurements.

I start right now with platter speed measurements for platter drives not having a speed regulator with quartz reference.
Somewhen in the next weeks, some of you will get their maxon DC motor from me and i cannot give you exact voltages for exact speeds, only rough guesses. But we have to get the speed precisely on the value; most of you will find they are quite sensitive AFA PRaT in connection with wrong speed is concerned.

The easy and precise way to measure platter speed is to use a repeating flashlight flash at a strobe disk having a bar pattern and lying on top of the platter: a stroboscope.

The flashlight has a fixed 120Hz flash frequency and a very short duty cycle, say, less than 5%. Means: the light is on 5% of the time only. The shorter the better.

Strobe disk:
The strobe disk has the right count of (usually radially oriented) bars in equal angular spacing so that at proper speed, the angular progression time between two bars is exactly equal to the fixed flash frequency. Then the bar pattern appears to stand still; if the platter speed is higher, the pattern slowly rotates clockwise, if lower, the pattern rotates counterclockwise.

Formula for bar count: 120*60/speed
Right count for:
33.33 rpm: 216 bars
45rpm: 160 bars
78.26 rpm: 92 bars
The strobe disk can be drawn and printed with any CAD program able to create polar element arrays. Any shape of the bar will do, even dots or the number 33 or 45 works fine: just rotate the pattern element the right count of times in equal angular spacing.

One problem: how to cut the hole for the platter spindle into the strobe disc and not cut it too small, too big, too excentric? A hard task w/o fancy optical and mechanical aids.

My work-around for this problem: Radius of the platter spindle is 3.6mm. Lets assume we use a bit more stiff and heavy-weight paper.
Please use a scalpel and make a vertical straight cut in 3.6 mm distance from the center haircross in 03:00 position. Then make a horizontal straight cut in 3.6 mm distance from the center haircross in 06:00 position. Cuts should intersect. Now you can carefully round-bend a dog-ear upwards. Do not bend the dog-ear sharply.
The dog ear will act as a spring pushing the spindle against the straight edges, allowing no play and not clamping the template as a too small circular hole would do. As the hole is triangular (hence not airtight), the strobe disc will not suck itself on the platter surface. This workaround is good for a strobe disc but also for any tonearm adjusting templates.

Strobe flashlight:
I decided to use a quartz-stabilized oscillator triggering a monoflop with 250µsec pulse width; this pulse drives a transistor switching a green LED with 11 candela @30mA. This is constant current rating, so the pulse current can be considerably higher without destroying the LED. I made the experience that beyond 200mA, such a LED won't increase in brightness, so 150-200 mA pulse current are a wise choice.

Of course, the flashlight could be made using a 555 timer and a driver trasistor, but this circuit will not have inherent frequency stability and it must be tuned to right frequency. And on later re-check, frequency may be not on track.
Been there, done that.

An easy way to make such a flashlight is using a 3.93216 MHz quartz and divide this frequency by 2^15(=327678). CD4060 is a CMOS chip having the oscillator and a binary divider of up to 2^14 onboard. I use a CD4013 (2x D-flop) for another division by 2 and for the monoflop.
A quartz, two cheap CMOS chips, a driver transistor and some resistors and pF caps, and an expensivish green LED, that's all. IF the oscillator oscillates at all, it does so at exactly 120Hz.
I build one as as soon as it works, i post circuit and details.
__________________
Greets,
Bernhard
  Reply With Quote
Old 2nd October 2002, 11:00 AM   #2
diyAudio Member
 
Join Date: Feb 2002
Location: Belgium
If going the quartz oscillator route, there is no need to use 120Hz as your base frequency. Easiest source for cheap x-tals are 32.768kHz watch x-tals. These can be divided down to any convenient power of 2. The formulas of Dice are usable for any base frequency if you substitute your frequency for the 120Hz.
  Reply With Quote
Old 2nd October 2002, 12:02 PM   #3
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Default Re: DIY TT: motor, motor PS, platter speed measurements

Quote:
Originally posted by dice45
An easy way to make such a flashlight is using a 3.93216 MHz quartz and divide this frequency by 2^15(=327678). ....
Bernhard, have you ever thought about of some small 8-pin microcontroller?

1. PIC 12Cxx or AVR ATTiny12 (cheap) If you don't have stuff for programmning I can be at your service.

2. No crystal! Built in oscillators are _very_ good but it doesn't harm to use a crystal.

3. LED

4. Plus output to a PLL.

The LED: I'm not totally sure about higher current -> stronger light. You come to certain point when the light don't get brighter. I don't know if it is only because of the heat or something else.

I have been a real analog guy but recently I have started to like microcontrollers a lot. You can do so many nice things with them especially when it comes to generate pulses and detect pulses, like in your case. You can even create a PLL also with software.

And while we're at it: You need detection of the speed also. Check for opto readers LED + phototransistor together. Works nicely if you have strobo pattern on the platter.
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 2nd October 2002, 04:28 PM   #4
dice45 is offline dice45  Germany
diyAudio Member
 
Join Date: Jan 2002
Location: Munich, Bavaria
peranders,
agreed, PIC would be fine if someone does it. I have no PIC experience, i am a Motorola µC person and if pain is enough, by friend MHuber can convince me to forget motorola and use a hypermodern ATMEL which has everything onboard except a coffee warmer. But you won't get me using PICs. There are small areas of unconvincible prejudice in me, this is one of them. Rather use a 8051 or 8080.

Havoc,
you are right, but i had those 32kHz watch Xtals in my hand; they are huge. I want to have a neat lil thing, maybe even SMT-CMOS piggy-back on the Xtal and p2p wired and no PCB. And i want to have it right now. I want to be able to add a kit to the maxon motors ordered to anyone who asks how to measure platter speed and is willing to refund component costs.

I am completely sure on can come up with a smarter solution, no Q, but i wanted to be able to do it quick'n dirty, not even muse how to avoid the RC timeconstant needed for the monoflop.
And i want to provide it right now. I consider this as a secondary war scenario, low priority but nasty and necessary right now. I bought the components already.

As soon as it works i post schematic and pix and anyone can have or leave it and build a better version

before i forget it: i used Amercian 120Hz as this is the only reasonable frequency i could find giving integer counts of bars for all three popular platter speeds. And even if someone is unbale to print a strobe disk himself, he can order 60/120Hz version from US websites.
__________________
Greets,
Bernhard
  Reply With Quote
Old 2nd October 2002, 05:07 PM   #5
diyAudio Member
 
Join Date: Feb 2002
Location: Belgium
Dice,

Don't know where you got your watch crystal, but there is one in each cheap watch! These are mostly a small metal cilinder about 3mm diameter, 5-7mm long.
  Reply With Quote
Old 2nd October 2002, 06:22 PM   #6
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Quote:
Originally posted by dice45
peranders, agreed, PIC would be fine if someone does it. I have no PIC experience,..
I have a PIC program more or less ready. If you hate PIC I can fix an ATMEL program instead. I have very little experience about AVR but my collegue is a real AVR nerd. (He thinks PIC is pure crap and AVR is gods gift to the mankind... He has a point, I have made a large PIC program, PIC is like MS, not too god but everyone uses it...therefore it must be good)

If you could give me a sketch over the whole concept including the PLL I could see what I could do about it. Send it privately if you want by I don't mind if it's a joint venture.
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 3rd October 2002, 03:07 PM   #7
peterr is offline peterr  Netherlands
diyAudio Member
 
peterr's Avatar
 
Join Date: Apr 2002
Location: Amsterdam
I am probably very naive, but what is wrong with normal 50Hz light? I have a strobe disc that works fine that way.
__________________
Keep an open mind. It helps.
Peter
  Reply With Quote
Old 3rd October 2002, 03:28 PM   #8
UrSv is offline UrSv  Sweden
diyAudio Member
 
UrSv's Avatar
 
Join Date: Jan 2002
Location: Sweden
There is nothing wrong with normal 50 Hz light except the fact that I think it is rarely 50 Hz. I think it is not only rarely 50 Hz but also varies during the day according to power demand on the line network. So in the wee hours of the morning you might play everything a little fast and in the evening a little slow...

The solution thus is something not relying on the mains frequency.

/UrSv
  Reply With Quote
Old 3rd October 2002, 04:55 PM   #9
diyAudio Member
 
Join Date: Feb 2002
Location: Belgium
50Hz is more stable than you think. It has to be. These days with internationally coupled networks, 50Hz has to be 50Hz. It would not surprise me if these guys are as well locked to the timing standards as television broadcasters.

But it more difficult to work digitally with 50Hz than with something like 32.768kHz or higher. In the digital world 50Hz is an eternity, and dividing by 5 is not as straightforward as dividing by 2.
  Reply With Quote
Old 3rd October 2002, 04:57 PM   #10
UrSv is offline UrSv  Sweden
diyAudio Member
 
UrSv's Avatar
 
Join Date: Jan 2002
Location: Sweden
Not that it is the topic of the thread but I think most international connections are DC.

I really can't see why 50 Hz would be more difficult than anything else. Dividing by 5 is not harder than dividing by 2 AFAIK.

/UrSv
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
DC motor speed control winggo Analogue Source 13 25th August 2008 02:48 AM
12V DC Motor Speed Controller - DIY? GlidingDutchman Everything Else 15 24th January 2008 06:03 PM
Motor Speed JannaCassandra Analogue Source 6 7th July 2007 12:29 PM
DC motor speed controller Matt Rowland Analogue Source 144 28th March 2006 06:39 AM
Asking help for tt motor speed unstable chanharvey Analogue Source 1 21st September 2005 07:15 AM


New To Site? Need Help?

All times are GMT. The time now is 10:16 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2