 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
In Reply to: Thanks posted by Thomas on March 24, 2002 at 12:19:50:
The Lingo has no pots to the best of my knowledge. The latest revision of the Valhalla had a single pot but I think earlier boards had one or two more. I once built an electronic speed control from an Audio Amature article by Gary Galo and it had a number of pots. One for gain, distortion, symetry, and speed adjustment. It took some effort to set up.
Follow Ups:
I have very poor knowledge of how these things work and also about electronics in general. To generate two artificial sine waves, there must be some kind of stable oscillator curcuit that later is amplified and then that signal drives the motor. How does the Valhalla and Lingo work to generate the sine waves? I've read the Lingo use some kind of crystal, but how does the Valhalla work?I really don't get how the Linn Axis PSU work to generate the artifical sine waves. There should be some similarity with the Valhalla, but I don't know whether the Valhalla decreases the voltage to drive the motor silently as the Linn Axis PSU does. Doesn't the Lingo decrease voltage fed to the motor after power-up?
Thomas
Well I cannot pretend to know a great deal more about how they work either but I do know both the Lingo and the Valhalla use crystals to generate their sine waves. The DIY one I build used an oscilator circuit for what it's worth.The Lingo is direct coupled and offers separate drives for both phases of the motor.
The Valhalla uses only one drive for both phases of the motor with a single capcitor to achieve close to 90 degrees phase shift between them.
I do not remember the Valhalla or Lingo changing voltages except for the Lingo in 45 RPM only - it took some time to get up to speed and change modes. Both also put out around 80 volts when measured during use. My experiments with similar circuits and motors suggest that you need at least 60 volts not only to get up to speed but to navigate difficult passages.
I don't know what the Axis motor control board does but it looks like a pretty simple circuit and I'd wonder if if even generates a proper sine wave or just makes do with a square or trangle wave which are far easier to achieve.
Maybe its Wein bridge oscillator? I'll measure with a oscilloscope next weekend, if I find one.http://sound.westhost.com/project22.htm
Thomas
Thomas, you almost make me laugh with nostalgia! ;-)
In 1974, I moved to Switzerland and I needed a 60 Hz source to run my Ampex tape recorder. I built it with an Xtal source that Ampex had made for motor drives. When I got my Linn, I got the 60Hz version and used the same source. In those days, Linn was bigtime into using the powerline only. In 1977, when back in the USA, I ran the Linn straight off the AC line, and Ivor (the terrible) came to visit one day. We discussed Xtal control and Wien bridges, and he said it was NOT the right thing to do. The powerline, to him at the time, as almost perfect. I begged to differ. Now, it would seem that he has changed his mind, and that virtually any artificial source is OK, so long as it still drives an AC motor. I think that either Xtal or Wien bridged oscillator could be OK in this case, as good as the AC line.
If you live in Europe, and have 50 Hz AC, then try this test, if you get a scope. Lock the scope to the line and monitor the artificial source going to your motor. Note if you see any phase shifting of the AC line. This is of course best seen and believed when you have a precision Xtal source, because you can see it weaving back and forth, because the 50 or 60 Hz AC is locked to the sweep and IT is weaving back and forth. It is an eye opener!
The motor initially starts with high voltage. It is 115 volt when measured between the right and leftmost connection. This drops to about 36 volts after a few seconds and the motor stops running. It starts again if you "help" the pulley by hand. So my understanding is that once the platter is up in speed, the movement of the platter itself that keeps the motor running via the belt. So wow/flutter control is mainly set by the platter spinning, while the motor only has power enough to keep the speed at 33.3 or 45 RPM constantly.I remember reading some quite expensive turntable designs have very weak motors and very heavy platters that required a manual start by turning the platter by hand.
Thomas
An XTAL is a crystal. Make sense now? The reason for low voltage is to keep the torque pulses from the motor, low . The scope comparison is not important here.
I see now. Thanks. :-)
Thomas
Well, I have no idea what an Xtal source is. Also, I will need to study the Wein bridge oscillator curcuit more to understand it. I am still curious how this Axis motor control board works. I found this on rec.audio.tech:"Motor is driven by two analog high voltage power stages,which provide two artifical generated sine waves with 90 degree phase shift.
So far I tracked down the circuitry. It consists of standard OPs,comparators and CMOS-analog-switches. A little bit tricky,as it incorporates what I call a mixed analog/digital feedback loop.Maybe a zero crossing detector on the motor-windings,which is coupled trough flip-flops and analog switches to the oscillator."Would this info ring a bell?
When I meaure, do you mean that I should measure both the AC line and the line going to the motor?
Thomas
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
