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Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
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Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
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In Reply to: DC motors sap PRaT? posted by dvb on August 28, 2001 at 11:03:03:
by busybusy:Vinyl Asylum
Engineering perspective not favorable to DC motor. Re: ORIGIN LIVE DC MOTOR FOR LP12?
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Posted by Busybusy (i) on January 19, 2001 at 16:10:00:
In Reply to: ORIGIN LIVE DC MOTOR FOR LP12? posted by horace on January 18, 2001 at 11:48:16:
Not hearing the actual OL DC motor kit myself, I would have guessed that the rhythmic part of LP12 will be gone. Judging from one of the respondent, my guess is correct.
The reason behind a DC source vs. an AC source is the fundamental difference that the variability on the DC is the voltage, and variability on the AC is the frequency. To get the motor spinning correctly, all we need to do is to synthesize or capture the power line AC frequency. So long as 60Hz is maintained, the motor works fine. Now, for a DC motor, the speed accuracy is directly related to the voltage. So you cannot have a good and accurate RPM unless a true battery is used.Why ? All the DC regulation from AC uses fundamentally a feedback adjustment. In a microscopic sense, the feedback is always working to correct the voltage. Think in terms of time-domain. When the DC regulation first started, it will try to clamp the voltage down towards 5V. Hyperthetically, say we have a regulated 5V supply. Let's say the voltage is initially powered-up to be 6V, so that's too much, it will correct it down strongly, to 4.7V, too little, let's bring it back to 5.1V, so on and so forth. At a steady state, the voltage 'looks like' 5V DC, but it is always 'oscillating' and micro-correcting (for lack of better terms) itself, say between 5.001V to 4.9997V back and forth. Given the price point and the sophistication, unless a switch-mode DC power supply is used, and the frequency of correction is way higher than human hearing, most linear DC regulation probably works at a fairly low frequency, so the impact on PRAT will be obvious.
However, for AC motor, there is no such issue. Think about it. Is it easier to build a circuit to generate a DC, and use a DC motor, or more easy to build a synthesizer to use a crystal for a pure 60 Hz signal, then use amplifier to drive a motor (i.e. Lingo). Did the Linn engineer not thinking, I don't think so.
From a speculative point of view, the only way to implement DC motor correctly is to use a battery, or a large mechanical fly-wheel is employed that will eliminate the variability from the microfluctuation of the incoming DC. The fly-wheel concept can also be a large and heavy platter and driven by a slippable belt, such as the Forsell turntable (driven by dental floss) or the Micro Seiki (driven by an Aramid string).
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- Here is the earlier post - dvb 08/28/0113:03:36 08/28/01 (0)
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