2. analog
  3. 1070086184

DC v AC

I've seen some posts on this forum where people seem to indicate a preference for a DC powered motor and was wondering what the rationale is? I've seem some people mention noise, but I would think that if you have an awesome power conditioner and really nice AC cord that the AC motor would be better than the DC, so who can explain why one is better than the other?
arafel
jimbo3
304 posts
 
I'm by no means an expert on the topic, but here's how I understand it. Pure DC doesn't have power fluctuations as AC does, motors are more efficient, quieter and easier to maintain a stable speed. No matter how much AC conditioning and power cord upgrading one does, the AC motor is still an AC motor and can hum. AC motors can be more powerful, but not much power is needed to drive a platter, which is why you see a few AC-driven decks use some sort of current-reducing circuit to reduce power after the platter is up to speed. (Less current equals less noise.)

Don't know how technically correct this information is, but I think it's a start to answering your question.
dougdeacon
3,338 posts
 
In addition to Jimbo3's points there's this crucial one: all AC motors have cogs. At each cog the motor gives the spindle a little push. Between cogs the spindle just coasts along, losing speed to friction of course, until it reaches the next cog. IOW, no AC motor ever spins at a true steady speed. They all proceed in an endless series of pushes and coasts. Clearly this is less than ideal.

Cogging effects can be reduced by having more cogs, by using a lower torque motor and by isolating platter from motor with a stetchy drive belt. But these are bandaids. In the end no AC motor can match the inherently stable velocity of a DC motor, and a stretchy drive belt opens the door to stylus drag that a dimensionally stable drive belt or DD mechanism would play through much better.

DC motors have their own set of problems of course, but they are easier to overcome without audible compromises. Read the motor information on the Teres website for a description of the best solution I know of for TT's under $10K.
jimbo3
304 posts
 
The cogging factor Doug points out is one of the larger differences between AC and DC motors. Synchronous AC motors reduce cogging, but not as effective as DC in this area.

I chose to go with the OL DC motor kit because, for $500, it solved problems that would take at least $2000 to solve with an AC motor. (conditioning, motor controller, power cords, etc.)

Jim
More to discover