Motor power for a turntable

[DeonisP]

Hello, everyone!
My first question here is about power.
Well, if a turtable fail to keep right RPM while cutting, i'll probably build one.
What power of a motor is okay for spinning disc surely without losing rpm? Maybe 40 Watts? Or 20?
Thanks in advanse for your responds.

[markrob]

Hi,

The Bodine motors used on the Presto 6N were 1/25 HP. This seems to have more than enough torque for the application. So, this should give you a good starting point. Its probably a bit overkill as the 6N also had to drive the overhead mech. On the other hand, the typical modern direct drive turntable (e.g. SL1200) seem to be on the marginal send of the power scale.

Mark

[DeonisP]

Wow. Almost a Kilowatt. Thanks. I'll probably try a 250W motor.
And one more question. How much pressure should a needle have?

[markrob]

Hi,

Not sure how you cam up with that number! 1Hp = 746 watts, so 1/25HP ~ 30 Watts.

Mark

[DeonisP]

Oh, lol. I just usually use decimal fractions, so i thought it's 1,25 HP. Lol, sorry.
Thanks. And what about needle pressure on a disc?

[markrob]

Hi,

The pressure is not normally something you measure. Typically, the head is mounted on floating spring suspension and and the downward forced is adjusted by changing the spring tension such that the designed groove width is obtained.

Mark

[DeonisP]

Thank you so much, Mark.
And the last question) What is optimal power for speakers used for cutting?

[markrob]

Hi,

For moving coil heads, the max power rating is in the 5-10 watt range. Don't take this to imply that a 10 watt amp is all you need. While 1 watt will typically cut a reference level 5 cm/sec at 1Khz, it takes considerable more power to cut the high frequencies. In pro setups you find 400 watt/channel drive amps. This extra headroom is needed to handle short term transients. So you need a good deal of power reserve, but have to take great care to prevent head meltdown. My advice would be to start with a smaller amp in the range of 25-50 watts/channel and add some fast acting fuses (maybe .5 to 1A) in line with each driver. Work within those limits until you get a feel for how hard you can push the system. I'd be very careful in your case, because its not clear how you will get the head repaired in the event it fails.

Mark

[DeonisP]

Hello, Mark. I heard something about your IRIAA plug-in. Can you give it me? I hope it is easy enough to use.
And by the way, what range is OK for recording speakers? Usually people write about simple full-range speakers, but I saw one DIY cutter with 60W tweeters, and I am not sure what kind of speakers I should choose.
Thanks in advance.

[markrob]

Hi,

Just send me a PM with you email and I'll send it your way.

The stated frequency response is not relevant in this application. Power handling, moving mass, size, BL product, and ease of coupling to the stylus, and mounting considerations are all important. They all interact, to some degree, so you have to make some tradeoffs to find a driver that will work for you. For example, you may find a driver with great power handling (say 60 watts). But when you look deeper, you might discover that the moving mass is high as compared to smaller, lower power driver. It may actually perform worse than the smaller lighter driver that does not need to move as much mass.

Mark

[DeonisP]

Thanks. I think I'll just try the same as your speakers, which model I found on your site, "Digikey P/N 102-1306-ND"

[markrob]

Hi,

I would also look at the drivers Bryan is using on his DIY head.

NSW1-205-8A

These are better specified than the CUI drivers (I had to use WT3 software to obtain all of the parameters). When I finally get to doing a rev 2, I'll give these a good look as well.

Mark