The Secret Society of Lathe Trolls

JayDC · Posted: Tue May 06, 2008 11:38 pm Post subject: presto motor noise

anyone have any ideas on how to lower the noise of the motor on my presto 6n, without replacing the motor and drive train? the motor is making a lower pitched sound that is filling the quiet areas on my cuts, although the area with signal present the noise is inaudible.

I just had the rollers rebuilt by terry, and they have eliminated the rumbling sound. now I just have to get rid of this hum.

btw, the low hum is not a ground loop, or anything with the amps, b/c this is also happening when cutting silence w/o any amps hooked up, and no vacuum.

I'm pretty sure that it's the vibrations from the motor carrying through the body of the turntable.

I'm baffled.... any ideas?..

cuttercollector · Joined: 11 Jun 2006 Posts: 219 Location: San Jose, CA

The standard thing would be to make sure the motor is running as smoothly as possible. Make sure it is adeqitly lubricated.
Also and perhaps more important, how are the motor isolation/suspension rubber mounts? If they are hard or partially gone the vibration will carry right through.
Last, don't expect miracles. This was made a long time ago and standards were not a high regarding turntable rumble as they are today.

JayDC · Posted: Wed May 07, 2008 4:01 am Post subject:

cuttercollector · Joined: 11 Jun 2006 Posts: 219 Location: San Jose, CA

I don't own one with the motor suspended this way. As I recall, they are supposed to be pretty flexible. I don't know what you could do to make something like them. In some other cases like other record players I was able to use various sizes of standard rubber grommets to replace the existing deteriorated rubber pieces. It has to hold the motor firmly enough to drive the platter but still isolate the parts that attach to the motor from the part it is mounted to. Is it 2,3 or 4 point suspension?
I think I am thinking of the older Presto portable units where the motor shaft drove against the outside of the platter and was on a very elastic mount perhaps with some springs and rubber bushings. Yours is not like that?

JayDC · Posted: Wed May 07, 2008 3:52 pm Post subject:

it's a 2 point suspension.. I'll take some pictures tonight. I was think rubber stoppers or washers.

Doug 6N · Joined: 21 May 2007 Posts: 57 Location: Washington

Hi:

There is a product called "Sorbothane" That has excellent isolation abilities. I have'nt tried it yet on my Presto but have used the material on other equipment in years gone by with really good results

Doug

JayDC · Posted: Thu May 08, 2008 5:02 am Post subject:

I found this company: http://www.avproductsinc.com/ seems to have all kinds of isolators.

I made some adjustments to the hex bolts that go through the current isolators. Seems to drop the noise a bit. Now I can't feel any vibration on the body of the turntable. Test cuts also sound a bit more like silence.

I wonder if replacing them would be a good idea, since the seem very dry and quite worn. Although they seem to be functioning well. I'm going to contact this company and see what the cost will be.

Now it sounds like air. Maybe a slight hiss. I'm wondering if maybe the head needs to be adjusted, or possibly a new needle. I inspected the needle under the microscope, and it looks fine to me.

Doug 6N · Joined: 21 May 2007 Posts: 57 Location: Washington

The rubber isolators should be very soft and pliable. So you probably need to replace them.

On my own 6N I have silence in unmodulated grooves between cuts. Now if I crank the volumne I can hear some low freq components as compared to a modern record. However it is not objectionable or noticeable at normal levels. No noticeable hiss with unheated stylus. Noise off the stylus is measurable once again at high volumne with hi freg eq advanced. As compared to heated stylus. I've measured both and found the heated styli will drop the noise a good 10Db. But with all properly adjusted it's acceptable either way.

Hiss is more then likely stylus adjustment. So long as styli are good. I've found it's very difficult to get right. probably with practice it gets easier.

I'm cutting LP at 224 LPI. With the 90B Amp.Amp RIAA Eq. Sounds pretty good for an amature. Very Happy

JayDC · Posted: Thu May 08, 2008 5:11 pm Post subject:

looks if for the presto 6n you'd need a center bounded mount, type T.