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: 317 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: 317 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: 68 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: 68 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.

Steve E. · Posted: Sun Aug 17, 2008 8:14 pm Post subject:

My 6N is not yet functioning as a cutter. I'm about to get the cutting head rebuilt. However, in the meantime, I'm enjoying playing records on it.

I am noticing a hum in the playback. It seems to be electronic. Can anyone help? I am a total electrical novice.

I spent several hours trying to reduce the hum the other night. I tried changing outlets, grounding (which made it MUCH WORSE--now I understand ground loops better) and eventually, after several hours of reconnecting wires, simply turning the 2-prong plug around.

Well, I'll be, turning the plug 180 degrees decreased it by a radical degree. Partial triumph!

The hum is FAR worse when the motor is running than when it is not. The hum is identical whether I am playing 78's or 33's. It doesn't seem to increase or decrease depending on where the tonearm is located.

The motor is a Bodine, 115 volt, 1 amp, type NYC-34. The switch is connected to an old fashioned metal capacitor rated at 2.75 MF, though my manual recommends a 3.75 MF capacitor.

There is also a loud annoying "pop" when the motor is switched on. I'd love to get rid of that, too.

So...I wonder if I can further isolate the motor hum, and why it is getting picked up anyway. The wires from the motor are attached to a little terminal screwed to the underside of the 6N, and further connected to the metal 2.75 MF capacitor. Should I remove them from the body of the 6N and attach them to the desk the 6N is mounted in? Would this make a difference?

*** *** *** ***

Details:

It is at its worst at 60 Hz. (no great surprise).
At 60hz the hum is -32 db below the loudest sound on some LPs.
When the motor is not running, the 60Hz sound is only -50 db.

There are neglible hum peaks at 120 Hz and its multiples (240, 360, etc.)

There are more significant peaks at 180 Hz and every 120 Hz above that. In other words, the odd-numbered multiples of 60 Hz: 300 Hz, 420 Hz, 540 Hz, etc. Still, these are -65 db when the motor is running and about -70 when it isn't. Not as disturbing.

Steve E. · Posted: Sun Aug 17, 2008 9:30 pm Post subject:

Here are some visuals:

Grey line: hum when the motor is on
Red line: hum when motor is off

Same thing, zoomed in:

60 Hz:

180 Hz:

300 Hz:

Green line: surface noise of a slightly crackly 33 record, between cuts
Grey line: hum when the motor is on, no record being played

Doug 6N · Joined: 21 May 2007 Posts: 68 Location: Washington

Hi Steve:

There should be a capacitor across the motor switch on the 6N it could bad or have been removed. That is the pop issue when switch is turned on and off.

Secondly I have replaced the original power cord on mine with a 3 wire cord so I can ground it. Also have replaced pickup cartridge lead wires. I now don't have any significant electronicaly caused hum issues.

Motor vibration hum seams only slight. Yes it's not as quiet as a modern turntable but's it's not all that bad either.

The condition of the rubber drive rollers and there tension against the turntable is very critical. If the drive wheels press to hard on turntable the noise is god awful. On the other hand if too lose it will lose power and slip.

Seams to be a matter of trial and error for this.

And the rubber bushings that mount the motor are another critical area

Doug

cd4cutter · Joined: 08 Jul 2008 Posts: 37

Steve, those spectral plots look interesting. I've been looking for a cheap spectrum analyzer program. What software are you using?
_________________
Collecting moss, phonos, and radios in the mountains of WNC

Steve E. · Posted: Tue Aug 19, 2008 4:23 pm Post subject:

I'm using a good old ancient version of Steinberg Wavelab, v. 4.0 I think. Great, great PC based program!! I don't know if the newer ones are an improvement.

motorino · Joined: 24 Aug 2005 Posts: 212

FFT graphics are exactly the same as in version 6.0, everything depends on the resolution and the quality of the graphics card pc

about the ac noise in the motor..... http://www.floka.com/lofi/portable_lathe.html

i believe if you put (very good put) some asfaltic roll (with a hand heater) inside the 6N and some crystal rock or like....better for low the noise