Hummmming (not a grounding issue, I think)

[pgiampi1]

I have a Technics SL1700 that I've been using for a few weeks now...it's occurred to me that it has a persistent hum whenever the tone arm is not at rest (although the platter does NOT need to be spinning). I've found that the dust cover will amplify this humming, especially when it is in the raised position.

I am pretty sure that this sound is not being picked up by my stylus and therefore by my speakers - if it is, I don't notice it. However, my ears have to compete with the droning of that hum...and I was so excited today when I accidentally dropped a cleaning brush onto the turntable, it struck around where the 33/45 RPM selector is located at the front left hand corner, and the humming stopped! It returned later on, and I attempted some strategic whacking of the body of the turntable but nothing happened.

I would love to stop the humming altogether if possible, since, as I said, it is just another sound in the room that my system competes with. Anyone know what I can try to do to fix it? I am not very mechanically inclined but I can give it a shot.

[markyk]

I think there was somebody who was having a similar problem recently and it turned out to be that the stylus was loose. So - some easy things to do: check to see that the headshell is securely screwed to the tonearm. Check to see if the wires in the headshell are fully and tightly secured and then make sure the stylus is all the way in the cartridge. You could check the tiny circuit board that is used between the tonearm wires and the phono cables (this is a bit unlikely) but in order to do that you'd have to take apart the two halves of the turntable so I'd check the cartridge area first.

[pgiampi1]

I should reiterate/clear up that this Hum doesn't travel through the speakers, it's some aspect of the turntable vibrating and putting out sound.

I left a clean record on my SL1700 overnight to dry and when I turned it on to brush it before putting it away, the hum was gone again. Weird.

[josephazannieri]

Yo pgiampi1:

This sounds like something has come loose and is vibrating in resonance with the motor. I would touch the various points on chassis and see if you can stop the noise by touching things. You can also get 2 or 3 feet of 1/8 inch automotive vacuum hose or a stethoscope and listen to the turntable and see if you can determine what's vibrating. Stick one end of the hose in your ear and hold the other end close to turntable and listen. By this means you should be able to locate the vibrating component.

And good luck from the old vibrator himself,

Joe Z.

[brianmch]

While on this topic I ran across a post a couple days ago about putting the stylus down on a non spinning record and turing the input to phono to see if there is any noise.

When on my other inputs it is quiet. When on phono it's kind of hummy but not like guitar amp or mic feedback. Just a hum. And, there is hum when I just turn it to the phono input with the arm in its cradle. Any thoughts?

btw this is on my Grado Platinum>Linn Axis>Nad 3020.

[josephazannieri]

Yo other hum seekers and Brianmch:

All phono inputs have a certain residual hiss and hum. This is because phono inputs will have a much higher gain than line input due to low output of magnetic cartridges. CD player or a tuner has about 100 times the output of a magnetic cartridge. Also, phono inputs have a bass boost on them that compensates for the rolled off low frequencies on a record. This makes the phono input much more sensitive to hum, and also makes it generally noisier.

To check residual noise level, unplug the turntable from the phono input set switch to "phono" and set the volume to a normal listening position. That's your residual hum from the amp. Now plug the turntable into the phono input and hook the ground wire, if you have one, to the amp chassis. Be sure to turn volume down all the way before plugging the truntable in or you will get horrifying hum on insertion. Set the volume to normal listening level and that will tell you the residual hum from the turntable.

In this case, since it may be mechanical noises unrelated to amplifier, also plug the turntable into the wall but NOT into the amp and see if it still makes the noise when you turn it on and operate it with it not plugged into amp. If it does, your sound is a mechanical resonance phenomenon. You can locate it by using the vacuum hose stethoscope like I described, or by touching different spots on turntable and seeing if the sound changes when you touch things. The thing that changes the sound when you touch it is the problem item.

The test where you lay the arm on a stopped turntable and advance the volume tests for turntable isolation and feedback. If you get an increasing hum or rumble when you advance the volume to normal listening level or beyond, you need to get the turntable away from the speakers and isolate it from speakers. If your problem is really an electronic hum problem, then feedback, if present, will make it worse.

First, you need to identify the source of your problem. And that's all for what it's worth. And good luck from the old diagnostician,

Joe Z.

[markyk]

So ...

You have a noise (hum is a confusing term in this situation) that happens when the turntable is on, even when the motor is not running.

This noise is not audible from the speakers.

Perhaps the neon strobe light? Neon lights can emit noise but the one in the turntable is pretty small. That may also explain why dropping your brush near the speed selector switch stopped the noise (temporarily) since it's near the strobe.

[brianmch]

Yo other hum seekers and Brianmch:

All phono inputs have a certain residual hiss and hum. This is because phono inputs will have a much higher gain than line input due to low output of magnetic cartridges.

To check residual noise level, unplug the turntable from the phono input set switch to "phono" and set the volume to a normal listening position. That's your residual hum from the amp. Now plug the turntable into the phono input and hook the ground wire, if you have one, to the amp chassis. Set the volume to normal listening level and that will tell you the residual hum from the turntable.

In this case, since it may be mechanical noises unrelated to amplifier, also plug the turntable into the wall but NOT into the amp and see if it still makes the noise when you turn it on and operate it with it not plugged into amp. If it does, your sound is a mechanical resonance phenomenon.

The test where you lay the arm on a stopped turntable and advance the volume tests for turntable isolation and feedback.

First, you need to identify the source of your problem. And that's all for what it's worth. And good luck from the old diagnostician,

Joe Z.

Thks Joe. So you identify 4 types of hum/noise/etc.
Barring isloation issues (T4) and mechanical resonance, is there a way to reduce types 1, or 2 for either rigs with built-in phono stages or external stages, which would in effect be a variant of T1?

Greatly appreciate your time.

[josephazannieri]

Yo brianmch and other hummers:

I am not one to cavalierly alter the design of an operating amplifier that is in good condition. However, with tube amps I was sometimes able to get an improvement in residual noise levels by changing tubes for the premium or "industrial" variants of the original tubes. For example, my best memory is that the 7025 (industrial) replaces the 12AX7. This may have been because I was using tubes that were noisy or microphonic to start with. Try tapping the tube with your fingernail or a pencil eraser while you have the amp on and the volume nailed. You'll hear the noises when you tap the tube. If it's noisy, replace it.

You may also be able to decrease the hum from turntable by careful placement of signal leads, keeping the signal leads away from power cords, and maybe by changing to a better grade of shielded cable for turntable leads. This may be a considerable effort for a small improvement in noise, but the unit may sound better generally due to improved cables.

And good luck from the old tube switcher,

Joe Z.

[brianmch]

Thanks Joe Z. I've sent an e-mail to Immedia to get them to weigh in on the baseline noise (hiss) of my external phono stage. They may say that it shouldn't be noisy and that it may be related to my turntable cable.

BTW, I use a Rega that doesn't have a grounding cable and is a straight run from end to end. The RB 301 arm supposedly has better wiring than the former RB300's internal wiring but this is starting to sound suspect if my phono stage is to be quiet.

[cafe latte]

While on this topic I ran across a post a couple days ago about putting the stylus down on a non spinning record and turing the input to phono to see if there is any noise.

When on my other inputs it is quiet. When on phono it's kind of hummy but not like guitar amp or mic feedback. Just a hum. And, there is hum when I just turn it to the phono input with the arm in its cradle. Any thoughts?

btw this is on my Grado Platinum>Linn Axis>Nad 3020.

I did this experiment ages ago with lid on and off and up and I got feedback unless the lid was off altogether as the lid acts like an ear during play feeding the music from the speakers back into the stylus smering the music. This may not be your problem but remove your lid altogether whenever you play a record.
Regards
CL

[brianmch]

btw this is on my Grado Platinum>Linn Axis>Nad 3020.

I did this experiment ages ago with lid on and off and up and I got feedback unless the lid was off altogether as the lid acts like an ear during play feeding the music from the speakers back into the stylus smering the music. This may not be your problem but remove your lid altogether whenever you play a record.
Regards
CL

Thanks CL. The lid is off my Axis and you're right...with it on its a like a noise funnel from the world to the stylus/record intersection.

Further note.
Nice guys at Immedia. Lengthy conversation with them yesterday about hum/noise etc which was very informative to me and gracious of them.

A couple items of note. The most significant was regarding isolation though and the implementation of constrained layer damping (CLD) options to isolate the table and the use of other methods on the phono pre (separately) as it is a sensitive and powerful amplifier of very low level signals.

Any successful CLD implementation suggestions are welcome, as are those for a phono pre. I've got some sorbothane pucks employed here and there. There are a wide array of options and I'm pretty new to this sort of thing.