cutting angle and background noise

[sat159p1]

Any thoughts when cutting PC/plastic? I keep my stylus angle around 30*. Too much? Also, I have low-volume hum on my all records (like "G" note 50 or 60hz i think) - tried without the sucking machine, tried without the singnal/power amp off, it's always there. What causes it?

[The Shank]

Any thoughts when cutting PC/plastic? I keep my stylus angle around 30*. Too much? Also, I have low-volume hum on my all records (like "G" note 50 or 60hz i think) - tried without the sucking machine, tried without the singnal/power amp off, it's always there. What causes it?

Stylus angle about 30°??? Are you sure about that?

If yes, it's obviously too much...

I guess you are using T560 right? So just be sure to have the cutting head perfectly parallel to your blank when pulled down. that's all
And you will have a 10/12° angle (tolerance of Souri are wide...)

cheers

[sat159p1]

Thanks. Will check it. Maybe i saw it wrong way And that low-end hum?

[handcut]

And that low-end hum?

It could be a grounding issue or it could be your turntable bearing or even feedback. Was it always there, or is it a new problem? Does it come and go? What triggers it? Is it a single frequency or several?

[marcy108]

>And that low-end hum?
vibration from vacuum can make it.
is your chip tank normal setup(same table with machine)?
if you set same table,you should divide them.
i guess this thread is for you.
http://www.lathetrolls.com/viewtopic.php?f=1&t=6068&p=37989&hilit=t560#p37989

[grooveguy]

Re: the hum, I didn't see a make and model of your lathe. Sounds like motor noise to me. Rim-drive turntables, especially, are prone to that. Try this: disengage the motor; that is, turn it off completely, and being very careful, try rotating the turntable by hand and cut a couple of grooves. Is the noise still there? An AC motor "pulls" twice for each cycle of the mains voltage, so it has a ripple torque component of 120Hz or 100Hz, depending on where you are. But a heavy motor and turntable are their own good low-pass filters, so you rarely get flutter at this frequency. But flutter would not come across as a noise so much as frequency modulation of the music you're cutting. The motor will vibrate at 60Hz or 50Hz, with harmonics at twice and three times the mains frequency. Put your ear against the cabinet... is that the same background noise you hear?

[sat159p1]

This is the hum (the hiss is from my new prototype pvc material, so I'm not talking about it), and yes you were right - it's not 50hz only, it has upper harmonics like shown on the pic.. (50,100,…)so, it might me the vacuum?

hum: https://www.dropbox.com/s/lhunqtte0wlauev/noise.wav?dl=0

[handcut]

That looks/sounds like classic mains hum. The most prominent peak, at -70dBfs, is 50Hz. With peaks at f2, f3.... Welcome to analogue studio operation.

Possible causes? Grounding scheme of the studio, poor EMF shielding, use of switch-mode psu's on the same phase as your studio, mixed small-signal & large signal environments, cabling... Hours of fun!

[grooveguy]

It's certainly a mains-related hum, but still sounds somewhat mechanical to me. Try this: disconnect the cutterhead completely and cut a groove. Noise still there?

[handcut]

It's certainly a mains-related hum, but still sounds somewhat mechanical to me. Try this: disconnect the cutterhead completely and cut a groove. Noise still there?

Good idea! That's how I worked out my turntable bearing was causing hum issues a while back. It was significantly louder than what our friend here is experiencing though and I belive he/she is using the same system (T560).

[grooveguy]

You know, Sat has already said that the hum is there even with his power amp turned off. So it's got to be mechanical. If it's not the turntable motor, I'd look for something else that is coupling to the deckplate. Even a power transformer on the same table could induce enough vibration into the system to be heard on playback. If you think it's the vacuum motor, try cutting 'cold' without the vacuum, if you can, or put the vacuum motor somewhere else with a long hose. If you put your ear right against the cabinet or deckplate you ought to be able to hear this.

[sat159p1]

The system is T560 w/external motor (running in paraarell with tehcnics motor)
So I did the tests:

- without cutterhead connected (and in general - everything off) - the same HUM
- without internal, technics motor (technics off the socket) - the same hum
- without external motor (just the technics motor) - the same hum
- without the T560 cutterhead moving motor (i moved by hand) - the same hum
- without sucking machine (but did only for 1 second, dont want to ruin the stylus) - the same hum

So, I think this is a noise from motor, external & internal, but it;s strange than switching to different motors (technics, external and external+technics together) gives the same amount of hum.

I give up...

[markrob]

Hi,

Are you sure the hum pickup is not from the playback chain? Since you have eliminated all of the mechanical sources at the lathe it would seem to point there. Have you captured your playback system noise floor including the turntable running without playing a record. Its hard to say how bad the noise floor is since you have not cut a standard reference to compare against. Do you have a test record with a 1 Khz 5 cm/sec rms signal set as a playback reference? If you set this to a reasonable level of -10 dBfs at playback, you can make a better assessment of the noise floor. Otherwise its hard to say how bad this is.

Mark

[grooveguy]

Good idea. Also, play your silent grooves at 78 r.p.m. Does the hum go up in frequency? It should if it's 'in the groove.'

[sat159p1]

Damn… it's my studio Pro-Ject turntable humming. Simple as that. You are right. Thank you grooveguy, markrob..!