Silent groove noise, anyone familiar with this sound?

[lulu]

Hi,

I am more like observer. I don't post much, but I have learned a lot from this forum. I am working on my diy lathe for years and at last I am getting some consistent bearable sounding resuts.

The lathe:

stereo dynamic diy head, heated stylus, oil dashpot, lenco heavy platter, belt driven by capstan motor from Revox A77, platter speed and cutting arm controlled by AVR microprocessor, remote control from PC DAW by MIDI over USB, cutter arm driven by a stepper motor, chip suction by side channel blower.

lathe001.jpg

head001.jpg

Cuts:

I cut black MyShank blanks, heated to +- 35C, 12g on stylus, stylus heat on 5V/500mA, slight back angle. Diamond is also from Steven of MyShank.

Here is audio of my latest cut attempt, the low end rumble is from the platter motor and i can live with it, it is not that loud and it is much better than when I drove the platter by stepper. But there is that sssh sound that has been there from the start of my cutting attempts, It is there no matter what I do, I tried to alter the temperature of the blank and stylus, no change. Is it just normal surface noise? It is not audible during the song, in between songs it is a bit anoying. Does anyone of you long time experimenters recognise this kind of noise? Could it be stylus damage or some missalignment? My tools are not exactly precise, but i try my best and I think that the silent groove could be a bit more silent.

If anyone is interested I also included the cut of a bit of music, so you have an idea about how the head sounds, there is of course heavy EQ and processing on the way out of the PC.

Thank you,

Lukas.

[markrob]

Hi,

Are the two playback captures done at the same phono preamp and audio interface gain so that we can determine the level of the background noise relative to program? It would be good to cut a 5 cm/sec ref tone followed by a silent groove to get an handle on the relative levels.

Mark

[markrob]

HI,

Took a quick look at the file. I think what you are hearing is a peak caused by the head system resonance at about 1Khz that is excited by the cutting stylus as it cuts. See the attached spectrum plot. Its a pretty high Q resonance and since its in the mid range its more audible. I think you could improve this if you add some damping to tame the peak a bit. I also see a second resonance on only one channel in the 600-700 hz range. That is odd to me. EQ won't cure either peak as it is exciting the head physical resonance. Kind of like blowing on a soda bottle. After adding damping, re-run the silent cut and see if the peak goes away or is improved. You will need to EQ the head again after you add the damping. Hope that helps.

Mark

Silent.png

[lulu]

Hi,

Thank you for your reply! The files are recorded trough the same preamp, same pickup and the same interface, but the music file has been normalized to -14 LUFS-I, so it is probably louder than the silent groove recording, but you can hear the same noise when the song ends, so that is the level. I can try to cut the tone, but now all my styluses are at MyShank for resharpening. The lower peak in just one channel is weird indeed. I am not sure what do you mean by head damping, what material and where should I try to add? I am not sure if that would be possible, because the head is mostly glued together with epoxy, so it is almost impossible to disassemble... Or it's maybe some pratice that I don't know about.

Thank you,

Lukas.

[markrob]

Hi Lukas,

By damping , I mean adding some material to the driver cones and any of the push rods to try and reduce the peak caused by the main head system resonance. You can do this to the head as is. Something like applying a rubberized product like Plasti-Dip or maybe RTV Silicone, for example might work. If you look at pictures of the the VR head, you can see that the drives were coated with a plastic material to tame some resonances. You will have to experiment. Too much damping will kill the sensitivity of the head and require more power to reach decent cutting levels.

Hope that makes sense. To be honest, I didn't find the noise to be that bad. It seems you did a pretty nice job on your head build.

Mark

[zdenek]

Anyone who has cut or stamped grooves with a head with or without feedback immediately knows what type of recording they are listening to.
Your head does not have feedback coils and the crackling in the recording comes from the head with feedback.
So ?

[lulu]

What? I think I don't understand, yes the cut has been done with the head in the photo in the first post and it is just two Visaton BF32 speakers, so no feedback coils. It is actually inspired by KNOP's design which I have found on this forum years ago. If you mean the clicks in the sound It is just dust, because I left the record on a shelf for a few days without cover.

Ok, thank you Mark! I will try to experiment with some damping. Maybe you're right, maybe it's not that bad. I listened to sample audio from this post https://www.lathetrolls.com/viewtopic.php?f=1&t=10065 and I hear similar sound between the audio clips..

Lu.

[lulu]

So after months of silence, I did the platter mottor assembly again, now i have no platter noise in the groovea and I would say acceptable wow and flutter. But the main PITA was the ssshhhh whistling like noise in the groove. I have tried everything, setting different back angles, lowering the downforce, nothing made a difference to the ssshh sound. Then I tried to cut a silent groove while slowly lowering the spped of the side channel blower that I use for the suction system... And that's it! The sshh noise slowly dissapeared. I have the nozzle about 1,5mm from the top of the record and from the diamond. When I lower the blower speed to the point where it barely picks up the chip, it is still audible a bit. Anyone had this struggle? Any ideas? Anyway i am really happy that I finally found the source of that noise.


Thanks,

Lukas.

[diy_cutter]

You are absolutely right, the sound from the tube that sucks up the chips can affect the noise level. Keep it about 2 mm from the surface of the record and 2 mm from the cutter.

[lulu]

Yep. but I am affraid that 0.5 mm wont make a big difference... Here is recording of the silent groove while the speed of the suction motor is slowly turned down and in the end the motor is completely off.

[Thelatheofus]

Thanks for the audio example ! What vacuum do you use ? how loud would you say it is in the room ? Is it close to the lathe ? Could it be mechanically coupled to the lathe (its vibrations transit through your metal table to the platter or the cutting head), or did you put some rubber dampening where needed ?

[lulu]

I use Elmo-Rietchle side channel blower. It is in the same room and I don't have any enclosure for it yet, so it is pretty loud in the room. I am waiting for a silencer to arrive, but I don't think that the lathe picks up the noise from the room so much, the blower is pretty far from it on the other side of the room. On the other hand, I found that the lathe, especially the cutting arm and the metal table is very sensitive to any vibrations, but I am not sure if the suction noise is transfered to the groove by the air that is flowing around the diamond and maybe vibrates it, or if it is mechanically transfered trough the arm and the head. The suction tube is not sitting directly on the cutting arm, but on the carriage of the linear guide, but maybe it can still transfer some vibrations, I don't know. I am sending some photos of the system. Maybe if I put some rubber between the metal part and the red plastic part that has the nozzle in it? Or modify the nozzle somehow so that is not whistling that much.. Any ideas?

Thanks,

Lukas.

lathe002.jpg

lathe003.jpg

lathe_blower.jpg

[Thelatheofus]

I have my lathe on a table. Once I hit the table while cutting a record and I could hear the low frequencies of that hit in the silent grooves (even thought the feet of the lathe have rubber). I would guess your sound is to high to be coming from mechanical coupling, but it's easy to put some absorbing material under the table and the vacuum just to check.

Compared to the VR suction tube the hole on yours looks big, but it's hard to tell from those pics. As you said I would also guess that the noise you hear is from the noise from the airflow at the tip of your suction tube.

[lulu]

Yes, that's true, it is a bit bigger, originally i had there 5mm diameter alu pipe, now there is 10mm brass pipe, The smaller one had problems picking up the swarf, the bigger one works just fine except the noise. A friend of mine has the end of the pipe pointed down to the record - I am posting a photo, do you think that this could help?

nozzle.jpg

[Thelatheofus]

So about your last question I just had an issue with my suction tube. I saw that it vibrated when collecting the swarf. It could be heard on the record on a silent groove (it made kind of an helicopter noise, repetitive ticking noise, so really different from yours). I changed its angle to put it more in line with the thread of swarf just being cut and it worked much better (so less paralel to the disc, pointing downwards). My guess is that the force caused by the vacuum and the force coming from the thread that wanted to stay on the record (because of static and the angle and distance between the record and the suction tube) were fighting, resulting in vibration that changed the speed of rotation and were transmitted to the record. I think that for my issue the suction tube that your friend has would help.
I'm still not 100% sure that my problem came from that, but so far it's the best explanation I found.

[farmersplow]

I can confirm that all four of these factors leave a noise in the groove.
The air noise when the airflow passes over the diamond at too high a speed.
The thread noise when the thread is pulled by the suction tube and pulls at the point where the diamond is cutting. This is particularly noticeable when the suction tube is positioned to the side. It is less if the suction tube is in the middle.
The thread noise when the thread passes over the edge of the suction tube. Similar to a violin when the violin bow passes over the string.
Resonances of the pump that is located near the lathe and transmits rumbling.
Cutting is more sensitive in this respect than you might think. I once had a recording and while I was cutting, my dog was barking in the room four meters away. My dog has since died, but I still have the recording because the barking was audible.
However, the problems are usually quite easy to prevent. Only as much air intake as necessary (with an even side channel blower). The suction pipe as close as possible to the panel blank so that the thread is not lifted too steeply. Good antistatic properties (so that the thread can be easily sucked up.