Weird bass sounds/skipping on T560

[mxlusky]

Hi trolls,

I have a problem with my T560. It makes weird skipping/bass sounds at 12" diameter (even with quiet groove). When I get around 10" diameter it stops and cuts normally. Heating of stylus made it worse. Is here anyone who have this issue and fixed it? First I thought that the problem is faulty stylus, but it isn't. Help will be much appreciated. Thanks.

[Dub Studio]

This could be chatter, “humping”, subsonic frequencies, too much stereo width.. the list goes on. Without seeing the lathe set up, inspecting the disc, and hearing the audio, it's hard to say. But here are some pointers:

When the stylus hits a warp in the disc, like a car hitting a hump in the road, it can cause the cutting head to start oscillating uncontrollably, and warps are always worse around the edge due to the break in surface tension, which might explain why it’s not happening further into the disc. Let's call this humping to differentiate it from chattering (which looks similar but has a completely different cause).

Assuming the disc is flat and smooth (i.e. little or no detectable ripple on the outer edge of the disc), then it's probably not humping. BTW its not necessarily the amplitude of the hump, but the length that is the issue here. The cutting head suspension has a resonant frequency and if your hump hits that frequency, it will sing.

Some audio, especially slowed down samples from vinyl or other sources, contains lots of sub sonic content which is just messing with your cut and doing nothing useful at all. Your tonearm also has a resonant frequency which is normally set below the human hearing range for obvious reasons, but again, if your subsonic content hits that frequency, the tonearm itself will start to sing (you can sometimes see this if you slow down the record on playback and observe the tonearm). Assuming you have a high pass filter applied at a reasonable frequency (try 20Hz, but your personal default is up to you), then its probably not subsonic.

Assuming you have centred the low end (try 300hz downwards, but again, your personal default is up to you), then its probably not stereo width.

If all the above are eliminated it could be chatter, and this is probably the most complicated to deal with.

NB: chatter is a factor of surface speed (not rpm) … so that could be why its only happening around the edge.

Other factors that combine with surface speed to cause chatter are: too much heat (stylus and or plate), bad rake angle, too much weight, too little weight, bad dash pot, bad counterweight, etc.

Some things to try:

- set the counterweight to 50 grams, then adjust the dashpot spring to give you a net weight of around 12.5 grams on the spring scales. If that doesnt work, add a little more until you reach 15. If that still doesn’t work, it’s probably not your stylus weight.

- adjust the rake angle in a more negative direction (making it more perpendicular to the plate, but not as far 90 degrees). Chances are your rake angle is just too positive, so the stylus is just digging in too much and then bouncing back out. BEWARE, changing the rake angle will mean repeating the previous step again, because the net weight will now be very different.

- check your dashpot to ensure the plunger is free moving, and completely immersed in oil AT ALL TIMES. If the end of the plunger goes too near to the surface of the oil, it can sometimes suck air underneath itself and dramatically reduce its ability to dampen the resonance of the suspension. If this happens, you can either top up the oil (if you have some) or raise the height of the cutting head. BEWARE, raising the cutting head height means you also need to raise the turntable height using the four supporting feet.

- try cutting without any heating lamps. Sometimes the surface of the disc can be hotter around the edge than it is in the middle, which will again cause the cutting stylus to go too deep.

- try reducing the heating coil temperature, for similar reasons as above.

Good luck!

[Dub Studio]

BTW the above answer covers all the possible causes of low frequency skipping that I can think of at the time of writing... but looking at the picture it looks like its mainly a disc temperature issue.

[tragwag]

Like Dub Studio I'm going to assume a lot of details about your setup to give you lots of options:
If it's the stock 1200 turntable, I'd guess it's a torque issue.
If the blank is warped at all, it's that. Check for the head moving up and down when cutting, even slightly.
Like DS said, excessive heat during cutting or too close heat lamp could cause a warp of an otherwise flat blank.
Next down the line - head weight is too heavy, which causes torque issues or worse, disc slippage from the turntable.

best of luck hunting down the issue!

[mxlusky]

This could be chatter, “humping”, subsonic frequencies, too much stereo width.. the list goes on. Without seeing the lathe set up, inspecting the disc, and hearing the audio, it's hard to say. But here are some pointers:

When the stylus hits a warp in the disc, like a car hitting a hump in the road, it can cause the cutting head to start oscillating uncontrollably, and warps are always worse around the edge due to the break in surface tension, which might explain why it’s not happening further into the disc. Let's call this humping to differentiate it from chattering (which looks similar but has a completely different cause).

Assuming the disc is flat and smooth (i.e. little or no detectable ripple on the outer edge of the disc), then it's probably not humping. BTW its not necessarily the amplitude of the hump, but the length that is the issue here. The cutting head suspension has a resonant frequency and if your hump hits that frequency, it will sing.

Some audio, especially slowed down samples from vinyl or other sources, contains lots of sub sonic content which is just messing with your cut and doing nothing useful at all. Your tonearm also has a resonant frequency which is normally set below the human hearing range for obvious reasons, but again, if your subsonic content hits that frequency, the tonearm itself will start to sing (you can sometimes see this if you slow down the record on playback and observe the tonearm). Assuming you have a high pass filter applied at a reasonable frequency (try 20Hz, but your personal default is up to you), then its probably not subsonic.

Assuming you have centred the low end (try 300hz downwards, but again, your personal default is up to you), then its probably not stereo width.

If all the above are eliminated it could be chatter, and this is probably the most complicated to deal with.

NB: chatter is a factor of surface speed (not rpm) … so that could be why its only happening around the edge.

Other factors that combine with surface speed to cause chatter are: too much heat (stylus and or plate), bad rake angle, too much weight, too little weight, bad dash pot, bad counterweight, etc.

Some things to try:

- set the counterweight to 50 grams, then adjust the dashpot spring to give you a net weight of around 12.5 grams on the spring scales. If that doesnt work, add a little more until you reach 15. If that still doesn’t work, it’s probably not your stylus weight.

- adjust the rake angle in a more negative direction (making it more perpendicular to the plate, but not as far 90 degrees). Chances are your rake angle is just too positive, so the stylus is just digging in too much and then bouncing back out. BEWARE, changing the rake angle will mean repeating the previous step again, because the net weight will now be very different.

- check your dashpot to ensure the plunger is free moving, and completely immersed in oil AT ALL TIMES. If the end of the plunger goes too near to the surface of the oil, it can sometimes suck air underneath itself and dramatically reduce its ability to dampen the resonance of the suspension. If this happens, you can either top up the oil (if you have some) or raise the height of the cutting head. BEWARE, raising the cutting head height means you also need to raise the turntable height using the four supporting feet.

- try cutting without any heating lamps. Sometimes the surface of the disc can be hotter around the edge than it is in the middle, which will again cause the cutting stylus to go too deep.

- try reducing the heating coil temperature, for similar reasons as above.

Good luck!

Thanks a lot for sharing your amazing knowledge. In the meantime I set up everything again from scratch and now it is much better. There were probably some problem with counterweight but maybe also with dashpot. I add some oil in it and now it looks to work better. It still occur from time to time, which is weird, but it happened only twice instead of everytime, when I cut stuff before resetting the machine. Temperature should be probably ok, I cut around 40-42 celsius of disk temperature. They are almost flat everytime, so this should be ok too. Audio is also ok because it happens even when I cut silent groove. Well there is still lot to learn about this machine and cutting blanks. I am really grateful that there are people like you in this forum, who are ready to help. Thanks a lot!

[mxlusky]

Like Dub Studio I'm going to assume a lot of details about your setup to give you lots of options:
If it's the stock 1200 turntable, I'd guess it's a torque issue.
If the blank is warped at all, it's that. Check for the head moving up and down when cutting, even slightly.
Like DS said, excessive heat during cutting or too close heat lamp could cause a warp of an otherwise flat blank.
Next down the line - head weight is too heavy, which causes torque issues or worse, disc slippage from the turntable.

best of luck hunting down the issue!

Also big thanks to you. I think that you are on point that it could be combination of torque issue and bad set weight. My Technics is old and weary and I noticed it started to lose speed form time to time. Maybe I should buy external motor for it to prevent this from happening. Thanks!

[Dub Studio]

Audio is also ok because it happens even when I cut silent groove.

Ok this is an important bit of information which helps to narrow down the list of potential causes.. it's definitely mechanical.

Temperature should be probably ok, I cut around 40-42 celsius of disk temperature.

This could be the cause. Personally, I don't heat plates at all (just room temperature) for several reasons:

- it takes time
- it's hard to get consistent temperature across the entire plate
- it can get too hot (causing chatter, which I think is the issue here, or worse still deformation of the disc)

In order to get good flat plates, and very smooth cuts, I use a combination of two things: deburring, and a dished platter.

- deburring removes any small burrs around the edge of the disc that prevent good contact with the platter. This gets rid of any ripples, which can slow the platter and cause wow and flutter.

- a dished platter helps create enough tension in the disc to keep it locked on really well. Just remember, you need to adjust the angle of the Technics slighty so that the height remains constant across the plate (raise the left hand side slightly).

If you don't have a dished platter (or one that is not dished enough) you can easily make one... all you need to do is get a rubber gasket (say 1-2mm in thickness 12" in diameter) and place it on the turnable platter. Then use another disc (a 14" lacquer works really well) and place it on top of the gasket. When you place your disc on top, you just need to push it down in order to dish the disc, and then clamp it in place really tightly (you don't want it springing back up during a cut!).

Obvously, you need to then raise the cutting head and torque tube, and adjust the angle of the TT (as mentioned above). But once this is done, you will get flat cuts every time.

[Dub Studio]

If it's the stock 1200 turntable, I'd guess it's a torque issue.

I have never noticed torque creating stability issues (other than wow and flutter) so I would be surprised if that's the cause. In any case, you need to do the resistor mod to get good results with a Technics 1200 / 1210 so I would look into that as a separate issue.

I have never tried the external motor, but I would try the mod first because I have used it with good results.