squealing noise with periodic modulation

[subkontrabob]

Hi folks,

today I had the opportunity to cut again with the Neumann AM31 with Ortofon DS 501 cutterhead driven by a GO 511.

I'm experimenting with old lacquers, that I had cut 5 months ago with good results.

But tonight I got a very annoying squealing noise in the cut, that got worse the closer the groove was to the center.

I recorded a little bit with the noise, and some random reggae stuff dialed in after a while. LPI was too low, which results in a few skips and the recording ending in a funny loop.

you can listen to it here (couldn't embed it properly, sorry!):

http://soundcloud.com/mrkrabbz/testcut

Can anyone tell me what this noise is about? Wrong feedback adjustment?

feeling stupid.......

[subkontrabob]

*BUMP*

still no comments? Please you guys......

[dubcutter89]

hmm,
for me it sounds like the head is oscillating (don't know why it has that
strange modulation, maybe because it's actually cutting...) - that's not good!!! you can damage the head easily!!!
maybe it gets better if you turn down the feedback,
at least it works out for mine (DS522 / Custom Amp)
or you do a complete recalibration of the system...

reagrds
Lukas

ps: do you have some Ortofon sytli left you could trade? or anybody else?

[subkontrabob]

thank you for your post dubcutter89!

For some reason, it didn't cross my mind to change the feedback setting.
The noise wasn't that loud, and I expected cutterhead oscillation to be much more violent = louder.

So I concentrated on the cutting angle.....

Have to check next time I get there.

[dubcutter89]

hmm, i think nobody wants to change feedback setting, because you can destroy your cutter...
and maybe some do not know how to adjust...

but maybe you want to...

first i would mark the monentary setting, so you can "reset" if the
following procedur doesn't work or sounds bad (or whatever)...
then start the procedure. turn the feedback to minimum (zero or whatever),
and do the feedback calibration as said in the manual (thank you for
posting!)
->
feed 100Hz sine wave - measure the fb output (monitor?) with a scope
go up to 1000Hz - measure the fb output. it schould increase as the the
frequency increases...
Turn up the feedback (I think its called damping on the early ortofons)
until the fb output is the same as it was at 100Hz, but not oscillating!
then you should have recallibrated the system!

again, this is just how i would do it - maybe somebody else has better tips for you...

regards Lukas

[subkontrabob]

thanks for the reminder Lukas!

regarding ortofon styli: I don't own the lathe, and don't remember how many new styli there are. Probably too few new ones to sell or trade. But the owner has a lot of "broken" styli (at least the box they are in says so), that could maybe be recycled. These came with the lathe from the previous owners, so I don't know what criteria were applied. Maybe they are totally dead and dull, or have lots of charcoal, or were just replaced after a certain cutting time and are still functional - I don't know.

I can ask the owner if he would mind sending you a few if you like

best regards,

Robert

[flozki]

adjusting feedback at resonance frequency is quite dangerous.
so on neumann, sc99 you do it on 5k.
but riaa off!!!!

switch riaa off
use around 100mA of cutter current.
use a fast 0.5A fuse
then slowly increase until you reach oscillating point. if you watch on the fb signal on a scope you will notice way before the max. point.
remember how many dbs you decreased the fb signal.
then use at least 3 dB of reserve. or more.


for example on a neumann head
fb on zero
you feed in 5k . set the relative level to zero on peakmeter or note actual value.
increase fb
fb outputlevel drops..
then you reach oscillating point. on neumann typically 14-15db but min 12dB
then set the feedback to 9db

[dubcutter89]

hmm,
for sx68/74 and sc99 it's like that, but with ortofon you don't have any proposal on how many dB at which freq (or at least i don't)....
and for the DS522 cutter i would also suggest to use a 100mA fuse, because the head only takes 200mA continuous current!!!

...just try to prevent smoking cuttingheads

[markrob]

Hi,

One other thing to check. Try cutting a silent grrove with no electrical connection to the head to make sure its not some sort of mechanical issue.

Mark

[leo gonzalez]

what's that clip at the begining? is that you turning the amp on?

I think you have an ultra low and high freq oscillation oscillation.

can u feel the modulation if u put your finger (gently) on the stylus?.

if you do that, is it vertical?

sounds to me that its happening in one of the channels. possibly the left if you bounced the channels correctly left-right.

[subkontrabob]

@ Leo: a mono head was used