Reshaping a cartridge

[ALustyGhost]

I'm using a Grado Prestige Red on a Technics EPA501 arm, and I've never been able to get it aligned quite right. The Grado is a little too wide in the back to move all the way back in the mounting slots on the headshell, which is where it needs to be to get the proper overhang.

Since I have an extra cartridge, I just tried grinding a bit of the plastic off of the top rear edge and was able to get it properly aligned finally, which really helped with the inner groove distortion (not so much mistracking on sibilant vocals and such, but more a constant, woolly, almost tube-like distortion on most vocals, harmonica, horns and anything else in that general range, mainly on the center channel and increassing dramatically in the last inch or so on each side) that's been bothering me for a while, but became WAY more obvious since I upgraded to a tube amp.

Basically, if you look at the photo below, I ground the plastic top behind the mounting holes down by about 1mm, and rounded the back corners of the flanges that the holes are in.



The one thing that worries me is that there is a small spot (maybe .25mmx1mm) on the top where I ground through the plastic, but I can't see if there is metal uderneath or if I've actually made a little hole into the body of the cartridge. Should I cover it with something? What?

Other than that it seems fine, I was able to get it pretty much dead on, the distortion is almost gone even on the most challenging passages I've played so far, and I had no trouble getting the VTA or weight set (no surprise there). It DOES seem to be slightly quieter, but that could be because I'm using a different (older) cartridge, or it could be my imagination, or it could have been the distortion making it sound a bit louder before.

I guess I don't have any specific questions, just wanted to throw this out to the poeple on here with a lot more experience than me, and see if there was anything I should be aware of, any risks involved in reshaping a cartridge body that aren't immediately obvious to me, etc. My ears can live with a less than perfect sound, I just don't want to damage my records.

[ALustyGhost]

UPDATE:

It seems like the distortion has shifted to the outer grooves now. I don't even know what to think. This is all happening over maybe 1mm of cartridge movement on the headshell. I've pretty much tried swapping out everything at one point or another - different stylus, different cartridge, different speakers, different amp. Basically everything in the vocal range that is centered in the mix sounds like it's being played through a tube amp that is distortiing, with a blanket thrown over the speakers, everything that is happening to the right and left of the mix sounds relatively good, especially percussion. Flutes, saxophone, and voice are the worst.

I've tried aligning to different null points, etc. etc.

This has been a problem for at least a year.

[Panicos K]

If the Grado is a bit more front than ideal,you can align it using a good alignment protractor by turning it on the headshell so that the mounting screw on the outside is slightly more front than the inner one.When the cartridge is correct on the protractor tighten both screws.In this position,the cartridge will not be parallel to the headshell,but it will be correct on the alignment protractor.This will help much to lower the distortion.

[ALustyGhost]

I was doing that for a while, but I've managed to fidget the unmodified cartridge back farther and I think it's pretty much dead on now, at least well withing the margin of error on my print-out protractor. I think shaving off the plastic on the old one may have made it a little too light to match up well with my arm.

Another surprising thing I discovered this afternoon was that the antiskate, which I've been setting at just over 1.5 to match the tracking force, actually wants to be closer to 2.5. I only recently found a record in my collection with enough space after the trail-off to actually set the antiskate properly, and it turns out it doesn't hold its position until the antiskate is at around 2.48 with the TF at 1.5.

Not what I expected at all, although my first cartridge years ago (some sort of Shure) actually specified an antiskate of something like 3 with a TF of 2.

Anyhow, I'm wondering now if maybe I've worn out my stylus a lot sooner than usual since I switched to working entirely from home this summer and have had more time to play records. In the past I needed to change it every 10-12 months, but this one is jsut under 5 months old. Unfortunately, I don't have a microscope powerful enough to check for wear, but I have a new stylus on order, so hopefully when I try it out things will sound better.

[ALustyGhost]

Another thought:

Back when I worked at a record store, I got a bottle of the cheap stylus cleaning fluid we carried and didn't think much of it. I was also pretty bad about cleaning the stylus regularly back then. Recently, I looked at the label and noticed that the fluid (this stuff ) contains alcohol, which I've heard can damage the material used for the cantilever pivot. So maybe cleaning my stylus more often has actually made it wear out faster (albeit not the same kind of wear I assumed).

Again, the distortion I'm getting is not really characterized by mistracking on sibilance and other high frequency sounds, it's more in the midrange and is kind of a fuzzy, almost warm (but not in a good way) distortion, mainly on vocals, but usually not affecting anything else in the mix. Almost like the singer's voice is running through an overdriven guitar amplifier or something.

[oshifis]

Some very stubborn contamination on the stylus may cause similar symptoms. Such sticky stuff can not be removed by using the usual stylus cleaning fluid and brush. Perhaps an ultrasonic stylus cleaner may help - but you need to check the stylus tip with a microscope.

[AMV8]

Is it possible that what sounds to be distortion to your ears is actually the cartridge playing back the upper mid and treble at a higher level than the mid and lows.

When this occurs in a cartridge it does often sound the way you describe it. How do I know? I own a few garrott decca cartridges.

The cure with the garrott deccas is to alter the input resistence that the cartridge sees in the preamp input. Your preamp presumably has a standard 47k ohms impedance on the disc input. You can lower this by adding a resistor between the + and _ on each channel of the pre amp input. Try 47k ohms first of all which lowers the input impedance of the preamp to 23.5k. If that reduces the "distortion" too much try a higher value of resistor. If you want more reduction try 25k ohms.

You may find this makes a big difference as it normally helps or cures the problem with forward sounding cartridges.

Don

[ALustyGhost]

I have a stereo microscope that goes up to about 40x, which seems OK for checking for dirt on the stylus, even though it's nowhere near strong enough to look for wear.

This morning I had the local print shop print me the Stephanolouv arc protractor for the Technics epa-100 (which has the same geometry as the 500), checked the scale with a machinist's rule, had it laminated, came home and checked my alignment with it. Lo and behold, when I've got things lined up really well at the inner null point, by the outer null point it's drifted off by just about -2mm from where it should be. Instead of resting at the center of the outer null point crosshair, the stylus is right on the line of the little circle of the crosshair. Maybe the tonearm was installed a little off at the factory or has shifted a bit from decades of use by people who weren't as careful as me. Anyhow, I set it up so that it's just a fraction of a millimeter over at the inner null point and about 1.5mm under at the outer null point, and am going to have to call that the best I can do. Sometime I'll take it to a professional and have them check it, but for now it's as well aligned as I'm going to get it with the tools I have available.

That's interesting advice about the input impedence on the preamp. The Scott 299c is definitely a more forward amp than my previous one, so it makes sense that if this were my issue to begin with the new amp would make it more objectionable. I'd rather not modify the amp itself (vintage gear and all), but I should be able to put something together on perfboard and patch it in line between the turntable and the preamp input, right? I could even build one channel with a trimpot, tune that channel to my liking, measure the value of the trimpot and build a final two-channel version with quality resistors. I'd rather add a little more cable and some more plugs to my signal path that mess with my reciever right now, especially since I'm not sure yet that it's the problem. Definitely great advice, though, I'll try it for sure!

[ALustyGhost]

I am getting a bit of classic inner groove distortion on sibilance IN ADDITION, but it's minor.

[Panicos K]

Reason why it does not align on both null points is I believe because you have to pull the cartridge slightly forward and find an angle on the headshell where it is correct on both points.Similar alignment is true for rega tonearms too.You have nothing to lose trying.If not,I would align correctly on the inner null point.