Arm & Cart xyz

[Craig B]

@Craig B aha.. I get -no- continuity between cart mount screw & pillar grub screw, or to the pillar itself.

So that's good the armtube's proven to be grounded, at least.

Thanks, Capt

Chaps, Im a bit confused about this ground thing. I've re-read the replies, but alot I can't understand (sip, black-yellow wires which I don't have.. I don't have sufficient knowledge to understand what the dickens any of this is).

So I've currently established that: there is sufficient grounding of the arm tube, I think this has relevance to my blue wire with an extra wire attatched (@ the cart's blue pin), this extra wire presumably being a ground connection; but to where it goes is unknown, but I don't think anything to worry about, if it seems to be 'working'.

So it's just this arm pillar situation (IE no continuity found between the cart mount screw & pillar grub screw), & more specifically the cueing arm buzz. All I can do is to presume the two are related. But my presumption, with my knowledge, results in an extremely vague situation. And any more than that I'm just totally struggling to comprehend (especially why this cueing arm buzz only occurs with AT carts, but does the ground plate thing differently located on the 540 green cart pin suggest.. well dies it suggest anything relating to this situation at all-? Logic seems to suggest so, but I can't make any sense of this discrepency). I'm still very confused by all this.

Thanks, Capt

We are actually making progress here, @The Captain.

As I suspected, your arm tube and arm pillar are not sharing a common same potential ground connection. This is why there exists a buzz whilst touching the cueing lever. If you were to touch both the cueing lever and cartridge mounting screw at the same time, the buzz will cease.

As to why there exists different ground potential between tube and pillar has to do with which way round things are wired at the red plug/socket/external ground wire end (i.e. we've eliminated the tube as culprit). When the arm was rewired, connections may have been transposed here.

Regardless, what counts here is whether or not there exists any buzz or hum whilst playing records. As you had indicated this to be a none issue (vs. it buzzing when touched being a niggle), I would suggest not obsessing over it.

Sorry for any confusion, but you did ask.

P.S. If it helps visualize the ground scheme any, here are the paths.

Lch-ve tag ===== tonearm tube
Lch-ve tag ===== Lch-ve SIP pin/socket ===== PCB mounting hole 'D' ===== external ground wire ===== NAC
​

In combination, the above paths electrically conjoin arm tube to pillar via the same low resistance wire.

P.P.S. SIP = Single Inline (row) Pins, it's just a type of connector, in this case 4-pins, small, red, and, unfortunately, no longer made.

 

[Avon]

I get continuity between blue tag & cartridge screw.

You don’t need continuity between the cartridge bolts and the blue tag. Paint on the headshell may insulate them and the cartridge’s “captive nuts” are just mounted in plastic anyway. AT cartridges attach (internally) one of the 0V wires (blue or green) to the metal body of the cartridge. You have got the cartridge tags wired correctly, with blue and green at the bottom? So green below red and blue below white.

On the wonky bass, which is more important, I think the AT cartridges must be putting energy back into the arm, making it vibrate at a loose joint (where either end of the arm wand attaches or even at the bearings perhaps). I’m not sure if this got ignored or not:

https://www.vinylengine.com/library/mission/774-(original).shtml

 

[The Captain]

@Craig B ok thanks so much Craig, this clarifies most things up nicely.

No, once arm swings away from rest area & onto an Lp, both buzz & hum disappear & I'm fine.

So without knowing why the buzz only happens with AT carts, I guess I'll never know. Nor why there's a ground plate thing on their green cart pins, instead of the blue pin as per all other carts (as far as I can establish that is: there may be other mfrs who also use the green pin, but I haven't come across their products yet). Nor why there's a discrepancy between this ground pin position, between cart mfrs, or between arms & AT, or if some arms have an extra wire on their green pin.. complicating things further. I'm -totally- confused by this I admit.

Just one thing missing in my imagining of my situation. If the extra wire added to my blue pin is an earth relating to the arm tube, & this goes back to the sip block connector (I cannot recall taking the mission sticker off & ever connecting -any- wire behind here).. where does it go from there..? Where does it terminate? Maybe you have no idea either!

 

[The Captain]

You don’t need continuity between the cartridge bolts and the blue tag. Paint on the headshell may insulate them and the cartridge’s “captive nuts” are just mounted in plastic anyway. AT cartridges attach (internally) one of the 0V wires (blue or green) to the metal body of the cartridge. You have got the cartridge tags wired correctly, with blue and green at the bottom? So green below red and blue below white.

On the wonky bass, which is more important, I think the AT cartridges must be putting energy back into the arm, making it vibrate at a loose joint (where either end of the arm wand attaches or even at the bearings perhaps). I’m not sure if this got ignored or not:

https://www.vinylengine.com/library/mission/774-(original).shtml

Hi Avon. Yes I've ruled out any page 1 basic mistakes as having the colours connected incorrectly. I always remember red & green as a pair for one channel, the green below the red. And I know white sits on the top row next to the red, leaving only the blue possible in the vacant spot below it. I triple check this too.

The wonky bass- well there's absolutely nothing to suggest anything is loose in the arm bearings area. Nor anything else not tightened firmly (but not excessively). I've kinda just concluded by trial & error, I have a mismatch between a AT95ML cart, a Linn k9 cart, a Linn k9 & SH stylus cart, & the AT 540 ML cart.. with my mission 774 arm, or with the mission 774 arm + suspended Linn Lp12 tt.

If I pop back on my humble Shelter, & the wonky bass is simply awol again, I can only possible land at this conclusion really. I'd think if it were loose arm bearings, this wonky bass facet would simply appear with the Shelter too, not vanish. If only very marginally heard.

But I'm only adding logic I admit. And my arm/ cart physics knowledge is still hopelessly poor I also admit. But even an idiot can do simple ruling out of a, then b, & his conclusion will be just as per a TT expert. He may even naturally have a better ear than the TT expert.

Thanks, Capt

 

[Craig B]

You don’t need continuity between the cartridge bolts and the blue tag. Paint on the headshell may insulate them and the cartridge’s “captive nuts” are just mounted in plastic anyway. AT cartridges attach (internally) one of the 0V wires (blue or green) to the metal body of the cartridge. You have got the cartridge tags wired correctly, with blue and green at the bottom?

On the wonky bass, which is more important, I think the AT cartridges must be putting energy back into the arm, making it vibrate at a loose joint (where either end of the arm wand attaches or even at the bearings perhaps). I’m not sure if this got ignored or not:

https://www.vinylengine.com/library/mission/774-(original).shtml[/user]

I think you may have missed a point wrt continuity testing here. The cartridge mounting screws thread into the headshell block (at least they do on The Captain's undrilled through original) and therefore represent the least resistance path to tube metal for testing continuity between Lch-ve tag and tonearm tube. Were his cartridge off he could just as well touch one probe to bare metal within the threaded hole. No matter what else is going on, we know that his tube has connection to Lch-ve tag, independent of what pin this happens to connect to at the cartridge (or where Lch-ve wire happens to connect to down the SIP plug end now).

 

[Craig B]

Hi Avon. Yes I've ruled out any page 1 basic mistakes as having the colours connected incorrectly. I always remember red & green as a pair for one channel, the green below the red. And I know white sits on the top row next to the red, leaving only the blue possible in the vacant spot below it. I triple check this too.

The wonky bass- well there's absolutely nothing to suggest anything is loose in the arm bearings area. Nor anything else not tightened firmly (but not excessively). I've kinda just concluded by trial & error, I have a mismatch between a AT95ML cart, a Linn k9 cart, a Linn k9 & SH stylus cart, & the AT 540 ML cart.. with my mission 774 arm, or with the mission 774 arm + suspended Linn Lp12 tt.

If I pop back on my humble Shelter, & the wonky bass is simply awol again, I can only possible land at this conclusion really. I'd think if it were loose arm bearings, this wonky bass facet would simply appear with the Shelter too, not vanish. If only very marginally heard.

But I'm only adding logic I admit. And my arm/ cart physics knowledge is still hopelessly poor I also admit. But even an idiot can do simple ruling out of a, then b, & his conclusion will be just as per a TT expert. He may even naturally have a better ear than the TT expert.

Thanks, Capt

Like most all MM cartridges, A-T connect Rch-ve to shield. This doesn't necessarily mean that this should match the tonearms earth path, as all will work out in the wash down the phone stage or amp end. All MMs require a shield connection to one -ve path, with many making the connection within. Rega MMs have an extra length of coil lead extending off the Rch-ve pin within that is soldered to the inside of their shield. Ortofon's old F/FF/VMS have a metal washer fitted as larger flange round Lch-ve pin within that pressed against the inside of the fitted metal shield. 2M series are the tiny OM series generator within, hence, an external tab connecting to green like with the A-T VMs. The list goes on, but the point is that MM cartridges are more susceptible to hum due to higher internal impedance relative to MC types (some more or less than others, with Grado being the lowest), hence MC cartridges not requiring metal shields on (yet tonearms still need grounding).

Shelter don't mention internal impedance for 201, however, I suspect this to be lower than that of A-T, particularly the VM models with dual coils per channel.

 

[Avon]

The wonky bass- well there's absolutely nothing to suggest anything is loose in the arm bearings area. Nor anything else not tightened firmly (but not excessively).

But that Vinyl Engine link does describe exactly the problem you’re having. I would guess that different cartridges put different frequencies into the arm? I use PTFE tape at each end of the wand, but I don’t know whether that’d help with the Mission or not. Even the arm weight could be loose?

The cartridge mounting screws thread into the headshell block (at least they do on The Captain's undrilled through original)

If both the headshell and the cartridge are threaded, then the cartridge body cannot mate with the headshell?

 

[Craig B]

If both the headshell and the cartridge are threaded, then the cartridge body cannot mate with the headshell?

Oh, I see what you were getting at here now. The Captain had managed to persuade the headshell block screws to pass through the VM95 captive nuts and into the headshell block. He did end up with a very tiny gap on one side but reported that the cartridge was on quite solidly and, of course, the arm tube was easily aligned for correct azimuth.

I had previously suggested that he seek out captive screws but these proved to be difficult (and/or too expensive) to source in quantities of two.

 

[Avon]

Oh, I see what you were getting at here now. The Captain had managed to persuade the headshell block screws to pass through the VM95 captive nuts and into the headshell block. He did end up with a very tiny gap on one side but reported that the cartridge was on quite solidly and, of course, the arm tube was easily aligned for correct azimuth.

I had previously suggested he seek out captive screws but these proved to be difficult (and/or too expensive) to source in quantities of two.

QED. The cartridge must be in full contact with the headshell, otherwise it will rattle.

 

[Craig B]

QED. The cartridge must be in full contact with the headshell, otherwise it will rattle.

Regardless, I believe that his VM95 experiments have passed, since replaced with VM540ML vs. Linn K9 with original vs. VMN95SH replacement stylus on.

As my dearly departed maternal Grandmother would have quipped, 'There are no flies on The Captain'.

 

[The Captain]

But that Vinyl Engine link does describe exactly the problem you’re having. I would guess that different cartridges put different frequencies into the arm? I use PTFE tape at each end of the wand, but I don’t know whether that’d help with the Mission or not. Even the arm weight could be loose?


If both the headshell and the cartridge are threaded, then the cartridge body cannot mate with the headshell?

Hi Avon, aha ok I'll try & find that specific info on that page. Thanks for this link btw, I did read it, but only noted the arm bearings loose situation, which I couldn't relate to my arm. The CW seems not to be loose.

PTFE tape?? that's got to be the cheapest mod on pfm! So what's your thinking of adding this though? I can't quite understand the notion of "different carts put different frequencies into the arm" as surely all the carts I've used & listed share a pretty similar 'frequency something', frequency range? (I don't know, I cannot understand what a frequency curve actually is, & so -utterly- lost amidst discussion on any particular point of this alien curve frequency shape.. if you are referring to a particular point that is).

This frequency thing is into the physics arena I am completely blind to any understanding of even with many hours pouring over the very basics, on the www: I cannot understand the tiniest bit of it all. "Frequency response" remains stalwartly incomprehensible, two arbitrary words put next to each other. I understand only that 'frequency' has an intrinsic link to the pitch of a note (the higher the frequency, the higher the note). But how the pitch of a note could relate to 'putting different ones, into an arm'.. is like my brain trying to feed a triangle shape into a round hole. Nos comprendas!

 

[Avon]

Captain, both ends of my arm wand go into holes, which are slightly too big for the wand. A single screw holds each end of the wand in place, so there’s wiggle room without the PTFE tape.

Your Mission looks better than that though, as it seems to have a “wrap around” metal strap, held in place with a bolt, which should stop any vibration. But since the AT cartridges have the wonky bass, then my thinking is that PFTE tape might tame any vibration in the joints.

That’s just a guess and I have no experience of the Mission arm of course.

 

[cobbers]

8"?

That’s just a guess and I have no experience of the Mission arm of course.

The tube is tightly clamped - even bare.

 

[cobbers]

Pity nobody with experience of the arm close to you.

 

[The Captain]

Captain, both ends of my arm wand go into holes, which are slightly too big for the wand. A single screw holds each end of the wand in place, so there’s wiggle room without the PTFE tape.

Your Mission looks better than that though, as it seems to have a “wrap around” metal strap, held in place with a bolt, which should stop any vibration. But since the AT cartridges have the wonky bass, then my thinking is that PFTE tape might tame any vibration in the joints.

That’s just a guess and I have no experience of the Mission arm of course.

Hi Avon, what arm do you have? I can't quite figure out how you could be doing this idea. I am far better at building work than understanding arms & carts, so know what this ptfe stuff is. I had a nightmare when a bit of bluetack got stuck on my CW thread (panic on as I only just unscrew the CW to remove it) so I don't want anything similar getting on the thread you see.

Tbh all of the AT's Ive recently tried you see, not only share this awful bloomy bass, but generally poor bass quality too: the lowest notes totally awol, wooden, & low half definition distinctly average- so my mind's made up categorically that these special-stylus shape AT's, are excellent up top, & some other aspects also extremely good on the 540.. but the low half from the k9 to the 540, is kinda like just 'tagged on', almost an irrelevance to the showy top end. Like a stunning blonde, with a fine frontage, but with flatulence spoiling the show. Strange, you can't quite understand it, & you try every remedy, even ptfe tape, but she still farts excessively. She has to go.

 

[Craig B]

@The Captain,

Suggest you try taking the paddle out (of the goop) before abandoning ship.

Craig

 

[The Captain]

@The Captain,

Suggest you try taking the paddle out (of the goop) before abandoning ship.

Craig

Yes I could do, but to be very honest I couldn't hear any difference between lightest paddle (& apparantly in 60k too-light goop) & the biggest paddle in the thick 300k goop. I kidded myself innitially that I could discern a fraction more x & y, but I was only fooling myself bc I wanted to believe it was a tiny bit better.

I have tried everything, but if this wonky bass is just inherently in the cart/ part of the cart's sound.. then I'm flogging a dead horse trying to get rid of it- it simply can't be done if it's "in the cart". On the other hand, I might have just fluked the cartridge before, which had an exceptionally good bass quality. Or, it just worked spot-on here, in this room with these es14's, for whatever lucky reason, & -every other- cart I might try instead, exhibit the same bad habit. I'd think both those very unlikely though; the most plausible is simply this, that these AT's just ain't great in the lower half.

If cobbers brought his 774 & 740 here, & swapped onto my Lp12, 95% likelihood the bass would be wonky (the 5% is only that it's a metal bodied version of my 540). It -would- boom & bloom identically. I'd bet my house on it. Now cobbers -might- say that sounds fine, really good, to him.. & so I'd dig out my old cart (now sold alas) & show him this bass.. & he might be astounded. But no. He'd hear the his arm & cart boom & bloom too.

 

[The Captain]

@cobbers did you try your 740 vs a 540ML? I can't help wondering what the benefit could actually manifest as/ sound like with the metal body.

As you say how happy you are with it & the 774 arm, I can't help wondering if the better body might produce a better, more controlled bass. Many things I thought vg & addictive about the 540, that I actually miss (inneviatble in a way with such a cracking top half, despite it being slightly 'hard'). Possibly enough for me to forgo the bloomin bass-? I wonder, hmm..

Thanks Capt

 

[Avon]

Have you tried listening to it through headphones?

 

[cobbers]

did you try your 740 vs a 540ML? I can't help wondering what the benefit could actually manifest as/ sound like with the metal body.

Never had a 540ML - had a 530EN and did a straight swap - did not notice a difference in the bass but what was blindingly obvious was the difference in the treble quality.
The only other cartridge I have at the moment is an old Empire 440D quadraphonic with a tip profile similar to Shibata - no problems with that either.

I think I said before that when I first fitted the 774 onto the PT1 it was onto an MDF armboard which resulted in similar bass quality to what you have described - changing the armboard to a homemade alloy/balsa/CF sandwich immediately cleaned it up.