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In Reply to: RE: Suspect Jelco specs and geometry posted by hesson11 on January 17, 2010 at 05:04:03
Jelco have been making tonearms for years, and there is no doubting the accuracy of their technical drawings.
The SA-750D tonearm has an effective length of 229mm, but if you want to align it so that the null radii fall at 66.0mm and 120.9mm then it might be better to mount it so that the centre of the base is at a distance of 211mm from the spindle
Best regards,
BK
Follow Ups:
I've owned several of these arms and rightly don't care how long Jelco's been making tonearms.You find me one, JUST ONE, cartridge that can be mounted on the 750D with the stock headshell and achieve a 229mm effective length (pivot point to stylus distance) and I'll concede that it's possible - but I dare say you will never find one.
It has nothing to do with the "extra long" headshell slots and zip to do with where the cartridge ends up in relation to the slots - it has everything to do with the ability to mount a cartridge at the spec'd effective length. Those pics of my 20XL mounted 3/4's of the way back in the headshell reflect an effective length of around 236mm. The 20XL would have to move a full 7mm back in the headshell to achieve 229mm, which, is plainly not possible.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
Edits: 01/17/10
You mounted your tonearm at 214 mm from the spindle, and aligned it to acheive an effective length of 232 mm. This is accroding to the information in YOUR OWN post below.
YOUR OWN cartridge could have been aligned to provide an effective length of 229 mm by moving the cartridge back in the headshell by about 3 mm. In fact, there is another 5 mm in the headshell according to YOUR OWN information. So based on YOUR OWN information, the effective length could have been reduced to ~227 mm by pushing the cartridge fully back in the headshell.
So the "JUST ONE" cartridge that you are looking for is YOUR OWN Dynavector 20XL.
Incidentally, the way you measured the mounting distance is not accurate. You need to measure from the centre of the mounting hole to the spindle. An elevated measurement is going to add an uncertainty of ~+/-1 mm, and using the edges of a piece of corrigated cardboard is going add further uncertainty to the measurement.
BK
I'm, frankly, getting a bit tired of beating this topic to death! I would recommend you actually go get one of these arms, mount it at 214mm, THEN get back to me...The arm was mounted at precisely 214mm - precisely.
The effective length of the arm with the cart mounted via Baerwald is 232mm. It would be impossible to move the cart back any further, 1mm much less 3mm. Look at the pictures on my post. There's not 5mm of slot remaining first of all and, more importantly, the headshell and cartridge leads are TOUCHING each other at 232mm. What do you propose, cutting the pins?
I've confirmed, re-confirmed, etc. the FACT that the effective length of this arm CAN NOT be 229mm. No way, no how.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
Edits: 01/18/10
In the picture there is a clear 5mm behind the bolts.In your oritinal post, you said: "the cartridge is mounted 2/3 of the way back"; 1/3 of 15mm = 5mm. GET IT YET, OR IS THAT TOO HARD TO UNDERSTAND?????????
I agree on one point: this 'discussion' is a waste of time; moreover, you're not the first person to chime in out of nowhere claiming that a manufacturer had got it wrong: Actually, you have it wrong.
And while I'm on the subject, the pins don't touch with the cartridge fully back in the headshell.
BK
Edits: 01/18/10
Enough said. Your taking the specs as Gospel (are you an engineer for Jelco?) and I'm speaking from actual experience. I'm not beating his to death any more and stand firmly behind my findings ubtil you PROVE me wrong with an actual arm mounted at 214mm and a cartridge shown ON A 750D with a 229m effective length.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
NT
Shure V15VxMR mounted in Jelco headshell, providing effective length of ~226mm
HFS
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
The pictures are of the headshell with Shure V15 mounted to illustrate that the cartridge can be accommodated all the way at the back of the headshell.
It's the demonstration that you requested above.
You said that this was impossible.
So ADMIT you were WRONG or demonstrate that you are IMPERVIOUS to logic.
BK
And even if it was a 750D it would STILL PROVE MY POINT - the technical drawing prescribes that the the stylus should fall just in front of the headshell slots with the stylus positioned at 229mm from the pivot point (hence giving an effective length of 229mm).
Look, this is so very simple - according to the technical drawings from Jelco and their spec's - if you take a length of thread and stretch it from the pivot point of the arm to the point identified on the drawing just in front of the slots - it should measure PRECISELY 229mm.
I'll help you out since you're having trouble following along - look at the drawing I've attached - see the big line with the arrow on it with the big R229 above it??? You with me so far??? Now go get your hands on a ACTUAL 750D arm and measure that distance - and you'll quickly find that it's NOT 229MM - not even close, it's more like 233mm+.
Go back to my original post - I linked it to help - the stylus on the 20XL is at 232mm from the pivot point - giving AN EFFECTIVE LENGTH OF 232mm. The stylus is BEHIND the prescribed 229mm point.
I'm beginning to think you're just messing with me at this point, getting your jollies watching me repeat the same thing over and over again when a ten year old would understand what I'm saying is true. NOBODY can be this dense.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
Why would anyone think you are being a jerk? NT
Are you saying that, based on the SA-750D drawing above, if you were to move the cartridge 3mm further forward than your picture, you would have a stylus tip to tonearm pivot distance of exactly the 229mm as shown on the drawing above?
That's assuming a mounting position with a spindle to pivot distance of 214mm, of course.
Basically, that was what I was trying to show.The stylus is about 7.5mm from the front of the headshell, so if the Shure V15VxMR was mounted on a Jelko SA750D it would produce an effective length in the order of 4mm less than the nominal effective lenght (229mm). The nominal effective length occurs when the stylus is about 3mm from the front of the headshell - see Jelco drawings.
The minimum possible effective would variy for each cartridge because the distance from the stylus tip to the mounting bolts is not a constant - for example a Denon DL103 at the same position in the headshell would produce an effective length about 6mm short of 229mm. That's why most tonearms have slots in the headshell.
However, I disagree with your last point: the mounting distance does not change the effective length. It just changes the null radii.
BK
Edits: 01/19/10
You're clearly saying that if I take that cartridge mounted exactly as you have it and put it on the 750D I would have an effective length of 225mm. Here's your quote:
"so if the Shure V15VxMR was mounted on a Jelko SA750D it would produce an effective length in the order of 4mm less than the nominal effective lenght (229mm)."
So, please explain how my 20XL is mounted AND MEASURED with an effective length of 232mm (see the picture...) and the stylus is within a mm or two of your Shure.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
Spot the difference:
"You're clearly saying that if I take that cartridge mounted exactly as you have it and put it on the 750D I would have an effective length of 225mm. Here's your quote:
"so if the Shure V15VxMR was mounted on a Jelko SA750D it would produce an effective length in the order of 4mm less than the nominal effective lenght (229mm).""
nt
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
I don't mean to butt in, VinylTap and B.K., but I took a close look at both your pictures. It APPEARS that there may be two main differences in your setups:
1. The distance from the cartridge mounting screws to the back end of the carts appears to be shorter on B.K.'s Shure than on VinylTap's Dynavector.
2. The tonearm wire clips appear to be shorter on B.K.'s headshell than on VinylTap's.
Could this account for the the fact that B.K. can move his cart further back than VinylTap can? (Just taking a wild stab at it!)
-Bob
Thanks for trying; however, for the pictures, the cartridge is mounted on a Graham Robin, and it isn't set up on any turntable.
The point of the pictures was to illustrate that the cartridge can be accommodated all the way at the back of the headshell, and to demonstrate that the stylus falls well short of the position in the drawings which produces an effective length of 229mm.
The headshell leads are the same litz wires on all of the Jelco arms. There are only two headshells available, a grey version and a black version.
I have no idea what leads or headshell Mr Vinyl Tap is using.
BK
Which makes this all the more mysterious. Not sure why he's so hellbent to defend them.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
BK owns 2 Jelco arms NT
you have none listed in your profile. You seem to be going under the assumption that I'm trying to be a jerk here - it's not my intent.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
Edits: 01/19/10
Your whole contribution here has been antagonistic, packed with clever dick remarks and comments which were based strongly on bold CAPTILISED assertion and not ACTUAL FACTS. EG "the pins touch", "the cartridge cant be moved any further back", "the effective lenght is 236mm", "the length of the headshell slots has zip to do with it" etc etc - all these points are wrong.
I don't own an SA 750D and never claimed to own one. I have two SA 750L tonearms, an Audioquest PT9, a Graham Robin, and a Grado Reference - all of which were made by Jelco.
You measured the technical drawing provided with the tonearm and concluded that the tonearm was out of spec, but you forgot to check if the drawing is produced accurately to scale - it isn't.
Put the mounting template (which is accurately to a 1:1 scale) over the technical drawing; hold the two drawings up to the light and try to line them up. They don't line up. So you can't make conclusions from measurements on the drawing.
As regards your pictures - you didn't show the headshell from the side, your pictures are shot at an angle, but it looks to me that your stylus falls close to the front of the headshell and a one or two mm ahead of the point for an effective length 229mm. Roughly, consistent with your deduction that the effective length is 232mm and roughly consistent with the tonearm drawings.
If you had started out by saying that a user might just as well mount the tonearm at a greater distance than the manufacturer's recommended value, then I would have agreed.
The extra long slots in the headshell allow the tonearm to be mounted anywhere from ~211mm to 222mm, and for alignment still to be possible.
It's a benefit, not a drawback.
If you want the cartridge bolts to fall right in the middle of the slots, for null radii at 66mm and 121mm then you should mount the tonearm at ~216mm
BK
And by the way, I certainly don't need to prove my credentials to you.
'nuf said. It doesn't matter if the drawing is to scale - all I need to use are the printed dimensions on the drawing in comparison to the ACTUAL ARM SITTING IN FRONT OF ME to know they're incorrect.I'm using caps in hopes of getting it to sink in. Yes, I'm now being an ass and with good reason.
Answer the one post you haven't so we can be done with this. Simply and plainly explain how I'm able to achieve 232mm effective length with the stylus several mm's BEHIND the specd 229mm mark. If I'm wrong I'm man enough to freely admit it. Are you?
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
Edits: 01/19/10
"Yes, I'm now being an ass" that's correct you are. NT
...and lend your firsthand experience, of which I have none. This tonearm gets interestinger and interestinger all the time! Do you still have it mounted on your SL-1200? How's it doing? THANKS.
-Bob
But every other cartridge I used worked better with the KAB mod'd stock arm. Not. Worth the time and expense in my opinion unless you're ONLY going to use the Denon. Even then I'm not sure it's really worth it.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
I hope you're right, B.K., and I'd like to think Jelco got it right. But I'm wondering whether you've read the thread I linked to and what you think of it.
-Bob
Hi,
I had a quick look through the thread.
The Jelco tonearms are designed having headshells with extra long slots (15mm).
A standard cartridge will be positioned much further back that many people are used to with other universal fit headshells.
In fact you could easily get away with having the tonearm mounted at 214 mm, align for null radii at 66 mm and 121 mm, making use of the long headshell slots and producing an effective lentth of 232mm.
Best regards,
BK
most carts end up barely fitting due to the cartridge and headshell pins being so close together. Many cartridges will not mount at all at this setting.Remember, Baerwald / Lofgren A geometry typically pushes most cartridges further out towards the end of the headshell and away from the headhshell pins. The length of the slots is irrelevant in this case as I'm not away of any alignment geometry that could utilize them at the Jelco prescribed mounting distance. Please enlighten me if you're aware of one.
What makes this most odd - Jelco spec's a 229mm effective length - not sure what the null points would be on a cart mounted to that effective length - which is impossible to achieve with every cartridge I have ever seen.
If you look at the technical drawing you posted in your other response, you'll see that the STYLUS is spec'd to fall right at the front of the headshell slots and the distance from the pivot point to the stylus tip SHOULD be 229mm - as I clearly show in the other post it's not even close to 229mm.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
Edits: 01/17/10 01/17/10
"as I clearly show in the other post it's not even close to 229mm"
In your original post, you didn't clearly show that the effective length is not even close to 229mm.
Unless I am reading the wrong post.
Also you are wrong about fitting cartridges to the headshell; most cartridges will fit even with their mounting bolts as far back in the headshell as the slots allow.
BK
and even prove it by showing PICTURES of it aligning perfectly with the 232mm arc on the Baerwald template.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
I stated that you failed to show that the effective length is NOT 229mm.
Read it again.
BK
and looking at where my cartridge measures 232mm to determine that. It couldn't be simpler.
"I'll play it and tell you what it is later..." - Miles Davis
Vynyltap's System
I didn't realize until checking just now that my Nagaoka, ADC, AT, and Technics headshells are all the same overall length and have the same length and placement of mounting slots, but my Jelco example is mysteriously longer by about 15 mm I'd guess (and with longer slots).
It would have been so much better if Jelco communicated this tidbit! I can't find a reference in anything they produce to indicate their choice in making a headshell with different dimensions than the rest of the world's universal fit ones. Or why they did it.
This explains everything regardng the mystery of mounting distance and headshell/cartridge appearance, for me anyway, and might give a person reason to source a Jelco arm without the Jelco headshell!
Thanks and regards,
Jim
n/t
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