View Full Version : jelco 750D kick off!
thanxs everybody that encouraged me for it. Very happy, at least this is the impression after few spins of vinyl.
Its a musical tonearm and in crescendo stays uncompressed and do not mix it up intruments. Very nice.
Now, what the hell shall i do with the damping oil? Read somewhere to put three drops only, in other places i read no nedd. Whats the best intake on this? Thanx
Hi Daniele,
Glad that the Jelco is hitting the spot for you. It's an excellent tonearm, which performs far in excess of its price tag! As for the damping oil, just put a few drops in (NO MORE), as the effect will improve the performance of most cartridges.
Put too much in, and it will KILL the sound - and getting the oil out afterwards is a rather more difficult process than putting it in!! ;)
Marco.
I have not experimented 'with' vs 'without' on my Jelco. A starting point would be to follow the follow the guidance in the manual. If you did not get this Arm new there is a manual available at http://www.vinylengine.com/library/jelco/sa-750d.shtml
Oldpinkman
24-02-2014, 06:31
Surely the answer is going to depend on the cartridge fitted. As a broad general rule don't add damping if you don't have to. The arm has quite a high effective mass and so should naturally work best with relatively low compliance moving coil cartridges. If you want to use it with a v15 then you may need some damping.
That makes sense, Richard. However, I listened to the 'before & after' effects of adding damping oil to the Jelco, using a DL-103 as a reference (a cartridge that one could argue wouldn't benefit from damping), and adding a few drops of fluid definitely improved the performance of the tonearm and cartridge :)
You mustn't overdo it, though!!
Marco.
Being pragmatic.....as it seems impossible to remove the oil when there, it makes sense to use a universal approach that can fit the majority of carts that would be used in the Jelco lifetime.
I have a Goldring 2400 currently and with test record I got 11 Hz resonance. I think it is acceptable per se....
By the way....I had addressed once more the Jelco mass value with Huchida san. I was explaining that there are several different values, depending from the forum and I asked him the true value of mass. You guess what?
13,48 gr only!
Cheers
Indeed, but that all depends on what headshell is fitted to it! ;)
Marco.
Is it not the case? And if not always, how much is the weight of the standard headshell giving the figure 13.48gr? So I can put it over my spaghetti weighter and will know my case with precision....................." Hey my dear, a strange object is floating in the spaghetti bowl, any clue?"
Lol...... :D
Yes, he'll have arrived at that figure using the stock headshell as a reference. However, the point I was making was that one can adjust the effective mass of the Jelco simply by fitting a lighter or heavier headshell.
That's the beauty of detachable headshell arms (plus, fitting cartridges is a damn sight easier, too)! :)
Marco.
Just to make sure i have the standard one...Sometimes packing error might arise?Although in my experience Japanese friends are extremely precise in whatever they do as a business
Hi Daniele,
Sorry, I no longer have a Jelco tonearm or its original headshell. However, the Jelco headshell is near-identical to the Sumiko one, which is widely sold on the Internet, and that one weighs 12g, so this is what the Jelco headshell should also weigh.
Hope this helps :)
Marco.
Oldpinkman
24-02-2014, 19:20
I'm sure wise virgins like Marco remember this, but maybe a freshman like Daniele could be forgiven for not appreciating it
Effective mass is not the weight of the object on the kitchen scales. If you take a 12g headshell and an 8g arm tube you do not (necessarily) have an arm with a 20g effective mass. It all gets a bit confudling when people talk about moments of inertia and fulcrums, so we'll just glaze over that last bit, but it is worth remembering some thoughts
Effective mass is quoted at the effective length (the stylus distance from the pivot). It will be different (less) at different points along the armtube although the armtube weighs the same on the kitchen scales
Effective mass can be different in the vertical plane to the horizontal plane (the most extreme example being Martin T's beloved Dynavector arm). The arm weighs the same actual weight on the kitchen scales - but has a (very) different lateral effective mass (estimated at around 50g) from its vertical effective mass (I believe about 6g)
Mass near the effective length has significantly more effect on effective mass than mass near the pivot
This last perhaps gives the easiest way for non-tech's like me to get our head round this strange concept. We are talking about a system resonance - a frequency at which relatively low energy is needed to "excite" the system, between the spring which is the cantilever joint, and the mass which is the arm. Stay with me.
If you get a plastic ruler and a heavy rubber (pencil eraser Marco, please) and attach the rubber to the end of the ruler with a rubber band, then if you hold the other end of the ruler and wobble it, there will be a frequency ( a wobbling speed) where it just keeps going with relatively little, almost no, effort. Trying to make it wobble faster or slower can be done but needs much more effort. The frequency at which the least effort is needed (least energy) to keep it going, or "excite" the system is the resonant frequency.
If you add mass, or add compliance, that frequency gets lower. (Attach another rubber with a rubber band and prove it). Reduce compliance (bendiness) by holding the ruler nearer the weight - ie not right at the other end - which makes the ruler stiffer.
Now - if you add the mass of the 2nd rubber right at the end with the first rubber, it will have a big effect on the system resonance (the speed at which the ruler wobbles most easily). If you attach the 2nd rubber near to your hand (the pivot point) it will have much less effect (none you would notice) on the system resonance. But the rubber weighs the same on the kitchen scales regardless of where you attach it to the ruler. If you put the ruler and rubber at the end on the scales, it will weigh the same as the ruler and the rubber in the middle of it.
Effective mass is not the same as weight! Simples ;)
The effective mass of a pickup arm is the second moment of inertia of the arm about the pivot point divided by the square of the effective length. The effective length is the distance between the pivot point and the stylus of the cartridge.
The effective mass of any arm can be altered by changing the headshell. And, to a first approximation, since the headshell is situated more or less directly above the stylus and far from the pivot, the change in effective mass is equal to the change in dead weight of the headshell.
one day will understand it. For nowi just smell the sense. Thanxs
The effective mass of any arm can be altered by changing the headshell. And, to a first approximation, since the headshell is situated more or less directly above the stylus and far from the pivot, the change in effective mass is equal to the change in dead weight of the headshell.
Exactly! :thumbsup:
Marco.
Could someone point me in the right direction where to get hold of a protractor for the 750D? Should I just use a "stupid" two-point protractor? Would you recommend Baerwald, Stevenson or something else?
All replies will be appreciated :)
Could someone point me in the right direction where to get hold of a protractor for the 750D? Should I just use a "stupid" two-point protractor? Would you recommend Baerwald, Stevenson or something else?
All replies will be appreciated :)
Anyone?
Stratmangler
17-07-2014, 16:39
http://www.accutrak.us/jelco-sa-750d.html
According to vinylengine.com the “vital statistics” for your Jelco 750D are as follows:
Effective length (arm pivot to stylus): 229mm
Overhang: 15mm
Arm mounting point to turntable spigot distance: 214mm
Offset angle: 22°.
Then using the equations in http://theartofsound.net/forum/showthread.php?20109-Tonearm-alignment, the two radial null points (i.e. .the two points on the alignment protractor) should be at 59.1mm and at 112.5mm.
These two radii differ from the usual (Baerwald) null-radii of 66mm and 120.9mm, since the Jelco arm has not been designed to follow the Baerwald geometry. Nor have the designers chosen to follow the Stevenson’s geometry, though the geometry of the 750D is closer to that of Stevenson than to that of Baerwald.
337alant
18-07-2014, 12:06
According to vinylengine.com the “vital statistics” for your Jelco 750D are as follows:
Effective length (arm pivot to stylus): 229mm
Overhang: 15mm
Arm mounting point to turntable spigot distance: 214mm
Offset angle: 22°.
Then using the equations in http://theartofsound.net/forum/showthread.php?20109-Tonearm-alignment, the two radial null points (i.e. .the two points on the alignment protractor) should be at 59.1mm and at 112.5mm.
These two radii differ from the usual (Baerwald) null-radii of 66mm and 120.9mm, since the Jelco arm has not been designed to follow the Baerwald geometry. Nor have the designers chosen to follow the Stevenson’s geometry, though the geometry of the 750D is closer to that of Stevenson than to that of Baerwald.
Barry,
Thanks for posting that link, Im glad that's cleared the alignment mystery up in easy to read lay mans terms :rolleyes: :D
Alan:cool:
Barry,
Thanks for posting that link, Im glad that's cleared the alignment mystery up in easy to read lay mans terms :rolleyes: :D
Alan:cool:
+1. A lot of it beyond me but still beneficial.
Spectral Morn
19-07-2014, 07:33
Mint Tractor best option for your arm. when ordering tell Yip which turntable you are using it on + length of arm 9in or longer. Each tractor specific to arm and turntable, so you can't use it with another combination.
http://mintlp.com/best.htm
Regards Neil
Barry,
Thanks for posting that link, Im glad that's cleared the alignment mystery up in easy to read lay mans terms :rolleyes: :D
Alan:cool:
Your sarcasm is noted - however the whole subject of tonearm geometry is quite complicated and therefore implies a fair amount of mathematics. Because of that, most people are happy to use the alignment protractor supplied by the manufacturer, but if it is not available then one has to either calculate the two null-point radii, or try to use a commercial protractor. Most commercial protractors are set up for the Baerwald geometry, which if your arm has a different geometry makes it difficult (but not impossible) to achieve.
337alant
20-07-2014, 12:45
Barry I was only joking, actually I did read it all and it was very interesting but a little over my head TBH
I use the HIFI news ARR protractor with pin holes at nul points taken from the Tonearm data base alignment protractor calculator where you can switch between Stephenson Lofgren A & B , Jelco 750L / Ortofon Kontrapunkt B
http://www.vinylengine.com/tonearm_alignment_calculator_pro.php
Alan
I suspected that might be the case, but I was worried that I might have been less than successful in trying to make a difficult subject accessible and understandable to the lay-reader.
Love the avatar by the way: Revox PR99?
I see in the latest Hi-Fi Choice that Electrocompaniet has made its first turntable: It is fitted with the Jelco 750EB which is the 10 inch version of the 750D loved by techie owners. They aspire to the high-end and the turntable called the ECG-1 retails for £2890. So I guess this is quite a compliment to Jelco and an affirmation to all us Jelco owners.
337alant
30-07-2014, 12:47
Barry
Yes the avavter is my Revox PR99 Mk2, nice R2R
I agree the Jelco is a fine arm and a good price, I thought the Shuggie mounting was worthwhile as well
I have also just replaced the arm lead from the mogarmi one with a silver job from ebay and I thought that was cleaner as well
I think the heavy counter weight is well over priced though so I just used 2 Stainless Steel washers superglued together and them blue tacked onto the original counter weight.
Here is my Jelco 750L on Garrard 401 and Ortofon Kontrapunkt B
https://farm8.staticflickr.com/7324/9302181084_5be3f6fbf0_o.jpg (https://flic.kr/p/fb17mu)Garrard (https://flic.kr/p/fb17mu) by 337alant (https://www.flickr.com/people//), on Flickr
Alan
Barry
Yes the avavter is my Revox PR99 Mk2, nice R2R
I agree the Jelco is a fine arm and a good price, I thought the Shuggie mounting was worthwhile as well
I have also just replaced the arm lead from the mogarmi one with a silver job from ebay and I thought that was cleaner as well
I think the heavy counter weight is well over priced though so I just used 2 Stainless Steel washers superglued together and them blue tacked onto the original counter weight.
Here is my Jelco 750L on Garrard 401 and Ortofon Kontrapunkt B
https://farm8.staticflickr.com/7324/9302181084_5be3f6fbf0_o.jpg (https://flic.kr/p/fb17mu)Garrard (https://flic.kr/p/fb17mu) by 337alant (https://www.flickr.com/people//), on Flickr
Alan
Very nice Alan!:eek:
I've joined the Jelco club a couple of weeks ago. I'v bougth a 750D ungraded with Cardas pure silver wire. It's a terriffic tonearm and a nice upgrade compared to a standard tonearm upgraded with fluid damper and Cardas wiring. The difference is not night and day, but I think the Jelco is a bit better in every way. The next upgrade will be a low slung counterweigth from Speedy.Steve and a magnesium headshell.
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