View Full Version : Curiosity got the better of me ...
Stratmangler
07-09-2012, 20:29
and I ended up ordering one of these counterweights and rear end stubs, to try on my tweaked up RB250.
I'm glad I did.
http://www.cabezon.eu/product_info.php?products_id=59
Prior to this I was using the OL stub and counterweight, so from an engineering approach they're very similar.
I was hoping that the asymmetrical counterweight would improve tracking capability, and it has just done exactly that, bringing with it greater resolution and improved low level detail retrieval.
All in all I'm a very happy bunny :cool:
Reid Malenfant
07-09-2012, 20:37
It does make some sense Chris :) Keep the weight of a motorcycle low down & it'll handle better, being able to change direction much faster.
While that may not appear to be a sensible comparison, think of a ship, top heavy isn't much fun for the passengers :eyebrows:
Keeping the weight low will have less stress on the bearings at the very least... I guess you'd call it more stable.
Stratmangler
07-09-2012, 20:46
It does make some sense Chris :) Keep the weight of a motorcycle low down & it'll handle better, being able to change direction much faster.
While that may not appear to be a sensible comparison, think of a ship, top heavy isn't much fun for the passengers :eyebrows:
Keeping the weight low will have less stress on the bearings at the very least... I guess you'd call it more stable.
Both are very good analogies Mark.
I'd attribute the subtle improvements to this increase in stability.
Curiously I have some recollection of reading an interview with Mark Baker of OL saying that he'd tried asymmetrical counterweights, and couldn't hear any difference between them and the symmetrical ones that OL use.
Maybe he needs some
http://www.healthyoptionsdirect.com/images/Earex.gif
:eyebrows:
A DIY bodgers approach!
http://i94.photobucket.com/albums/l82/_NRG_/other/PL-71/DSCF6935.jpg
Works well. :eyebrows:
Stratmangler
07-09-2012, 22:50
A DIY bodgers approach!
http://i94.photobucket.com/albums/l82/_NRG_/other/PL-71/DSCF6935.jpg
Works well. :eyebrows:
It has a face only its Mother could love :D
It does prove an engineering point though, which results in improved sound quality, which is ultimately all that matters.
Lowering the counterweight doesn't reduce stress on the bearings - the only way to do that is to reduce the weight. Having said that, there is no need to reduce the stress the bearings see as even the most delicate bearings are more than strong enough to support any armtube, cartridge and counterweight.
I've done quite a bit of CAD modelling of counterweight geometry. There is an advantage with regard to riding and recovering from warps if the mass of the counterweight is below the plane of the bearing - but that is a geometry and not a mass issue.
What does make a difference is how the counterweight mass is coupled to the support stub. I see your new weight has a plastic insert between the counterweight and the stub - this will be offering an element of decoupling. What also makes a difference is how closely the counterweight is positioned relative to the bearing. If you have the opportunity I would try the tungsten stub and counterweight that Rega make.
What cartridge are you using? When using a DL-110 in my 250 I found a directly coupled CW design sounded far superior to the Rega decoupled RB300 solution...but the new one was also low slung.
I think Johnnie at AO recommends direct for MC & decoupled for MM?
Richard
walpurgis
08-09-2012, 09:42
A big counterweight near the pivot (as adopted by SME years ago) makes more sense than a smaller one further away.
Be careful using large or low slung counterweights with Rega (derived) arms, as they can foul the arm pillar easily.
The only thing achieved by using a low or underslung weight, is a lowering of the centre of gravity (diagonally towards the rear). This is of course required on unipivot arms, but not necessarily of benefit with other types.
The jury is still out on weight decoupling. It seems to have benefits in some arm/cartridge set-ups, but not in others (still trying to track down a solid counterweight for my Mission 774, maybe I'll make one).
and I ended up ordering one of these counterweights and rear end stubs, to try on my tweaked up RB250.
I'm glad I did.
http://www.cabezon.eu/product_info.php?products_id=59
Prior to this I was using the OL stub and counterweight, so from an engineering approach they're very similar.
I was hoping that the asymmetrical counterweight would improve tracking capability, and it has just done exactly that, bringing with it greater resolution and improved low level detail retrieval.
All in all I'm a very happy bunny :cool:
Check this out7187 AT 1010 from the 70s, another that appeared later in the 70s with a low-slung counterweight was the Mission 774
It's not a new concept & I'm pleased that you got the improvements you were looking for.
Decoupling the counterweight will alter the resonant frequency of the arm/cartridge/counterweight combo; how exactly that is altered depends on the masses involved and the compliance of both the cartridge suspension and the counterweight decoupling (if decoupling is used).
The geometrical advantage of lowering the counterweight mass is that the momment alters as one rides and recovers from warps. As stated above, with a gimbal bearing arm there is no advantage in lowering the centre of gravity as such.
Check this out7187 AT 1010 from the 70s, another that appeared later in the 70s with a low-slung counterweight was the Mission 774
It's not a new concept & I'm pleased that you got the improvements you were looking for.
Yes, the bearings are in the same plane as the stylus and the counterweight mass is a little below that - my modelling would suggest this as optimum.
walpurgis
08-09-2012, 11:25
Underslung counterweights direct horizontal (forward & backwards) and vertical torque generated by vertical movements (riding warps etc.) though the arm and horizontal pivot, the torque action being hard to predict, especially with 'pendulum' weights like the Roksan design.
Just making an observation, my maths isn't good enough to work it all out, but I can 'see' the general principles at work here.
It's not really torque that is the issue (there is only tiny levels of torque applied to an arm) but the moment of inertia, the pendulum effect, of the counterweight.
Yes, the bearings are in the same plane as the stylus and the counterweight mass is a little below that - my modelling would suggest this as optimum.
Hi Mark, thats interesting & pretty much what AT claimed at the time.
I agree with you about the 774, the sorbothane decoupling system is well thought out & is a major reason why the arm sounds as it does.
I'm not necessarily recommending the decoupling of the counterweight - I'm just describing the mechanism :).
awkwardbydesign
08-09-2012, 14:22
Keep the weight of a motorcycle low down & it'll handle better, being able to change direction much faster.
Being a nerd, I note that the new Yamaha YZR-M1 has a raised C-of-G to improve performance. :lol:
The Dynavector arm is interesting, having a decoupled counterweight for the vertical motion which is quite floppy. Being such a short stub-arm means that vertical warp-riding performance is outstanding.
The horizontal counterweight is not decoupled, however, and is much more massive. It is eddy-current damped, though. I think Dynavector spent a long time thinking about this arm design, which has seen a few iterations now.
http://farm9.staticflickr.com/8200/8221270513_7b2872742c_b.jpg
walpurgis
08-09-2012, 15:48
Never had a proper look at one of these. How is the eddy current damping applied? is there some sort of inductance device in the horizontal pivot?
Re. The 774 - I replaced my modified RB250 with a solidly coupled CW 774 (the 774 fitted to their later 773 decks had these...budget version I believe). Never compared it to a decoupled version given my experience with same on 250, but the 774 was preferable to the 250 & remains on my LP12.
Johnnie at AO can make up a solid 774 CW for you if desired...with weight designed around ur cartridge to keep it as close to bearing as possible.
Richard
Rare Bird
08-09-2012, 16:00
You mean '775' decks ;) '773' were cartridges back then
Never had a proper look at one of these. How is the eddy current damping applied? is there some sort of inductance device in the horizontal pivot?
Take a look at the back of the arm and you'll see an arc attached to the arm passing through a pair of very powerful static neodymium magnets.
A shame that "proper" tests of arm-cartridge compatibility aren't regularly done these days. The 774 tonearm was originally designed to have a very soft sorbothane decoupling of the main mass of the counterweight, damping resonances and with very gentle application of the damping trough (the smallest paddle just stroking the fluid), the results could be very good. I wouldn't mind trying one again as the finish improved over mine from the very first batch of 25 and re-wiring is so easy, although I think the arm tubes were stuffed internally...
My 774 arm tube wasn't stuffed, dont think any were? Easy to rewire.
Richard
Actually, short arm tubes aren't geometrically better at riding warps - in fact, it's rather the opposite way round; the amplitude of a warp is seen as more severe the shorter the stylus to pivot distance is, although the moving mass is lower.
the amplitude of a warp is seen as more severe the shorter the stylus to pivot distance is, although the moving mass is lower.
I can confirm from observation that the low mass of the short arm tube overrides other concerns as the DV can track warped records that previous SME IV and Jelco SA-250ST arms jumped on. Press reviews have also favourably noticed the DV's good tracking in this respect.
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