Anti-skate on RB300 ???

[hughmc2]

Hi all,
I have a newly acquired Michell Gyro Se with an RB300 arm but no matter what I set the little 0-1-2 slider at the anti-skate is not doing very much. The arm still veers off to the right. I had to put a stopper against it just to set the vtf !
I have put spirit levels on the sub-chassis, platter and arm housing. Everything looks level.
What am I not doing ??

It sounds good but it all seems massively primitive compared to my previous techy SL1210 ( stock arm )

 

[RickyC6]

It should work fine. Have you def set the tracking weight correctly for the cart? You need to do that with anti-skate at 0 and then move it up to match cart tracking weight.

 

[YNWOAN]

Even when set to the minimum, there is always some bias on an RB300 (as you have found) - it is designed that way.

In fact, the bias setting is a little crude on the RB300 in my opinion. I would use a blank record (if you have such a thing) and set the bias so that the cartridge proceeds toward the centre of the record at a moderate speed (not so that the cartridge remains stationery).

it all seems massively primitive compared to my previous techy SL1210 ( stock arm )

Perhaps in terms of setting the bias, but in terms of mechanical integrity the RB300 is streets ahead of the Technics.

 

[Mike-B]

I use the vinyl blank method & I've done the same for a number of RB300 & other Rega arms
The vinyl puts around the right drag on the arm & that affects bias - but thats another subject & best not to go there unless terminally neurotic.
When I set the bias to run the arm at aprx centre disc, the bias slider is normally lower than the cart tracking weight.
e.g. my arm is running 1.85g with a smiggin more than "1" bias
I have seen slider positions on other arms ranging from a little less than 1 to almost the same - but always lower - than cart weight

If I was setting bias on a Rega arm & did not have my blank vinyl disc, then I would set the bias about "0.5" less than cart weight
So if cart is 1.8g, set bias at half way between 1 & 1.5.

 

[deltaunit]

I thought the aim of the blank vinyl method was to keep the cart centred (and not swinging either way), is that not correct?

 

[YNWOAN]

No, that used to be the recommendation; but more recent thought on the matter suggests that this results in too high a bias application.

 

[Mike-B]

I have yet to see an arm swinging in textbook fashion every time.
They follow static electricity on your clothes & react to your breath, so in my book its plus or minus a knats doodoo.
I set mine to slowly - like 2 seconds - slide across the deck & stop at a position more or less where the "out" grooves are on a record.
But TBH if it stops at somewhere past the centre point, thats OK, as the movement needed to be applied to the Rega slider to get it perfect is less than a knats doodoo.
Past that stage & you are verging at terminally neurotic.

 

[johncee]

I have found the HFN test record to be an invaluable aid in optimising bias setting (and tracking force). 20-odd quid well spent, in my view.

 

[hughmc2]

I can't even get the arm to stay above the record when set at zero. When the arm is floating, balanced a couple of mill' above the record it drifts quickly off the edge of the turntable ??

 

[Nik]

No, that used to be the recommendation; but more recent thought on the matter suggests that this results in too high a bias application.

That's interesting. You would think that a flat, smooth vinyl surface would produce less drag on the stylus, and therefore bias compensation set to counter that would be too low.

 

[Mike-B]

I can't even get the arm to stay above the record when set at zero. When the arm is floating, balanced a couple of mill' above the record it drifts quickly off the edge of the turntable ??

Thats exactly what should happen with a floating arm.

Can I give you a quick whats happening & what to do
The bias adjuster is to neutralise the cart drag on a rotating record & overcome the centrifugal force that applies increased pressure on the groove wall which contains the sound of the left channel.
In order to neutralise this force & apply equal pressure to each channel wall, the bias force applies a counteracting side thrust.
This is done by means of a weight or as with Rega, a magnetic force.

The bias is set with the cart weight applied & the TT rotating with a blank vinyl disc or with a test or ordinary record + your ears
- OR -
You believe what Rega say to do & set the slider to the same as the cart weight
- OR -
I do and set it to be 0.5 slider numbers less than cart wieght.

 

[Mike-B]

That's interesting. You would think that a flat, smooth vinyl surface would produce less drag on the stylus, and therefore bias compensation set to counter that would be too low.

Past that stage & you are verging at terminally neurotic.

 

[YNWOAN]

That's interesting. You would think that a flat, smooth vinyl surface would produce less drag on the stylus, and therefore bias compensation set to counter that would be too low.

Well yes, except it isn't drag on the tip of the stylus that generates the force, it is the discrepancy between the surface velocity of the left and right surfaces of the groove, coupled with the offset angle of the stylus - hence bias varies across the surface of the record.
___________________

On most arms the bias can be set to true zero, or removed altogether. It is a specific anomaly of the design of the RB300 that, even when the bias is set to zero, there is always some bias applied (this is not a fault, but relates to the specific implementation of the magnetic bias that the RB300 uses).

 

[hughmc2]

I can't even get the arm to stay above the record when set at zero. When the arm is floating, balanced a couple of mill' above the record it drifts quickly off the edge of the turntable ??

Thats exactly what should happen with a floating arm.

Can I give you a quick whats happening & what to do
The bias adjuster is to neutralise the cart drag on a rotating record & overcome the centrifugal force that applies increased pressure on the groove wall which contains the sound of the left channel.
In order to neutralise this force & apply equal pressure to each channel wall, the bias force applies a counteracting side thrust.
This is done by means of a weight or as with Rega, a magnetic force.

The bias is set with the cart weight applied & the TT rotating with a blank vinyl disc or with a test or ordinary record + your ears
- OR -
You believe what Rega say to do & set the slider to the same as the cart weight
- OR -
I do and set it to be 0.5 slider numbers less than cart wieght.

Nope, sorry, still don't get it

If the centrifugal force is trying to push the stylus out, away from the centre of the turntable shouldn't we be trying to set the anti-skate so that it counteracts this ? Why is it not set so that the arm has a tendancy to drift towards the centre. Relieving the pressure of the stylus being pushed against the outside face of the groove ?

Or should I just admit I'm too thick, set the slider to 0.5 below, pour a glass of something and enjoy.

 

[YNWOAN]

Sorry, you misunderstand, it has nothing to do with centrifugal force (centrifugal force does not operate to any significant extent in this situation). In fact, the natural force (generated by the record groove acting on the stylus) is to pull the stylus toward the centre of the record; the added bias force is to counter that.
_________________________

set the slider to 0.5 below, pour a glass of something and enjoy.

Yes, do that.

 

[Nik]

I can't even get the arm to stay above the record when set at zero. When the arm is floating, balanced a couple of mill' above the record it drifts quickly off the edge of the turntable ??

If bias compensation on an arm applies some torque even when set to zero, you would expect to see what you describe. My RB300 does this: with arm floating and bias compensation slider set to zero, it swings outwards (away from the platter centre). Increasing the setting increases the torque further so it swings out more rapidly.

Perhaps there's a misunderstanding here? Bias (the torque we are trying to compensate for) is caused by the drag on the stylus acting on a line to the outside of the arm pivot. This torque is clockwise as seen from above and increases tracking force on the inner groove while reducing it on the outer. The aim of bias compensation is to counteract this so the tracking forces are equal, so bias compensation must act outwards (anticlockwise as seen from above).

 

[Nik]

Past that stage & you are verging at terminally neurotic.

I suspect you are right, but test records such as the HFN one have modulated grooves for setting bias compensation for this reason.

I have to say that I find it makes little difference, and in any case wouldn't you need bias for difference records?! (Now, that would be neurotic.)

 

[Nik]

Sorry, you misunderstand, it has nothing to do with centrifugal force (centrifugal force does not operate to any significant extent in this situation). In fact, the natural force (generated by the record groove acting on the stylus) is to pull the stylus toward the centre of the record; the added bias force is to counter that.
_________________________



Yes, do that.

Strictly speaking, bias is the force (actually a torque) produced by an arm's offset geometry. Bias compensation is what we are applying at the arm pivot using springs, magnets, hanging weights, etc., to cancel out the bias.

 

[Mike-B]

Why is it not set so that the arm has a tendancy to drift towards the centre. Relieving the pressure of the stylus being pushed against the outside face of the groove ?

Thats correct, you do get it
I think your floating arm drifting in an outwards direction is fooling you.
What it does when floating is nothing to do with the CF acting on the tracking (cart) weight. The force needed to move the arm sideways when floating is close to nothing, your breath, static from clothes, the cat walking by all are enough to move a floating arm. 1.8g is like a tonne compared to that force.

Can I recommend a Fairvew 2009 Pinotage - if you can get it in UK.
I downed a bottle last evening at a friends house - awesome - nicest red I have tasted for a long while.

 

[hughmc2]

Sounds like a good idea.

unlike Chateauneuf Du Tat,......perfect to drink whilst watching the King try on his new clothes.


It must be nice, everyone says it is