
Home  Forums  Rules  Articles  The diyAudio Store  Gallery  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc. 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
28th February 2012, 09:54 AM  #341 
diyAudio Member
Join Date: Feb 2006
Location: Willy, VIC

I take that back (can't edit otherwise I would) and assume that by "offset" you mean the angle of the pivoting head vs the rest of the tonearm.
If so, it should be obvious by inspection that no pivoting tangential tonearm can have constant offset. The nearest you can get is to lengthen the pivoting head so it becomes a pivoting wand, like the Schroeder 
28th February 2012, 02:17 PM  #342 
diyAudio Member
Join Date: Jul 2011
Location: Portugal

AS long as head cantilever and Diamond to pivot line are not perfectly aligned, you will get an centipede force. Hence distortion.
__________________
Ultimate Protection and more.“The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein 
28th February 2012, 03:35 PM  #343  
diyAudio Member
Join Date: Nov 2005

Quote:
"This tonearm, published in 1970, is the best known solution working almost tangential. The cartridge tip was mounted exactly below a pivotpoint. This idea made it possible to reduce the tracking error to +0.025 / 0.018°" The Thales Simplicity tonearm is able to "reduce the tracking error to 0.008° which is three times less than all solution published so far." __________________________________________________ The other published specs that I am aware of is from the Slovakian inventor Marek Bundzel. And this is his DIY tonearm that looks like a variant of the Garrard Zero 100: And the error is +0.009° / 0.040° and you can download the specs from his whitepaper. 

29th February 2012, 04:03 AM  #344 
diyAudio Member
Join Date: Jan 2011
Location: Willamette Valley

offset
Please understand: I just a mechanic. Maybe I cannot love music as much as an engineer, or a physicist, or (of course not) a mathematician. Nevertheless, I view a bit, a schosche maybe, of skating force to be useful in getting that wee little stylus from here to there. So my question is, suppose the offset of a Garrardtype arm was about the same at both extremes of its traverse of the record. I do get that the angle must increase in the middle due to the arc. I conceive of the two arms as converging at a finite pivot about 24 inches from the stylus. The VE calculator doesn't go that far so I'll use 13 degrees. I have collected most of the bits for this experiment; now I'll just have to do it.
It won't be pretty. 
29th February 2012, 02:33 PM  #345  
diyAudio Member
Join Date: Feb 2006
Location: Willy, VIC

An Analysis of Skate force
Quote:
Quote:
We will perform a force balance on the arm by considering the longer segment of the arm as a free body. The coordinate system is established by making the X axis the axial length of this body , Y the horizontal axis orthogonal to this and Z the vertical. We need only consider three degrees of freedom, namely X and Y translation and Z axis rotation, the other three being controlled by the vertical bearing and counterweight. All forces in any direction must balance for the arm to resist translation, similarly all torques around any pivot must balance for the arm to resist rotation. Since the object of the design is to achieve zero tracking error, we posit that all the frictional reaction force (Ff) acting at point C due to groove contact is in the X direction and normalise this to one force unit. (This force is usually of the order of 10mN). Any skate force (Fs) will act in the Y direction though point C. The torque around the pivot P must be zero, otherwise the arm PD would rotate. Thus the force acting at pivot D (Fd) must be axial to the segment DP. The angle PDE is known for any arm position so we can resolve this into an X vector Fd*cosPDE and a Y vector Fd*sinPDE. If the guide at point E is frictionless the force it exerts on the arm at this point (Fe) must be normal to the tangent of the curve, otherwise the force would move the pivot along the curve. Again the angle θ between this normal force and the body is known for any arm position so we can resolve this into an X vector Fe*cosθ and a Y vector Fe*sinθ. Force balance in the X direction requires that: 1) Fe*cosθ + Fd*cosPDE + Ff = 0 Since Ff = 1 we have 2) Fe*cosθ + Fd*cosPDE +1 = 0 Force balance in the Y direction requires that: 3) Fe*sinθ + Fd*sinPDE + Fs = 0 Torque balance around point D requires that: 4) Fe*sinθ*ED = Fs*DC which rearranges to 4a) Fs = Fe*sinθ*ED/DC Substituting eqn 4a into eqn 3 gives 5) Fe*sinθ + Fd*sinPDE + Fe*sinθ*ED/DC = 0 which rearranges to 5a) Fe*sinθ(1+ED/DC) + Fd*sinPDE = 0 Sinx = cosx/tanx so from eqn 2 we write 6) Fd*sinPDE/tanPDE + Fe*sinθ/tanθ + 1 = 0 which rearranges to 6a) Fd*sinPDE =  tanPDE( Fe*sinθ/tanθ + 1) which rearranges to 6b) Fd*sinPDE = Fe*sinθ*tanPDE/tanθ  tanPDE Substituting eqn 6b into eqn5a we get 7) Fe*sinθ(1+ED/DC)  Fe*sinθ*tanPDE/tanθ  tanPDE =0 which rearranges to Fe*sinθ(1+ED/DC  tanPDE/tanθ) = tanPDE which rearranges to Fe*sinθ = tanPDE/(1+ED/DC  tanPDE/tanθ) all of which are known quantities for any arm position. Once we know Fe * sinθ we can easily calculate Fs by substitution of the known value into eqn 4a. As a reality check if the angle between the tangent to the curve at point E and the free body is 90 degrees then all the frictional force will be taken by this point and all other forces should fall to zero, so substituting a value of zero for sinθ should give Fe = 1, Fs = Fd +0 which it does so we shouldn't be too far from the truth. For plausible values of the segments PD, DE and DC the range of skate force is from about 50% of Ff at the outer groove to under 20* at the inner groove. For reference, the skate force on a standard arm is around 45% of Ff. We can therefore conclude that skate compensation is a requirement for this type of arm. The variation of skate force with position can make this difficult to achieve. Last edited by Mark Kelly; 29th February 2012 at 02:39 PM. 

29th February 2012, 04:20 PM  #346  
diyAudio Member
Join Date: Nov 2005

Quote:


29th February 2012, 04:24 PM  #347  
diyAudio Member
Join Date: Feb 2006
Location: Willy, VIC

Quote:
Note that the analysis says that if it were possible to make the curve at E so that the segment ED was always normal to the tangent, this would remove the need for antiskate. The only such curve is a circle (or section thereof) which would take us back to Birch geometry. No free lunch. Last edited by Mark Kelly; 29th February 2012 at 04:33 PM. 

29th February 2012, 06:14 PM  #348  
diyAudio Member
Join Date: Nov 2009
Location: Gwynedd North Wales

Quote:
Cheers Steve
__________________
steve if it ain't broke, I ain't fixed it 

20th March 2012, 04:08 AM  #349 
diyAudio Member
Join Date: Nov 2005

string driven tonearm
From a post here. I cannot read Japanese. We need a translator here!
Looks like the pivoting headshell is being rotated by the strings to correct for tangency. Clever. Clearly the above tonearm works in the same concept as this mysterious arm. Last edited by directdriver; 20th March 2012 at 04:29 AM. 
20th March 2012, 10:20 AM  #350 
diyAudio Member
Join Date: Mar 2011

Interesting and fine solution. The only problem I can see there is a skating force, gradually decreasing to 0 in the middle of record, and than changing direction to the opposite, and slowly increasing up to the record end. As a result, to construct proper compensation would be close to Mission Impossible. Good news is that stylus wear will be symmetrically equal.

Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
GLIDING FOR 90°  mechanical linear tonearms: no airpump, no servo  directdriver  Analogue Source  30  7th April 2015 06:13 PM 
Angling of ports and/or drivers?  Dave McReeferson  Full Range  11  27th March 2012 08:45 PM 
String suspension vs. uni pivot or gimball tonearms  nghiep  Analogue Source  26  13th August 2011 05:27 AM 
Angling drivers left and right in a vertical linearray????  ozziozzi  MultiWay  12  16th January 2009 05:23 AM 
Need Amp For 90090 V DC  Drafance007  Solid State  15  12th October 2003 09:03 PM 
New To Site?  Need Help? 