Bumblebee's can't fly
Thinking about these statements led me to one of those 'stupid' questions that one can only ask, usually because said one is completely missing something obvious. So, here goes...
Consider what happens when an arm such as we are considering experiences a warp. The front goes up causing the upper magnet to tilt towards the back. Since the magnets are configured as opposite polarity, the back experiences an increase in attraction due to it's gap being reduced and the front experiences a reduction in attraction. If the differential in attraction is enough this will cause the arm to continue to pivot until the magnets touch in the back. Even if it is not enough to lift the front of the arm, it represents a force that the arm must overcome when it goes down the other side of the warp.
This strikes me as a problem. What am I missing in this picture?
As to achieving equal VTF and azimuth across the record; I'm stumped. Unless it has something to do with the horizontal angle of the cartridge with respect to the arm tube axis (what's this angle called?).
Thanks.
Paul Ebert
berlinta said:
Thinking about these statements led me to one of those 'stupid' questions that one can only ask, usually because said one is completely missing something obvious. So, here goes...
Consider what happens when an arm such as we are considering experiences a warp. The front goes up causing the upper magnet to tilt towards the back. Since the magnets are configured as opposite polarity, the back experiences an increase in attraction due to it's gap being reduced and the front experiences a reduction in attraction. If the differential in attraction is enough this will cause the arm to continue to pivot until the magnets touch in the back. Even if it is not enough to lift the front of the arm, it represents a force that the arm must overcome when it goes down the other side of the warp.
This strikes me as a problem. What am I missing in this picture?
As to achieving equal VTF and azimuth across the record; I'm stumped. Unless it has something to do with the horizontal angle of the cartridge with respect to the arm tube axis (what's this angle called?).
Thanks.
Paul Ebert
Dear Paul,
Not a stupid question at all!.. But, as with any Unipivot arm(this design is NOT a true unipivot, though!), the center of gravity of the whole moving assembly is below the pivot point. As a result, the tracking force increases as the cart/arm "travels" up hill. The effect you described would ameliorate this "unipivot "- flaw (to a degree at least) and should therefore be welcome. In practice it is inconsequential, since the variation of the tracking angle caused by warped records is very small , consequentially the upper magnet doesn't get tilted enough to show such behaviour. On top of that, the other end is raised by a similar distance so that the overall flux density remains the same(close enough ...).
As for your second question, - the armwand can rotate(slightly) around it's axis and horizontally too, off course. If the magnets used aren't perfectly centered/drilled(same for the pole pieces), or if they're not cut perfectly the effect you described first will then indeed have a negative effect. Imagine two discs(the magnets) with magnetic "hotspots" on their surface(same as imperfections which are weak spots). As they get closer to each other while the arm travels across the record, the attracting forces vary and, depending upon their location on the surface, the VTF and/or Azimuth will be affected.
In other words, adjusting the magnets is no simple task.
Build it and then measure VTF at the beginning and then the end of the record. No change? Well done!
Cheers,
Frank
Not a stupid question at all!.. But, as with any Unipivot arm(this design is NOT a true unipivot, though!), the center of gravity of the whole moving assembly is below the pivot point. As a result, the tracking force increases as the cart/arm "travels" up hill. The effect you described would ameliorate this "unipivot "- flaw (to a degree at least) and should therefore be welcome. In practice it is inconsequential, since the variation of the tracking angle caused by warped records is very small , consequentially the upper magnet doesn't get tilted enough to show such behaviour. On top of that, the other end is raised by a similar distance so that the overall flux density remains the same(close enough ...).
As for your second question, - the armwand can rotate(slightly) around it's axis and horizontally too, off course. If the magnets used aren't perfectly centered/drilled(same for the pole pieces), or if they're not cut perfectly the effect you described first will then indeed have a negative effect. Imagine two discs(the magnets) with magnetic "hotspots" on their surface(same as imperfections which are weak spots). As they get closer to each other while the arm travels across the record, the attracting forces vary and, depending upon their location on the surface, the VTF and/or Azimuth will be affected.
In other words, adjusting the magnets is no simple task.
Build it and then measure VTF at the beginning and then the end of the record. No change? Well done!
Cheers,
Frank
Hi all
I'm a new member hereand I ran across this thread. I thought you all might be interested in seeing my version of the "schroeder" tonearm.
It replaced the standard tonearm on a Denon DP-62L. I just finished construction this past weekend and am still in the process of fine tuning.
I did the test mentioned by Frank and found my tracking force varies by 0.2 g with no apparent change in azimuth.
Has anyone else tested theirs? or would like to exchange experiences?
Bobbi
I'm a new member hereand I ran across this thread. I thought you all might be interested in seeing my version of the "schroeder" tonearm.
An externally hosted image should be here but it was not working when we last tested it.
It replaced the standard tonearm on a Denon DP-62L. I just finished construction this past weekend and am still in the process of fine tuning.
I did the test mentioned by Frank and found my tracking force varies by 0.2 g with no apparent change in azimuth.
Has anyone else tested theirs? or would like to exchange experiences?
Bobbi
Looks great, Bobbi! Very well done! Care to fill us in on materials used and design decisions / features?
Also, how did you measure the VTF?
Thanks.
I've been thinking about the problem of magnetic strength variation within a ring and I wonder if a smaller diameter magnet would be better. Taking this to an extreme, perhaps a cylindrical pair of magnets of, say, 1/8" diameter would work well. Can anyone think of a downside to this approach?
Paul Ebert
Also, how did you measure the VTF?
Thanks.
I've been thinking about the problem of magnetic strength variation within a ring and I wonder if a smaller diameter magnet would be better. Taking this to an extreme, perhaps a cylindrical pair of magnets of, say, 1/8" diameter would work well. Can anyone think of a downside to this approach?
Paul Ebert
Thanks Paul!
Big question! As I think you can tell, the support structure is acrylic....chosen mostly for ease of tooling. I thought for appearance, the mixture of clear and black would look good and I am quite pleased with the look. The arm is a brass tube (originally intended to be aluminum - but the tube was too thin) with the headshell assembly fashioned from solid brass stock. The counterweight is stainless steel. Wiring is 33ga Cardas with Cardas cartridge clips and Eichmann bullet plugs at the phono input end. The magnets I chose are non-sintered - so, I gave up a bit in field strength, but they seem to be working well. All set-screws etc. are stainless steel. The lifter was obtained from the manufacturer in Japan.
Adjustability is almost too much .... as I have spent hours, literally, adjusting each parameter. Offset angle, VTA, VTF, overhang, and antiskating are all adjustable as in the Schroeder except that in mine the VTA adjustment is loaded with a stainless steel spring in lieu of the concealed adjustment in the original.
VTF was measured with a digital guage with +/- 0.1 gm accuracy. I think the thickness of the scale is influencing the readings and there may not be quite as much variation as the scale indicates. I have found the the angle of the vertical support can produce large variation in VTF. I played with the angle and got as much as a 1.0 gm variation from inner to outer groove.
Having only attempted speaker construction previously, I was a bit reluctent to commit a lot of funds to this project, not knowing if it would even work. The difference over the original arm is quite startling, especially in much tighter bass, much better detail, improved dynamics and a much lower noise floor. The improvement over the original Denon arm is NOT subtle! In fact, due to my beginner's luck, I'm now thinking about making a second arm, with much better materials and a stronger magnet.
If you can find a 1/8" diameter magnet with adequate strength, I think the smaller the better. I believe it would lessen any areas of field variations and would also lessen any problems maintaining the consistency of the gap between the magnets during arm rotation. Has anyone tried various magnets to see what effect they have?
Bobbi
Anti-skating
Paul,
The knob above the suspension string is threaded into the top suspension arm. There is a smaller allen-head type bolt that is threaded axially through this bolt. The "hook" that captures the string is passed through another axially drilled hole that passes through the smaller bolt. Basically, one is used to adjust the gap between the magnets and the other is used to place a small counter-clockwise pre-twist on the string. This pre-twist acts to balance out the arms natural tendency to travel inward. If you read the user's manual posted on Frank's website, he gives a great description of how to make this adjustment.
Bobbi
Paul,
The knob above the suspension string is threaded into the top suspension arm. There is a smaller allen-head type bolt that is threaded axially through this bolt. The "hook" that captures the string is passed through another axially drilled hole that passes through the smaller bolt. Basically, one is used to adjust the gap between the magnets and the other is used to place a small counter-clockwise pre-twist on the string. This pre-twist acts to balance out the arms natural tendency to travel inward. If you read the user's manual posted on Frank's website, he gives a great description of how to make this adjustment.
Bobbi
magnet size
Hello to everybody and especially to Frank Schröder
I am lathing a schroeder inspired tonearm at the moment and have not decided which magnet to use yet.
There are two sizes ready to go in: D15×H5mm and a smaller one measuring just 10mm in diameter. Which one should i use? Both are Neodym N40 or N50 (i do not remember exactly).
What would be advantages/disadvantages of a bigger/smaller magnet? Will increased magnet force lead to any problems?
Your help is appreciated.
Cheers
Christian.
Hello to everybody and especially to Frank Schröder
I am lathing a schroeder inspired tonearm at the moment and have not decided which magnet to use yet.
There are two sizes ready to go in: D15×H5mm and a smaller one measuring just 10mm in diameter. Which one should i use? Both are Neodym N40 or N50 (i do not remember exactly).
What would be advantages/disadvantages of a bigger/smaller magnet? Will increased magnet force lead to any problems?
Your help is appreciated.
Cheers
Christian.
Hello Krishu,
Making the magnet larger means you have to increase the diameter or rather the strength of the thread(=higher friction). Eventually you will end up with a thread that is too thick to allow for a suitable adjustment range/evenness for the antiskating.
You could make that thread longer but then it will pick up more airborne vibrations.
Increasing magnet size/strength also increases the damping(sometimes there is too much of a good thing..)
What do you do about shielding the magnetic field?
Properly implemented 10mm x 5mm(N50) should suffice...
Cheers,
Frank
Making the magnet larger means you have to increase the diameter or rather the strength of the thread(=higher friction). Eventually you will end up with a thread that is too thick to allow for a suitable adjustment range/evenness for the antiskating.
You could make that thread longer but then it will pick up more airborne vibrations.
Increasing magnet size/strength also increases the damping(sometimes there is too much of a good thing..)
What do you do about shielding the magnetic field?
Properly implemented 10mm x 5mm(N50) should suffice...
Cheers,
Frank
Hi Frank;
thank you for your quick response.
I will make all metal parts out of bronce, "behind" the magnets small steel cylinders in the same size as the magnets. I will use standard steel (like C45, ST35 ...) for that. This is what I understood from your patent paper.
Using the smaller magnets will make it easier to glue in the arm pipe (more contacting surface). the arm pipe will be carbon fibre.
the magnets i have are N48 15x5 and 10x4mm. So you say the smaller one would be sufficient?
Or should i go for 12x5 N48? (do not know if this is available yet)
Thanks again
regards
Christian.
thank you for your quick response.
I will make all metal parts out of bronce, "behind" the magnets small steel cylinders in the same size as the magnets. I will use standard steel (like C45, ST35 ...) for that. This is what I understood from your patent paper.
Using the smaller magnets will make it easier to glue in the arm pipe (more contacting surface). the arm pipe will be carbon fibre.
the magnets i have are N48 15x5 and 10x4mm. So you say the smaller one would be sufficient?
Or should i go for 12x5 N48? (do not know if this is available yet)
Thanks again
regards
Christian.
Hi Christian,
If you stick with simple pole pieces - in german: Polronden oder Polrueckschlussplatten - you should go for the 12 x 5mm magnets.
Avoid glueing! I don't use any glue in the construction of my arms.
Don't use a plain carbon fiber wand(except for prelimenary tests), if you must use it, you need to dampen it internally or externally.
Sorry, I'm on vacation right now, gotta go...
Cheers,
Frank
If you stick with simple pole pieces - in german: Polronden oder Polrueckschlussplatten - you should go for the 12 x 5mm magnets.
Avoid glueing! I don't use any glue in the construction of my arms.
Don't use a plain carbon fiber wand(except for prelimenary tests), if you must use it, you need to dampen it internally or externally.
Sorry, I'm on vacation right now, gotta go...
Cheers,
Frank
Hi again,
The magnets are press fitted, which makes the maschining time consuming since they vary(sample to sample) in diameter by as much as 0.1mm in diameter. Batch to batch variation can be even higher.
Other joints are either press fit or thermally bonded(in german: aufgeschrumpft).
Greetings from the pacific coast...
Frank
The magnets are press fitted, which makes the maschining time consuming since they vary(sample to sample) in diameter by as much as 0.1mm in diameter. Batch to batch variation can be even higher.
Other joints are either press fit or thermally bonded(in german: aufgeschrumpft).
Greetings from the pacific coast...
Frank
Hi Jonathan!
Where exactly are you? Nonwithstanding the absolutely breathtaking displays of nature's prowess(I took my family to Mt. St. Helens yesterday), another mountain(the Olympos, haha) makes it almost as difficult to raise my jaw off the floor(I know this is off topic , sorry...), - and I do get to enjoy it more often!
You'll hear from me soon,
Cheers,
Frank
Where exactly are you? Nonwithstanding the absolutely breathtaking displays of nature's prowess(I took my family to Mt. St. Helens yesterday), another mountain(the Olympos, haha) makes it almost as difficult to raise my jaw off the floor(I know this is off topic , sorry...), - and I do get to enjoy it more often
!You'll hear from me soon,
Cheers,
Frank
Frank:
>Where exactly are you?<
Tokyo, Japan. ADSL and irregular sleeping hours are what bring us together.
>another mountain<
My 4th mountain is currently also in the processes of revision, and it is clearly becoming taller and more beautiful.
Speaking of travelling, I strongly recommend you to visit Cosmos Hi-Fi in Ciudad Real, Spain. Even at the very worst, Cliff's main system must be among the 10 best-sounding audio systems in the world, and most probably it ranks within the top 5. Needless to say, it made any place in Frankfurt seem like a joke, and a very, very bad one at that.
>You'll hear from me soon.<
Looking forward to it!
take care, jonathan
>Where exactly are you?<
Tokyo, Japan. ADSL and irregular sleeping hours are what bring us together.
>another mountain<
My 4th mountain is currently also in the processes of revision, and it is clearly becoming taller and more beautiful.
Speaking of travelling, I strongly recommend you to visit Cosmos Hi-Fi in Ciudad Real, Spain. Even at the very worst, Cliff's main system must be among the 10 best-sounding audio systems in the world, and most probably it ranks within the top 5. Needless to say, it made any place in Frankfurt seem like a joke, and a very, very bad one at that.
>You'll hear from me soon.<
Looking forward to it!
take care, jonathan
Second Prototype
I've decided to build another. While relatively happy with the first, I know there are areas where improvements can be made. While the first was mainly acrylic, this one will be fashioned from a few different metals.
I've already have the new magnets - 1/2"x1/8" N45 and am constructing steel backers for them. The magnets will be installed in an aluminum housing.
The arm tube will be multi-layer. Brass outer tube followed by an aluminum tube followed by a ceramic tube. I plan to use a dampning material in between each layer. The ceramic tube is a multi-bore type with 4 bores.
That's about as far as I've gotten so far.
In the meantime I'm enjoying prototype 1.
I've decided to build another. While relatively happy with the first, I know there are areas where improvements can be made. While the first was mainly acrylic, this one will be fashioned from a few different metals.
I've already have the new magnets - 1/2"x1/8" N45 and am constructing steel backers for them. The magnets will be installed in an aluminum housing.
The arm tube will be multi-layer. Brass outer tube followed by an aluminum tube followed by a ceramic tube. I plan to use a dampning material in between each layer. The ceramic tube is a multi-bore type with 4 bores.
That's about as far as I've gotten so far.
In the meantime I'm enjoying prototype 1.