DIY Schroeder Tonearm???

[dsa]

Hello, I was alerted to this thread and thought I would weigh in.

Has anyone considered the effects the magnets would have on the materials used for the arm wand and the effect that may have on the wiring from the cartridge to plinth? I know from playing with magnets as a kid that their magnetic force is transferrable over time and depending on the material being exposed.

That is why I think Frank exits the tonearm wire way before the magnets and then takes them straight into the plinth away from harm. Also, look at the two materials Frank has used- Carbon Fibre and Wood. I don't know psysics, but I can guess that both of those materials would not hold (to any great degree) an magnetic residue that could leave a 'sonic signature' on the audio signal. Just a thought...

I wonder why Frank didn't pursue ceramic solutions in his tonearm design? I'm not convinced of the sonic neutrality of wood. Wood may sound 'good', but neutral?

[krishu]

Hello,

the materials used for this tonearm are mainly not ferro-magnetic.

Frank Schoeder does not use wood as it is cut from the tree but treates it heavily until it has no resonances which would be typical for natural wood.

Christian

[bear]

I've been wondering about Herr Schroeder's arm design.

He calls for 34kg attraction between the two lower magnets.
Then we have a string that supports the pivot point from the top.

Now, as a thought experiment, it seems to me that we could replace the magnets with a longish string suspended below the TT (work with me on this...) that has a 34kg weight suspended on it.

Is this the equivalent to the magnet? Yes/No?

If it is the equivalent, then when the arm tries to pivot, what happens? Seems like there is a force that tries to keep the "string(s)" taut?

Now, if we assume no force in the axies other than vertical due to the magnets, does the arm them rotate to the front/back as the headshell goes up/down?

I suppose that if the pivot point for the upper string is at the bottom of the magnet on the arm, then this is minimized, but what keeps the arm from rocking, side to side?

Otoh, if the pivot (upper string attachment) is higher up than the bottom of the arm (where the magnet is) then there is a "Z" sort of effect/issue??

Sorry, but these things may have been covered in the thread already - I admit to not having read it all (yet).

_-_-bear

[konstantin]

Originally posted by krishu
Hello,

the materials used for this tonearm are mainly not ferro-magnetic.

Frank Schoeder does not use wood as it is cut from the tree but treates it heavily until it has no resonances which would be typical for natural wood.

Christian

Hi,

The main reason why there are non ferrous metals in the tonearm assembly is the "bleeding" of the magnetic field.
If you use ferrous metals the magnetic field will "bent" around making the magnets less strong.

There is no such thing as a rigid no resonant material, each material has it's own resonance, you can change the frequency and the amplitude of a material's resonance but you can completely eliminate it.

Wood as a material has an ear friendly type of resonance, some call it a coloration, anyway, the most important thing here as it is used as an armtube is shape-form stability. Wood is "alive" and if it is not treated as it should it may bend the least.
The best wood I have found over the years of DIYing tonearms is Ekki or Azobe, it is brown-red and very hard. I start with solid square, oven stabilized (dried) for a week at 120-130 degree celsius, machined and drilled to a make a tube out of it and then soak into violin spirit varnish made from natural resins to seal it against moisture.

Regards

[konstantin]

Originally posted by krishu


If VTF depends on VTA then warped records vary VTF (heavily!). This is the same behaviour as my first attempt to build a Schroeder clone showed. I had the opportunity to talk to Frank some time ago about this problem. He explained a bit and now I know that it is not easy if not impossible to make a Schroeder clone. We read a lot about Schroeder clones; I would rather call them tonearms inspired by the Schroeder design.

Cheers
Christian

Hi,

I had the opportunity to have a closer look at an original Schroeder tonearm some time ago, the one string design, also "suffers" from this but to a lesser degree.
If you want to minimize the effect of "VTF depends on VTA" you have to drill through the magnet in a way that the the knot of the string that carries the tonearm is as close as possible to the lower side of the upper magnet and make sure that in normal operation the only part that is in contact with the armtube assembly is only that knot. A very difficult task as neodymium is brittle and very prone to corrosion. The two string design is not suffering from that effect though.
Here you can find some pre-drilled neodymium magnets that will probably make the construction easier.

Pre-drilled Neo magnets

[berlinta]

Hi Konstantin, hello bear,

My bearing(single or divided string) can be built to have a restoring force(in regard to VTF), to be completely neutral or to exhibit an unstable character.

The determining factor is the size of the magnets and the attachment point of the thread relative to the magnet. On the SQ version of the Reference arm, changes in VTA will not cause changes in VTF, despite the increased stability around the armwand axis. To achieve this, the top magnet's "face" is barrel-segment shaped, the bottom magnet's face is semi-spherical.

The actual attracting force is always lower than the maximum "holding" force obtainable from a given set of magnets. In typical setups, the effect would be similar to having 10-12kg hanging from that thread, BUT, in reality, the total suspended mass is no higher than 300gr for a 12" arm with a heavy cartridge(~230gr for a 9,4"er).
Energy storage is considerably lower than on a similar size, unipivot arm that mostly relies on a mass loaded pivot/cup assembly.
Many gimballed arm are far superior in that respect. The RS-Labs arm or earlier Roksan arms with detached counterweights have a very tight bass(no overhang, often mistaken for "bass power" or "solid low frequency foundation") but the dangling counterweight can cause wavering images and puts additional stress on the cantilever suspension.

When the bearing is built to be "self restoring", the actual pivot point is below the bottom magnet, not at the lower exit point of the thread. This helps to reduce or even eliminate warp wow, without having to build the arm like the original Immedia arm(pivot point at record level).

I've elaborated on the following many times: Though I have used pretty much anything obtainable* to build armwands out of it, certain kinds of wood(or laminates) remain the best material for an arm that cannot rely on "draining" energy via it's base. Waterfall plots show what one can easily hear too: Some woods exhibit a high amount of broadband damping with no spikes or elevated areas.
Impregnating the wands increases the damping further(off course Konstantin is correct, there will never be a 100% nonresonant structure)and insures dimensional stability.
Others are the exact opposite. There are no "sympathetic" resonances, any resonance is plain detrimental to the original signal. A tonearm is not a music instrument, it ought to be seen like a measuring instrument(imho).

DIYers, stay away from kiln dried wood if you can. Go to an instrument maker(guitar, woodwinds...) and ask for a leftover piece, AIRDRIED for at least 10 years. When you tell them what you need it for, they might even give it to you for free...

* I also tried various types of ceramic wands. At the time, they all exhibited considerable ringing, newer generations can be made to be physically extremely inert(through varying thickness, pre-stressing...)

The restoring force(a change in VTA causing a change of VTF) observed by Konstantin is what you'll get when you buy or build a unipivot arm(Bob Graham's Phantom is an exception), due to the center of gravity of the arm/counterweight assembly being situated below the pivot point. The distance between the two and the associated mass determines the extent of this effect.
But you should reset VTF when changing VTA on most unipivots or other arms with "low slung" counterweights.

Krishu is correct, the term Schroeder "clone" is a misnomer. There are several features of the original which I have yet so see realized or written about by DIYers. But since nearly all who built "their" Schroeder arm seem to like it better than what they'd used before, I can go to sleep with a smile :-)

Greetings from Berlin,

Frank

[konstantin]

Originally posted by berlinta

My bearing(single or divided string) can be built to have a restoring force(in regard to VTF), to be completely neutral or to exhibit an unstable character.

The determining factor is the size of the magnets and the attachment point of the thread relative to the magnet. On the SQ version of the Reference arm, changes in VTA will not cause changes in VTF, despite the increased stability around the armwand axis. To achieve this, the top magnet's "face" is barrel-segment shaped, the bottom magnet's face is semi-spherical.

When the bearing is built to be "self restoring", the actual pivot point is below the bottom magnet, not at the lower exit point of the thread. This helps to reduce or even eliminate warp wow, without having to build the arm like the original Immedia arm(pivot point at record level).

Hello Frank,

I understand exactly what do you mean but, when the bearing is build to achieve zero restoring force the "virtual" pivot point is higher than the record surface so in reality it doesn't do anything to reduce WOW. When the bearing is build to have a restoring force it's "virtual" pivot point is at record surface, WOW is minimized but changes in vertical tracking angle (VTA) caused by warped records will also cause changes in vertical tracking force (VTF), these are maybe minor changes but if you have a very expensive cartridge that works best, at say, 1.75grams sudden changes in VTF will degrade the sound and will put some not so very pleasant stress at the cartridges suspension.
The two strings design on the other hand can more easily build with a zero restoring force AND pivot point at record surface by making sure that the string exit point and the lower surface of the upper magnet is at the same level with the record surface. That way you can have zero restoring force AND minimized warp WOW.

Originally posted by berlinta

I've elaborated on the following many times: Though I have used pretty much anything obtainable* to build armwands out of it, certain kinds of wood(or laminates) remain the best material for an arm that cannot rely on "draining" energy via it's base. Waterfall plots show what one can easily hear too: Some woods exhibit a high amount of broadband damping with no spikes or elevated areas.
Impregnating the wands increases the damping further(off course Konstantin is correct, there will never be a 100% nonresonant structure)and insures dimensional stability.
Others are the exact opposite. There are no "sympathetic" resonances, any resonance is plain detrimental to the original signal. A tonearm is not a music instrument, it ought to be seen like a measuring instrument(imho).

DIYers, stay away from kiln dried wood if you can. Go to an instrument maker(guitar, woodwinds...) and ask for a leftover piece, AIRDRIED for at least 10 years. When you tell them what you need it for, they might even give it to you for free...

Agreed 100%, the best resonance is no resonance at all but since we cannot avoid it I choose to have a bit wider and rounder type of resonance (wood armtubes) than narrower and spiked (carbon, ceramic armtubes) and I'm sure that this what you saw on the CSD plot.

Air dried hard wood is the best but in a humidity controlled environment. I had the chance to discuss the subject some years ago with an expert, a 72 years old traditional musical instrument maker, he explained to me that hardwoods can absorb environment moisture and it will not completely dry, most of the woods he is working on (some 200 years old, if I remember correctly) are paraffin wax covered to protect them from air moisture, when he is about to work on a piece he put it in an oven at a bit over 100degrees (water boiling point) for a week or so, given the reputation he has as an instrument maker I have no reason not to trust his method.

Originally posted by berlinta


Krishu is correct, the term Schroeder "clone" is a misnomer. There are several features of the original which I have yet so see realized or written about by DIYers. But since nearly all who built "their" Schroeder arm seem to like it better than what they'd used before, I can go to sleep with a smile :-)

Of course there are other features, I believe that the reason non of these features are mentioned is the main attraction of the design, the magnetic bearing, looks so easy to build and make it work (but it's not). There are several other tonearm in the market with bunch of features but non with the simplicity (to the naked and inexperienced eye, at least) that makes an average DIYer to try his luck on building one.
Sleeved counterweight, very important, decouples the heavier part from the armtube and prevents energy storage, grounded (flat) cartridge mounting surface, thickness and length of the string, the string also sets the antiskating force, too thick and will give you too much increase as the cartridge is moving to center of the disc too thin and will not set the correct amount.
The hardwood armtube is I thing the most difficult part, it was a real sock for me to discover that two hardwood armtubes cut from the SAME block, given the SAME treatment sound different, go figure.
At that time a very good friend (and audiophile) of mine was making some experiments on non destructing metal stress analysis at the university lab, he manage to borrow a tiny accelerometer with the suitable preamp and I did some tests to find out what is going on.
I discovered that what looks same on the outside it's not necessarily the same on the ................... inside, drilling a perfect hole through a 200mm long hardwood rod is not easy job. It took some custom made drills and I eventually made the armtube with three different diameter holes at 1/3rd of the length each.

I believe that the worst enemy of a good product is a better one, I have the feeling that there is room for improvements on your tonearms, you can make for instance the bearing and the mounting center on the same vertical axis just to make sure that overhang doesn't run away when you adjust VTF.
I really admire your work.

Regards from Greece
Konstantinos

[berlinta]

Hi Konstantin,

Allow me to add a few remarks:


..." when the bearing is build to achieve zero restoring force the "virtual" pivot point is higher than the record surface so in reality it doesn't do anything to reduce WOW"

Not quite correct. The bearing point is still below the lower magnet, albeit higher than if the bearing had a strong restoring force. Only when the lower bearing magnet is an infinitely small point, your assumption holds true.

" When the bearing is build to have a restoring force it's "virtual" pivot point is at record surface, WOW is minimized..."

If the arm bearing is exactly at record level, warp wow is zero only for a cartridge with an inifintely low compliance. In real life, different "heights" of cartridge bodies, different VTA/SRA setting(deviating from a horizontal orientation of the armwand and therefore cartridge) will cause the bearing point to end up slightly below(or more likely) above record level.

..."changes in vertical tracking angle (VTA) caused by warped records will also cause changes in vertical tracking force (VTF), these are maybe minor changes but if you have a very expensive cartridge that works best, at say, 1.75grams sudden changes in VTF will degrade the sound and will put some not so very pleasant stress at the cartridges suspension"...

Changes in VTF will occur as a result of warps, but on an arm with no self restoring force, the deviation will be solely dependent upon the inertia of the arm cartridge combination and the bearing friction. Those changes do not occur suddely, just periodically.
According to several cartridge manufacturers i talked to, it is bearing chatter or excessive friction which decreases(mechanically) the life span of a cartridge suspension.


"The two strings design on the other hand can more easily build with a zero restoring force AND pivot point at record surface by making sure that the string exit point and the lower surface of the upper magnet is at the same level with the record surface. That way you can have zero restoring force AND minimized warp WOW."

It's not a two string design a la Well Tempered, it's a divided string which can be seen as a single string. So it is possible to build a single string bearing arm the puts the magnets at or near record level AND have zero restoring force. Quite a contraption it would end up being with the added parts count and mechanical interfaces being far more detrimental to the sound than the advantage of reduced warp wow. Aren't records supposed to be flat?


"Agreed 100%, the best resonance is no resonance at all but since we cannot avoid it I choose to have a bit wider and rounder type of resonance (wood armtubes) than narrower and spiked (carbon, ceramic armtubes) and I'm sure that this what you saw on the CSD plot."

It's mostly about WHERE the resonances occur. Please remember that the signal embedded in the grooves is pre-equalized = non linear. Higher frequency content is mechanically/physically overrepresented and so more prone to excite such resonances in the cartridge-armwand-bearing system.
If you had chosen the term faster decay instead of "rounder type of resonance", I'd wholeheartedly agree.

"Air dried hard wood is the best but in a humidity controlled environment. I had the chance to discuss the subject some years ago with an expert, a 72 years old traditional musical instrument maker, he explained to me that hardwoods can absorb environment moisture and it will not completely dry, most of the woods he is working on (some 200 years old, if I remember correctly) are paraffin wax covered to protect them from air moisture, when he is about to work on a piece he put it in an oven at a bit over 100degrees (water boiling point) for a week or so, given the reputation he has as an instrument maker I have no reason not to trust his method."

I source most of my wood blanks/logs from instrument makers and one supplier to fine cabinet makers. They all have their own "ways" and all of them cover the ends of the logs in Parrafin wax(standard procedure). But certain woods have either a very high oil content(preventing them from reacting to humidity changes) or they don't exhibit the typical hydrostatic behaviour after being stored for 20years + . But a sudden temperature change like you described, will not only drive out remaining moisture, but cause the wood to build up internal tension(more or less depending upon the cut), leading to an increased risk of warping within a few days after turning, routing or milling the piece to size.
If your friend treats(oil, wax, shellac...) the pieces right after that, he should be fine.


"The hardwood armtube is I thing the most difficult part, it was a real sock for me to discover that two hardwood armtubes cut from the SAME block, given the SAME treatment sound different, go figure."

That's why I treat each armwand individually :-)

"I discovered that what looks same on the outside it's not necessarily the same on the ................... inside, drilling a perfect hole through a 200mm long hardwood rod is not easy job. It took some custom made drills and I eventually made the armtube with three different diameter holes at 1/3rd of the length each."

The hole through my armwands is typically 2mm or less in diameter and the wands(before drilling) are effectively between 245 and 300mm long.

"I believe that the worst enemy of a good product is a better one, I have the feeling that there is room for improvements on your tonearms, you can make for instance the bearing and the mounting center on the same vertical axis just to make sure that overhang doesn't run away when you adjust VTF. "

As in the No.2 arms? It makes no difference. Any change in VTA will change overhang to a small extent on any arm. The only exception that comes to mind: The ET2 linear tracking arm.
It was my goal to make the arm as simple(technically and aesthetically) as possible without sacrificing sound quality(and adjustability). In short: I favor the KISS approach :-)

"I really admire your work."

Thanks for your kind words.

All the best,

Frank

[moray james]

my first experience with cryo treatment came back in the late 1980's. The company that built the system we used (Applied Cryogenics) told us of a customer of theirs who made flutes in metal and wood. They were at the point where they were about to stop building in wood as they were loosing to large a percentage of blanks (wood) when they drilled them out length wise. The failure rate was approaching 70 %. Once they started to cryo treat the wood blanks prior to drilling the precentage reversed. The cryo treatment destresses the wood by creating micro cracks in the wood structure which removes internal stresses. Not only did the process reduce the expensive waste but the flutes were more uniform in performance and with improved tone over their range. You might give this process a try. You will also experience improvements with metals as well.

[berlinta]

Hi moray james,

Thanks for the bit of advice. My failure rate is below one screwup out of 20 and it happens mostly when I'm too tired to do this kind of work...
I do have extensive experience with cryoing arm parts and wiring. Yes, in some areas it makes a worthwhile difference... :-)

BTW, I do play the flute and I have both metal(muramatsu) and wooden(2 antique, german made) flutes. I actually appreciate the difference in sound between all three of them a lot!

Cheerio,

Frank