Project: OsoMiso - ONO. A rocking bridge stereo head.

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EpicenterBryan
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Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43524Unread post EpicenterBryan
Wed Aug 10, 2016 10:20 pm

Here is the first official post about the OsoMiso head I call "ONO". As briefly mentioned in another post, this is inspired by the rocking bridge Ortofon design (rather than 45/45 designs). I have to thank MarkRob for sharing some details about this design with me! Thanks Mark!

This is a Non-Feedback head design. In this head, there are 2 drivers in the same plane which move a bridge at opposite ends, and the bridge holds a stylus in the center. It's like a seesaw. This head design has several unique properties, and several issues that make it hard to implement from a construction standpoint.

The first time I posted mention of this head, it looked like this and had a Balsa wood bridge:
IMG_4786.JPG
To gain some understanding of why it is constructed the way it is, the short version is this: This head is designed such that the back body is perpendicular to the disc surface (90 degrees to the disc). The cutting stylus rests at 90 degrees to the disc surface as well. But the body is designed such that the drivers actually push and pull toward the disc surface at 20 degrees back angle. This matches the typical 20 degrees of playback Vertical Tracking Angle (VTA) in most modern cartridges. The stylus holder, and / or the bridge have a combined 20 degree forward angle which places the stylus (at rest) perpendicular to the disc surface.

Since this design has the drivers pushing and pulling on a bridge directly, there is no "cantilever" effect to account for like in a standard 45/45 design where one end of the torque tube is moved and the other end is fixed. In the Torque tube design the movements of the tube results in an arc around the fixed end relative to the moving end of the torque tube where the cutting stylus is mounted.

The next big thing to know is how the geometry works. There is a distance between the drivers. This distance needs to be small. To form a right angle triangle exactly where the stylus tip is located, the distance needs to be 1/2 the distance between the drivers at exactly where the bridge is able to "rock". That's the first trick...

Let me jump to photos of the V1 "ONO" head. This head was a failure, but there are lessons to be learned here, and are being applied to the V2 version I'm working on now.

In this shot you see the the plastic head, the drivers (I won't mention what they are since they suck) and an alignment jig to glue pivot tubes on the drivers for the rocking bridge at 20mm spacing. Also, you will see what the internals of a driver looked like since super glue seeped in a froze this one solid. I obviously replaced it.
OsoMiso V1 photo1.jpg
The ideal way this style head should be constructed would have a spring member that would only move side to side, and not front to back between the driver and bridge. In the first version I used a tube on it's side. The small contact point had some semi-flexible glue applied which allowed for side to side movement without a spring. That will be changed in the V2 version.

The next step was to make the bridge. I wanted the moving parts to be as light as possible and in the first quick test, I used Balsa wood for the bridge. But it needed strength and density where the Neumann 320 stylus had to mount. So I tried a crazy experiment to infuse super glue into the wood. I put a section of wood (longer than needed) into a food saver bag, along with super glue and ran it through a vacuum sealer to remove air from the wood and replace it with super glue.

After some time, I removed the wood and let the glue set. You see the before and after weight for the same section of balsa wood. The glue actually did penetrate the wood. I tried a quick test to see if I could drill a tapered hole and found that below about 1mm the glue had not penetrated, so I made a small aluminum stylus holder to be glued on the balsa wood.

Next, I took a section of Balsa wood and made a jig so I could sand it with a 20 degree face and to the correct dimensions. Then infused it with super glue and attached the stylus holder.
OsoMiso V1 photo2.jpg
Then I did some test cuts. Although the channel separation was remarkable, the frequency response fell off a cliff after 4khz. I naturally assumed it had to do with the balsa wood. This is when I decided to try all aluminum parts for the rocker bridge. This next test was still part of the V1 development.

In this shot you see my attempt to make a batch of stylus holders on my mill. Some how, I messed up in the drilling process but had one that was right on. The stylus holder has a Neuman taper made with my home made 20:1 taper. You will also see a section of super miniature extruded aluminum called NanoBeam that I used to make a lightened version for the rocking bridge, and the super miniature screws and nut plates I used to create the whole assembly. And you see the weight including a broken stylus for fit checking amounted to just 0.9 grams! You can also get a sense of the size next to this US dime.

Also, you see the bridge installed!
OsoMiso V1 Photo4.jpg
The really great thing about this is the dimensions were nearly spot on. I installed an actual Neuman 320 stylus and took the head to my friends machine shop. He used an ancient optical comparator to measure the distance from the stylus tip to the base of the rocking bridge. That measurement should have been 10.00mm. It was actually just 0.12mm short. Not bad! In theory, that distance error would drop the channel separation from infinity to 38db. Again, in theory. I would be thrilled with 20db, and the cool thing about that bridge is I could actually insert shims under the stylus holder if actually needed.

Then I did new test cuts:

Damn, if the channel separation wasn't great but the frequency response was nearly identical. The response was limited by the drivers.

CONTINUED ON NEXT POST
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Last edited by EpicenterBryan on Wed Aug 10, 2016 10:26 pm, edited 1 time in total.

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EpicenterBryan
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43525Unread post EpicenterBryan
Wed Aug 10, 2016 10:23 pm

CONTINUED FROM PREVIOUS POST:

So here is a look at the new drivers I'm using on the V2 version. A total re-design. More posts to follow in the next few days...
IMG_4821.JPG
Bryan
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43544Unread post EpicenterBryan
Thu Aug 11, 2016 9:41 pm

More details on the OsoMiso ONO head project:

The drivers I'm using in the V2 version are Tang Band 13-1761S 1/2" Silk Dome Tweeters. Since these have a silk dome, I have hardened it with two layers of super glue in the dome area only. Also, the center section of plastic needs to be removed. This is what a stock driver looks like.
Tang Band 13-1761S Silk Dome Tweeter .jpg
The body of the V2 head looks like this. Notice there are cavities for the drivers to be inserted from the bottom. There is a hole to route wires up, and also a hole to secure the driver in place (there is a threaded nut on the back of the driver). Notice there are 6 extra holes in the bottom for attaching a double X-spring on the bottom of the head. Holes in the back are standard spacing to mount on a Presto.
Ono V2 body.jpg
Below is more of a bottom view where you can see the drivers installed from the bottom. In the center of the domes will be a push rod of sorts - really a short segment of aluminum tubing glued to the dome and with a slit cut into it on the other end. And you also see a "Double X" structure on the bottom attached to the body and it will also be glued to each push rod. This is what insures the drivers only move in and out exactly at 20 degrees based on the body design.

Here you also see the bridge and stylus holder. The bridge will also have slits cut into it. The actual length of the push rods and space between the rods and rocking bridge is exaggerated in this view for clarity. In between the rods and bridge will be a straight spring segment that will allow movement "side to side" but not "front to back".
Ono bottom mechanical.jpg
Here is a side rendering where you can see the angles involved. Remember, the Neumann 320 stylus will be inserted in the angled stylus holder at the bottom and will be perpendicular to the surface of the disc at rest.
Ono side.jpg
As of tonight, The body has been printed in ABS plastic. The Double X springs have been printed in Nylon and the driver domes have been coated. However, I broke one of the coil wires trying to take off the outer ring /center cap on a driver. New drivers will arrive on Friday. I have also printed the alignment jig needed for centering the push rods.

What's left to do before the next big test?
  • Harden the dome on the new driver.
  • Make jigs to slot the ends of the push rods and bridge.
  • Use the jig I have already made to glue the rods to the domes.
  • Make the springs.
  • Assemble and wire.
  • Run the head through the optical comparator and measure distance from the spring flex point to the tip of the stylus and adjust / modify the stylus holder as needed.
  • Then use the optical comparator to make sure the stylus is at the center of the bridge.
Oh, crap. So much to do. Ever wonder why stuff like this takes so long?

Bryan
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43555Unread post EpicenterBryan
Sat Aug 13, 2016 9:55 pm

OsoMiso ONO head update for the day:

I made a jig to slot the ends of 3mm OD, 2mm ID aluminum tube for the push rods. It worked really well! I clamped it in a vise on the mill and used a diamond cutoff tool to clut a 2mm deep slot in the tubes.
IMG_4875.JPG
I thought you guys would like to see the internals of these drivers. I opened one up that I damaged when removing the outer rim to coat the dome in super glue. On the left, you see that the driver has ferrofluid cooling dripping off the coil. Some how I missed the detail that these use fluid cooling when I ran across these drivers. I have no clue what the implications will be since I plan to use these at 20 degrees off vertical! Will the fluid migrate to the lowest point and just add moving mass to the stuff I want to move?
ONO drivers.jpg
The twists and turns are so interesting when experimenting!

In this shot, you see the drivers with slotted rods installed. And the secret sauce. Double X-springs.
I can't stress enough that a centering control mechanism like this is needed to keep ANY driver to move in only the direction you want. In this case in and out at 20 degrees, but exactly in and out relative to the driver.

The yet to be discussed Picante head used this secret sauce as well. More on that later.
Driver install.jpg
That's it for tonight.
Several things left to do but the check list is getting shorter.

Bryan
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43558Unread post Radardoug
Sun Aug 14, 2016 4:32 pm

The ferrofluid is held by the mag field, so should stay in place. That should help make the drivers more linear.
Love your work Brian! Always good to see what you are up to.

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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43559Unread post EpicenterBryan
Sun Aug 14, 2016 10:13 pm

Radardoug wrote:The ferrofluid is held by the mag field, so should stay in place.
Thanks for the inputs! I knew someone would clear that up!

Here is the mini update for the weekend.

I made a jig to be able to cut the slots in the bridge for the springs. In that application, the bridge needs to be held vertically for my cut off tool to cut the slots. I'll also use it to cut the edges of the area that needs to be milled out. Then the jig gets mounted horizontally for milling the excess in the center. If all goes well, the bridge will be blue this time. If I mess it up I have a black one ready to go...

This tool is really intended to be a one-time use item but we will see.
Bridge tool.jpg
The next big thing is the spring. That's going to be a bit more tricky. I'll go into that once I have a pair that I'm happy with.

That's all folks!

Bryan
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43571Unread post EpicenterBryan
Mon Aug 15, 2016 10:31 pm

Monday update:

The jig worked well. If I had it to do again, I would make the jug so the bridge sticks out by 0.5mm so the blade could be physically aligned with the end rather than by eye. Then subtract 1/2 the cutoff wheel thickness and reset the zero... All the other cuts were relative to that first cut, so not such a bad mess up.
IMG_4887.JPG
But, the main thing I needed was that the two spring slots be exactly 20.00mm apart. And they are! :D

The stylus holder (and Neumann 320) will be positioned on the bridge in the optical center between the spring slots, so if the ends of the bridge (outside of the spring slots) are not exactly the same dimensions relative to that center position it really doesn't matter for this test version.
IMG_4889.JPG
That's it for tonight. Next up are the springs...

Bryan
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43700Unread post Snug Music
Fri Aug 26, 2016 6:41 am

hey brian, .. sorry that I was far from being online, I was in an accident and was in hospital. now all is well again. hey, I just follow your new posting, that's great. I will set the day and again on the bench. your concept I really like, let's see if I can put this also.

Btw: tomorow is my birthday,..hehee,..i can celebrate my birthday in 2 times now...i m so Lucky! !! :wink:



best regards Scotty 8) :wink:
I'm still not a professional, but I learn pretty fast. especially with my eyes and ears!

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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43705Unread post EpicenterBryan
Fri Aug 26, 2016 10:51 pm

Snug Music wrote:I was in an accident and was in hospital.
Hi Scotty!
I'm glad you are alive. And happy birthday to you.
happy b-day scotty.jpg
Don't dive too deep into this design yet. Several things have been learned and there are several questions yet to be answered.

Bryan
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43706Unread post EpicenterBryan
Fri Aug 26, 2016 11:27 pm

A mini update for Friday Night:

I ended up making the springs from 0.1mm (0.004 ") stainless shim stock right at 5mm x 5mm. The slots I cut were right around 0.6mm based on the diamond cut off wheel I have. So I needed to fill the gap and used some 0.2mm thick x 4mm Magnesium strips. At first I cut little shims, but then I just split the strip in half and used long strips and cut off excess once the gap was filled.
IMG_4918.JPG
Here is what the bridge looked like after the 5mmx5mm springs were shimmed, glued and excess cut off.
IMG_4921.JPG
The next step was to temporary position the X spring so I could glue the bridge and 0.1mm springs to the driver push rods. This is where I ran into big problems. When I did a test fit I found the 2mm depth of the slot correct on each driver but the total length was off a bit from one driver to the other. It could have been an error in cutting the length of the tubes, or more glue applied at the top of one driver dome before gluing the push rods to the dome or something else. So I printed a spacer to go under one driver to make the distances correct.

However, when I decided on the length of the rods I didn't fully account for the thickness of the double X nylon spring. That had to be below the bottom of the slot so I could glue the upper portion of the spring to the push rod with the shims installed. Once all that was glued, then the double X spring could be glued.

On the driver end, it was not possible to use 2 shims on each rod. Since it took some force to insert those and the spring and the drives wanted to move. So in the end, I installed the spring and only one spring and then slightly crimped the tube to grab the spring and shim prior to applying glue. Perhaps one side was not exactly at the bottom of the slot when it got crimped. I just don't know.
IMG_4923.JPG
In the end, the bridge was not parallel. One end was off by about 0.5mm. So did I put the shim on the wrong driver? Did I end up positioning one of the drivers in a negative "neutral position" when the nylon spring got glued? I don't know.
IMG_4926.JPG
I decided to do a test cut and see what happened. So I tilted the head to make the bridge parallel to the disc.
More on all this tomorrow when I have more time to post...

Bryan
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43781Unread post EpicenterBryan
Thu Sep 01, 2016 6:26 pm

An update:

Last weekend, I prepared to do a test cut. And like usual I promptly blew up a driver because of operator error.
Having said that, I went ahead a did a test cut with only one channel. The information was useful.

First, the test conditions: (left channel blown - only driving the right channel)
No EQ, No iRIAA (record), No RIAA (playback), No heat, No heated stylus.
Cut diameter 10" @45rpm.
Wayne's Flat Preamp, Shure M95ed phono cart.
0db level using CBS STR-100 reference, and same level for sweep from 20hz to 20Khz.

For 0db 1Khz The following readings were made:
V =1.636V rms
A = 0.175A
Power calculated was 0.286W

I compared the driven channel playback to the non-driven playback. It resulted in only 12.6db of channel separation. The phono cartridge separation is 25db so that is not the source.

The first thing that came to mind is that in the first version of the bridge / stylus mount, the dimensions were assuming the rocking point was exactly at the bottom of the bridge. Now that I've added springs that distance from the rocking point to the tip of the stylus has increased by about 1mm. The Bridge or stylus holder should have been trimmed. That does change the separation calculation but should still have resulted in about 20db of separation.

The next thing that came to mind was perhaps the stylus holder wasn't exactly in the center of the bridge. I did a quick check but couldn't fit enough in the field of view on my microscope. I really needed to use my machinist friends optical comparator but it was the weekend and he wasn't there. However, I did use my 3D printer platform (lead screw) to check locations of the cuts for the springs with the microscope. They are off by 0.2mm. Not a big deal in the equations either.

I also looked at the harmonic distortion and zoomed in on the 1Khz wave form as shown below. Yes, the wave form is not symmetrical. There is something different about the up vs down movement. It's possible some of that may be either cutting VCA or playback VTA. I'll have to check that stuff next time. It's also possible there is something going on with mechanical loading on the driver. I mentioned in an earlier post that I am concerned the driver might not have been centered when the nylon spring was glued.
harmonic distortion.jpg
Below is the frequency response. The LF is as would be expected. The dip at 3Khz will need to be looked at. But the steep fall off after 6khz is a show stopper. There is a spike out there at 16Khz that I've seen before in silent grooves - usually goes away when I spend more time checking stylus alignment.
Response.jpg
I had several conversations with MarkRob about this, and he has a theory. Some back ground about the drivers needs to be re-visited:

These drivers have a one peice silk spider and dome. I coated the dome with 2 coats of super glue to harden it all the way to the edge of the dome and before the lowest ripple in the spider. Putting glue too far into the spider stiffens it and so I was careful only to coat as far as I thought was reasonable and slightly beyond where the voice coil attaches from the other side.

Mark's theory is either the dome is not stiff enough, or the edge nearest where the coil is glued inside the driver is decoupling movement of the mass at high frequencies. It's also possible the high frequencies are decoupling at one of the other mechanical connection points involved from the dome to the stylus.

This is where it gets interesting. Mark has graciously offered to check the drivers with his eddy current sensors! And it gets even better! Mark is going to blow up several drivers and determine how much power they can really take since the spec sheets are not 100% clear. He is also going to check the first driver I used on Ono, and both the proposed drivers for Picante. Since one of the drivers I was planning to use on Picante is also a silk dome driver, it might have the same issue as the second Ono driver.

So keep an eye on the post and as Mark has time to play, one or both of us will post some results.
Thanks again to Mark for the help!
And let's all hope he doesn't burn the place down blowing up all those drivers!

Oh, the smell of burnt coils in the morning.

Bryan
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 43863Unread post inspector77
Tue Sep 06, 2016 12:35 pm

Following this thread with great attention, thanks for the update Bryan.

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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 44111Unread post grooveguy
Mon Sep 26, 2016 1:55 pm

Nice work, Bryan! I was not familiar with Ortofon's 'rocking bridge' design, but in many respects it looks like a good DIYers approach. One question: you explain that the transducers are offset from vertical by 20 degrees to approximate the 20-degree vertical tracking angle of most playback cartridges. Does this cancel some form of distortion or improve separation? I can't quite get my mind wrapped around anything other than vertical and lateral groove displacement. It's as though you are compensating for some sort of Doppler effect, as transducer offset from vertical would seem to change the cutting stylus relation to the direction of groove travel, adding and subtracting very slightly from the groove velocity at an audio-modulation rate.

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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 44336Unread post grooveguy
Wed Oct 12, 2016 6:15 pm

Hi again, Bryan! I did some further thinking on this 'rocking bridge' stereo head concept. I still think that, for whipping-up something with minimum time, energy and money spent, it has advantages. I did bounce the idea off a friend of mine, who had some (mono) disc recording experience years ago, and he isn't in love with the concept, thinking that a direct 45-degree "thrust and parry" approach is still the best. I'm not convinced, and I feel that shortcomings you have found can be worked-around.

For instance, stereo separation. Clearly, the drivers go up and down only, so vertical modulation is a direct 1:1 relationship. That is, if the two drivers go up and down in sync by ±5 mils, you'll get a groove with exactly ±5 mil excursions (neglecting the 20-degree-offset business for now). But if you feed the two drivers out of phase, then you get the rocking motion. But the lateral displacement is not going to be the same ±5 mils, because you have a "mechanical disadvantage," I think. Correct me if I'm in error here, but isn't you lateral stylus tip displacement going to depend on how long the stylus is? There is a 'rocking axis' midway between the drivers and, I think in the other plane, at the top of your bridge where the springs join it to the drivers. But unless the distance between the drivers is the same as from the top of the bridge to the stylus tip, the lateral motion of the stylus is going to be less than the total rocking excursion. Maybe that's why separation isn't better than it is.

This can be fixed, of course, by matrixing L and R into L+R and L-R, giving more gain to L+R (or putting loss in the L-R signal) and then de-matrixing back into L and R. In fact, you could put a pot in there as a 'separation control.'

And as far as the even-order distortion goes, that should not pose a problem either. Try to find the source of this, of course, but if it can't be reduced or eliminated mechanically by a change in the design, then just introduce compensating distortion (pre-distortion) in the drive signal. As we found out in the era of magnetic recording, predistortion can materially reduce the THD in the reproduced signal. In fact, "tape compression distortion," which is historically around 1% at zero-VU operating level, and as much as 6% some 10dB above that, can be nulled to almost nothing by using diodes to introduce complementary nonlinearity in the recording process. The only downside to this is that the recording process (or the cutterhead?) is still nonlinear, so you get intermodulation products; in fact, the predistortion can exacerbate these to some extent. But all of analog recording is a tradeoff of some sort anyway, and again you can put a pot in there to fine-tune for minimum audible artifacts.

I think I know where your first drivers came from, I got some too. If they are the same, they are those bone-conduction headset drivers, which I figured might have some use in a cutterhead, but they are horribly crude and won't take much power. I didn't burn one up, but it sure got toasty. Keep up the good work and keep us in the loop!

Jim

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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 44338Unread post markrob
Thu Oct 13, 2016 10:42 am

Hi,

Maybe this will help. Below is a CAD drawing I did to show how the rocker works (click the images to see a larger version).

The triangles represent the two drivers and the stylus tip. I show the neutral position of the rocker and the effect of the L&R driver moving a fixed distance about a central pivot point. In the first case, the triangle is a 45/45/90 with the point of the stylus tip being the 90 degree angle. I have rotated the rocker 10 degrees from the neutral position. You can see that the distance moved is the same for each point of the triangle. This picture represents the correct geometry between the drivers and the stylus.
Rocker Correct Stylus.jpg
In the second image, I have shortened the distance of the stylus in relation to the two drivers. You can see that the same rotation and driver move distance yields a shorter lateral move distance as compared to the drivers.
Rocker Short Stylus.jpg
As you might guess the case in which the stylus is longer than the correct length yields more movement as compared with the drivers.

Hope this helps you visualize the rocker action.

Mark
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 44340Unread post grooveguy
Thu Oct 13, 2016 11:28 am

Thanks for that, Mark; it confirms what I suspected. What this seems to mean is that, if the center-to-center distance between the drivers is an inch, then the stylus tip has to be an inch below the virtual rocket pivot. Since this implies either mass added to the rocker bridge, or a long stylus shank subject to bending, then the L+R program component needs to be increased over the L-R to optimize stereo separation. Fortunately an easy matter in the electronics domain.

Of perhaps more concern is the precipitous dropoff above 6kHz in Bryan's measurement plot. Looks like a straight-line 18dB/octave; I wonder if that could be EQ'd or whether feedback might straighten it out. Keep at it, guys!

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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 44346Unread post markrob
Thu Oct 13, 2016 2:38 pm

Hi,

Actually, 1/2" below. That would yield two .5" - .5" - .707" right triangles given the 1" driver to driver dimension.

I'm thinking that the Bryan's current method of coupling the dome of the driver to the rocker is decoupling at high frequencies due to excess compliance. I'm doing some testing on this right now to see if I can improve.

Mark

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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 44347Unread post grooveguy
Thu Oct 13, 2016 3:05 pm

Ah, right you are about the trigonometry. Being a cheapskate/minimalist, myself, I'm wondering if Bryan's 'springs' are absolutely necessary? If one driver, alone, pumps up and down, wouldn't it just force the other voice coil at an angle? Kinda like holding one point of a speaker cone and preventing the voice coil from going only in and out; that is, it has to angle a bit as it works. I know that disturbing the axis of a driver isn't ideal, but for the dimensions involved, would it be a show-stopper? As long as the voice coil didn't rub on the magnetic structure, I would think that, even if it were forced off-axis at an angle, it's movement from its own drive would still be a symmetrical function.

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markrob
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 44358Unread post markrob
Fri Oct 14, 2016 9:37 am

Hi,

You are probably right given the small deflections involved. Aside from the springs keeping the drivers centered, the spring also moves the main resonance up in frequency by adding stiffness. You trade off sensitivity for less effect of the load on the open loop frequency response when cutting. You will also need less corrective EQ since the transition to mass control from the compliance control region is moved higher. I'm not sure if that ends up being a wash in terms of required drive. In effect, the moving mass sets the force (and drive current) required to accelerate the stylus above resonance. In a closed loop design, you try to minimize the moving mass at all costs and use the feedback loop to keep the head stiff against load variations (within its servo abilities). That approach also keeps drive efficiency up. In an open loop design, you need to make sure the head is not affected by the load so much or you will be dealing with changing response with different cutting loads. On moving iron heads like the 1D, the system resonance is set quite high (8-10 Khz) via the stiffness employed. However its much easier to get a stronger motor going to compensate since the coil is not moving. There are quite a few trade offs to consider.

Mark

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KNOP
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Re: Project: OsoMiso - ONO. A rocking bridge stereo head.

Post: # 45298Unread post KNOP
Fri Dec 23, 2016 7:01 am

Ok this is a really interesting project. I had no clue to the workings of such a head, but now it seems pretty clear reading this thread. Really cool stuff.

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