Stereo Cutting Head - based on Grooveguys design

[farmersplow]

Perhaps my experience can be of some help here.
The coils are large and therefore somewhat heavier than coils with a small diameter. But that is the only disadvantage.
The big advantage is the better heat dissipation due to the larger surface area. As a result, these coils are much more resilient.

However, resonance drivers in this form are only suitable up to a certain limit. The reason is the coil suspension. The shape is too stiff, the material is poorly suited and the weight is far too high!
This holder weighs 7.6 grams! In your case, there is also the aluminium mass with the drive rod (I estimate another 3 grams).

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I tried to grind the material thinner and drill out unnecessary weight. This reduces the weight to 5.4 grams. But it is not reproducible - I can never make two identical parts with the same properties.
The main resonance was at 400Hz.

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But an improvement is possible (20% improvement needs 80% more effort). I replaced the metal part with a cut-to-size loudspeaker spider and made a cone from carbon fibre.
This was even lighter. The coil was securely centred and the resonance curve was flatter. The main resonance increased, but was around 550Hz (I think) due to the ‘soft’ suspension.

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By coating the spider and cone with epoxy resin (increasing stiffness), the main resonance rose to 800Hz, which was already quite good.

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However, further improvement is possible (another 20% improvement requires another 80% more effort). I then replaced the fabric spiders with lightweight metal spiders. This further increases the resonance frequency, but too hard also has other disadvantages.
A lot of experimentation with material and material thickness is required here.

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However, further improvement is possible (another 20% improvement requires another 80% more effort). Replace the cones with thin aircraft aluminium. Here, too, weight must be harmonised with material thickness (natural resonances).

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However, a further improvement is possible (another 20% improvement requires another 80% more effort). Feedback coils with feedback control.

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However, further improvement is possible. Fine tuning and minor resonances can be filtered by damping.

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But further improvement is possible. - Because it's a never-ending story. It will never be perfect.


By the way, the suggestion from "Thelatheofus" with the 1:20 drill bit actually achieves a lot. The weight saving by removing the support rod (and mountings) on the torsion tube is considerable.

Good luck with your build!
Thomas

[zdenek]

the moving elements are at least 10 times too heavy, but let everyone love what they want and I don't encourage anything, I'm sorry

[Estrada]

Perhaps my experience can be of some help here.

Thank you for your comments Thomas. I've been following your project and your results are amazing. I'd be a happy man if I could build something of such high quality.

I built the head with these drivers over a couple of days knowing that a lot of work would need to be done to adapt the suspension, having read your thread. The reason I built the head was really just to see what these drivers could do in stock form compared to the other head I had built. I guess, I wanted to see if the starting point of these drivers was better than what I was getting with the smaller drivers. I think the answer was no. This is not surprising given all that mass, but sometimes it is better learn in practice than in theory.

One thing I am interested to know, what is the black material that you have used as a dampening material? I am keen to try out some other materials.

I may not progress much with this head for a while, but when I do I will no doubt have some questions for you.

Thanks again for your comments.

[Estrada]

the moving elements are at least 10 times too heavy, but let everyone love what they want and I don't encourage anything, I'm sorry

We have a saying in my country "there is more than one way to skin a cat" which is a rather unpleasant saying, but I guess the point of it is that there is usually more than one way of approaching a problem. Certainly true of cutting heads.

[zdenek]

I am also like that, that I make mistakes against reason and logic, often with the stubbornness of a maniac it seems to me that something who says that it works perfectly, that I do and I imitate and I put, I pump a lot of money to achieve the same effect, but I do not succeed and then I look for the reason of my mistake and I wonder if maybe someone made a fool of me?

I look for answers to my mistakes and I ask people who cut their teeth on these devices and tell me the truth, but I am not so gullible anymore, but I check what this man who does such things professionally tells me.

Mr. Swiss Flo wrote publicly maybe twenty years ago, or more, that I will achieve much better results if I use high-frequency speakers and I checked it, yes, it is the truth! With high-frequency speakers you will go far, so says the Swiss! I started to stick to this truth, it works perfectly!

[farmersplow]

One thing I am interested to know, what is the black material that you have used as a dampening material? I am keen to try out some other materials.

It is a mixture of liquid rubber and resin (developed in-house because the liquid rubber alone does not adhere permanently)

Go your own way and gather your own experiences. Look left and right at what others are doing. Nothing is right and nothing is wrong. Keep learning from your own experiences and keep experimenting. (Don't believe everything you read, because those who know nothing must believe everything).
You are doing a great job. Keep going!

Thomas

[themagician]

^ This last paragraph here is the biggest take away from many topics / posts on this forum. You have to give some of this stuff a go yourself! Learning is fun and very rewarding. Happy building!

[PhilFW]

Hi Estrada,

Fascinating post.
I am particularly interested in your diamond faceting efforts. I have purchased a polishing machine just for this purpose. Would really benefit from your experience.

cheers
Phil

[Estrada]

Hi Estrada,

Fascinating post.
I am particularly interested in your diamond faceting efforts. I have purchased a polishing machine just for this purpose. Would really benefit from your experience.

cheers
Phil

Hi Phil,

Diamond grinding is a mix of skill, engineering, accuracy, luck, patience and the dark arts I think this will probably require its own thread. Perhaps it is time I started one, there is not a lot of info on this site. I'll let you know once I get something up

[PhilFW]

Great. Look forward to it. You're right very hard to find information.
Cheers

[grooveguy]

I, for one, certainly look forward to it as well. Not to grind my own, but with expectation that someone here will become professionally proficient and offer styli for sale at affordable prices. Somewhere in the past I recall reading a short article on why diamonds are not the ideal material for lacquer-cutting, but perhaps they are the only option at present for recording onto the various sheet plastics we trolls have at our ready disposal. If other experimenters turn their attention to coating aluminum (or even plastic?) blanks with a suitable lacquer surface, synthetic sapphire historically proved the ideal material for cutting styli. And, yes, by all means let's start a thread on this endeavor.

[Estrada]

Somewhere in the past I recall reading a short article on why diamonds are not the ideal material for lacquer-cutting, but perhaps they are the only option at present for recording onto the various sheet plastics we trolls have at our ready disposal.

I read an article on this somewhere, I believe the main issue with diamond for cutting lacquers is that diamond creates static electricity whereas sapphire does not. I think there are solutions to this, one of which was some kind of coating on the mirror face. I know that Myshank has a lacquer cutting diamond, I don't think they sell them but rent them out instead.

I've done a little experimenting with sapphire. It is much easier to work with than diamond because it is so much softer. forming 3-5 micron burnishing facets is a challenge though.

I will gather my thoughts together and start a new thread about this with more detail, I'll drop a link in here when I've got this stared.

[grooveguy]

Estrada: you say, "...forming 3-5 micron burnishing facets is a challenge though." Back in the 1970s, when I was buying sapphire microgroove styli from Capps, they didn't list any actual dimensions, but noted that the styli were "barely burnished." Any idea what this means? Also, the Capps patent (#2,530,584) that defines a cutting stylus, albeit a wide-groove one, went into detail concerning the need for multiple burnishing facets, maintaining a very narrow face of each facet. Capps also offered their proprietary 'ANM V Groove' stylus, the ANM standing for Anti Noise-Modulation. Do you know anything about that? I must profess total ignorance on the physics and black magic of cutting styli, and am glad that you and a few others have some familiarity and can "guide and supply" us.

[Estrada]

There is information, including typical stylus dimensions, for a number of different cutting styli in the Larry Boden's Basic Disc Mastering Book, such as the one below

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Here are some images of a micro-point stylus a friend of mine lent me to look at. They aren't the best images but you can sort of make out the burnishing facets.

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I'm not familiar with the Capps stylus, I might have to look up the patent. I believe that main purpose of the burnishing facets it to reduce noise so perhaps this is what ANM refers to?

I think the hardest part of this is forming the radius at the tip. Unlike a diamond which must gets sharpened to a point, the tip of a sapphire stylus is rounded to a 2-3 micron radius. I haven't figured out how one would actually achieve this.

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[Estrada]

Looks like the Capps stylus had more than one facet. Now that. would be tricky to form.

[Estrada]

Hi all,

I've just started a new thread about diamond sharpening, here is the link

https://www.lathetrolls.com/viewtopic.php?f=15&t=10495

I'll aim to load more info up shortly


Cheers
Craig

[zdenek]

A nice diamond blade for soft materials, but not for copper, too long, too stiff. I checked such mounts, the knife handle is not stiff enough for copper, copper sheet, that's why we used a diamond insert, it is embedded in sintered carbide, mechanical resonances partially disappear but not completely, you can hear, you can see spontaneous vibrations in the range of a dozen or so kilohertz on the analyzer, or you can hear them when the turntable is slowed down, then you can see stripes in the acoustic band. I recently ground boron nitride, cheap and easier to grind but much weaker, softer than diamond, I cut 15 minutes in copper and it dulled..., it must be a diamond and properly split, experts know...

Regarding the head on these transducers with 1 inch coils, they are simply very heavy, they receive a current pulse but do not have time to move the knife because their mass, weight is too large and there is another current pulse and again there is a very large delay due to mass and inertia. It is like a ship, a tanker with a 50 thousand horsepower engine, which will not start with high acceleration, a motorboat with a 100 horsepower engine is enough, which will cover the ship 1000 times because it is light. The transducers must have very light movement units, at least 10 times lighter, as I wrote, I checked it, it is a waste of time on these heads with transducers and 1 inch coils

[Estrada]

Hello all,

Just thought I'd share on a bit of progress with the cutting head. I had been struggling with distortion at higher volumes so I went back to basics and did another pink noise test and found that I had a resonant peak around the 5khz mark. I seemed to have missed this before, probably because I was not cutting the pink noise loud enough.

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This must be a secondary resonance because the main resonance is quite low, between 400 and 500hz but the damping seems to eliminate that. So it seems that the distortion I was getting was due to my corrective eq not taking this resonance into account. Once I corrected the eq I found that I was able to cut much loader without distortion which was great.

So I tried to cut a record and was finding something odd happening in the low end. I'd do a bit of a test cut which would sound good, but when it came to cutting a side I was getting some very wild low end excursions. I still haven't worked out what was causing this or if it is still an issue. I tried to look into what was happening in low end with some test tones and accidentally sent a 50hz tone at high volume to the head and cooked one of the coils. This was very annoying. I've replaced the burnt out coil but had to make a few modifications along the way.

When I last assembled the head, I made some tiny aluminium push rods on the lathe with a flat base that I could glue to the funnels.

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Only issue with these was that I couldn't remove them without destroying them. So I decided that there needed to be a better way of attaching the push rods. So I remade the funnels and press fitted a small bit of copper rod into the funnel to allow the push rods to be soldered.

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This allowed me to install new 1mm brass pushrods that could be soldered to the funnels. Before the new driver goes in, my damping is fitted.

The damper is formed with scotch mounting tape. I laminate 3 strips of this together and cut a strip that is around 3-4mm wide. This is wrapped around a small piece of plastic tube, around 10mm diameter to form a tyre shape.

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The tricky part is fitting it into the centre of the driver. It is very sticky stuff so I try to leave the plastic backing on the outside edge as long as I can while gently pushing it under the black plastic rim of the driver. It took a couple of attempts to get this right, the first couple were a bit too wide and needed to be squashed a lot to get under the rim. This would likely have provided too much resistance and lowered the response of the head. In fact, this still may have happened to some extent as the right channel (which I replaced) is now a little lower than the left (although, this may could actually be the cartridge as I noticed a similar thing looking at playback of a test record).

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The driver with the damping fitted.

With that done I can now mount the driver and connect up the pushrods. A bit messy, and the funnels are not particularly well centred on the drivers, but is seems to have worked.

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The good news is it seems to be working and it seems to have tamed the 5khz resonance somewhat. This is the rip of my pink noise test. There is no iRIAA or corrective eq on this, just pink noise straight into the amplifier.

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Still a bit of a rise around 5khz, but not as bad.

I set up a new corrective eq and did a quick audio test which sounded promising, but I need to do a bit more testing and see what is happening in the low end. Hopefully without frying a coil this time.

[acemc]

Hi everyone. I'm a total newbie to the forum & actually to the entire record lathe scene. I would love to be able to cut my own records & extremely keen to try my luck building a diy lathe. This has been an incredibly informative & helpful thread. Thank you Estrada & everyone else for sharing all your knowledge here. Quick question, apart from the size/weight of bigger drivers, is there any reason for not going with a high efficiency 3 or 4inch driver with good motor force & good linear response? And.... a low resonant frequency? (I noticed a few mentions of lower resonant freq seemed to suggest that is a bad thing). Due to the fact the RIAA curve will be dropping the low end, I would think that having the resonant freq lower would help with resonance issues. Also distortion is not really perceived as easily in the lower frequencies, so this seems beneficial, or have I got this wrong? Estrada, pls can I ask if you would share your cad files with me. PM sent.

[Semar]

Hi everyone. I'm a total newbie to the forum & actually to the entire record lathe scene. I would love to be able to cut my own records & extremely keen to try my luck building a diy lathe. This has been an incredibly informative & helpful thread. Thank you Estrada & everyone else for sharing all your knowledge here. Quick question, apart from the size/weight of bigger drivers, is there any reason for not going with a high efficiency 3 or 4inch driver with good motor force & good linear response? And.... a low resonant frequency? (I noticed a few mentions of lower resonant freq seemed to suggest that is a bad thing). Due to the fact the RIAA curve will be dropping the low end, I would think that having the resonant freq lower would help with resonance issues. Also distortion is not really perceived as easily in the lower frequencies, so this seems beneficial, or have I got this wrong? Estrada, pls can I ask if you would share your cad files with me. PM sent.

Building a tower is a great adventure. When choosing drivers, be aware that it's very easy, perhaps too easy, to get good bass frequencies when engraving, unlike treble. Those who build multiple heads often end up using tweeters. I personally used 40mm full-range drivers, and if I were to do it again, I would definitely choose good quality tweeters...