The farmer and his plow - When I set out to build a record cutter

[farmersplow]

Cutterhead CH-6 – continued
(02 2023)

Since I have to wait again for raw material and also have no access to the workbench, I will continue to work on the Cutterhead. Some parts are already prepared and so it's time for the wedding! Now coil, spider, driver magnets will be married. (Till death do us part).
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While the adhesive parts are drying, the torsion bar with the V-spring is prepared: The V-spring was laser-cut and driven open with a tool to accommodate the torsion bar. (I made different materials and material thicknesses to explore the changes in the resonance curve).
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Here is a picture of a small carbon part I made. It is to hold the wire, which is then used to hold the torsion bar.
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The marriage continues. Here with carbon cones and rod.
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Then the feedback coils are attached. Whether these feedback coils ultimately close the loop is not important at the moment. It is also not the reason why I already install them. For me the installation is important because I want to check the function (signal present, polarity, signal shift, signal strength and so on).
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Greetings from Austria
Thomas

[farmersplow]

Overall device – continued
(02 2023)

The completion of the cutterhead will have to wait. It can't be tested anyway if the overall unit doesn't work. Therefore, I continue with the assembly.

Next, I build the rail for the optical position sensors. In principle, a single sensor would be enough. It only has to detect the start position and the processor can count the steps to calculate the changed position. But I also use the sensors for position finding in case of malfunctions, basic settings that should be independent from the counter and for correction in case the stepper motor has dropouts. This is nearly impossible with the chosen dimensioning, except: If you change the number of pulses on the stepper driver during operation (from 1600 pulses/rev to 200 pulses/rev). This would have the advantage of switching between a fast mode and a precise (microstep) mode.
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Overall unit - suction tube
(02 2023)

On my small CNC mill I build the brass parts for the mounting and adjustment of the exhaust pipe.
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Greetings from Austria
Thomas

[farmersplow]

The Turntable Drive
(03 2023)

In March, I finally received the material (blocks of thermoset plastic). These can be milled, turned, sawn and filed very well. They have good damping, are temperature resistant, are electrically insulating and of course anti-magnetic. The only drawback to this material is sustainability. But if the end-use equipment stays in service for a long time before being scrapped, the environmental impact is relatively low from my point of view. This is also one of the reasons why I build the entire device out of metal or wood. (Only for this part, neither material is an option).
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Sometimes it's just satisfying to see a "normal" lathe in action, especially when the chip comes off so nicely!
(see this video)
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Satisfying video of a lathe chip.mp4

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The two retaining rings for the motor drive are produced on the lathe:
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The finished parts are assembled with the motor and the platter retaining plate. The recirculating ball bearing bushings are mounted on the underside:
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Besides the ribbon cable for signal transmission, a good ground connection must not be forgotten!
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An optical position sensor is also included to provide a trigger signal when needed.
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An LED band is also installed in the turntable receptacle to make the status easily recognizable visually (cold phase, heating phase, recording phase, cool-down phase, etc.).
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In addition, an adapter for the stroboscope lamp and a massive adapter for tone arm and/or microscopes are mounted on the plate holding plate.
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Greetings from Austria
Thomas

[zdenek]

You're doing all this great! I wonder if the motor from this turntable has enough power to cut a GROOVE
copper plate ?

[farmersplow]

You're doing all this great! I wonder if the motor from this turntable has enough power to cut a GROOVE
copper plate ?

it is certainly not

[farmersplow]

The turntable drive
(03 2023)

More days and weeks pass in which the disk drive is adapted, disassembled and reassembled countless times. Numerous adjustments are made to the printed circuit boards, insulation, adapter cables, brackets and plug connections until everything finally fits.
All boring and nerve-wracking! I keep this chapter short because it is so boring. Or do you want to hear how I changed the documentation of every change hundreds of times on the PC? - I don't! But a couple of pictures can give you an impression.

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Because everything was so boring, I decided to treat myself to an amplifier. Because when everything is ready for cutting, I want to be prepared and have enough power to process all frequencies. My normal stereo amplifier with its 120W might reach its limits. So I decided to use a 2x450W (max. at 4 Ohm) Class A/B amplifier (Crown XLi 1500) plus some good cables. The unit has a robust analog circuit design, powered by a conventional power supply. That should be enough

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Greetings from Austria
Thomas

[zdenek]

Hello, calm down, Farmer, Vienna wasn't built in a day... right?
I read a little about recording machines, there is very little about American ones, but a lot about German ones. I was in Germany and in fact the Germans work slowly and precisely, just like the Swiss and Austria is a neighbor of these countries, you know... Of course, I'm waiting for your Austrian version of the head, because there are no new German heads, I think, and Swiss ones if anyone is there. is produced somewhere and it is not known whether they are suitable for mastering at all because no one has yet boasted that they are really good, but I know that they are very expensive and absolutely unaffordable in my budget, although I am not very poor, but I will not take the risk , you understand me, I think... I checked my heads, my work is primitive, but I am completely dissatisfied with them, the coils burn out in a fraction of a second and I've given up on small speakers for now. I'm waiting for yours because I TRUST you and your work. I'll wait patiently for the heads you make, my friend!

[zdenek]

Hallo, beruhige dich, Bauer, Wien wurde nicht an einem Tag erbaut... oder?
Ich habe ein wenig über Aufnahmegeräte gelesen, über amerikanische gibt es sehr wenig, aber viel über deutsche. Ich war in Deutschland und tatsächlich arbeiten die Deutschen langsam und präzise, ​​genau wie die Schweizer und Österreich ist ein Nachbar dieser Länder, wissen Sie ... Natürlich warte ich auf Ihre österreichische Version des Kopfes, denn die gibt es keine neuen deutschen Köpfe, glaube ich, und Schweizer, falls jemand da ist. wird irgendwo produziert und es ist nicht bekannt, ob sie überhaupt zum Mastern geeignet sind, weil noch niemand damit geprahlt hat, dass sie wirklich gut sind, aber ich weiß, dass sie sehr teuer und in meinem Budget absolut unerschwinglich sind, obwohl ich nicht sehr arm bin, Aber ich werde das Risiko nicht eingehen, Sie verstehen mich, denke ich... Ich habe meine Köpfe überprüft, meine Arbeit ist primitiv, aber ich bin völlig unzufrieden mit ihnen, die Spulen brennen im Bruchteil einer Sekunde durch und ich habe aufgegeben vorerst auf kleine Lautsprecher. Ich warte auf Ihre, weil ich Ihnen und Ihrer Arbeit VERTRAUE. Ich werde geduldig auf die Köpfe warten, die du machst, mein Freund!

[farmersplow]

Hello, calm down, Farmer, Vienna wasn't built in a day... right?
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Thank you for the trust and I will do everything to make good quality. I know well the problem with the small speakers and their small coils. I have a whole bucket full of their blown coils. That is why I have focused on large coils. So far, I have never had one of the big coils burn out. Unfortunately, it is difficult to make a good frequency characteristic with the big coils. But with the right materials and extremely low weight of the moving masses, you can get good and better results right away without the coils burning up so easily. But you have to do a lot of experiments and research. In the end, a good result must be achieved.
And it is true, Vienna was not built in one day (it took at least two)
Greetings from Austria
Thomas

[farmersplow]

The Dashpot
(03 2023)

Reminder of Jan. 2023. I had rotated the outer housing of the dashpot at that time:
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Now I have found the time and turned and milled the remaining parts. The gap dimensions at the piston and its suspensions were carried out very precisely.
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The assembled dashpot is filled with oil and dampens extremely well. With the small holes, the damping effect can be reduced in the rough. By changing the damper oil, the effect can also be changed.
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The short video shows a first damping test with the not yet finished cutterhead.
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Dashpot damping test.mp4

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Greetings from Austria
Thomas

[Thelatheofus]

This is incredible !

[farmersplow]

This is incredible !

THX

[farmersplow]

The Cutterhead
(04 2023)

How time flies! It's already April and time to finish the cutting head. Most parts are already finished, but there are still some details to work out. For example the inner connection plate for the feedback coils. This will be underlaid with insulating paper to prevent short circuits.
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Of course, the feedback coils have to be manufactured again. According to the same principle as last time, only a little more precise!
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The housing of the cutterhead also needs a front plate to which the connections for the heating wire of the stylus can be attached. I made the connecting parts from brass on the lathe. Brass is not the best conductor, but since the heating coil is not a precision signal, this does not matter. It looks good and does not corrode as fast as copper or aluminum. (Gold would be even better, but I would have to melt down my wedding ring and my love for the cutting head does not go that far).
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Now the torsion bar with V-spring is mounted and the magnets for the feedback coils are inserted.
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After the driving coils are inserted the feedback coils are soldered on.
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Finally, only the LED lighting is attached and the lid is mounted.
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The CH-6 cutting head is ready. When my dear wife saw it for the first time, she said, "It looks nice, but does it have to be that big?"
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I frowned and thought, unfortunately, she's right. The thing is already quite large. Since then, we call it "Big Mac"! But anyway, I like it and if it's technically okay, then I'll just can build another smaller model...

What do you think, looks nice, doesn't it?

Greetings from Austria
Thomas

[Fela Borbone]

You are doing an incredible good job, congratulations!
Following with interest.

[farmersplow]

You are doing an incredible good job, congratulations!
Following with interest.

Hello Fela, thank you for the positive feedback. I'm always happy when someone gives their opinion on my project. Especially when someone with great experience expresses positive.

[farmersplow]

The Cutterhead
(04 2023)

I almost forgot to describe the connector pinout. The connector is a d-sub 15 female connector with 15 pins (one is free).
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This information is only important for those who didn't know it yet! The polarity of the drive coils is of great importance for stereo cuts.
If the left and right drive coils were connected in correct polarity, a good stereo cut would not be possible.
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Example 1: Connections with constant polarity
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If everything is done according to the usual correct connection diagram, the connections would look like in figure 1. But what happens when cutting the signal in the case when a 1kHz sine tone is running at the left and right signal at the same time?
Both driver coils would extend (as if mirrored) at the same time and then retract at the same time.
This in turn would move the cutting stylus up and down only (not sideways). It would work but cutting down would be much more forceful than cutting up, leading to sound changes on the one hand and also to the limits of performance on the other (see also deep cut method). The cutting pattern would look like figure 2.
Stereo Drive Coil Polarity
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figure 1

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figure 2

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Example 2: Connections with crossed polarity
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If the polarity is crossed (reversed) at one of the two driver coils, the connections would look like in figure 3. Now, what happens when the signal is cut in the case where a 1kHz sine wave is running simultaneously on the left and right signals?
While the left driver coil is moving out, the right driver coil would move in at the same time (and vice versa). So they move in opposite directions. This in turn would move the cutting stylus only to the left and to the right (not up-down). The result is a lateral movement (serpentine line) with constant force (see also lateral cutting method).
The cutting pattern would look like Figure 4. (This is how it should be)
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figure 3

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figure 4

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Stereo Drive Coil Polarity Crossing Out

The above mentioned "crossing out" of the polarity has already been done here inside the cutting head (Figure 5).
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figure 5

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Greetings from Austria
Thomas

[zdenek]

Hello, good, but if the coils move in antiphase horizontally, lower figure, then there should be no stereo effect, only a mono effect, because the stereo signal is the difference of the left and right channels with vertical modulation, that's right, so how will you get stereo in the recording?

[farmersplow]

Hello, good, but if the coils move in antiphase horizontally, lower figure, then there should be no stereo effect, only a mono effect, because the stereo signal is the difference of the left and right channels with vertical modulation, that's right, so how will you get stereo in the recording?

With mono heads there is only one driver coil. In stereo there are two driver coils, each offset 45° from the center axis (edge cut).
If (as in the above example) the same signal is applied to both driver coils (e.g. 1kHz), this results in 1kHz on both channels. This has the same effect as mono. (Regardless of whether Example 1 or Example 2 is used).

You get a stereo effect if you apply different frequencies to both channels!

The explanation why you reverse the polarity of one driver coil is that if the frequencies are approximately the same, you prefer a sideways movement rather than an up-down movement.
Since in 90% (this is a rough personal estimate) of all music pieces nearly mono is predominant and stereo is rather rare (only in certain passages and where the band wants to achieve an effect), the sideways movement should be done.
Both work, but sideways movement is better.
"Vinylrecorder" has made a good animation for this: https://www.vinylrecorder.com/stereo-de.html
I hope it is understandable

[farmersplow]

A small addition to explain why you should connect a driver coil reversed:
History:

When the vinyl record slowly replaced the shellac record in the 1930s, it was recorded and played back exclusively in mono. The "Seitenschrift" (horizontal cut) method was adopted, which had already been introduced in 1888. The advantage over "Tiefenschrift " (deep type) is a larger dynamic range and easier copy production. Also, in contrast to "Tiefenschrift" (deep type), crackling is significantly reduced.

Stereo with the "Flankenschrift" (flank type or V-cut) process was developed in 1930, but was not marketed until 1957. The direction of deflection of the cutting stylus is in antiphase for the left and right channels, so that a mono signal recorded with a stereo cutting head produces a sideways typeface. This ensures backward compatibility with mono systems: When a stereo record is played back on a mono player, only the horizontal deflection of the groove is reproduced. This corresponds to the sum (L + R) of both channels.

If one of the two driver coils were not swapped, the pure up-down movements would remain almost silent when played back with a mono pickup.

[zdenek]

Hello, Do you have a test vinyl record? I have such a vinyl record, the left channel and the right channel are recorded separately, then two channels are simultaneously in phase and anti-phase, and you can hear the difference between the left and right channels precisely, and, for example, the signal from the right channel slightly penetrates the left channel and vice versa. Recording a stereo signal in one groove is not a simple process, more is needed than the appropriate polarization of the drive coils. If anyone knows this topic, please speak up on this matter, I will be happy to learn more, best regards