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

[zdenek]

We were thinking about such a solution for extracting copper chips, but unfortunately the relative vacuum pressure is too low and we had to decide on a much more powerful relative screw pump and, as a last resort, we used a supercharger compressor from a Volkswagen, [a real madness of noise], it must be in the garage, if maybe Farmer then check the attenuation, how many dB will the noise drop after closing the housing, ok?

[farmersplow]

We were thinking about such a solution for extracting copper chips, but unfortunately the relative vacuum pressure is too low and we had to decide on a much more powerful relative screw pump and, as a last resort, we used a supercharger compressor from a Volkswagen, [a real madness of noise], it must be in the garage, if maybe Farmer then check the attenuation, how many dB will the noise drop after closing the housing, ok?

If the G60 compressor from Volkswagen is not enough, there is also the Roots blower from the Lancia Volumex. If that is still not enough, there is also the Dodge Challenger Hellcat supercharger (still in production). I come from the automotive industry and had a lot to do with turbochargers and superchargers (had three Volumex myself). But I don't think a supercharger will fit.

[farmersplow]

We were thinking about such a solution for extracting copper chips, but unfortunately the relative vacuum pressure is too low and we had to decide on a much more powerful relative screw pump and, as a last resort, we used a supercharger compressor from a Volkswagen, [a real madness of noise], it must be in the garage, if maybe Farmer then check the attenuation, how many dB will the noise drop after closing the housing, ok?

If you really need a high vacuum, then it is better to use a multi-piston pump with a compensation diaphragm. This ensures that the vacuum remains constant and the air column does not "oscillate". This is also relatively quiet.

[zdenek]

We were thinking about such a solution for extracting copper chips, but unfortunately the relative vacuum pressure is too low and we had to decide on a much more powerful relative screw pump and, as a last resort, we used a supercharger compressor from a Volkswagen, [a real madness of noise], it must be in the garage, if maybe Farmer then check the attenuation, how many dB will the noise drop after closing the housing, ok?

If you really need a high vacuum, then it is better to use a multi-piston pump with a compensation diaphragm. This ensures that the vacuum remains constant and the air column does not "oscillate". This is also relatively quiet.

Thanks, currently the compressor is pumping quite well, but you know what the noise of this charging and suction is... I had to add a compensating and balancing air tank to even out the fluidity [the electric motor drives 1.5 kW, plus a wheel twice as large belts on it than on the compressor of this Volkswagen, revolutions around 3k, etc.]. Generally, we accidentally took this compressor because it was cheap [after a wrecked car], but I will tell you that it works. If there is a problem with it, we will look for something like yours. tips, thanks very much Farmer!

[farmersplow]

VACUUM Part 4 - The chip container

I actually built the chip container much later, but it fits in with the theme. I would therefore like to present the work here.
First I had to rework the CNC-manufactured lid on the lathe. The grooves for the sealing rubber were not deep enough and so the lid would not fit over the container.
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Then I drilled the holes for the air inlet (from the suction pipe), the air outlet (to the vacuum pump) and the pressure gauge connection.
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In my desperate search for the right adapter pieces, hoses and filters, I came across the following parts:
A pressure gauge, A brass straight-through adapter and a filter with valve.
I also found a PVC pipe, a cover for the PCV pipe, a rubber seal and a quick connector for the suction hose (coming from the cutterhead).
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Then I finally assembled the lid:
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I was very proud because it looks so good.

But unfortunately not all that glitters is gold! The design has a few flaws.

First of all, the seal. The lid went on the pipe well and was also super tight. But unfortunately I could no longer remove the lid! The contact pressure of the seal was too great and it was not possible to remove the cover even with three people. It was only by blowing compressed air into the container that I was able to remove the lid. It took several more adjustments on the lathe until it now works perfectly. It now goes up and down easily and is still tight.

The next problem is the pressure gauge. Unfortunately, there are only vacuum pressure gauges with a range down to -1 bar (-30 in Hg). However, the side channel blower has a maximum vacuum of -0.11 bar. So the pressure gauge practically shows nothing!
If anyone knows of a vacuum pressure gauge that has a maximum range of -100mBar (-3 in HG), please let me know.
It has nothing to do with the function, but with the aesthetics.
A negative pressure of -100mBar is completely sufficient, because the side channel blower has a very high air flow rate, which is much more important! If you consider that an air flow rate of 80m³/h can flow through an opening of 2mm², then this is an enormous suction on the suction pipe and easily takes the chip with it.

The third problem is the brass filter with valve (in the tank). The valve chattering and cannot be removed without destroying the filter. The filter is also too coarse-meshed. However, the filter is very important because no filaments or other parts must get into the side channel blower (otherwise the pump blades will be destroyed).
I was able to solve the problem by replacing the part with a brass flange with a filter sock. I made a suitable filter myself on the sewing machine. More precisely, my wife sewed it (thanks darling).
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I can proudly say that this part works perfectly!
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Greetings from Austria
Thomas

[nikc]

Hi Thomas
Great project, amazing, thanks for posting the project. Good to read. I am swapping to a channel blower from a vacuum pump. Just got an old one on ebay to try out. Need more power.
Best
Nik

[C-Pilote]

Hey !
Nice vacuum set up!
Well built !
For the filter on mine I use makeup little
Cotton rags tape under the succion intake and it work well.
Looks a bit like your filter.

[farmersplow]

Hi Thomas
Great project, amazing, thanks for posting the project. Good to read. I am swapping to a channel blower from a vacuum pump. Just got an old one on ebay to try out. Need more power.
Best
Nik

Yes, the disadvantage of the vacuum pump is the lack of air volume (and the pulsating air column). I once tried to inflate an air castle (one of those things that children can jump on) with a compressor. It worked, but took over an hour. With the channel blower, the thing was up in 20 seconds. There is a suitable device for every application. (I need the compressor for my air-brush work).

[farmersplow]

Hey !
Nice vacuum set up!
Well built !
For the filter on mine I use makeup little
Cotton rags tape under the succion intake and it work well.
Looks a bit like your filter.

Thank you and glad you like it. My filter consists of the coarse dust filter that usually comes with the dust bags for household vacuum cleaners.

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[farmersplow]

Feedback Amplifier - Part 1

I wasn't able to post anything last month. But not because I didn't do anything. On the contrary, I worked so much on my project that there was no time for the presentation. And because I also want to do my contribution properly, I first had to find some time to prepare this chapter. Because just throwing in a few pictures without any explanation didn't seem good to me. So I found some time - between one and four in the night, when some people are partying and most people are asleep.

Now let's talk about the Feedback Cutterhead and Feedback Amplifier. I prefer to call it the ‘Feedback Compensation Amplifier’ because this part is supposed to compensate for the resonances of the drive of the driver coils. Ideally, it should compensate for the main resonances that occur in the range from 500Hz to 2kHz (depending on the cutterhead) in order to achieve the flattest possible output curve.
In addition (if the amplifier works well), it should also compensate for the second head resonance, which can be found at around 10kHz. The amplifier can also take over another task: the use of the IRIAA filter, which reduce the low frequencies for cutting and boosts the high frequencies.

So I had spent months trying to develop a circuit for it. There were many attempts that did not lead to a satisfactory result. I do have some knowledge of electronic circuits, but this is where my limits became apparent.

About two and a half years ago (Jan. 2022 https://www.lathetrolls.com/viewtopic.php?f=15&t=9578#p61050 ) I rebuilt the circuit of the Caruso amplifier, with 50% success. One channel had not worked as it should, which had repeatedly led to the destruction of my first cutting heads. The smoke threads rose up in delicate spirals and there was a smell of burnt resin in the air. It confirmed my theory that there must be a lot of smoke in all the electronic parts (tightly sealed). As long as the smoke stays in there, the part works. But as soon as the smoke comes out, the part is broken.

About a year and a half ago, I visited Flo (the master craftsman) in his workshop in Switzerland. There were lathes, electronic measuring devices and audio equipment everywhere. There were circuit boards here and cutting heads from all decades there. It smelled of machined metal and soldered circuit boards. Each box contained a jewel from the past that the master craftsman had brought into the present day. But also current, new and fresh things like the coffee he offered me. I love coffee and the machine he used to make it was in keeping with tradition! All in all, it was a special experience for me and I humbly tried to soak up the knowledge from decades of experience. As a parting gift, Flo gave me two circuit boards of the Flokason-Caruso feedback amplifier. Thank you Flo!

After consulting Flo again, I decided to use this circuit diagram from the Caruso board - simply because it works. With his permission, I can also present my MOD. The circuit diagram corresponds to that of the Caruso board (Flo had thankfully published it) - I have redrawn the circuit diagram because I want to make my own circuit boards in the future. Not because Flo's boards are bad, but simply because they don't fit into my case in terms of space. I also need to make some changes to the resistors and capacitors for my head to customise the board.

So first of all, here is the circuit diagram of my feedback compensation amplifier (based on the Caruso board).
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A01 FP9_FB-comp-amp 1_3.png

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There are a few things to consider:
R24/C25 regulate the lowpass at the line-in (to filter out high frequencies)
R7 regulates the gain of the feedback coil (more or less gain is required depending on the coil/magnet)
C33 adjusts the forward compensation for the first resonance
R33 adjusts the bass forward correction at low end. (~ 30dB)
C32 adjusts the forward compensation for the second resonance
C37/R37 is responsible for feedback activation
R39 adjusts the gain of the feedback (higher resistance = higher FB)

Here is the component list:
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A02 FP9_FB_Comp_Amp_1.3 parts.pdf

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In one of my first posts, I wrote about the recommended fuses with protective circuit. I found these in connection with the Caruso board.
https://www.lathetrolls.com/viewtopic.php?f=15&t=9578&start=20#p61061
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A03 FP9_FB-comp-amp 1_3.png

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Later I realised that this RC circuit causes a strong bass drop and therefore left it out again (I only kept the fuses):
https://www.lathetrolls.com/viewtopic.php?f=15&t=9578&start=40#p61137

Now, however, the IRIAA characteristic and the structure of the feedback compensation amplifier require this part of the bass cut at least partially outside the amplifier board.
This means that the amplifier board is only complete with the external RC circuit.
So I installed it again. Directly at the socket input of the amplifier in my device. (Power amplifier input to the fuse, then RC and then on to the cutterhead with a cable).

How is everything connected together?

1: Audio signal source (usually PC to sound card, or tape or other line source)
This signal can be EQ-processed, but does not require an IRIAA EQ!
2: LINE-IN Feedback Compensation Amplifier
3: LINE-OUT Feedback Compensation Amplifier
4: This LINE-OUT is routed to the Power Amplifier input
5: Then it goes on to the fuse and the RC circuit (bass damping)
6: From there the cable goes directly to the DRIVE-COIL of the cutterhead

A: The movement of the drive rod (to which the feedback coil is attached) induces a corresponding voltage (FB signal) due to the movement in the magnetic field. +/- is passed on by cable from the cutterhead.
B: The FB voltage +/- is connected to the FEEDBACK-COIL-IN of the Feedback Compensation Amplifier. The line-in is ‘compared’ with the FB-in. Resonances (i.e. unwanted increases in volume) are then compensated for.
C: A commercially available dB meter is connected to the MONITOR connection. It is used to calibrate the stereo compensation correctly. I will show how this works in practice in one of the following reports.

Here is a diagram showing the basic setup as described:
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A04 FP9_FB-comp-amp 1_3.jpg

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Greetings from Austria
Thomas