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

[zdenek]

Feedback Amplifier - Part 4

These circuit boards should ultimately fit into the housing of my lathe. In the following picture you can clearly see that there is not much space in this area. However, I didn't want to hide it somewhere in the device, as this would make it more difficult to carry out a proper calibration.

Rendering image of the installation location of the FB-Comp.Amplifier. I have hidden the side panel:
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D01 FP9_FP-comp-amp 1_3 PCB.JPG
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The calibration is then carried out from the rear. The IRIAA EQ should be deactivated for the calibration process.
Rendering image of the rear calibration area
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D02 FP9_FP-comp-amp 1_3 PCB.JPG
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And so I'm getting closer and closer to my goal - or so it seems.

Greetings from Austria
Thomas

nice, of course: the end justifies the means"

[Thelatheofus]

Amazing work, thanks again for sharing all this!

[farmersplow]

Amazing work, thanks again for sharing all this!

Thx

[farmersplow]

Feedback Amplifier - Part 5

With a temporary holder for the circuit boards, it's time for the installation.

I use shielded cables and channel separation for all audio signals (one cable per channel). The cables are each two-pole with shielding. After all, I don't want any hum.

The following two pictures clearly show why I developed my own customised PCBs. Unfortunately, the Caruso board didn't fit and the plug-in connections on the Flokason Caruso board were also omitted because I wire directly in the lathe.

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E01 FP9_FP-comp-amp 1_3 PCB.jpg

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E02 FP9_FP-comp-amp 1_3 PCB.jpg

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E03 FP9_FP-comp-amp 1_3 PCB Adjust Video Pix.jpg

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But now everything fits very well and is perfectly integrated. It's almost a shame that you won't be able to see it all when a housing is put over it at some point.

Now I'm getting ready to calibrate the FB control unit! I will create a few videos for the next few posts.

Greetings from Austria
Thomas

[farmersplow]

Feedback Amplifier - Part 6

Calibration Feedback Compensation Amplifier

First of all, I have to make an important prediction! I now know why I always burnt out one channel of the Cutterhead years ago! Because even with this calibration, the fuse always blew on one channel. Fortunately, these coils are very stable and so they didn't suffer any damage. The reason is simple and straightforward if you know it!

As in previous reports, I have already explained why the polarity of a driver coil in a stereo head must be reversed (side cut instead of depth cut). In my meticulous and precise adherence to all connection instructions, I have also done this. However, I only did it with the driver coil, not with the feedback coil! Experienced specialists already know what's coming next. The FB coil sends an inverted signal to the FB amp. The amp tries to compensate for this and ‘corrects’ it. This gives the driver coil even more juice and the FB amp corrects and amplifies with everything it has! - Everyone knows the scenario of feedback and what happens in the loudspeakers.

No matter! The fault has been rectified and I used the oscilloscope to check again whether the driver signal and FB coil signal are in harmony.

I use a frequency of 1kHz for the calibration. (Or even better, the resonance frequency of the cutterhead). Why don't I use a white noise? Because there is too great a risk that something will go wrong with the amplification and the calibration will take some time. I don't want to chase 16kHz (or more) through my cutterhead in the long term. It works just as well with 1kHz.

IMPORTANT NOTE: Ideally, a test signal without IRIAA and without EQ should be cut with the cutterhead beforehand to find out the main resonance. Play this signal on the turntable and view it with spectral analysis. If the main resonance is 1350Hz, then you should (ideally) make the settings with this frequency.
I show here in general how the setting is made for a cutting head with a main resonance of 1kHz.
My electronics also differ from the original Caruso board because the direction of rotation of the potentiometers is reversed. On the Caruso board, the three potentiometers have to be turned in the other direction beforehand and this also applies to the settings.
Finally important: I show an ‘attenuation’ of -27dB! This value differs for each type of cutting head and can be -15dB or even -42dB! It depends on the characteristic curve of the cutting head (and which attenuation it requires).

Flo (inventor of the Caruso Board) wrote a lot about this in a post many years ago:
https://www.lathetrolls.com/viewtopic.php?f=15&t=5250&p=38871&hilit=caruso+head#p38871

[farmersplow]

SETTING in the PRACTICE:

I switch the IRIAA to OFF (so that no high frequencies are amplified). In my case at 1kHz it would not matter whether the switch is on or off.

Here is the arrangement of the components:
Below the control knobs with the IRIAA switch
Above the DB meter
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F01 FP9_FP-comp-amp 1_3 PCB Adjust Video Pix.jpg

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BASIC SETTING:

Before a signal is sent, I set the amplifier to the basic setting:
Connect the dB meter to the dB MONITOR input (both channels)
FB-dB MONITOR Pot. --- turn fully anti-clockwise (both channels)
FB-COIL MODULATION --- turn fully clockwise (both channels)
LINE-IN MODULATION --- turn fully clockwise (both channels)
IRIAA-OFF

See video:
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F02 FP9_FP-comp-amp 1_3 PCB Adjust Video.mp4

[farmersplow]

SETTING LEFT CHANNEL

Play a 1kHz signal (Line In connection of the FB-AMP.).
Power Amplifier (left channel only) slightly above the centre position:

LINE-IN MODULATION --- turn slowly anti-clockwise (left channel)

• After two or three turns, the signal should be audible.

• Continue turning slowly until it becomes loud (but not so loud that the coil melts!)

• A display should already be visible on the dB meter. Ideally, this should be set to a value between -3dB and -15dB

• If the value on the dB meter is above 0dB or below -18dB when the signal is ‘loud’, you should stop and readjust the dB meter (both channels). You can then start again.

Read off the displayed START VALUE:

• In my case, I have set the volume to a displayed value of -15dB.

• My target setting is an ‘attenuation’ of -27dB. I do this in three steps (-9dB; -9dB; -9dB). In between, I always increase the line-in modulation. If your cutting head requires less attenuation (e.g.: -18dB) then only do the process twice. If your cutting head requires more attenuation (e.g.: -33dB) then do the process once more (-9dB; -9dB; -9dB; -6dB).

FB-COIL-MODULATION --- turn slowly anti-clockwise (left channel)

• The signal becomes quieter and the DB metre decreases. Set to a value that is -9dB lower than the START VALUE

• In my case, this is a display value of -24dB (-15dB -9dB = -24dB).

• Now I have an attenuation of -9 dB

LINE-IN MODULATION --- turn slowly anti-clockwise (left channel)

• The signal becomes louder again.

• Turn until the START VALUE is reached again (in my case -15dB).

FB-COIL-MODULATION --- turn slowly anti-clockwise (left channel)

• The signal becomes quieter again and the DB metre decreases. Set to a value that is -9dB lower than the START VALUE

• In my case, this is a display value of -24dB (-15dB -9dB = -24dB).

• I have now achieved an attenuation of two times -9 dB, i.e. -18 dB

LINE-IN MODULATION --- turn slowly anti-clockwise (left channel)

• The signal becomes louder again.

• Turn until the START VALUE is reached again (in my case -15dB).

FB-COIL-MODULATION --- turn slowly anti-clockwise (left channel)

• The signal becomes quieter again and the DB metre drops. Set to a value that is -9dB lower than the START VALUE

• In my case, this is a display value of -24dB (-15dB -9dB = -24dB).

• I have now achieved an attenuation of three times -9 dB, i.e. -27 dB

LINE-IN MODULATION --- turn slowly anti-clockwise (left channel)

• The signal becomes louder again.

• Turn until the START VALUE is reached again (in my case -15dB).

• This ensures that no loss of overall volume is caused by the attenuation.

Before continuing, turn the power amplifier (left channel) down again!

If the signal is distorted during attenuation, turn it back a little (one turn) and switch it off. The limits of the attenuation options have been reached at this point!

Video about the setting:

F03 FP9_FP-comp-amp 1_3 PCB Adjust Video.mp4

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[farmersplow]

SETTING RIGHT CHANNEL

Play a 1kHz signal (Line In connection of the FB-AMP.).
Power Amplifier (right channel only) slightly above the centre position (same position as before for the left channel):

LINE-IN MODULATION --- turn slowly anti-clockwise (left channel)

• After two or three turns, the signal should be audible.

• Continue turning slowly until it becomes loud (but not so loud that the coil melts!)

• A display should already be visible on the dB meter. Ideally, this should be set to a value between -3dB and -15dB

• If the value on the dB meter is above 0dB or below -18dB when the signal is ‘loud’, you should stop and readjust the dB meter (both channels). You can then start again.

Read off the displayed START VALUE:

• The same starting value should be set as for the left channel

• Here too, my aim is to set an ‘attenuation’ of -27dB. Again, I do this in three steps (-9dB; -9dB; -9dB). In between, I always increase the line-in modulation.

• Now everything is the same as for the left channel

When everything is set, turn the power amplifier back again!

If the signal is distorted during attenuation, turn it back a little (one turn) and switch it off. The limits of the attenuation options have been reached at this point!

Video for setting the right channel:

F04 FP9_FP-comp-amp 1_3 PCB Adjust Video.mp4

[farmersplow]

CONTROL BOTH CHANNELS SIMULTANEOUSLY

Play a 1kHz signal (Line In connection of the FB-AMP.).
Power Amplifier (both channels) approximately centre position (as before for the left channel):

The display on the dB meter should be the same.

Video to check both channels for equality:

F05 FP9_FP-comp-amp 1_3 PCB Adjust Video.mp4

[farmersplow]

CHECK BOTH CHANNELS DISTORTION

Play a 1kHz signal (Line In connection of the FB-AMP.).
Slowly increase the power amplifier (both channels) (slightly louder than during the calibration procedures) to check for distortion.

Video to check both channels for distortion:
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F06 FP9_FP-comp-amp 1_3 PCB Adjust Video.mp4

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I hope it was helpful. It was very reassuring for me to see that everything works. The next step for me is to fine-tune the circuit boards with the right resistors and capacitors so that the board fits my cutterhead perfectly.

Greetings from Austria
Thomas

[farmersplow]

Control panel

At the beginning of the year, I decided to tackle the control panel as well. This came about because the provisional operation of my lathe was already quite confusing. I always had to press small switches on the motherboard and the touch display was always lying around somewhere between the cables. I also lacked a simple way to control the volume and balance. Always having to use the power amplifier or PC was getting annoying. And I couldn't see the VU meter well either, because it was also somewhere on the huge breadboard between the cables and twisted around.
I wanted it to be simpler and clearer. And because I had just created the PCBs for the feedback amplifiers anyway, I wanted to make the PCBs for the control panel at the same time. With VU meter and peak control, volume and balance control, all the necessary buttons, the touch panel and various control LEDs should be controlled via the PCB.
So I designed a layout and then had it professionally milled and printed. I also planned the threaded rods on the back for mounting the components.

The big part finally arrived. The milling turned out very well and the surface, including the print, is also flawless.
What do you think?

Next I'll screw the displays, buttons and potentiometers into place.
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Panel A 01.jpg

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Panel A 02.jpg

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Panel A 03.jpg

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Greetings from Austria
Thomas

[Alfred]

Hi Thomas,
as always without comments. It's amazing..¡¡¡¡

[farmersplow]

Hi Thomas,
as always without comments. It's amazing..¡¡¡¡

Muchas gracias Alfred

[farmersplow]

Control panel (part 2)

Now I install the components in the front panel. First the LEDs, then the switches and potentiometers (from ALPS). I chose nice stainless steel pushbutton switches and for the potentiometers I made knurled aluminium knobs. The feel is really great!
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Panel B 01.jpg

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Then I installed the large analogue VU meters and the large touch panel. I built the whole panel into a small box (for the time being). Until I have the housing, the control panel has to stay in the box. This way I can mount it provisionally on my lathe and see if everything works well.
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Panel B 02.jpg

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Here are two more detailed pictures. I think it turned out well. This is how I imagined it and I like it.
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Panel B 03.jpg

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Panel B 04.jpg

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Now I just have to build the right electronics.

Greetings from Austria
Thomas

[Fela Borbone]

Nice!

[farmersplow]

Nice!

Muchas Gracias

[farmersplow]

Control panel (part 3)

The PCBs for the front panel are already there, as are the necessary components. Unfortunately, the electronic components have become quite expensive in the meantime. And then there are the plugs! (I just wanted to make a quick comment). The PCBs, on the other hand, were quite cheap.
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Panel C 01.jpg

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Once assembled, the whole thing looks quite nice. Ultimately, there's not too much to the board. Most of it is controlled externally by micro controllers. The only things on the board are the connectors for the inputs of the Mirco controllers and the outputs to the control panel. And of course the electronics for the VU and peak displays.
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Panel C 02.jpg

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Here is a detailed picture.
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Panel C 03.jpg

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I next have to test whether everything works as planned.

But first I'm going on holiday for a while (after several years).

Greetings from Austria
Thomas

[PLD]

A 'holiday', you say? I've heard of those, but never experienced one.

Fantastic work as ever. We shall be waiting for when you get back!

[Semar]

This let me without voice (coil )
Amazing work from start to here, step by step, and i'm sure that you have 10000 ideas for the next steps....

[farmersplow]

Hi PLD & Semar. Thank you very much.
FYI, holidays are when you are not physically working on your project. HaHa. So only my brain was working but only 1000 ideas came up. Probably because the heat affected the neuronal connections.