KNOP lathe DIY build

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KNOP
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Re: KNOP lathe DIY build

Post: # 49236Unread post KNOP
Mon Feb 05, 2018 9:22 am

Hey everone.
For the people interested here are the 3D files for the plastic parts of the cutterhead. Still working on the alu parts.
I would advise to use a profesional SLS type service, not FDM home 3D printer.

parts lists:

2x insert spirol series 16 m4
3x insert spirol series 16 m3
2x bolt WS 9335 M4x8mm (for mounting head to overhead, may vary)
8x bolt DIN 912 M2x16mm
8x washer M2
8x nyloc nut M2
4x bolt DIN 912 M3x6mm
metal stock 2mm x 10mm
steel wire 1mm
alu tube outer diameter 6mm
2x bolt DIN 912 M3x18mm
2x nut M3 (for V spring, nyloc will be very hard to mount)
2x nyloc nut M3(for weight adjustment)
2x bolt DIN 912 M2x8mm (for heating wire clips)
2x alligator clips (small ones)
2x Fischer Elektronik ICK S R 285X185 heatsink
1x Kerafol Keratherm KL 90 40x40 thermal tape 0,3mm
2x M3 spacers 20mm
1x Dsub female connector
1x setscrew DIN 916 A2 - M3x3mm (crater head) alu if you can find it.
2mm alu or carbon fibre rod for pushrods
2x visaton BF32 drivers
general purpose epoxy for glueing everything

That's probably it. Use and modify as you please, as long as you keep it "open source". No guarantees.
cutterhead v5 spirol inserts.rar
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jjwharris
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Re: KNOP lathe DIY build

Post: # 49253Unread post jjwharris
Wed Feb 07, 2018 6:10 am

Nice!

Good to see you're releasing the files, I intended to do something similar but became a little too attached to them and let mine get way too unorganized...
Record Lathe Embossing Supplies - http://www.supplies.johnnyelectric.co.nz/

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KNOP
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Re: KNOP lathe DIY build

Post: # 49462Unread post KNOP
Mon Feb 26, 2018 5:05 pm

Found out that in the latest beta of Room EQ Wizard you can finally enter wav files instead of taking realtime measurements.

So I did a few experiments and got a not so flattering THD plot out of it:
THD KNOPRECONE.png
Upwards of 3 Khz the THD goes way above 2% upto 18% at 10Khz. (Horizontal line is about 2%)
Did some Eq changes and got the THD a little bit down to about 12% THD at 10 Khz at the expense of the frequency response.
At 1Khz the THD would be 0,7% which would seem ok but conceils the reality of the other frequencies.
No idea how to tackle this without using feedback of some sort, but did try a half speed cutting session, and the music did seem to sound quite a lot better.
waterfall.png
I made a waterfall plot as well, 20Ms window time. Not sure what to make of it, but looks fancy.
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markrob
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Re: KNOP lathe DIY build

Post: # 49475Unread post markrob
Tue Feb 27, 2018 9:31 am

Hi,

I'm very skeptical of your THD measurements at high frequencies. Can you provide more information on how they were calculated. If this is based on data digitally sampled what is the bandwidth and sample rate used? At 10 Khz, the 2nd harmonic would be at 20 Khz . That's within the bandwidth of your measuring system. But any harmonic beyond that would seem to be out of range and maybe irrelevant. Also not given was the cutting level used to make the test cut.
Are you sure that your cutting system is not reaching curvature limits that occur when the cutting stylus back angle hits previously cut slope? Is the playback system having issues due to scanning loss? If you are getting .7% at 1 Khz, I would consider that pretty good results. Also note that the addition of feedback would probably not improve on the high frequency THD performance since its would be mostly nonexistent by this point.

Mark

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KNOP
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Re: KNOP lathe DIY build

Post: # 49484Unread post KNOP
Tue Feb 27, 2018 2:29 pm

It was calculated using a sine wave log sweep wav file put trough the fabfilter correction EQ onto the record. sampled at 44khz 16 bit. Cutting level not very scientific but not far below burning 0.4A T fuses. It is not unthinkable I made a few errors during the process.
Unfortunately no time to investigate further atm, got some deadlines by the end of the week and on holiday leave next week.

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markrob
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Re: KNOP lathe DIY build

Post: # 49487Unread post markrob
Tue Feb 27, 2018 3:42 pm

Hi,

Let us know if you get to the bottom of this. I always second guess any measurements. Its easy to get take down a wrong path.

Maybe try cutting a single 10 Khz sine tone at a normal operating level and look at the play back spectrum. You should only see the fundamental and 2nd harmonic on a spectral plot. If you measure how many db down the harmonic is from the 10Khz fundamental, you can calculate the THD directly. For example, -40db represents 1:100 or 1% THD. If you sample at 192 KHZ and your audio interface has actual bandwidth to 96Khz, you will see higher order harmonics. If you do the same at 1Khz, you can see harmonics up to the 20th at 44.1 Khz. Even order harmonics represent non-symmetrical linearity (e.g. positive parts of the wave are deformed differently than negative going parts). Odd order represent symmetrical non-linearity (think "S" shaped transfer functions).

Mark

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KNOP
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Re: KNOP lathe DIY build

Post: # 49804Unread post KNOP
Wed Mar 21, 2018 2:10 am

Hey everyone, made a new version cutterhead yesterday. I used perfume funnels this time and added ferrofluid to the drivers. I fucked up the aluminium torque tube, by not threading the hole for the setscrew properly I got the setscrew stuck inside. So I used a plastic one. Got a little distortion on one channel, I think because the bonding between the funnel and the cone of the driver was not perfect. I used a 1 min cure epoxy, which was way too fast to properly handle.
The weird 3khz issue is gone, so I think the previous 3d printed cones were at fault. There is no signal above 11khz, which is then probably due to the plastic torque tube. Stereo separation was very low as well, about 6db or so, I will need to look into that. There is now also a 2khz resonance peak, but I checked using a 1khz tone and the 2nd harmonic was about 40dB down so this should not be a result of harmonic distortion. Made some tracks and it soundend close to the original with a lpf at 12khz.
IMG_20180321_064713.jpg
IMG_20180319_162424.jpg
IMG_20180321_065123.jpg
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KNOP
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Re: KNOP lathe DIY build

Post: # 49838Unread post KNOP
Fri Mar 23, 2018 4:16 am

I feel like it's time to move to 320 neumann stylus in the project.
Made a new torque tube with a fitting for a 320 stylus, which hopefully will hold. Calculated weight is down to 0,54gram, and the stylus should now be right below the pushrod /funnels. Added some stubs to easily attach the funnels. I wish I had such a fancy 3D printer at home, but helas I will have to wait a few weeks for the new parts....

320 torque tube.png
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KNOP
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Re: KNOP lathe DIY build

Post: # 50071Unread post KNOP
Fri Apr 13, 2018 8:58 am

Small update..
Got 2 new torque tubes. Weight is now 0,55gram. No stylus to test the tapered hole yet.... So more waiting again....
IMG-20180413-WA0000.jpeg
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grooveguy
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Re: KNOP lathe DIY build

Post: # 50074Unread post grooveguy
Fri Apr 13, 2018 12:53 pm

Very pretty! I'm still trying to wrap my mind around 'vertical tracking angle'; does your cantilever go straight back (parallel to the disc surface) or does it angle up as it goes back? I've read the papers, but if anyone can amplify on this in strictly layman's terms, I, for one, would be forever grateful.

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Pedreguero
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Re: KNOP lathe DIY build

Post: # 50100Unread post Pedreguero
Tue Apr 17, 2018 6:36 am

The sound should not touch the cutting needle directly?


another question.
How important is the power of Speakers

Thanks
Pedreguero

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KNOP
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Re: KNOP lathe DIY build

Post: # 50379Unread post KNOP
Sat May 19, 2018 10:53 am

@grooveguy, I do not exactly understand what you mean by your question
@pedreguero
The power handling of the speakers is important for loud cuts. The speakers i have are 2w rms rated, i use ferrofluid and active cooling+heatsink to gain an extra 3-4db of usable power.

Finally got time to build a new head with the neumann style shank. The conical hole was a little to small, i used a round small file to widen it up a little(too much). It fitted, but used a dab of superglue for peace of mind. I needed to file of a couple of mm's of the body as well, as the tip of the stylus would not reach the blank.
IMG-20180518-WA0011.jpeg
IMG_20180518_163558.jpg
Freq response was white noise with a steep lpf at 16khz. Seems like almost all the resonances that shouldnt be are gone.

Anybody knows where you can find a tool for setting the neumann type stylii?
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grooveguy
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Re: KNOP lathe DIY build

Post: # 50381Unread post grooveguy
Sat May 19, 2018 12:51 pm

Splendid progress, can't wait to hear the results.

Regarding your comment on my question about vertical tracking angle, that's a subject I knew nothing about until I came across another reference of it somewhere on this forum. Rather than trying to explain something I don't fully understand myself, I invite you to check out this recap of the original Noel Keywood article:
http://www.hi-fiworld.co.uk/vinyl-lp/37-technology/73-vertical-tracking-angle.html
...plus a thoughtful rebuttal from Geoff Husband:
http://www.tnt-audio.com/sorgenti/vta_e.html

A quick Web search just now failed to find the more explicit condensation of the 1979 Keywood article, but I have it as a PDF and can email it to anyone who's interested. Likewise, if anyone has the very original 1979 Keywood article, perhaps they'd share.

Again, I don't fully understand what's going on with this, but my first reaction to the original citation was that maybe we should be doing something about this in the design of our homebrew stereo cutterheads. Keep in mind that VTA has no implication in monaural recording.

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KNOP
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Re: KNOP lathe DIY build

Post: # 50382Unread post KNOP
Sat May 19, 2018 1:28 pm

Yes i've adjusted the head to a cutting angle of about 30 degrees, as I've heard there is a springback effect on laquers, so I presume on the myshank blanks as well. My first heads were around 12 degrees.
IMG_20180518_180018.jpg
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grooveguy
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Re: KNOP lathe DIY build

Post: # 50383Unread post grooveguy
Sat May 19, 2018 1:54 pm

I think you've got it. Either the VTA can be built into the head, or the vertical angle of the entire head adjusted to give the same result; that is, left-only or right-only groove modulation is not at 45° angles to true vertical from the record surface. Rather they sort of 'dig backward' with relation to the groove as it's being engraved. Your cantilever has an angled offset from horizontal where the stylus is secured. Then as you bring the stylus more toward vertical with respect to the record surface (by angling the cutterhead back), that angle built into your cantilever becomes the VTA.
Snap4.jpg
The importance of this is to match a similar angle in all cartridges, an angle assumed out of necessity because it would be extremely difficult to bring the cartridge magnetic/motor structure down to the same level as the stylus in the groove. Thus all cartridges angle back... like your cutterhead.

If I understand this concept correctly, cartridge manufacturers have standardized on something between 15° and 20° degrees, which is fundamentally what we should match. But the 'springback' you refer to is yet another factor in this complex equation. My limited math skills preclude much more than balancing my checkbook, so I'll defer to you on that.

Good job!
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KNOP
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Re: KNOP lathe DIY build

Post: # 50384Unread post KNOP
Sat May 19, 2018 2:29 pm

1526754335161.png
I think the vertical cutting angle is measured with the angle between the line between the point where the torque tube piano wire is fixed to the body, and the tip of the needle, and the record surface. Could be wrong though.
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KNOP
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Re: KNOP lathe DIY build

Post: # 50604Unread post KNOP
Sat Jun 16, 2018 9:53 am

Hi.

http://knoprec.be/opname%20neumann%20stylus.wav

A sample of recording with the latest prototype head.

Also some more 3D files for people interested. Includes cutterhead body with increased clearance from turntable, aluminium torque tube for mono stylii, and experimental torque tube files for 320 stylii (there are 2 slightly different hole sizes).
cutterhead files V6.zip
Had a glue malfunction between one driver and the funnel, but all fixed now. I did a measurement of the moving mass while at it. (add +0,5 gram moving mass per driver to the number)
IMG_20180616_104708.jpg
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grooveguy
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Re: KNOP lathe DIY build

Post: # 50607Unread post grooveguy
Sat Jun 16, 2018 1:23 pm

Absolutely spectacular. I thought you might be putting us on until I played to the end, cranked up the volume, and heard the characteristic needle-in-the-groove noise... way down in level, but inevitable and telltale. Otherwise it could have been a .wav ripped from the source CD (or whatever). Congratulations; job very well done!

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soeffingodly
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Re: KNOP lathe DIY build

Post: # 51139Unread post soeffingodly
Wed Aug 29, 2018 11:06 am

:hats off:

And thanks for sharing with the community. My friend is going to 3D print for me and I will be messing with this in the future alongside my programmer/engineer buddy. =)
"I wasn't lying. Things I said later seemed untrue."

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Xertz
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Re: KNOP lathe DIY build

Post: # 51173Unread post Xertz
Sat Sep 01, 2018 6:38 pm

Hey man, why do you use a 25 watt amp instead of a smaller amp like 5 watt amp or something?

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