KNOP lathe DIY build

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Re: KNOP lathe DIY build

Unread postby Gus » Mon Mar 20, 2017 7:33 am

Hi
Very nice improvement of your cutterhead, did you use carbon fibre as pushrods?
Keep it up!
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Re: KNOP lathe DIY build

Unread postby grooveguy » Tue Mar 21, 2017 1:07 am

VERY encouraging results, do keep us posted. Sounds fantastic.
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Re: KNOP lathe DIY build

Unread postby KNOP » Tue Mar 21, 2017 1:18 am

To Gus: Yes that is with the carbon fibre pushrods. They weight 0.3 grams instead of 1 gram for metal pushrods.

I have some days leave from work this week, I will install a new stylus and try to get the noise floor as low as possible, also try out the heating. On my current stylus the heating wire has come off.
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Re: KNOP lathe DIY build

Unread postby KNOP » Wed Mar 22, 2017 3:54 pm

Hello.

I've changed the stylus for a new one, took me most part of the day getting everything dialed in again. Needed to re-EQ the cutterhead, made some improvements on the cutterhead connection to the suspension mechanism, reajusted the counterweight and so on.

Noise floor is much better, recorded at 45RPM 140LPI this time. The wow issues are much less pronounced.
https://clyp.it/xvrlkgvh
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Re: KNOP lathe DIY build

Unread postby grooveguy » Wed Mar 22, 2017 4:17 pm

Boy, that sounds magnificent to me; if I can achieve results like that I will be happy as a clam. Remarkable stereo separation. In your closeup of the head, it appears that the 'torque tube' (or whatever you call the member that connects the stylus holder to the back of the head) goes straight back; that is, there is no obligatory 20-degree angle that Noel Keywood says is necessary in his paper. Any comment?

Question: You speak of a counterweight. Are you using a counterweight, exclusively, to support the head and set the depth of cut, or do you have a spring of any kind in use for that? Also, can you divulge: 1) distance from the stylus to the vertical pivot point of the head, and 2) height of the pivot point above the disc surface? (Don't tell if you'll have to kill me afterward, but I'm collecting this sort of info.)

Keep it up!
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Re: KNOP lathe DIY build

Unread postby KNOP » Thu Mar 23, 2017 4:43 am

In your closeup of the head, it appears that the 'torque tube' (or whatever you call the member that connects the stylus holder to the back of the head) goes straight back; that is, there is no obligatory 20-degree angle that Noel Keywood says is necessary in his paper. Any comment?

Well this is because I didn't know about this angle until recently. I'll have to do some research in this matter.

Question: You speak of a counterweight. Are you using a counterweight, exclusively, to support the head and set the depth of cut, or do you have a spring of any kind in use for that?

Only a counterweight at the moment. I made provisions for using a spring, but have not experimented with that option. The problem I have with the weight is that the wires on top of the cutterhead and the suction tube have quite an influence in the weight of the downforce, and its quite touchy to dial in.

Also, can you divulge: 1) distance from the stylus to the vertical pivot point of the head

The stylus to the V spring is 22mm (The V spring is the vertical pivot point I guess?)

, and 2) height of the pivot point above the disc surface?

About 10mm
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Re: KNOP lathe DIY build

Unread postby grooveguy » Thu Mar 23, 2017 12:53 pm

Okay, thanks for that info. As far as the pivot point goes, there seems to be quite a range among commercial machines, and even a wider one among homebrew ones. Mechanical engineers will argue this physics, but all these recorders seem to work just fine. I was looking for some magic 'golden mean,' but perhaps it's not as terribly important as the purists make out.

I thought I had posted the Keywood paper here somewhere, but can't find it. If you need it, it's here:
https://www.dropbox.com/s/140rmbnaulsl2xa/Vertical%20Tracking%20Angle.pdf?dl=0

An old Fairchild lathe I had years ago used only a counterweight, and I recall the same problem maintaining a constant depth of cut because of the vacuum hose and wires. I think I clamped those to the carriage near the pivot point, so at least the head was no longer sensitive to changes in the dressing of the longer run to the chip jar and amplifier. A spring allows adjustment on-the-fly, of course, but it does raise the resonant frequency of the vertical component, and if the 'Q' of the system is high, can lead to nasty vertical oscillation. I guess part of the trick is keeping the length of the spring as long as you can so that the stylus pressure doesn't change much as the vertical position of the head changes. I don't know about these mechanical analogies of equivalent electrical circuits.

But the bottom line is, of course, that you are getting splendid results. Good job and good luck!
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Re: KNOP lathe DIY build

Unread postby sifis1983 » Sat Mar 25, 2017 8:44 am

Hi,

Congratulations! That sounds excellent to me! And thank you for your great information...

Some queries:

What about the "new stylus" ? What kind of stylus you use now and what before?
Why you "re-EQ" your cutterhead? Is all about the resonances of your design? or you just compensate some frequencies to "flat" response, after iRIAA?
Is this audio example cut in PVC?

Regards,
Sifis
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Re: KNOP lathe DIY build

Unread postby KNOP » Sat Mar 25, 2017 3:34 pm

Hey,

The stylii are both from myshank, grampian type. The old one had a broken tip. The eq is for flattening the resonances and irregularities of the cutterhead, I do not use iriaa, as it is compensated directly via the fabfilter plugin. Its all cut on blanks from myshank as well. I had to redo it because of different weight on the stylus.

Took me and a friend about two days to get the weight and suction working reliable and consistant. Made about 20 records, ranging from meh to pretty awesome.

Added gmonobass in the signal chain, also JB multiband compressor for hf limiting, and a lfp and hpf at the end. The hf limiting goes a long way reducing distortions in the high frequencies.

Still looking for decent (free) vst plugins for de essing and stereo expansion.
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