Speed

This is where record cutters raise questions about cutting, and trade wisdom and experiment results. We love Scully, Neumann, Presto, & Rek-O-Kut lathes and Wilcox-Gay Recordios (among others). We are excited by the various modern pro and semi-pro systems, too, in production and development. We use strange, extinct disc-based dictation machines. And other stuff, too.

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Fred187
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Speed

Post: # 31390Unread post Fred187
Sat Sep 13, 2014 12:45 pm

I'm still undergoing my hunt for my first lathe, and was concerned over speed. Obviously most of the old hardware runs at 78, with a few that do 33⅓. I'd like to do 45, but haven't seen anything capable of this (so far). Obviously there's the possibility of modifying the motor, but I'd prefer not to have to get in to that (will have my hands pretty full with new things to learn as is).

I'll be mastering from a Studer 1/4" recorder, and it occurred to me that I could potentially just slow the tape down 26%, then cut at 33⅓. Played back at 45, it should sound right (in theory). I'm sure I'm neglecting something obvious, though. What problems could this cause?

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tragwag
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Re: Speed

Post: # 31391Unread post tragwag
Sat Sep 13, 2014 2:50 pm

I do the slowdown for 45 RPM on my 6N.
though it should be noted that there is a 45 speed adapter available for the 6N, its kinda a pain.
Either impossible to get ON, or impossible to REMOVE (ask PIAPTK).

I use the audacity "speed" plugin to get EXACTLY 45 -> 33 1/3 speed adjustment

When cutting slowed down audio, you lose the lower octave of frequency range.
I compensate with an EQ band, and it's normally fine.
I emboss onto polycarbonate so the results are not "hifi" in the first place, so most people either don't notice or don't care if the lower octave is a little askew.
That all being said, I think I do a great job of EQ-ing the audio to translate nicely.
making lathe cuts on a Presto 6N, HIFI stereo cuts on vinylrecorder
at Audio Geography Studios, Providence, RI USA
http://www.audiogeography.com

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Steve E.
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Re: Speed

Post: # 31393Unread post Steve E.
Sat Sep 13, 2014 4:15 pm

If the lathe in question has 78 and 33 speed on a single shaft as on a 6N, and you don't usually need the 78 speed, you can do a mod thusly, by creating a new replacement shaft and pucks, with the help of a machinist. (Thanks Alan Graves):

http://www.lathetrolls.com/viewtopic.php?f=9&t=3149&p=20651#p20647

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Fred187
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Re: Speed

Post: # 31396Unread post Fred187
Sun Sep 14, 2014 7:57 am

tragwag wrote:When cutting slowed down audio, you lose the lower octave of frequency range.
Would this problem be the same when the speed is adjusted using an analogue machine?

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Steve E.
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Re: Speed

Post: # 31410Unread post Steve E.
Mon Sep 15, 2014 8:59 am

I doubt the sound source, digital or analog, is the problem. Tragwag is probably describing either the RIAA curve being thrown off (do a search on RIAA curves) or the limitations of the cutterhead (or, the changed audio hitting its resonances differently).

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tragwag
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Re: Speed

Post: # 31423Unread post tragwag
Tue Sep 16, 2014 12:23 pm

it doesn't matter the source.
like steve said, it's a mechanical restriction.
The presto heads can cut down to about 50 Hz, but slowed down your 100 Hz signal is now much lower (I don't know the math), so it's significantly decreased upon playback.
You would need some kind of low end compensation cutting slowed down audio
making lathe cuts on a Presto 6N, HIFI stereo cuts on vinylrecorder
at Audio Geography Studios, Providence, RI USA
http://www.audiogeography.com

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Fred187
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Re: Speed

Post: # 31432Unread post Fred187
Wed Sep 17, 2014 7:59 am

Okay, I see now.

So if I was to cut sped up audio at 78 for 45 playback, I presume there would be a similar problem for the higher frequencies.

I think I'm going to go for a Telefunken Ela A107/1, unless a better option presents itself. This only cuts at 78, so I'll just have to modify the motor (or install a new motor, if it's simpler).

What kind of frequency response could I expect from such a machine? I'm assuming it wouldn't be exceptional. Are there methods one can use to improve the frequency response?

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rsimms3
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Re: Speed

Post: # 31435Unread post rsimms3
Wed Sep 17, 2014 8:49 am

Are you located in the U.S.? If so, I'd recommend holding out for a Presto. There's been a rash of K8s on eBay recently, one selling BIN for $450. There's another one up for auction now. Looks like it includes the capstan sleeve to run both 33 and 78 (default is 33). So, you could get a machine in the U.S. for lower shipping, less transit time, two speeds, and more folks with knowledge about the machine you are working with to ask questions.


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Fred187
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Re: Speed

Post: # 31436Unread post Fred187
Wed Sep 17, 2014 9:50 am

Yes, I was going to get a K-8. If I can get a good price, I'd be tempted.

I'm in Scotland, though, so the main issue is the 50Hz to 60Hz conversion. If I'm going to have to do mods come what may, I'd rather just get a machine in Europe.

That is a very attractive price at the moment, though.

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rsimms3
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Re: Speed

Post: # 31437Unread post rsimms3
Wed Sep 17, 2014 11:21 am

Ah, you would definitely be better off with a 50Hz native machine than converting a 60Hz machine based on the little bit I've read here on what goes into such a conversion. Good luck!

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Fred187
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Re: Speed

Post: # 31441Unread post Fred187
Wed Sep 17, 2014 1:14 pm

Thank you!

I think I'm going to need it - there don't seem to be too many lathes for sale here in Europe.

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Steve E.
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Re: Speed

Post: # 31442Unread post Steve E.
Wed Sep 17, 2014 2:10 pm

Fred187 wrote:Okay, I see now.

So if I was to cut sped up audio at 78 for 45 playback, I presume there would be a similar problem for the higher frequencies.
Yes, that would be worse.
Fred187 wrote:I think I'm going to go for a Telefunken Ela A107/1, unless a better option presents itself. This only cuts at 78, so I'll just have to modify the motor (or install a new motor, if it's simpler).

What kind of frequency response could I expect from such a machine? I'm assuming it wouldn't be exceptional. Are there methods one can use to improve the frequency response?
I don't know anything about that particular machine.

Here's something more about Prestos, since I mostly know about Prestos (specifically 6Ns):

1) With some EQing, and cutting at the playback speed, a restored 1D cutterhead (and maybe a 1C head, too) can give pretty great mono fidelity. If you are using the RIAA curve, you will find there is an additional, correctable bass rolloff that starts below 200 hz:

100 hz is -2 db
70 hz is -3.5 db
50 hz is -6 db
30 hz is -10 db

In the upper register, 14 khz is only off -1 db on my 1-D, and 15 khz is -3 db. That's pretty darn good. There are all kinds of other peaks and valleys in the head. They can be corrected for a nearly flat response.

The other thing you may have to contend with is wow and flutter in the motor, and other rumble from the motor making its way into the recording. I think this may be more prominent on the portable models like the K8.

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EpicenterBryan
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Re: Speed

Post: # 31447Unread post EpicenterBryan
Wed Sep 17, 2014 11:20 pm

Fred187 wrote: I'm in Scotland, though, so the main issue is the 50Hz to 60Hz conversion. If I'm going to have to do mods come what may, I'd rather just get a machine in Europe.
Don't give up on this yet. I should have some test results in the next 2 weeks from my project and I'm sure it will help your decision. I have an 8D which cuts a bit slow at 33 1/3 on USA 60hz mains. The motor is fine, pucks look good, adjustments on idler tension are fine but who knows what combination of 50hz and 60hz parts are in there these days. So, after looking into the motor details, I have decided to go with a variable frequency drive to adjust the RPM of the motor to correct the RPM error. I also have the special 33prm to 45rpm adapter that goes over the shaft so the 33 rpm position will run faster ... but again with an error in the 33 rpm speed and the extra hassle of removing the platter to install the adapter on an 8D, I opt for another solution.

If this VFD (variable frequency drive) works out to adjust the speed for 33 1/3, then there is nothing that says I can't crank up the frequency on the motor so the 33rpm position also becomes 45rpm with no physical changes to the lathe or damage to the motor. These VFD drives are very sophisticated and they also adjust the voltage to the motor when the frequency is changed.



The only reason this path will work is that the 6N , 8N and other such lathes use a Bodine motor that is synchronous. That is, the RPM of the motor is tied to the frequency of the input AC. In America, at 60hz, the Bodine motor runs at 1800 RPM at 60hz. But on your side of the pond on 50hz mains, it runs at 1500 RPM as I recall (correct me). So the rest of the mechanical bits that transfer the rotation to the platter need to be scaled differently in America and in other locations where the frequency is different to get the same platter rotation. It's all about the AC input frequency on a synchronous motor.

Most VFD drives are designed for industrial applications. Most are designed for 3 phase motors at high voltage. But there are some out there that are designed for lower power (fractional Horse Power) motors like what we need. These ones are single phase, and 120VAC in and out. Here is a link to one I bought on Ebay as noted above for my application:

http://www.invertekdrives.com/client-uploads/download-manager/user-guides/82-E21PH-IN%20Optidrive%20ODE-2%20Single%20Phase%20Output%20User%20Guide%20Iss%203.10.pdf

Please don't buy one on my word until I have had time to check it out...

Bryan

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Fred187
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Re: Speed

Post: # 31490Unread post Fred187
Sun Sep 21, 2014 7:47 am

Thank you, Bryan! This seems to be a very elegant solution.

I was also considering the possibility of fitting a cutterhead to a Technics deck (perhaps with a vacuum platter), but I'm sure this would present its own host of problems.

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EpicenterBryan
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Re: Speed

Post: # 31511Unread post EpicenterBryan
Mon Sep 22, 2014 11:36 pm

Fred187 wrote:Thank you, Bryan! This seems to be a very elegant solution.
Ok, I've got a quick update for you. I got the unit today, set up a few parameters via the menu structure and was able to solve my speed issue today. I think the additional applications will be of interest so I'll work up a new thread this weekend. Let me give you the quick version...

My 8D was recording fast. The motor is synchronous and the RPM relates directly to the frequency of the AC mains. But there is also a shaft adapter on the motor which may not be the correct size, and there are rubber pucks that may not be the right size either. So I decided to not mess with the mechanics not knowing specific dimensions of the parts in question.

As I mentioned I decided to buy a variable frequency drive to change the AC frequency to correct for the mechanical unknowns.

It worked.
IMG_2898.JPG
I added a pot (shown in my hand) to fine tune the frequency while looking at an RPM speed / strobe disc and as it turns out I needed to drop the frequency down to 58.6 Hz (from normal 60hz line frequency) to get the right RPM. I don't really care what is wrong with the mechanics at this point because it's fixed. What this also means is that if I drop the frequency down for the same setting on the lathe - all the sudden I can cut at 1/2 speed. Oh, and the 78 position that I have not checked yet can also be adjusted if in error. But it could also be adjusted down to the correct frequency for 45 RPM. All this without messing with adapters, pucks and such.

It gets better, a device like this could be used to make a gizmo purchased from one side of the pond work on the other side of the pond by changing the frequency. You would still need the correct version for your application but I'll hit that in another thread.

For fun, after setting some parameters up in the controller, I ran the motor down to 10hz, and up to 66 hz (10% over USA mains but chickened out past there). The motor was just as happy throughout the range with no extra heat. Awesome.

So again, don't give up! Now I can say buy what you really want and you can make it work (for a extra expense). Now the final issues related to cost. What I bought could be as high as $700 USD if purchased from an industrial automation dealer. What I bought was surplus on E-bay and the seller had several at $150 USD. I sent an offer at $100 which was accepted (plus shipping). Sure did the trick for me...and the price was right.

Bryan
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