Don't shoot new guy!!! I have some basic questions

[johnoisamanc]

Hi,

I'm not gonna refer to myself as a newbie, that's a Gearslutz term & well... enough said on that. I've also had some basic disc cutting experience/knowledge in the past & trying to get back into it, I need to relearn some of the basic workflow & technical points, I have a couple of questions I could do with going over and would appreciate any help, even if it's pointing me in the direction of an older post or a good reference. It's not easy finding good info and you guys know best.

I'm also gonna ask all these questions with a VMS-80 in mind as it's the only lathe I know (I use the term 'know' loosely).

So here are my few dumb-ass questions to get me re-started:

1. Why do I need to send the preview signal to the cutter head? I get that a feedback loop is fed back into the amp to lower distortion but if it's for the purpose of monitoring the audio before it's cut or for the pitch computer to look at the advanced signal then why does it go to the cutter-head first & not the amp, which what I remember is fed the mod? I can remember the delays times for different playback speeds etc.. just need to remember the point- fully.

2. The RIAA filter, where in the signal chain does it empathise & de-empathise??

3. I can't remember why I have to align the crosshair with the stylus in the side microscope, it's so the swathe discharges into the tube correct maybe, can anyone shred some light on this?

4. How does the lathe know the size of the disc i'm cutting? Is it purely from changing the size on the turntable itself or is there an alignment process.

5. When I cut markers and fast grooves, what exactly is it cutting, silence with a large land so that it's clearly marked on the disc ?


Thanks for any help, I know i've asked a fair few questions here.

[opcode66]

Welcome to the board!

1. Preview signal is only required for lathes with Pitch/Depth computers. If you are using a fixed pitch lathe then you need not a preview signal. Preview signal is sent to the P/D comp FIRST, then delayed signal is sent to the cutterhead. Delay times are dependent on the particular p/d comp you are using. 0.84 at 45rpm and 1.1 at 33rpm for stock Neumann p/d comp. The point is to pack the grooves tightly at times of lower volume and then expand back out to base pitch when louder. That way you can get the most play time out of a side possible dependent on the program material. Also, with signals that have a lot of stereo separation, the depth control is there to maintain a minimum groove depth.

2. Emphasis on recording. De-emphasis on playback.

3. What???? For a Neumann there are two scopes. One on the lathe that is for viewing cut grooves. The other is a standalone scope that the cutterhead goes on to. You use it to orient and align the cutting stylus when inserting a fresh one into the cutterhead. You align the stylus because it has specific facets and therefore an orientation. There is a front and back side. You also want to make sure the mirror surface is straight horizontal. Otherwise you grooves won't be cut correctly.

4. On a Neumann, the cutting process is completely automatic. So, it does in fact need to know what size disc you are cutting. This is determined by connections in the PS66 plug box. Those connections determine which microswitch is monitored in order to start the lead-in groove. I installed a mulit pole switch into mine so I can select the desired diameter. Also, the suction table (chuck table) where the blank goes has a setting to adjust what holes are opened for air flow. So, the diameter is set there too. Most lathes however have no setting at all since the start of the lead-in and the lead-in itself are controlled by the operator. The size of the disc has absolutely no bearing on the calculations for p/d computation fyi.

5. Uhhhh yeah. Didn't think that was much of a mystery. Unmodulated groove. Lower than usual LPI.

Ask whatever you like.... Ask a lot.... We have answers.

[concretecowboy71]

@opcode:

I don't think you caught the part where he is talking about a VMS80.

There are two scopes and I don't think it has controller boxes.

The second scope on a VMS80 is for watching the chip pick up.

That is why you would want the stylus centered.

[concretecowboy71]

A VMS80 is a completely different machine than the 60/66/70.

The answers to some of these question will ONLY apply to the 80. If you are seeking more general information, I would suggest asking the questions in a more general format unless you will be using or owning an 80. If you are new to all of this, more general information is going to help you a lot more that specific info about a machine you may or may not be using.

[johnoisamanc]

Thanks for the replies guys..

Much appreciated.

[opcode66]

Yes, I did totally glaze over that detail. Ok, well, ignore that which doesn't apply...

[johnoisamanc]

The point is to pack the grooves tightly at times of lower volume and then expand back out to base pitch when louder.

Cool, so the land is increased when the groove is louder & shorter when lower in level, obviously to maximise the amount you can fit onto one disc.

Emphasis on recording. De-emphasis on playback.

Sure but where is this filter in the electronic chain? I know not everything is modular like a tape machine to be honest that's all I probably need to worry about for know.

This is determined by connections in the PS66 plug box

Where is this plugbox? In an operational sense whats the best way to tell the cutter-head where to cut the lead in groove? Sorry if i've misunderstood this. I do have the setting for the asir holes are you saying this could potentially do both?

Does anyone have any tips on how to calibrate recording levels using a VU? Is it like tape in this sense, what analogies can be drawn from other ways of working?

Thanks

[opcode66]

The RIAA EQ curve is prior to the power operational amplifier.

Not sure if an 80/82 model has a programmer box. This might be specific to 60/70's models.

[concretecowboy71]

Does anyone have any tips on how to calibrate recording levels using a VU? Is it like tape in this sense, what analogies can be drawn from other ways of working?

Get a NAB or equivalent test record to get the proper levels for setting up your signal chain.

The standard for set 0 on your meters is the standard reference level of 7cm per second peak velocity.

Some guys who need to cut hotter choose to use a different ref level for 0, but if you are new, you are gambling on smoking your cutter head by going hotter.

I would suggest buying a copy of the Larry Boden book, Basic Disc Mastering. It answers a lot of questions in a very short and uncomplicated way.

[jjgolden]

Also if you are using a turntable in the studio as your reference point for your cutting levels, you can use this interface box
to get from -10 consumer to +4 pro. There are also left & right level tweakers on the front for calibrating.
So, calibrate playback levels of your turntable with the easily obtained "Ultimate Analog test record", then adjust your cutting levels and overall approach around this standard. It's not identical to the 1964 nab record, but it's within 1db L&R at 1k. (I have both)

http://www.bhphotovideo.com/bnh/controller/home?O=&sku=297763&is=REG&Q=&A=details

http://www.musicdirect.com/p-8523-ultimate-analog-test-lp-analogue-productions-test-lp.aspx

JJG