The Secret Society of Lathe Trolls

Hi, Looks a lot like the old Astatic 89T ceramic pickups that were used in the Califone school record players. Maybe they could be driven to be an embosser. If so, that would require a high voltage, low current drive. Not a standard amp. https://www.thevoiceofmusic.com/catalog/part_detail.asp?PNumbe...

Hi, Great find! Thanks for posting. I was also interested in some of the other articles and ads. Its interesting how many of these companies are still in business and that some of the products are still being produced after all of these years. The last page shows an early ad for and HP VTVM. Not too...

Hi,

This could work for any head. Its just a way to create an EQ calibration curve. How severe that is depends on the head.

Mark

Hi Dave, Check out the excellent process that Spinnertown Blanks provided for developing the EQ for the VR head in this post: https://www.lathetrolls.com/viewtopic.php?f=1&t=10321 The same procedure would be used here. In effect, your are rolling the required curve into your EQ that flattens the ove...

Hi, That's basically what I did in my original plugin design. Rather than use the Bilinear Z transform with warping as is normally done, I used the matched Z transform that directly maps the poles and zeros into the z plane. It works well, but does deviate from the correct response as you get close ...

Hi, Great idea! Better results than I thought. The tilt is due to low frequency roll off. To get a flatter top at 50hz, you would need a low frequency cutoff of around 5Hz or even lower . The leading and trailing edge ringing seems like what you would expect if you hit the network with too steep of ...

Hi, Nice job making that work. The only issue I see with that approach is using a bunch of second order filters to approximate the amplitude response curve might not mimic the phase response of the cascade of first order filters used to define the standard. It would be interesting to see if that is ...

Hi,

Great idea and nice work getting it implemented! The track sounds awesome as well. I'll have to check out your setup sometime.

Mark

Hi Lukas, By damping , I mean adding some material to the driver cones and any of the push rods to try and reduce the peak caused by the main head system resonance. You can do this to the head as is. Something like applying a rubberized product like Plasti-Dip or maybe RTV Silicone, for example migh...

HI, Took a quick look at the file. I think what you are hearing is a peak caused by the head system resonance at about 1Khz that is excited by the cutting stylus as it cuts. See the attached spectrum plot. Its a pretty high Q resonance and since its in the mid range its more audible. I think you cou...

Hi,

Are the two playback captures done at the same phono preamp and audio interface gain so that we can determine the level of the background noise relative to program? It would be good to cut a 5 cm/sec ref tone followed by a silent groove to get an handle on the relative levels.

Mark

Hi, Its odd that its one channel only. Have you tried swapping the cables for L&R to see if the buzz moves from one channel to the other. I suspect a open ground on one of the cables. Adding the isolator, would make this worse, since there would no be no other way to complete the ground on the side ...

HI, As Sameal noted and your photos show, the damping material is suspect. It does look like the armature is a bit out of center. I've never worked on this model, but you can see the armature spring is a simple wire soldered and bolted to a tap on the right. It looks like you could adjust this, but ...

Hi, Is it possible your head has lost its centering and needs some adjustment. Also, if the screw is bent, maybe you need to replace it. Could be its rubbing. It doesn't take much to cause buzzing. It should be a standard US thread (maybe 0-80). What happens if you remove the stylus and only install...

Hi, This is a big project. What is your end goal here? On a DIY lathe setup, do you really need the time or cutting level gains that variable pitch provides? Do you tend to cut program material that has enough dynamic range that would benefit from variable pitch? Do you have your entire cutting syst...

Thanks for posting that. It was interesting. It sounded to me like the second recording started off very similar to the first and then the highs dropped out slowly. Maybe the damping heated up and changed its properties??

Mark

Hi Steve, That seems odd to me. Most moving iron heads have much higher main resonances. For example, the Presto 1C/D is up in the 4Khz range IIRC. I don't know the RCA heads well, but I wonder if it has lost its stiffness due to an incorrect mechanical adjustment or maybe metal fatigue?? How is the...

Hi,

You might get a better response if you indicate where you are located and what types of tubes you have to offer. Are they audio types like 6L6, EL34, 12AX7, KT88, etc.? Or, are they random TV and radio tubes.

Regards,

Mark

Hi Estacaco, 8 ohm is fine as long as you have an amp that can drive enough power into the head. The driver can only handle about 3 watts on a continuous basis. But, to cut a decent levels you could need 50-100 watts for short duration peaks to cut the high frequencies. When using an amp with that m...

Hi, The screws don't need to be very long. I only had 1/8" long 2-56 setscrews here and they worked fine. Once you get them so they just protrude from the surface, you are not moving them much higher. One turn is probably quite a bit of adjustment. A small change in height at the center of the platt...