Hara RM-805VA & RCA MI-11854-A cutter head. How much power🔌

[Liam walker 82]

Hi everyone,
Hope you are all well.
I have recently obtained a Hara RM-805-VA cutting lathe minus the cutter head. I have an old untested RCA mi-11853-a cutter head that is in tested which I am going to mount to the Hara lathe to get me cutting whilst I start plans to evolve over time into stereo cutting. I have information regarding my Hara that the output of the amp that drives the cutter head is 10w.
I’m trying to find out what power the RCA head requires for it to correctly function with a diamond stylus cutting onto PVC discs.
I have read somewhere that the the RCA lathe with this head uses an 18w amplifier to drive the cutter but i am most likely wrong.
It has also been suggested that this lathe applies the RIAA curve to the audio from a board inside the lathe. Can anyone confirm this?
I’ve attached some pictures for you to look at.
Many thanks!!

[markrob]

Hi,

Are you missing the Hara head? If so, then trying to use the RCA seems like a good way to get up and running. However, it may be a challenge to get the RCA head mounted and properly aligned to the centerline of the lathe. As far as RIAA goes, its a bit more complicated. When applying the RIAA curve as defined by the spec, its assumed your cutting system has flat velocity frequency response. That may not have been the case with the HARA head and the designer's probably have rolled the RIAA and head EQ into one. There is no doubt some EQ buried within the electronics to make the system reasonable flat up to some define limits (e.g. 50Hz - 5Khz). You also have to consider the possible differences in the impedances of the Hara vs. the RCA. From the spec you provided, the RCA is a 15 ohm head. If the Hara was the same or close, you can probably start out driving the RCA from the Hara amp. But, if the Hara was an 8 ohm head, then the Hara amp would only provide 1/2 of the rated power into 16 ohms. 10 Watts into 8 ohms is already on the low side. If you manage to get the RCA head to mount, I would ditch the Hara electronics and drive the head with an external amp capable of running up to 50 watts into 16 ohms. That will give you plenty of headroom and maybe enough extra power to push the upper frequency response a bit past the published 7.5Khz. Since that head appears to have flat response, you would just need to add the RIAA curve and perhaps some extra high end boost to flatten the response above the 7.5Khz max stated in the spec sheet. You will also need to see if the RCA head needs rebuilding. After sitting for many years, it is likely to need some TLC. That should not be too big of a deal. Hope this helps.

Mark

[Liam walker 82]

Hi Mark,
Thankyou so much for your reply and the fantastic information.
This has really helped me! I agree with using an external stand alone amp to drive the head. EQ is not a problem for me as I run everything through a vintage Ex BBC Calrec j series console.
My plan is to record live musicians in my studio direct to disc.
Nothing super Hi Fi but something original artists can come for the experience and take home a vinyl record of the session.
Aswell as this I have lots of very nice vintage outboard mastering equipment. So I plan to help friends out with very very small limited runs aswell as location recording at a couple of local cafe bar music venues. Acoustic type vibe.
Regarding the rca head I am confident I can do any work required to get it up to speed. I just don’t want to blow it up.
I have a really nice ex bbc quad power dump amp for studio monitoring but it’s 100w per channel. I was going to use ch1 to monitor audio and channel 2 to drive the cutterhead.
2 mono signals from my mixing consoles through my limiters snd compressors then to disc.
I’m not a fan of digital recording. I’m very much more of a physical in my hands kind of guy.

[socialroots]

Greetings,just wanna chime in on using diamond to cut pvc, in a nutshell,diamond will cut pvc,but not sure how many pvc blanks u gonna cut before you chew up that diamond.
If money isn't a problem ,then go for it. Getting and education cost money,learning bout the cutting game I guess isn't any different! Everyone's gotta pay their dues in this game.
Markrob made a very important point about the alignment issue.it could make or break your cutting aspirations.
Maximum respect,
Patrick