The Secret Society of Lathe Trolls

Aussie0zborn · Joined: 11 Mar 2006 Posts: 82 Location: Australia

After trolling through this forum and adding my two cents' worth, I have decided to set-up my Presto 6N with Grampian cutterhead.

I need an amplifier to suit.

Has anybody done this and does anybody have any advice, tips, etc.????

Lewis D

Hey there,

about a cutting amplifier for the Grampian head. I use the origianal Grampian cutter amp type R.A.7 but these were made in the 50s and are quite rare considering i have never seen another one. Gotham Audio Corporation in America made amps to go with the head but im not sure wot there like, there probs really good tho. There woz a gotham one on ebay a few weeks ago which didnt sell so it could come up again. But if your not looking for a specific tube cutter amp, I am not sure but I think just a normal Power amp might work. However on cutter amps there is equilisation which compensates for the RIAA curve when its reproduced so, i think you preamp would have to do the opposite of the RIAA curve before it goes into the power amp and i am not to sure about how you would do this, Some sort of box ting? Do not give up the grampian heads are amazing when they are set up correctly!!

Which model is your Grampian head?

Anyway I hope this helps,

Lewis, London

cuttercollector · Joined: 11 Jun 2006 Posts: 307 Location: San Jose, CA

For any feedback head, you need to introduce the feedback coil signal OUT OF PHASE to the amplifier you are driving the head with. Amps will vary and ideally you want an amp that has little phase shift and is not prone to oscillation on its own. There are probably specs for how much feeback this cutter requires and how much power it will take. Remember, in the days of tube amps when your head was made, 50 watts was cosidered pretty high power! The level of the discs you cut and the distortion will be controlled by how well the amp and feedback loop work. You can use a mixer to introduce both the feeback coil output and the signal to the cutter amp. You could probably pre-emphasisze the program material with some sort of eq to the opposite of the RIAA playback curve. Don't eq the feedback signal with the program signal. In the older disc cutting amps, the record eq MIGHT have been part of the overall feedback loop or done seperatly. Either way will effect the curve of the recording, though I think if you did choose to eq the feedback coil loop from the cutter and leave the program input "flat", the curve would be the same as the playback RIAA curve (perhaps use a commercial magnetic phono preamp off the feeback coil?) because it effect is inverted because it's in the negative feedback loop. Be careful in your experimentation, there are many ways to blow up heads and amps!

dhersk · Joined: 03 Jun 2006 Posts: 5

Lewis....

I tried emailing you directly and replying to your earlier post. I am intrigued that you are starting at an early age, as I did myself. I had the Grampian D head and the Gotham Amplifier. My system was modified by Howard Holzer (HECO) in California.

I had the 6N lathe, in fact two of them. One was fitted with the Grampian C head which is identical to the D except for the feedback coils. The Gotham amp had various eq settings.

I found by using different viscosities of damping fluid for the type D head this effected the sound qualitys. I would be interested in hearing more about what you are doing with your hobby. You can contact me directly at dhersk@hutman.net

chris muth · Joined: 21 Jun 2006 Posts: 3 Location: New York

Hi Aussie,

One of my best friends is Al Grundy. He has been cutting records for around 60 years and used to be the president of the Audio Engineering Society. He has a shop full of Presto, Grampian, Neumann, Scully, etc. etc. parts and amps. He can also rewind yer cutterhead and supply you with schematics and such. Whatta guy!

http://www.cutterhead.com/

Aussie0zborn · Joined: 11 Mar 2006 Posts: 82 Location: Australia

Thanks for the replies. I will check the model number of the head. I have emailed Al Grundy a few times and each time... no reply.