The Secret Society of Lathe Trolls

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

I Have Circuit and Info Could It Be Posted On Here[/code]
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JayDC · Posted: Thu Jun 21, 2007 12:24 pm Post subject:

cool.. post it..

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

http://sound.westhost.com/project80.htm

This link should help

It sums up what the filei s all about without all the Math!
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cuttercollector · Joined: 11 Jun 2006 Posts: 254 Location: San Jose, CA

Or this:

http://www.mcminone.com/product.asp?catalog%5Fname=MCMProducts&category%5Fname=3829530&product%5Fid=50%2D7240

It is important to remember that these sorts of devices beside giving you the inverse of RIAA playback, ALSO attenuate from standard line level (500-700mV.) to phono level, about 100 times less (2-4mV.) This means for what we would use them for you would then need to go from the output of the inverse RIAA device back into a flat (no eq.) high gain input like an insturment or perhaps mic. input to get enough gain to then drive your power amp for the cutter.

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

the point of the post is to show a simple RIAA inverse curve circuit which could be coupled to a common base amp at front for low Z input, or collector amp fo high Z input, small driver amp for output to mixer.

I have many small(Building block) circuits and am currently setting up me presto 8N
Could do with a section for circuits ect..
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cuttercollector · Joined: 11 Jun 2006 Posts: 254 Location: San Jose, CA

Yes and thanks for both designing and sharing this info.
Unfortunatly, probably a majority of people on this forum, including myself, are not capable of active filter design. or fully understanding how to impliment amp designs with op amps, much less discrete transistors or tubes. I am more of a systems level, plug boxes together sort, or if I have to, I can follow a detailed schematic designed by someone else, to build what is needed or repair something. The design of the electronics needed to drive a cutterhead, especially a feedback one, with proper inverse RIAA EQ and compensation for the frequency characteristics of the head itself is not trivial. Disc cutting and playback are the simplest of concepts, but to do it to the state of the art level it had evolved into is not easy!

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

I am only just getting into cutting. but I read and whot seem to be common is that the BEST cuts use very little compreson or EQ only RIAA curve, clean basic analogue systems, sorce,RIAA,mixer,amp,head. Read a article on a guy who worked at JVC he said the best sound on the trillon dollar mastering consol was on bypass and same on some things in the neumann rack. CLean seems good. I

Like you have found there is not a lot of easy circuits on the net about cutting most are 50 and 60 makes them hard for me(Im electronics en.) strange inductors and Q values,resonances ect. That Why I Posted. if intrested I could Post other stuff eg. simple power meter at 4 or 8 ohms, headphone amp, simple mixer ect.
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motorino · Joined: 24 Aug 2005 Posts: 179

cuttercollector · Joined: 11 Jun 2006 Posts: 254 Location: San Jose, CA

Yes, the ideal would be a system that needed no compensation eq other than the RIAA curve. Just as with speakers, a flat neutral system that adds no coloration of it's own and was designed that way mechanically speaking would be best. Then you could add whatever your production values dictated in terms of eq, compression etc.
But in the real world people use microphones for example, for their characteristic "sound" and most cutters have a "sound" too. This almost always stemming from their deviation from flat broad frequency response and their particular charicteristic distortion when pushed hard.
some have more of a "sound" than others and people use this sometimes to good effect, just like with microphones, or guitar amps are a great example of this. No guitarist typically wants to play through a completly flat 20-20K speaker system that won't distort at all no matter how hard you push it or loud you play. That would be an atypical electric guitar "sound", like plugging it into the mixer directly and having all the eq flat.
I think though that the reason I am into discs and disc cutting is that somehow even with their real world faults, nothing sounds closer to "real" than a good disc recording.
Anyway, thanks for the circuits and being involved with our quirky art.

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

From what I have found for grampian D feedback

250W min amp for headroom
500omh drive coil
20 ohms is for feedback seems very low Z

but mine has 4 ohm drive and slightly higher feedback 27 ohm.
Seem that you can wind coils to suit amp and electronics.

If I can find specs will post.
Am just simulating a amp power meter reading Power in Watts+dBm and current for monitering head would be a good post. Very usefull
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Lewis D · Posted: Mon Jun 25, 2007 6:11 am Post subject:

Hey, I have the manual for the grampian amp that was made for the type D head. Includes power supply and schemtics. If you would like, I could email them to you.