The PM-SC99 (The poorman's SC99, my first homemade head)

[Self-lather]

Wow Mike, thats very nice! Good to see other experiments. How is the sound quality of the head? I'm slowly working on my attempt #2. Some day when I get to that point I'll post some new pics.

-Thomas

[cymbalism]

does anyone have the photos of this diy project? i'm itching to get started on a stereo cutting head and i'm working together with some local electronic genius to get this to happen for all of us who have prestos or rekokuts.

any help would be great as i only have a few diagrams and schematics so i'm looking for ideas from other people and coupling them with the westrex design to get a smaller version made. i love my grampian type-c but i can only get so far with it, it's time to expand...

[fusionkid]

markrob:

I'm looking to add feedback to my head using an cheap electret condensor mic capsule. I've tried using magnetic windings as most pro heads do (see US patent 2522567), but its hard to eliminate cross coupling between the driver and feedback coils. My thought is that a capacitive pickup will not suffer from this problem.

I've been looking at yours (and other) projects with great interest, i intend to embark on my own soon. Thinking about getting feedback, you can get magnets with holes in so they can be screwed down. What about fitting small one of these on rod between tip of your tweeter and the stylus, then winding the coil on a short bit of plastic pipe mounted so that magnet moves inside the tube.
I've been studying neumann cutter from what i have seen it looks like they must have seperate magnet for the feedback coils although that part is not moving iron as i am suggesting. I'm new to this field, so may have missed something, seems possible.

[markrob]

Hi,

I want to get back to this head and modidfy it for the 6N. Very interested in any help or colaboration.

I've been looking at implementing the Fairchild system for feedback. This method uses an RF inductance bridge running at 10Mhz excitation. This gets the feedback signal out of the head actuator drive coils. Neumann whent to great lenths to solve this problem using magnetic shielding.

Before I get there, I'll have to look at the mechnical aspects of the design to try and rid the head of secondary resonances so that the feedack is eiasier to apply over the entire audio range.

[blacknwhite]

I've been looking at implementing the Fairchild system for feedback. This method uses an RF inductance bridge running at 10Mhz excitation. This gets the feedback signal out of the head actuator drive coils.

Markrob,

FASCINATING work!

RE: Your above post: do you mean Fairchild applied a 10Mhz carrier to the drive coil signal in order to prevent the feedback coils from undesireably magnetically interacting with the drive coils?

Or did I totally mis-interpret?

- Bob

[cuttercollector]

Hi,

I want to get back to this head and modidfy it for the 6N. Very interested in any help or colaboration.

I've been looking at implementing the Fairchild system for feedback. This method uses an RF inductance bridge running at 10Mhz excitation. This gets the feedback signal out of the head actuator drive coils. Neumann whent to great lenths to solve this problem using magnetic shielding.

Before I get there, I'll have to look at the mechnical aspects of the design to try and rid the head of secondary resonances so that the feedack is eiasier to apply over the entire audio range.

Not that the RF feedback would not work for a 45/45 cutter but the Fairchild was also Lat./Vert. Sum/Dif. M/S system which I personally think was a fascinating way to go. Used big transmitting type tubes in its amps. You can hear it on some early 60s DOT records which proudly announced on the back that they were cut with the Fairchild system.

BTW, how did Westrex deal with this issue of electrical transmission between the drive and feedback coils?

[markrob]

I've been looking at implementing the Fairchild system for feedback. This method uses an RF inductance bridge running at 10Mhz excitation. This gets the feedback signal out of the head actuator drive coils.

Markrob,

FASCINATING work!

RE: Your above post: do you mean Fairchild applied a 10Mhz carrier to the drive coil signal in order to prevent the feedback coils from undesireably magnetically interacting with the drive coils?

Or did I totally mis-interpret?

- Bob

Hi Bob,

Thats my understanding. The system is described in the AES book Vol 1 and shows the entire schematic. This is a posistion feedback system by nature, but its easy to convert to velocity. It would seem to have merit in this app because the carrier is so far removed from the baseband audio.

THe Nuemann and Westrex head desingers had to work hard to keep the drive signal out of the feedback. I thnk that the rf approach may turn out to be easier.

I certainly would not rule out a vert/lat system is it could be mad to fit better on a 6n.

[blacknwhite]

The system is described in the AES book Vol 1 and shows the entire schematic.

Page 253, got it.

Man, I *really* ought to make time to read those 2 books cover to cover at some point, rather than just skipping around

Thanks Markrob,
- Bob

[fusionkid]

whilst on the subject of the AES Disk Books, does anyone know if they are in the public (free) domain. Strictly for educational purposes though!

Many of the old texts on disk cutting are now collectors items and priced way beyond the reach of the mere mortal like me trying to further my knowledge!!

[blacknwhite]

whilst on the subject of the AES Disk Books, does anyone know if they are in the public (free) domain. Strictly for educational purposes though!

Many of the old texts on disk cutting are now collectors items and priced way beyond the reach of the mere mortal like me trying to further my knowledge!!

I know what you mean, we're all in the same boat.

I just hit up Wikipedia for copyright: Most of these articles in the book fall under the "pre-1964 copyrighted written works" category, in which case their original copyright gave them a term of 95 years of protection; and, if the copyright holder RENEWED it, even longer. The book itself was actually published with a "copyright 1980" mark, though; even more complicated...

I would say "whatever", and make a copy to mail to you, if I had a soft copy I could put on a CD, but these books are HUGE, it'd cost me more than $40 of time to scan it!!! (Large format 8x11, over 500 pages)

The Volume 1 is what really has the most info. Its currently in print from AES directly (exclusively), for US $40 + shipping. Considering how much is in there, its DEFINITELY worth it! If AES were to ever run out of these and deems it "not worth their while" to print more, I wouldn't be suprised to see their used prices shoot up to $300! Might consider making it a Christmas present to yourself

Here's a REVIEW I posted back in mid-2008, of the AES Vol. 1 book (the one on recording; Vol. 2 is on reproducing), with lots of scans, excerpts, and pictures:

https://lathetrolls.com/viewtopic.php?p=2932

And if you decide to get it, here's the order form page on AES: Scroll down to near the bottom:

http://www.aes.org/publications/anthologies/

- Bob

[fusionkid]

Thanks Blacknwhite
Guess i will have to invest in them eventually, i've already invested what i think is a lot of ££ for the amount of information you get. I know these books are copyrighted works etc, but for this subject matter they are a rare source of reliable data/info and importantly the "proprietry knowledge" on the subject. Because of the lack of material in the public domain, this knowledge is reserved for those with plenty of spare cash.
On the plus side i just won "Recording and Reproduction of Sound" 1st edition by Oliver Read on ebay. Published 1949 so prob. mono only. But hey what do you expect for $35 ?? In fact apart from the AES books this O.Read book is only the second book i've seen, and i've bought both of them.
And the posts about simple RIAA circuits, it's all good stuff that can be worked with, but i'm aiming to construct equipment that will give (realistically) useable disks for DJ'ing with. I'm in a funk band so i want to DJ our own records! So i'm looking for a pro design to work from, there are loads of old schematics of pro audio kit on web, just not the ones i'm looking for