Mechanics of a phono pickup

[fusionkid]

Hi all,
I'm interested in the workings of cartridges/stylii, and properties of the record "groove"
I've never really looked into this before so i don't know the correct terminology etc.
I want to understand the mechanical and electrical properties/workings of phono pickups and record grooves. I understand in very basic terms what is happening, now i want to further my knowledge.
I've seen terms like Velocity & acceleration used, i want to read-up on this so i understand the concept properly. Can anyone recommend any reading material, or correct terminology so that i can research this subject?
Any help would be very much appreciated.
Thankyou
R.
PS. At the top of the forum page there are 2 rows of pictures, on the top row there is a picture of (i think) a technics 1210, what is that tonearm?

[Oldpinkman]

The tonearm is a dynavector DV507 - and on a techie there must be a fair chance it belongs to Martin. See my post about "HiFi Choice" wanted for an alternative beginners guide to reproducing music from a vinyl disc. :)

[bob4333]

Hi all,
I've seen terms like Velocity & acceleration used, i want to read-up on this so i understand the concept properly.

Hello Rog, try John Crabbe's "hi-fi in the home" if you can track down a copy. Page 56 ('72 edition) when talking about a "groove being dragged past a stylus":-

"At one extreme, the very lowest recorded levels correspond to groove undulations of around two millionths of an inch in depth, or about one tenth of the wavelength of green light, while at the other end of the scale the stylus sometimes undergoes accelerations around a thousand times those experienced by a falling body under the action of gravity.

Looked at another way, if an acceleration of this order (say 1300 G) were maintained in one direction for one second, the stylus tip would then be four miles away and travelling at 30,000 mph!"

Mr Crabbe goes on to say:-

"Another fact providing food for thought is that with a playing weight of two grammes the actual pressure at the two tiny areas where a normal size stylus makes contact with the groove is something like ten tons per square inch, yet the tip may show only slight wear after passing 2,000 miles of groove".

A good read but keep the paracetamol handy.

[Mr Kipling]

Hi Rog,

The way I look at it is this:

One end gets jiggled about in the groove - and music comes out the other.

It's magic!

[fusionkid]

Hi and thanks for your responses, i'll see if i can get the book!
Just my luck! Why is it always "antique" books that i need?
My current interest of vinyl records in particular always seems to be written about in old hard to get books! And not modern up to date books, par for the cause i guess.
Thankyou all
R
While i'm on the subject, i have found a resource of out-of-copywrite books regarding vintage audio and the like. One that applies to this subject is Oliver reads'-Recording and reproduction of sound (listed under audio), this and other interesting texts can be downloaded here:
http://www.rsp-italy.it/Electronics/Books/index.htm

[sq225917]

The cantilever has a stylus at one end and a coil at the other end, it is pivoted part way down on a rubber doughnut suspension (usually). In the body of the cart is a series of magnets, these focus their flux roughly at the back of the stylus where the coil is. As the coils wiggles, in response to the movement of the stylus, the relative movement with respect to fixed lines of flux coming from the magnets/pole piece in the cart generates electricity, a tiny bit of voltage. The phonostage amplifies this voltage many, many times upto 1500 for a low output moving coil and passes that onto your pre-amp.

In a nutshell that's it. Different geometries of stylus, cantilever, pivot and suspension give different effects. Differences in magnet material, magnet strength, orientation, pole piece position, number of coil winding and wire thickness all make a difference.

As well as moving coil cartridges, detailed above you get moving magnet, where the cart has fixed coils on the body of the cart and a magnet is attached to the cantilever.

Everything matters, and every change is a trade off.

Visit vinyl engine there's some good info there.

[bob4333]

Hi and thanks for your responses, i'll see if i can get the book!
Just my luck! Why is it always "antique" books that i need?


Several copies on Amazon http://www.amazon.co.uk/Hi-fi-Home-John-Crabbe/dp/0713704942/ref=sr_1_1?ie=UTF8&qid=1374559665&sr=8-1&keywords=hi-fi+in+the+home and not too expensive.

The thing I have to remind myself with vinyl repro systems is that we are dealing with very small components and what at first appear to be very small forces, so there is a blasé feeling that can develop that suggests "well, it doesn't really matter if I only get close" - which is of course as wrong as wrong can be.

Micro engineering: small changes can make a huge difference.