Re: [ARSCLIST] Fw: [88sOn78s] Exit Grooves on Shellac and Early Vinyl

[Mwcpc6@xxxxxxx]

In a message dated 5/19/2005 5:51:27 PM Eastern Standard Time,
smolians@xxxxxxxxx writes:
Sending this to the ARSC list.

Steve Smolian
In a message dated 5/19/2005 2:12:20 PM Eastern Standard Time,
jodythornton@xxxxxxxxx writes:
My question is:  Why do electrically recorded shellac discs, and early
vinyl LPs have an exit groove that zig-zags back and forth, when it
spins?  Why did they go to a stationery exit groove in the early 60s?
Can anyone accurately/technically answer this.
***********

I have old record changers that use a ratchet and pall mechanism that is
dragged along by the tone arm to trip the change cycle as soon as the motion of
the arm is reversed. This allows the cycle to be started even if the eccentric
groove is at a large diameter, as on some short selections I've seen.

This is probably the simplest way to trip the changer, but it means there is
a constant drag on the arm so it was abandoned when very low tracking force
cartridges were developed. The "velocity trip" mechanism only requires a slight
tough on the trip pall once per revolution so it disturbs the arm much less.

Since most changers had a "fail safe" feature that would trip the cycle
eventually even without a reversal of the arm and as the eccentric groove required
a special mastering operation, it was eventually abandoned.

It seems to me that there was an organization, the RMA (Record Manufacturer's
Association) that coordinated these things but I am unable to find any
reference to it through the search engines. Does anyone have any links to the this
history on the Internet?

Mike Csontos