Speed of groove.


We all know that record spins at (let's take at this point) 33.5 rpm and while the rotational speed is the same the speed of the actual groove is not.
Our cartridges are specked at output voltage for a specific speed of the grove(cm/c). What happens when
a)the speed is higher than specified at outer grooves
b)the speed is lower than specified at inner grooves
c)the record spins at 45rpm or 78rpm
128x128marakanetz

Showing 4 responses by mihaitaa

One could easily tell that I'm not a phono guy, but I fail to understand why a phono cartridge's output voltage will be in any way correlated to the linear velocity of the record.
To me, if one would need to correlate the output voltage to a speed, it would make more sense that that speed would be the speed of the stylus relative to the cartridge itself (*vertical* movement) as that's the movement that induces the voltage to begin with.
For sake of simplicity, let's consider the vertical movement only and 1kHz sine wave shaped groove for a constant amplitude of the signal. And let's take only the positive semi-period, thus a nice rounded "bump".
At the outer edge of the record, the bump will be "elongated" whereas towards the center of the record it will be "shortened". But in both cases the time the stylus "climbs" from the bottom to the peak of the bump stays the same. And given the fact the the bump has the same height at its peak in both cases, so does the "climbing speed".
This is the speed I'm referring to and I still fail to understand how it could be correlated to the linear velocity of the spinning record.
The linear velocity was "abstracted away" by the "length of the bump".
I'm only trying to understand here, by no means my knowledge of electronics could even come close to Al's...
Precisely! That's all we are saying
Well, I understood this all along, but the original poster was talking about correlating the cartridge's output voltage with the linear velocity of the record.
This is the correlation I said I didn't understand and I don't believe exists.
Everything else is clear to me. Maybe I misunderstood the post itself, wouldn't be the first time... ;-)
There's variation in sound quality between outer tracks and inner ones, due to the in formation being more densely packed together on the inner grooves, but not "output level" differences. Nobody has to turn the volume up as the inner tracks are played.
The answer, as you realize, is that there is no effect, because what is relevant is stylus deflection velocity, not tangential groove velocity
Splendid, that was exactly my point as well.
Happy New Year, everybody.