RIAA EQ

[Grainger49]

If this is a duplication I will delete this thread.  But...

What are the turnovers for RIAA EQ?  there are two, maybe three micro-second time constants that comprise the RIAA playback EQ.  Edit: I have been told that the frequencies were designed for standard parts values but it seems that is wrong.  

I'm wondering if there is a difference when there is interstage, passive EQ and feedback EQ.

Any help would be appreciated.

[Grainger49]

A Google search came up with three frequencies/time constants:

3180us = 50.05 Hz

318us = 500.5 Hz

75us = 2122 Hz

All are depicted here with the actual curve (blue) and the straight line approximation (red) AKA Bodie Plot, of the equalizations.

http://www.stereophile.com/features/cut_and_thrust_riaa_lp_equalization/

The question about active and passive RIAA EQ is still unanswered.

[Paul Joppa]

As you can see from the numbers, they were not designed for convenient resistor and capacitor values. 50 and 500Hz are round numbers, as is 75uSec. There must be some historical reason that the low frequencies are in Hz (actually, cps - cycles per second - originally) and the high frequencies in microseconds, but I don't know what it is...  :^)

The target frequency response does not change - all implementations have to produce the same result in the end. The component values may change depending on the circuit used, of course. This seems too simple to be the answer to your real question, though. Perhaps if it does not, you can re-phrase the question?

[Grainger49]

PJ,

I think the simple answer is what I was looking for.  I have a drawing that depicts a number of old, maybe even classic, RIAA stages and the RIAA EQ component values.  I will take out the calculator, look at my Carter text to keep me straight and do some figuring. 

Thanks, I wonder why the frequencies/time constants were not standard values.  I mean, there were real life engineers designing the curves, wouldn't they have known the values that were standard?  And yes, why didn't they either stay with a time constant or a 3dB down point frequency?

Sometimes you wonder....

[Paul Joppa]

As I understand it, in the early days each record company made their own choices about equalization - sometimes in different countries. The choices were driven by performance when these equalizations were being developed. It's much like the various cell phone systems in use today. Eventually the industry agreed on the RIAA curve, but because of legacy records, audiophiles still needed a range of curves for many years during the transition. I have an old mono H.H. Scott receiver with six different curves, selected from the front panel. Also, if there were good stampers in the archives, an old record could be re-published but would not be re-equalized. The rumor mill is full of examples where the actual equalization on a pressing is different from what it says on the sleeve!

Actually, back in the day (early fifties?) everybody used tone controls, so getting the equalization right was not a big issue. Speakers in particular were so far from flat that you needed the controls anyhow.