Quote:
Originally Posted by kalee20
To that I could add, the use of the op-amp in the non-inverting mode! It's impossible to get the gain to roll-off to less than unity, though the RIAA curve is supposed to roll-off at 6db/octave indefinitely.
|
There is a theory that another (Neumann) pole was used when recording
"It was suggested by Wright in The Tube Preamp Cookbook (1995) that Neumann cutting lathes incorporated this bandwidth defining filter by means of an extra, high-frequency pole at 3.18µS (50 kHz) in the cutting equaliser."
http://www.pspatialaudio.com/neumann_pole.htm
It is debateable however whether such a pole exists.
As to which is better, passive or FB equalisation, you pays your money and you takes your choice.
A quick google search will bring up arguments in favour of both but personally, and it is a personal choice, I prefer passive, no feedback circuits when using valves and tend to use feedback when using op-amps.
One advantage of passive, no feedback circuits is that the circuit breaks down into sections, easily testable independantly.
To answer your question about how accurate an RIAA equalisation amplifier has to be I believe that it should be as accurate as you can reasonably make it. The key word being reasonable. As you can see from the photos I posted I am prepared to parallel capacitors to get close to the theoretical values but I use 1% resistors and 2.5% polystyrene capacitors and consider that good enough.
In practical terms if you end up within 1db that will be good enough unless you have golden ears (climbs into foxhole and awaits incoming fire).
Peter