The triode then inverts the signal and a global feedback loop keeps the output's DC offset in line (no coupling capacitor!) and it offers all of the usual advantages to using feedback, lower distortion, wider bandwidth, and lower output impedance.

RIAA Program
    If you have been wondering Where's the math? Here it is, in the form of a Windows program. Passive RIAA EQ Calculator quickly figures six basic RIAA equalization circuits.

feedback, to overwhelm the triode's output. The OP-37 and other Op-Amps are much quieter than the best triode... it's like receiving a large charitable contribution from a gangster: sure, you like the money, but at what hidden cost?

     Well, why not carry the DC coupled theme a little further and run the Op-Amp in an inverted cascode circuit, shown below. As the Op-Amp delivers current into the 200-ohm resistor, the variation in current drawn through its negative power supply pin will be transmitted to the drain load resistor, which in turn will deliver the signal to the triode below.

    This Windows program also displays the RIAA equalization curve and its inverse, while allowing specific frequency entry and mouse position readouts of amplitude and frequency. Added features include its ability to compensate for input impedance and load impedance in its calculations. The program is easy to use and if you have used any of the other GlassWare programs, you will have no difficulty getting results immediately from it.
    How much does it cost? It's free, with one string attached: it's available at the Beige Bag Software website, www.beigebag.com where a short survey must be filled out first. (In order to make a better Spice program for the audio enthusiast, you, in other words, they need to know what you want, so it is really a win-win offer.)


                                   //JRB

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