Conclusion

B² A/D Spice has showed itself quite capable of unraveling many RIAA equalization problems for us. What appeals to me most is how quickly the parameterized AC sweep test gave a useable idea of what an optimal value might be (and this is an admission from someone who has rubbed the numbers off of several calculators from extensive use). Furthermore, B² A/D Spice offers much more than just the parameterized AC sweep test; Monte Carlo analysis of the circuit would reveal which parts can make the biggest change to the equalization curve; and a distortion test would help reveal the overload voltages over frequency. The Single or Dual Parameterized DC Sweep test would help us quickly find the desired bias point for the triode by plotting plate voltage against cathode voltage increments.

Phono preamps are particularly nerve racking in the real world because of the difficulties that arise from the equalization curve and the miniscule input signals that are so easily contaminated by noise, but in the SPICE world, these issues disappear. Without melting any solder, we were able to design and refine several useable circuits. Of course, all the circuits we covered should be tested after being built, as the SPICE models are not perfect and actual parts differ from their ideal (and even from each other, the vacuum tubes being surprisingly consistent), but my guess is that the values found during this experiment will prove truly close.

If you have a circuit topic that you would like to see a case study on, please drop us an email johnb@beigebag.com.