Pacific Riaa


2010-03-20 7:15 pm
Hi, i've been looking at the threads about the pacific Riaa Phono amp and i would like to build it on a tag strip. I have attached the layout, could someone tell me if it looks correct, and point out any errors for me to correct.


By the way, the LF poles in this RIAA circuit are not particularly accurate. Maybe someone has adjusted it 'by ear' or using an inverse network instead of calculating it properly? Time constants should be 3180:318:75us - I calculate 2438:294:76. This means that bass-mid (below 500Hz) will be boosted by 0.7dB, but will roll off from 65Hz instead of 50Hz. It is not worth using lots of parallel capacitors to make up an exact inaccurate value!

The simplest way to improve it is to change the second gate resistor from 100K to 470K. Alternatively, move the 100K resistor from the second gate to the junction of the 0.47uF and 27K resistor. The first capacitor bank should be 106nF (0.1uF may be close enough), and the second should be 27.7nF (27nF is close enough).

The input resistor ought to be 47K for most MM cartridges.