PhonoII 3.18uS correction

[FAQ Team]

PhonoII 3.18uS correction

As standard the PhonoII corrects for the 75uS, 318uS and 3180uS RIAA equalization time constants, in addition many good quality RIAA phono designs also correct for the 3.18uS time constant. The reason for doing this is this time constant is often used during recording to protect the cutting head, it also has the benefit of compensating for roll off in the interconnects used during recording (ref: Allen Wright, 1994 The Tube Preamp Cookbook).

To introduce this correction simply insert an additional resistor between C16/17 and the junction of R31/32 and V4b/a connection 7/2. See diagram. The easiest way to do this is to lift one leg of C16/C17, the leg connected to R31/32 and solder the new resistors into position on the top side of the PCB between the lifted leg and the solder pad of R31/32.

The required value is 14K454 Ohm, absolute accuracy is not necessary or achievable so parallel either a 51K resistor with a 20K resistor to give 14K366 or an 18K resistor with a 75K to give 14K516. All resistors should be .6W 1%.

The effect is subtle but the sound should have more "air" around vocals.

NealG