The Steelhead, and possibly the Chinook, uses a 30 µF metallized film capacitor for output coupling between the phono section and the line section. Then there is a second 30 µF metallized film capacitor between the line stage section and the output. The single most revealing improvement you could make in the circuit is to replace both of those capacitors with better quality and lower value film capacitors. The question then becomes what is the minimum value of capacitance that would be sufficient. So far as I can tell the motorized volume control on the steelhead has a 5000 ohm input impedance. That is very low as volume controls go. Therefore you do need a fairly high amount of capacitance between the phono stage and the volume control. I chose to use 10 µF value, because that will still give you a very extended low bass response. For the output from the line stage to the amplifier, you can use any value that will give you an appropriate bass cut off in conjunction with the input impedance of the amplifier you are driving. So for example if your tube amplifier has an input impedance of 100K ohms, you could use a 1 µF capacitor. For amplifiers with a lower input impedance, you would want to increase the value of the coupling capacitor accordingly. That will give you a bass cut off at 2Hz. In addition to those capacitor changes, you could remove each of two 47 ohm resistors that are in series with the output of the line stage and the phono stage, respectively. Unless you are using very very high capacitance interconnects between your preamplifier and your amplifier, these changes will have absolutely no deleterious effect on performance.To the contrary the improvement in sound quality is very significant, far more significant and lasting than tube rolling can achieve. In my opinion, of course.
