To me, they sound very, very similar, as really they should, since both use a similar circuit topology. That is, both use a free running line stage driving an active tone control stage, with an anode follower output stage. Fisher simply chose to place the volume control before the tone control stage, while Scott placed it after this stage. Both use vacuum tube rectification, and DC power for the audio tube heaters.
From a design standpoint, the Fisher has an edge in that it also includes a low output impedance CF stage to drive the volume control/tone stage combination and the Tape Recording output jack, to virtually eliminate the effects of any outside connections to that jack on the audio signal. The signal at that jack is amplified and also inverted in polarity from the input signal. In later versions of the 400C, the Recording Output jack is also controlled by the Output Selector switch.
In the Scott design, the non-amplified Tape Output jack is simply wired across the input to the line amp, meaning that anything connected to that jack can affect the source supplying the preamp. With modern low impedance external sources, this is typically not a problem. But for vinyl enthusiasts using the internal phono preamps, and the Tape Output jacks for recording or loop purposes, the Fisher approach is quite superior.
Both units invert absolute polarity at their main outputs.
The Scott has a practical edge however in being easier to work on with it's nice big chassis, and is also quieter, since it uses an aluminum chassis rather than the Fisher's steel chassis. The difference in noise produced is notable.
The other notable difference is that the Scott has about 1/2 the gain in the line/tone stages than the Fisher does, which is more practical for most power amplifiers than the higher gain of the Fisher is. This, combined with the position of the volume control in Scott's design makes for lower quiescent noise as well.
So the biggest differences are more one of physical execution and features, rather than so much significant sonic differences. Properly restored, I think you will find that they both "sound" nearly the same. I enjoy both of my units immensely!
Dave
will need some obvious work as some wireing is missing and a few other issues.work begins this weekend ,full recap hunter
