I am puzzled why there are so many negative comments being posted regarding this pre-amp sounding harsh and bright.
It sounds good to me...clear and detailed.
This is a common complaint leveled at a lot of solid state preamps, and often for the same reason. They tend to make a small amount of higher ordered harmonic distortion, which is interpreted by the ear as harshness and brightness. It is also common for the brightness to be interpreted as greater detail.
IME when the presentation is relaxed, smooth **and** detailed then you are making progress.
The PAT4 was a nice entry level preamp in its day, but these days the design would be considered antiquated, and you certainly would not want to operate one without at least changing out the power supply filter capacitors so as to prevent damage to the power transformer, and also so that it would be able to sound right.
The reason the preamp tends to sound bright is that it doesn't run quite enough feedback for the circuit to be able to correct for the distortion caused by the feedback. I know this sounds recursive but its not. To really do the job right you need a lot of feedback, and the PAT4 circuit lacks the needed gain that you would need to do that. So its a bit of a compromise. On paper its specs appear benign, but if you investigate deeper you'll find that the distortion is only spec'ced at one frequency. What is common with designs like this is that as frequency is increased, the distortion goes up with it (this is because it lacks the needed Gain Bandwidth Product to do otherwise, in case you're interested). IOW it makes a big difference as to what frequency the distortion is being measured. Brightness is a common complaint of designs that have this quality.
