I, like Ralph, was going to cite distortion as the main culprit. I learned something new about how the brain processes music - limbic center vs. cerebral cortex. Thanks!
Biasing the transistor or tube correctly is key to getting the correct sonics from the preamp. When switched on, the unit it cold & the bias is quite a bit off + it's still drifting. As the electronics warms up the bias establishes itself at the design point & also stabilizes i.e. stops drifting. This takes anywhere from 30-60 mins; sometimes/often more. For example, Wadia claims that their CDP sounds best after 72 hrs of continuous on. I can attest to this. After 72 hrs the entire tank-like unit is warm to the touch (vs. stone cold when 1st switched on).
Tube amps too - most manuf say to not bother checking bias voltages for atleast 30 mins after turning unit on. Same deal with s.s. units.
Besides stabilization of bias voltages & currents the 2nd aspect would be what the actual bias voltage & current is as set by the designer. Is the tube being run "low & hard" i.e. low bias voltage, high current OR the opposite - "high & soft" i.e. higher bias voltage, lower current. The bias point will tell in which region the device is operating in terms of output distortion, output impedance, gain, output noise. And, this will affect the sonics. Of course, there is no way to know this by simply popping off the top lid & peeking inside. A tete-a-tete conversation with the designer will reveal this info (& many manuf are cagey to reveal this proprietary info for a good reason). There are plenty of 6922 & 12AX7 tubes in the market but some preamps using them sound really good & others so blah...
A 3rd possible reason is the quality of surrounding components - the resistors, signal capacitors, power supply capacitors, diode bridge rectifier, bypass caps, power supply snubber caps, grounding scheme, seperation of power supplies of the noisy output stage vs. the quieter input stage & the output impedance as higher output impedance has an interaction with the interconnect cable parasitic R, L, C + an interaction with the proceeding stage's input impedance that will affect sonics. For example, at one point a friend & I were messing around with a s.s. power amp's bridge rectifier circuit, power supply & bypass caps. Using a certain type of rectifier diodes + power supply caps + power supply bypass caps made the bass sound muddy compared to removing the bypass caps & using an even faster recovery Hexfred recitifier diode.
All of these items affect sonics....
Biasing the transistor or tube correctly is key to getting the correct sonics from the preamp. When switched on, the unit it cold & the bias is quite a bit off + it's still drifting. As the electronics warms up the bias establishes itself at the design point & also stabilizes i.e. stops drifting. This takes anywhere from 30-60 mins; sometimes/often more. For example, Wadia claims that their CDP sounds best after 72 hrs of continuous on. I can attest to this. After 72 hrs the entire tank-like unit is warm to the touch (vs. stone cold when 1st switched on).
Tube amps too - most manuf say to not bother checking bias voltages for atleast 30 mins after turning unit on. Same deal with s.s. units.
Besides stabilization of bias voltages & currents the 2nd aspect would be what the actual bias voltage & current is as set by the designer. Is the tube being run "low & hard" i.e. low bias voltage, high current OR the opposite - "high & soft" i.e. higher bias voltage, lower current. The bias point will tell in which region the device is operating in terms of output distortion, output impedance, gain, output noise. And, this will affect the sonics. Of course, there is no way to know this by simply popping off the top lid & peeking inside. A tete-a-tete conversation with the designer will reveal this info (& many manuf are cagey to reveal this proprietary info for a good reason). There are plenty of 6922 & 12AX7 tubes in the market but some preamps using them sound really good & others so blah...
A 3rd possible reason is the quality of surrounding components - the resistors, signal capacitors, power supply capacitors, diode bridge rectifier, bypass caps, power supply snubber caps, grounding scheme, seperation of power supplies of the noisy output stage vs. the quieter input stage & the output impedance as higher output impedance has an interaction with the interconnect cable parasitic R, L, C + an interaction with the proceeding stage's input impedance that will affect sonics. For example, at one point a friend & I were messing around with a s.s. power amp's bridge rectifier circuit, power supply & bypass caps. Using a certain type of rectifier diodes + power supply caps + power supply bypass caps made the bass sound muddy compared to removing the bypass caps & using an even faster recovery Hexfred recitifier diode.
All of these items affect sonics....