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Selectively enabling BJT buffers isn't bad. Under certain conditions BJT can be also used as analog switches, but with restricted signal level. Since 30 or 40 years, people prefer FETs or CMOS switches for this purpose.
you could use 1 spst switch to turn on & off your preamp's power suply , supposing that both preamp's are supplied from the same source . I think that audio signal should not pass when spst switch is off .
there will be a 3" delay circuit to prevent the boom, and a slow turn on power supply.
i have a couple of ne5532 and another couple of tl072, wich i could use, but this all about is a tube preamplifier, and i dont know if it is correct to use opamp before, even if the power of the signal stays low..
however the input signal will come from digital source , from pc or mp3 player... it will not be pure analog (ie phono)
so i dont know ...... wait for relays or build it with opamp?
thebadtall<< When you need to design something, it is very important to define the interface parameters. e.g. source and destination impedance and signal level. Keep this in mind next time.
You can also use Reed Relays which are very reliable and miniature.
When I used the 4066 a few decades ago the on resistance was a few hundred Ω, so perfect for line impedance of 10KΩ , but not so good for speakers or headset. Maybe they have improved or you can drive it with +/-9.0V split supply or center biased on 18V