[R-390] OT: Transistor Amplifier Question

[Roger Ruszkowski]

Barry,
The problem is complex and common.It is a bias stabilization method that works.In an audio pre amp any thing better is OK.
We were looking at some 7805 or 7905 or 7812 voltage regulators.The comment was why the pf cps on the input and outputs of theregulators. What is + / - 50 pf going to do for the DC voltage andcircuit bias.
It is not the exact value.At different device sizes, different pop corn noises get trapped insidethe specific device not the specific capacitor value.The science of what is going on in the circuit is complexand why RF is real squirrely compared to DC and Audio.Different cap types, silver mica, foil, ceramic, different dielectrics, and packaging all have different characteristics relevant to audio amplifiers.
However the discussion of why the extra caps are includedwith three terminal voltage regulators explains it all the circuit science in nerd.
The 50 pf caps do change the linearity of the amplifier stageeven if the improved nuisance misses your ears.The idea is that neutralizing the hysteresis on the transmission linebetween active amplification junctions is to retain signal fidelity.
The caps self resonate and this effect extends or boosts the high frequency response in the amplifier stage giving better detail to lower audio frequencies. (Richer harmonic content)Those little caps just let the circuit sound better when the signal is more than just a simple sine wave.
Roger AI4NI