[sdiy] A transistor question

[Justin Owen]

Hello,

I'm using a line level audio signal from an external source (at the moment it's from a soft-synth via a hardware audio interface - but it could potentially be from a hardware synth or an output from a pre-amp, soundcard, etc) running into an AC coupled op-amp buffer stage.

The output from the buffer is being fed to the Base of an NPN transistor (2N3904) - so it's basically configured as a switch. The Collector of the first transistor is then fed to the Base of a second transistor (also a 2N3904).

It all works fine - but I'm wondering if there is any need to swap the buffer for some sort of gain/amplifier stage?

I don't want to overload the Base of either transistor - but I would like to make sure that the audio signal is strong enough to use the full 'bandwidth' of the transistor.

Is there something specific I could measure at the output of the op-amp vs. a spec in the data sheet of the 3904 to make sure I'm not missing out on potential dynamic range/headroom?

Hope that makes some sense!

Thanks!

Justin