Can you use TS output buffer as a boost ???

[Melanhead]

May be a stupid question and I'm still not up to snuff on my transistor technology but is there potential to bias the transistor so it's set to a higher gain ... I guess the idea would be to switch between the normal buffer and tweaked buffer ( whatever the parts changes would be ... ) for a volume lead boost on a homemade ts808 or any other pedal with an output buffer...

I was reading RG's Tubsecreamer article and this strange idea poped into my head

Are there any good articles on the workings of transistors that don't involve a thousand formulas Basically I guess what I'm looking for is a "raising or lowering the value of this resistor will do this" kinda thing. I'm sure it's more complicated than that but I wanna get a basic idea how the surrounding components affect a transistors operation when set up as an amplifier...

[petemoore]

Buffer Q's [emitter or source followers] aren't set up as amplifiers.
 They should get very close to 1 to 1, or what goes in the base comes out the emitter [almost exactly, I believe buffers generally put out just ever so slightly less than what's put in].
 They provide low output impedance.

[Melanhead]

ahhh .... yup, that makes total sense. I guess I'd just have to build a boost in there, not something to distort  really, just a volume boost.

thanks ...

[R.G.]

It's possible, but complicated to do without compromising the function as a buffer normally.

It's far simpler from a design point of view to put another opamp before or after the buffer and switch that opamp's gain. If you do this properly, the switchable gain opamp eliminates the need for the buffer.

The problem is that the bufffer is a common collector amplifier. The output is taken from the emitter. No common emitter amplifier has voltage gain over unity. To do voltage gain, you need a common emitter or common base amplifier, and those have the output taken from the collector.

Worse, the necessary component values change a lot. A common collector (emitter follower) stage needs the collector resistor to be small or zero and the emitter resistor to be large. A common emitter stage needs a larger collector resistor and a small emitter resistor. That means that your switching has to swap a lot of resistors around and the chances of doing that without a switching pop is tiny, even if you can afford or concoct a switch that does what you want.

From a design point of view, it's easy to do the job you want to do. From the standpoint of just switching a couple of resistors on an existing pedal, it's going to require a lot of hacking.

[Melanhead]

It's far simpler from a design point of view to put another opamp before or after the buffer and switch that opamp's gain. If you do this properly, the switchable gain opamp eliminates the need for the buffer.

I'm assuming you mean have it setup so that it has a low output impedance and acts as the output buffer with a switchable gain ....

Interesting idea! ... thanks RG.

more research needed ....