Emitter follower verses Vr biased buffer before tone stack.

[Chugs]

I've built a few different pedals recently and placed a buffer, opamp or fet, biased from a VR source before the tonestack. I like doing this as the tone control works better and doesn't load the receeding corcuit down. I have, however, been looking at schemes for other pedals and notice that some circuits use just a basic emitter follower before the tone stack. What are the pro's and con's, if any, in using a vr source biased buffer verses a simple emitter follower before a tonestack?

[merlinb]

An opamp can drive heavy loads with negligible distortion. A single transistor (emittier/source follower) distorts when faced with even feather-weight loads. But sometimes it takes up less space on the board than an opamp...

[PRR]

An emitter-follower IS a buffer.

FETs and opamps may be "better" buffers. But sometimes you don't need a lot of buffering.

[Chugs]

Are there any particular situations would an emitter/source follower be sufficient rather than having to use a Vr bias buffer?

Would an emitter/source follower be fine for a simple LP filter like in a Rat. What about driving a BMP tone control?

Or are they, as Merlin B hinted at, generally used for parts/cost/layout consideration?

[merlinb]

Would an emitter/source follower be fine for a simple LP filter like in a Rat. What about driving a BMP tone control?

If you're not worried about distortion then an emitter follower may be fine. Obviously that goes without saying in a distortion pedal!

In a clean effect like EQ, for example, then low distortion may be more of an issue. Also, it may be more important to keep noise low, and that means using small resistances, which may require an opamp to drive them successfully.

On the other hand, some people like their "clean" effects to actually add a wee bit of distortion ("fatness", "colour" whatever), and some people aren't the least bit concerned with low-noise design and routinely use things like 1Meg pots even in pedals!

So it depends what sort of discerning customer you are!

Incidentally, there is some good reading in Doug Self's book about improving the emitter follower for better drive:
http://books.google.co.uk/books?id=PvKPEFu2PVkC&lpg=PP1&dq=small%20signal%20audio&pg=PA70#v=onepage&q&f=false

[slacker]

I'm probably just being thick, but what's a Vr bias buffer?

EDIT: ignore me, I wasn't being thick I just couldn't read