bootstrapped EF circuits and graphs

[Gus]

First a more flat bootstrapped emitter follower(EF)  Note that at about 50K series resistance from the volume control the high end bump is reduced.  R8 and R11 are a 250K volume control







Note how adjusting the bootstrap cap and a resistor you can change the bottom end curve also note the series resistance is 10k and look at the graph around 6KHz.  The bottom end roll off might be very nice at higher volumes




Who needs JFETs for buffers?

[Eric H]

This looks very interesting...almost interesting enough to break my 7 year building moratorium.

[John Lyons]

Interesting stuff here Gus.
How would you go about designing a better buff for a traditional wah into a fuzz.
I know this has been addressed before but you have a sharp mind. 

[Gus]

John two Bootstrapped EFs in a wha


I simmed the bottom bump EF because I like the sound of the NPN Boost ver. 2 I posted here before at min gain (x2). 
That EQ like curve seems to make a guitar or bass sound bigger at min gain of the NPN ver 2.  So I worked on a bootstrapped emitter follower(EF) sim for the same type of curve. 

The not flat buffer looks like it might be fun to build.

[DougH]

What you are doing with the bootstrap cap and resistor reminds me a little of a resonance control in an amp. This is usually a series cap/pot that affects NFB of bass and can control "deepness" of bass as well as damping.

[John Lyons]

Gus
Just trying to understand the circuit....
Does Q3 buffer Q1 from the output and Q2?
Just a bit unclear about and emitter follower before the emitter follower (Q3, Q2)
Thank you fro drawing that up.

[Gus]

Q3 buffers Q1 and allows the use of lower value wha pots and tapering resistors
R11 and R12 are one 100K wha pot
R15 and R14 are tapering resistors omit if you want
Grounded emitter gain stage so R3 might need to be larger in value
I have not built it yet

[John Lyons]

Thanks for the detail Gus.

[GFR]

What you are doing with the bootstrap cap and resistor reminds me a little of a resonance control in an amp. This is usually a series cap/pot that affects NFB of bass and can control "deepness" of bass as well as damping.

Well, with bootstrap you're adding positive feedback.