"new" boost Switchable between bootstrapped or non bootstrapped input resistance

[Gus]

If you read this thread I posted two schematics of a two stage NPN silicon transistor boost.  Look at the two graphs.
http://www.diystompboxes.com/smfforum/index.php?topic=98928.20

Now the next step is for something a little different that I have not seen in an effect before.  Lets use the bootstrapped input schematic. Switchable input resistance and EQ from the interaction of the guitar/bass, cable and input of this boost.

ADD a SPDT switch

Center terminal to the 100K 100K 820K node of the input transistor bias resistors
NO outside end to the base on the input transistor
NC between the 100K, 100k, 820k node and the end of the .047uf  

So the circuit will be as shown BUT when the switch is set the other way the 100K shorts out and the one leg of the .047 gets disconnected.  DO NOT SWITCH WHEN USING THE EFFECT YOU WILL GET A BIG POP.



For more first stage gain one can add a series cap and resistor in parallel with R2(standard circuit design)

So what is different? the input biasing switch between bootstrapped and non bootstrapped input.
What is nice about this design
Series resistors for gain stage stability R5, R8, R14  ( make R5 1K)
Bias points
easy to find transistors
standard part values
no trim potentiometers
emitter follower output

Left side is a guitar cable sim to the right of C3 is the input.

Gus

[Gus]

Note the change from bootstrapped to non bootstrapped.  Also note you can tune the bottom bump with the bootstrap capacitor.

[Kesh]

I'm fairly new to bootstrapping, so forgive me if this is nonsense, but wouldn't it be more illuminating to see the effect of just C6 open, rather than C6 open and R15 shorted, as shorting R15 is going to about halve input impedance anyway.

[Gus]

I wanted an input resistance closer to a LPB when not bootstrapped, also look at the ratio of R2 to R4||R3.
This circuit will let you hear the change of input resistance.  Most of the circuit stays the same the volume will go up a little with the reduced loading of the guitar or bass.

I picked a gain of about X10, 100K/10k

I selected a higher Hfe transistors, should be around 500 Hfe for a 2N5088, 2N5089, it is variable but 500 should be close enough.

First stage is set for lower collector current and uses a 10K emitter resistor.  Non bootstrapped input resistance is about 100K ||820K||(500x10000) about 87K

I also had a little fun with the bootstrapping.  I have posted in the past about the bottom end bump you can tune.  If you search for the NPN boost and NPN boost ver 2 note the curves at different gain settings.

[Gus]

As I am posting this bump I noticed this thread only has 171 views.
I think people can have fun with this circuit.
It is a textbook like circuit with the bootstrapping switched out. 

The switchable bootstrapping makes it different.  Note how small the bias change is in the sims screenshots

You can have a LPB like input resistance or a much higher input resistance with the flip of a switch.
You can add more gain to the input with the addition of a resistor and cap.
X10 gain should be fun with a bass or a guitar
There is an emitter follower for good drive.

Are there low amounts of reply's because it is not clear how to add the switch?

[pinkjimiphoton]

thanks gus, this looks fun, i hope to build it when i get a chance...so so sooooooo many pedals, so few years on the planet left...

[Gus]

Has anyone tried this?