As reported in the first schematic posted at the start of this thread, QGN5 with QFLOAT1: collector of one transistor is wried to the base of the other in a riing fashion.
Piercarlo
Hi Guys
With everything bootstrapped, it seems like the main goal is to reduce input capacitance and increase input impedance. R-IN seriously degrades the latter and could be much higher if you needed a really high z-in.
Otherwise, Doug Self showed how to achieve high z-in using just BJTs and liberal bootstrapping in his "Small Signal Audio Design" book. Bootstrapping has been around since tube days. Noise can sometimes be compromised using these methods and distortion more often is.
There are simpler ways to have a good signal buffer with low distortion and reasonable signal amplitude handling. But... like you say, sometimes you just have to try something for the sake of trying.
Have fun
Kevin O'Connor
With everything bootstrapped, it seems like the main goal is to reduce input capacitance and increase input impedance. R-IN seriously degrades the latter and could be much higher if you needed a really high z-in.
Otherwise, Doug Self showed how to achieve high z-in using just BJTs and liberal bootstrapping in his "Small Signal Audio Design" book. Bootstrapping has been around since tube days. Noise can sometimes be compromised using these methods and distortion more often is.
There are simpler ways to have a good signal buffer with low distortion and reasonable signal amplitude handling. But... like you say, sometimes you just have to try something for the sake of trying.
Have fun
Kevin O'Connor
Thanks for your considerations but the goal is not having an high input-z for itself (although the real INNER input Z is above 10 Megaohm: R-In is just for locking to ground DC the input coupling capacitor and may be chosen of any value below a couple of Megaohm).
Exactly!
One "psychological" goal is to show how a circuit can become complex if someone want to achieve without feedback the (near) same result obtained WITH feedback - that however is not really absent! Transistor used are of the cheapest and common type but however the circuit is neatly more expensive of a simple voltage follower implemend with any low cost good audio operational amplifier... ;-). Piercarlo
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Here is a very simple SS buffer I use. It allows me to use 1uf polypropylene input cap. 1uf PPM cap is reasonably sized to fit onto a PCB and not act as an antenna. "I-bias" is simply a Jfet bias Idss (Vgs=0V), a few mA or so. 4091 is like a J111 and has realitivily high conductance and Vgs is about 6-8V at a few mA.
Attachments
Good circuit but require the use (and even a coarse selection) of two JFET, a device which is progressively fading from the market, at least in other form than the SMD format, Even more require an addictional servo with its own circuitry.
Hi
Piercarlo
Not well refined (a bit cervellotic instead and even circuitally inconsisent: pheraps because is likely to be just a sketch to be evolved further
as those reported by you before.Hi
Piercarlo
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