Switchable Hi-Z input impedance, how ?

[juma]

Standard Q&A:
How much gain do you need ?
What's the input signal level?
What power supply you have?
What's the load ?

Source Follower can't give you voltage gain - to accomplish that the parts must be mixed together differently...

[tinitus]

ah, juma, glad you are still around

well, I thought now that Im going to use +/-12V like you suggested for the j310/CCS buffer.....
but I have regulated supply, and 2x 18Vac trafo, so it could be almost anything

not sure I have all the answers, yet
the plan was to replace the k170 in simple boz with the j310
I think you mentioned 12db
and with its lower gain I could have more gain stages, instead of buffers
and only have buffer at output

might be 3 gain stages
one at input, another at tone control, and with another one around the att before output buffer
and then the the j310/CCS buffer output

reposting old not yet revised layout, just in case

[tinitus]

here revised with your j310/CCS buffer
but still with jboz gain stages

[tinitus]

btw, also thinking about putting in 'optional' 12db active low pass and high pass xo

[juma]

Simple 12dB gain stage with J310 would look like this. J310 is quite different from 2sk170 so it has to be configured differently for this task (12dB gain and about 5V of clean swing). Id is low (about 1mA), Zout is high, but it works nice and buffer will be used at its output anyway...
For 9dB gain, change R2 to 3k6, it will also make the gain stage more linear.

[tinitus]

nice, thanks

now with +30V
but I suppose thats the price to pay for good voltage sving
will see if I can find a trafo for it

would it work with 12db active xo

I have tried to mate a 12db xo with the j310/CCS buffer, but not sure it will work
apart from some tube buffered curcuits, LC audio's xo is the only discretely built xo I could find
but he connects the feedback loop to ground instead

[juma]

It's OK.
You don't need two resistors to ground (HP section).
Look here:
Linkwitz-Riley Electronic Crossover

[tinitus]

ah, I see, the resistor is 80K for 200hz
great
this will be fun
better begin to order parts

[tinitus]

gosh, those J310 SMD are small...2.9 x 1.3 x 0.9mm

with SMD resitors and caps, a high or low pass wouldn't take up much space, almost like nothing
wonder if there would be a double BC547 SMD

ehh, that would be a junction type, I guess

juma, any ideas/suggestions ? or am I too crazy now ?

would that be like BC847
http://docs-europe.electrocomponents...6b80dabb08.pdf

[tinitus]

thinking about mounting buffer and active xo on small boards with a dil socket adapter
would make it easy to change xo
or if no active is wanted, just mount a buffer board without xo

Originally Posted by tinitus

now with +30V
will see if I can find a trafo for it

for the J310 gain stages
I have the 0/18Vac trafo Im using now for the simple jboz
maybe I could try with a voltage doubler