Switchable Hi-Z input impedance, how ?

[tinitus]

you didn't say no, so I guess its the right one 😀

box is getting on ok too
the back of an old TV is good for a piece of black plastic

 

[tinitus]

Some characteristics are the same, some are not...

hmm, instead of On-Semi I should have looked at original Fairchild spec sheet, and I would have known
http://www.fairchildsemi.com/ds/J3/J310.pdf

whatever, I will probably choose a bigger 19" box
the small one will be ok too, but for a smaller project
it does have a nice back, but not much space for connectors etc
so I cut away most of the old tuner front plate 😱😀

 

[tinitus]

moving on/off switch from the front to the back
Im using the hole where the removed mains voltage selector once was

looks like this preamp could turn into a 2-box affair

 

[tinitus]

added a cheap(scrap) mains out plug

 

[tinitus]

still cheap-skating

 

[tinitus]

wow, I had no idea a piece of 20year old and scratched poly plate could look this cool
just a bit of matte spray on the back, and voila, a fancy looking front

 

[tinitus]

this paint spray is heavily toxic
only for 'sniffer addicts'
man I got real dizzy and sick

whatever, has to be done, somehow
small box turned out ok
needs more work tho

 

[tinitus]

from old junk tuner to high end bass pre 😀
and this is the one I will use

 

[tinitus]

mains voltage, on/off switch, fuses, aux mains out, trafo

 

[tinitus]

hey, juma, are you watching ?

would like to ask you if you have a suggestion for a good simple gain stage with the J310
could the j310/CCS buffer be changed to a gain stage ?

 

[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.com/webdocs/0dab/0900766b80dabb08.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

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