Switchable Hi-Z input impedance, how ?

[tinitus]

found a nice sized midi box
might be good for this
but needs some 'reworking'

[tinitus]

Originally Posted by juma

And if you want a single ended buffer with J310 (like B1) you'll have to put up with Zout of few hundreds Ohms or to use coupling cap.

ah, I see what mean
if no cap, there would need to be resistors to adjust the dc, and thus higher zout

could a j310 output buffer look something like in this ?

[tinitus]

Originally Posted by tinitus

need to get hold of some veroboard, and more components

to-92 j310, says obsolete but available as surface mount, at least but 2N5459 seems available, and widely used
and seems I can find 5457/58, and a 5952, and maybe 2sk246

need to keep it straight and on track now...have to be a lower gain device like the j310

[juma]

Originally Posted by tinitus

...
could a j310 output buffer look something like in this ?

Yes it could, but since you have a lot of BC547 you can use them as CCS (see attached sch.). If you plan to use SMD J310 don't go over +/-12V PS voltage and to lower the Pd you can change R4 from 68R to 100R. Expect Zout in range of 100 to 150R (R6 included).

[tinitus]

hey, thats the one, I like it, simple and very cool looking buffer
thanks juma

any alternatives to the j310 ?
(and not to forget, I still have 2sk170)

and btw, also have some 2sj313/2sk2013
but again, different stuff, I know

oh, and it appears all my BC547B, are...B types, Motorola(736ZF)

[juma]

Originally Posted by tinitus

... any alternatives to the j310 ?
(and not to forget, I still have 2sk170)...

BF245C can be used - it's cheap and abundant, but with it you can expect a bit higher Zout (200 - 250R).
You better save k170 for hi-fi projects but if you insist to use them this way, set the current through BC547 CCS to about 80-90% of Idss (by means of R4 - higher resistance => less current)

Originally Posted by tinitus

...oh, and it appears all my BC547B, are...B types, Motorola(736ZF)

It doesn't change anything important here...

[tinitus]

j310 with CCS looks just perfect for me, thanks

I better ask you to look at the specsheet, to be absolutely certain its ok

http://docs-europe.electrocomponents...6b80a9d07e.pdf

[juma]

What do you mean by "absolutely certain it's ok" - what's troubling you ?

[tinitus]

oh, sorry, I just want to make sure that the SMD in the link(spec sheet) really is a j310 and the same as the TO-92 j301

[juma]

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