Switchable Hi-Z input impedance, how ?

[juma]

... like using two 2sk170 instead of the complementary pair...

What schematic (link, post nr.) ?

...would the trick work for combining j310 with BS170 ?

What trick ? Why/where combine J310 & BS170 ?

Sorry Tinitus, i can't see inside your head, please reference your ideas with links/post numbers...

 

[tinitus]

yeah, I get my silly ideas

well, like you said, maybe I better stick to the jboz, maybe with j310

my idea with j310 with BS170 ?
I might get burned forever for this
it would be like a bastard all N channel version of BA3 frontend

you have permission to shoot me now

 

[juma]

No need to shoot ... yet
BA3 is complementary, symmetrical, push-pull circuit. It' cannot be done with N ch. devices only. Same sex transistors allow for quasi-complementary, circlotron or single-ended arrangements, and neither of those can qualify for BA3

 

[tinitus]

OK, its already complicated enough

with the j310 being a tougher one, maybe a symmetric output buffer would be a better idea ?

but Im in doubt about all the resistors around the att pots

 

[juma]

1. What do you mean when you say: "with the j310 being a tougher one" ?

2. First you want all N ch. devices (and the buffer is a great place to do it) but now you want complementary pair, push-pull buffer ? It makes sense only if you want to drive the next stage which has 1k-3k of Zin...

 

[tinitus]

....... maybe a symmetric output buffer ....... ?

shoot, forgot I think you said j310 cannot replace a sk170, directly

any ideas ?

 

[tinitus]

1. What do you mean when you say: "with the j310 being a tougher one" ?

......makes sense only if you want to drive the next stage which has 1k-3k of Zin...

dont know
I think you said 5v out, and isnt that more than sk170 ?

power amp load ?
could be 100k one day, and 10k the next day
I dont know

 

[juma]

I think you said 5v out, and isnt that more than sk170

Right, it will produce more undistorted voltage swing in the same topological form due to differrent construction (long gate vs short gate JFET), lower gm (lower gain being the price to be paid).

 

[juma]

shoot, forgot I think you said j310 cannot replace a sk170, directly

any ideas ?

Not directly - they belong to different construction groups.
If you want complementary buffer with J310 first you have to find a P ch. complement for it.
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.

 

[tinitus]

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.

sounds good to me, and what I had in mind, eventually

introducing the j310 kind of changed the picture, with its lower gain, and no buffers needed, apart from maybe the output

 

[tinitus]

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

 

[tinitus]

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]

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]

...
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]

... 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)

...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.com/webdocs/0a9d/0900766b80a9d07e.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...