stupid question about hm2 input buffer

[Abyz0u]

i was planning on building the tagboardeffects hm2 ( https://tagboardeffects.blogspot.com/2014/05/boss-hm-2-heavy-metal.html )

but then i realised i dont have any bf jfets+i cant get my hands on any,if i only could find out where the buffer output goes to id put a normal ds-1 style npn buffer OR pop in a normal silicon npn since the circuit looks alot like a silicon npn buffer but i dont know if the biasing resistors need to be changed or which pin of the npn equals which pin of the fet...there is a lot going on that i cant get my head around

so long story short i want to use a normal npn buffer instead of this jfet buffer or socket a si npn instead of the bf245 but i should go about with either of these

[antonis]

Without a schematic we can tell you nothing.. 

https://www.hobby-hour.com/electronics/s/hm2-heavy-metal.php
(I'm not able for the moment to post an image..)

It might work for Q1, if it's a high gain n-p-n and substitute R8 with a 470K resistor..

Bear in mind Q1 V_BE voltage drop at Q2 Base and hence Q2 Emitter + Q1 Source voltage which currently is higher than 4.5V, so you might have to tweak R7 for proper Q1 Emitter voltage.. 

[Ice-9]

It is just a standard buffer, stick in a npn and it will work fine(Q1).

Most any N-Jfet will work ie, j201, 2n5457, 2sk117 etc and most any NPN Bipolar will play niceley.

[antonis]

@Mick: I'm not sure if simply sticking a n-p-n BJT in place of a n-channel JFET will DO work..

Mainly due to pin-out incombatibility (most of BJTs exhibit their Base on middle leg whereas JFETs exibit their Gate on side leg..)

Additionally, a non high beta BJT with 1M Base bias resistor fed from +4.5V leaves not enough Emitter voltage margins for negative cycle undistorted signal..