BOSS SD-2 Schematic/component help

[Vitrolin]

hi a friend, though very sceptic asked if it was possible to make an SD-2, he used to have on but someone stole it and seems to be out of production now, doesn't even figure on the BOSS page. but i found the schematic and now i have some questions

Which op amps would be a suitfull replacement?
i guess Q8,9,11,13,15 are somesort of switching, so they would be obsolete, since ill be using hard-switching.
Should the 1u caps and the 220K resistors before the abovementioned Q's also be omitted?
is the Q14 also a part of the switching? if so, should i also omit R46? if not what would be an suitable replacement?
and the Q7,10,12 what would be their replacement?
i was thinking maybe ill use the buffers any ideas on that?

[R O Tiree]

1. - 4558 opamps will be fine.

2. - Q8,9,11,13,15 are, indeed, the signal switching system. There are, clearly, a lot of components missing from this schem - this is just the guts of the signal chain.

3. - Someone else jump in if I read this wrong, but I think you could safely lose:

(a) C46, R65, Q15 and R50 from the entry to CRUNCH. C46 simply DC-decouples the signal going into the switch (JFET) and R65 and R50 set the operating point for the JFET. This reasoning applies to the rest of this section...
(b) C27, R48 and Q13 from the exit of CRUNCH.
(c) C26, R33, Q8 and R34 from the entry to LEAD.
(d) C25, R43 and Q11 from the exit of LEAD.
(e) C35, R42, Q9 and R45 from the output section.

4. - Q14 is a source-follower input buffer. This has a massive input impedance, which is good. Less good is that it has a high output impedance but everything downstream of it also has a high input impedance, so that's OK. The transistor buffer at the end has a low output impedance, so it's good for driving the next pedal/amp in the chain. Therefore, I think you could also safely lose the wire connecting Q14 source and Q12 base, Q12 itself and R47 as well. The emitter-follower buffer formed by Q12 is simply a means of eliminating the CRUNCH/LEAD signal feeding back on itself (which would be bad).

5. - Q7 and 10 (assuming you lose Q12 as above) can be anything like 2N5088, 2N3094, etc. Certainly Q10 is just an emitter-follower output buffer. I think that Q7 and its associated components are a high-pass filter to get rid of some treble frequencies from the signal being fed to the -ve input of IC2b so that treble ends up being boosted at pin 7. (I might have got this the wrong way round?)

6. - I'd keep the input buffer (Q14, R46, R62, R63 and C34) and the output buffer (Q10, R30, R31, R40, R41, C21 and C22)

If I got any of this wrong, someone please step in and put me, and the OP, right?

[Vitrolin]

ok thanks

3. - Someone else jump in if I read this wrong, but I think you could safely lose:

(a) C46, R65, Q15 and R50 from the entry to CRUNCH. C46 simply DC-decouples the signal going into the switch (JFET) and R65 and R50 set the operating point for the JFET. This reasoning applies to the rest of this section...
(b) C27, R48 and Q13 from the exit of CRUNCH.
(c) C26, R33, Q8 and R34 from the entry to LEAD.
(d) C25, R43 and Q11 from the exit of LEAD.
(e) C35, R42, Q9 and R45 from the output section.

ok so i should eliminate the above mentioned components and the Q12 buffer and of course the wire between Q12 and Q14
...and ill keep the buffers, Q14 if a jfet, right? would any of the usual be ok j201 mpf102 etc?

Again thank you very much

[R O Tiree]

I'd think something like a MPF102 would do the trick admirably. J201 is P-channel, isn't it? I'm still learning lots about FETs and I don't know what effect that would have. Might be none, but someone will pop in and put us right...

You could just as easily replace that input buffer with an ordinary NPN transistor emitter-follower buffer. Still have a high input impedance, but you also get a low output impedance. So, if you want to lose the JFET buffer and go with a BJT emitter-follower, try copying the style of the input buffer from something like a Ross-Comp (Dyna-Comp is identical).

[R O Tiree]

Bump...

Could someone check that my advice above makes sense? If there's something wrong, I'd like to know for my own understanding, and the OP won't build something that doesn't work right.

Thanks.

[Vitrolin]

I'd think something like a MPF102 would do the trick admirably. J201 is P-channel, isn't it? I'm still learning lots about FETs and I don't know what effect that would have. Might be none, but someone will pop in and put us right...

the j201 is N-channel, you can always google the components, when in doubt.
and you'll get the pinout as well

[R O Tiree]

That's bizarre - I did Google for the datasheet - must have typed the number wrongly and read "what I expected to see"?

So J201 looks like a player as well, then.

[rmachado]

Hello friends, good night!
Has anyone managed to build SD-2?
I have a lot of interest in the lead channel.
I believe this scheme would serve, no?



Sorry my english, i'm brazilian.
Thanks!!!