trying to understand this simple circuit

[Dimitree]

hello
I'd like to build this circuit (a section of the Suzuki Omnichord).
but first I'd like to understand what it does and how I can substitute parts if I'd like..



can you help me understand what the different sections do? what kind of transistor shoud I use in there (the original were 2SC828Q, but I'd like to use modern equivalent), and what happens if I use 5V instead of 12V (of course adapting some values)

[nocentelli]

Two simple booster circuits, with some treble roll off (quite a bit) and omit I a level control on the output of the first stage. Would probably start to clip a bit with heavy handed guitar playing when the harp control is cranked. 2N5088 or similar should work.

[Dimitree]

thank you for the reply,
the circuit is not for guitar, the input is a square wave.
some questions:
1) where is the treble roll off? maybe C4-C5-R5-R6?
2) the differences between the first stage and the second (a part from values) seems to be the presence of R1 in the first stage, while is missing in the second. What's for?
3) what's the purpose of R9 and R10?
4) how do you say 2N5088 instead of 2SC828Q? should I look only for equivalent hfe or something else too?
5) what if I change the voltage to 5V instead of 12V?

[nocentelli]

1) where is the treble roll off? maybe C4-C5-R5-R6?

C3 via the miller effect, and R6/C5. R5/C4 will also remove substantial amounts of lower frequency content.

2) the differences between the first stage and the second (a part from values) seems to be the presence of R1 in the first stage, while is missing in the second. What's for?

R1, R2+R3 and R4 set the bias of the first transistor, they dictate the voltages on the collector, base and emitter. R9-R13 set the bias for the second stage, it's a slightly different arrangement, with the lack of base-ground resistor in the first stage being the most obvious difference. The advantages of different biasing arrangements seems to be a trade off between number of parts and issues of stability/noise/will it work with any transistor?

3) what's the purpose of R9 and R10?

See above

4) how do you say 2N5088 instead of 2SC828Q? should I look only for equivalent hfe or something else too?

Similar specs, 5088 works in most places where NPN silicon BJT is required, it's one of rg's golden rules

5) what if I change the voltage to 5V instead of 12V?

Hmm, not so sure about this one. I'm going to guess that you'll have lower headroom before the input clips (i.e. you won't be be able to increase the harp knob as far before it clips, and with a lower output level than running it on 12v). I think it will probably still pass signal.

[smallbearelec]

This is two common-emitter amplifier stages, tone shaping not optimal for guitar. How come you want to build this particular circuit? Are you familiar with using a breadboard?

http://diy.smallbearelec.com/HowTos/Breadboarding/BreadboardIntro.htm

Whatever you end up building, you will want to do it on the breadboard first so that you can tweak easily.