What are the purpose of multiple transistors ?????

[SYK0T3K]

Hello Guys !! I am really excited that I found this awesome forum and helpful community, as I am starting to build my first pedal, which is a distortion pedal. I read the (Design Your OwnDistortion
By Rikupetteri Salminen) and I understood every bit in it, when when I started to look into other distortion pedals schematics (for example: GuildTM Foxey Lady) I really got lost, as the first question came to my head is that why there are multiple transistors used in (all) this pedal, what are the purpose of the other 4 or more transistors after the first one. so what is the need to use multiple transistors or op-amp(s) in the distortion pedal?, please help me ( I didn't get much sleep as I tried to find a reason for this an I still couldn't)

PS: I added the (GuildTM Foxey Lady) distortion pedal to make it more clear

link for the article I read :

[Pimpom]

Transistor Q1 amplifies the incoming signal from the guitar. Q2 is the first distortion stage and does it by further amplifying the signal and clamping it with D1 and D2. Q3 repeats the process and clamps the signal even harder. Q4 provides some more amplification.

[antonis]

Q4 provides some more amplification.

For tonestack signal loss recovery..
(and welcome, of course..)

@SYK0T3K: Search for "Big Muff pi analysis"..

[nejir]

Ok, I am not going to talk about the other parts of the circuit, and I am not going to talk about tubes vs transistors. The question talks about transistors, so here is what is happening:

Every transistor-based amplifier (in guitar electronics it is better to think about how a transistor is used as a block, meaning used with some resistors and capacitors to form a simple amplifier) has what is called an operating curve. It is something published in the tech manual for a given amplifier. For most electronics, a transistor-amp will take an input and enlarge it, but enlarge in such a way where the output is linearly similar to input. So imagine a sine wave with peaks at -4 and +4, then the outputted version coming from transistor-amp output having peaks -8 and +8, but otherwise looking the same.

Now with guitar signals, running a transistor-based amplifier (when I say amp I don't mean the whole collective amp, the big heavy thing, I literally mean the small transistor-based amplifier circuit that exists at various stages in the overall device), in the linear operating region just acts like a clean signal amp. But to get distortion, one has to push these amps into their clipping/saturation operating region. This means that with sufficiently high input signal (and getting it sufficiently high often requires input volume knobs, hot pickups on the guitar, etc), the output is distorted. It doesn't look like the sine wave that is coming from your guitar cable. The top part of the signal will clearly be crunched down (this is the distortion), clipped, and this is transistor-based distortion. A lot of guitar electronics use tubes because their distortion characteristics produce waveforms that are literally smoother compared to transistor-based distortion (you can actually see that visibly - just google transistor vs tube distortion and you will find some interesting images and explanations).

Anyway, there is a lot of mythology regarding guitar electronics, but in its most basic sense it is about the nature of signal processing (hence Fourier Analysis) and amplifier operating characteristics (which are not mysterious, but very well defined!).

[Rob Strand]

You can only get so much gain out of a single transistor stage.    High gain pedals need more than one stage.

Not so important for pedals but multiple stages can increase the bandwidth of an amplifier.    Audio tops out at 20kHz which is handled pretty much by all transistors but if you are dealing with video or RF and you need a decent amount of gain you will need two or more stages.      If you are dealing with 1GHz then you won't be able to use generic transistors regardless of how many transistors or stages you throw at it.
(There's other reasons for multiple stages as well.)

[R.G.]

You would probably like the "Technology Of..." series of articles at geofex.com.