How to design a circuit form scratch?

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How to design a circuit form scratch?

Postby shocki » 28 Aug 2012, 08:32

I am wondering how you guys or the big companies out there develop their circuits.
Basicly you have three options

1) Copy what is out there. Change some componentes and add some pots and switches. Try different Transistors. I think this is the way most companies do it today. The circuit in this case is nothing new.
2) Develop your schematic from a pure theoretical standpoint. With a software like sSpice and calculations. I think this must be pretty hard to judge how this will sound when it's finished. But the circuit in this case could be something new.
3) Build your effect step by step mainly be ear and trace the singal path. So lets say you put a transistor first. You add some pots and tweak them until it sounds good. Than add second transistor. Tweak it until it sounds good. Maybe add some caps to change the filter response. In the next stage you build a filter circuit. And so on.

Of course a combination of those 3 concepts could be possible. I am really wondering if someone has the knowledge to do like I described in 2) and if some every tried it like I described in 3)
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Re: How to design a circuit form scratch?

Postby meffcio » 28 Aug 2012, 09:37

I am pretty sure another kind of approach works for the 2nd option. You imagine what kind of sound you'd want to achieve. Then you build circuit up stage by stage from theoretical calculations. Like, let's say, we want a bassy distortion - so we take some approach on signal boosting and clipping (the kind that suits your imagined sound), and combine it with some sort of lowpass filter, or bass booster, or something else. It's still a lot of experimenting, but you're not that blind to how the circuit should look like. What I mean is that you can easily draw a block schematic, and then just suit individual circuit stages to achieve the sound you want.
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Re: How to design a circuit form scratch?

Postby jonasx26 » 28 Aug 2012, 11:35

Trying to do #2 without knowledge leads to doing #3..

I usually start with drawing a rough block diagram. Something like;
Input > 6dB gain > Invert > Mix with something else > Fullwave rectify > Trigger circuit > etc..

Next step is usually simulating and/or prototyping the less obvious circuit blocks or functions, comparing different configurations and variations.
Not very precise with math, just ballpark-values to start off with.
I do most of the math and "tuning" when the basic topology seems to do what I want.
Most of the time I'll have to go back and revise the block diagram for optimization (or changes in "design goals").

Of course it all depends on what effect you want to achieve, the circuits you're designing and how they interact, and so on..
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Re: How to design a circuit form scratch?

Postby FiveseveN » 28 Aug 2012, 12:28

1. learn electronic engineering
2. apply knowledge
3. ?
4. profit
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

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Re: How to design a circuit form scratch?

Postby jonasx26 » 28 Aug 2012, 13:11

I'm studying electrical engineering. (actually in class right now)
I personally don't think a formal education is strictly necessary.
Genuine interest and curiosity beats education every time IMHO.
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Re: How to design a circuit form scratch?

Postby meffcio » 28 Aug 2012, 13:59

jonasx26 wrote:I'm studying electrical engineering. (actually in class right now)
I personally don't think a formal education is strictly necessary.
Genuine interest and curiosity beats education every time IMHO.

Also applies for me at least. I'm also studying EE, and it was the knowledge from fsb and diysb (and some other diy boards) that helped me with some of the subjects.
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Re: How to design a circuit form scratch?

Postby FiveseveN » 28 Aug 2012, 14:08

jonasx26 wrote:I personally don't think a formal education is strictly necessary.

That should be fairly obvious, considering the number of successful effect and amp builders who didn't need one. I've also heard through the grapevine that the curriculum is fairly bloated and not very applicable to real-world scenarios.
I was being facetious, of course. What I mean is you need a systematic understanding. It matters not if it comes from a book or a college lecture or a YouTube video or a post by R.G. Keen.
You need to understand charge carriers, then Ohm's law, then semiconductors, then biasing and amplifiers and their nonlinearities and filters and so on.
There is also a fairly important distinction between designing a circuit to perform within a set of specs and designing an effect for various aesthetic goals. Sure, there are plenty of engineers that wouldn't know the difference between SRV and Metallica and there are plenty bootek cloth-insulated-wire-sniffers that don't know the difference between tantalum and ceramic dielectrics but swear that their circuit would not perform as well if one were used in place of the other.
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)
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Re: How to design a circuit form scratch?

Postby jonasx26 » 28 Aug 2012, 18:43

Totally agree with you FiveseveN.
Most formal education is very broad and generalized. You essentially 'learn to learn'.
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