checking as you go...

Ok, you got your soldering iron and nothing is going to hold you back, but you have no clue where to start or what to build. There were others before you with the same questions... read them first.

checking as you go...

Postby fireflyva » 28 Dec 2013, 20:40

First of all, I am a newbie. Let me dispel any myths anyone might have about my abilities.

I've spent a good amount of time reading books and articles and this forum about how to build, solder, etc.... and have attempted to build the janglebox pedal 3 times (at least) none of which ever works (obviously). After the last attempt, I put down my soldering iron and walked away for about 4 months because I was so frustrated. Now I'm returning hopefully with renewed enthusiasm and hunger.

My question: when building a pedal/stompbox, as you build it, do you go along and make measurements (measuring voltage/resistance/etc....) as you go along so that you don't complete the pedal before seeing if it works (like I've done)? Can this be done with someone with little experience, a lot of desire, and measuring box (measures voltage, resistance, etc....the name escapes me at the moment)? How would you know what the values should be?

I have all the components, the schematic and a breadboard. What do I do?

Thanks....
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Re: checking as you go...

Postby Nocentelli » 28 Dec 2013, 23:24

I would lay out the circuit on the breadboard (all in one go if it is relatively simple), and see if it worked. If so, great, time to make a pcb/vero layout and get building.

If it doesn't work, but you know it should (because others have built successfully from the same schematic), it's time to start debugging. This is relatively easy on a breadboard: First check every component is the correct value and is placed correctly according to the schem. If you're confident this is the case, check the power: You should have +9v or whatever where it says you should on the schem; Check the grounds - You should have zero volts everywhere it say ground on the schem; Check the Vbias if there is one (many schems have a half supply: if it's not denoted on the schem, it may well be present at the point of a voltage divider, i.e. two resistors, usually equal value connecting from zero volts and +9v/whatever max supply is) they are usually found on or connected to either input of an opamp, or the gate of a JFET, or occasionally the base of a BJT.
If you have a regulator (e.g. 5v regs for digital chips) also check this.

If the power, ground and any other fixed voltages look good, hook up the audio and see if there's a sound. If bypass works, but "in" is not working, the next approach is to "audio probe" from input to out to find where the signal disappears (I just use a crocodile clip and long wire hooked to the input of the volume pot, and touch it along the signal path from the input jack).

DIYstompboxes has a good debugging protocol that says to post schematic, any revisions/substitutions and post voltages from transistor and opamp pins: Many problems can be diagnosed from this information alone... Post here and at DIYSB and someone will help you track down the problem. Good luck.
mmolteratx wrote:absolutely zero commercial use allowed. If I find anyone selling these, I'll fly to your house and kick you in the nads. And you may or may not find yourself in trouble.

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Re: checking as you go...

Postby dwmorrin » 29 Dec 2013, 05:35

I would suggest starting with simpler projects than a compressor.
The more "in tune" you are to the workings of a circuit, the more likely you'll assemble it correctly, and the more likely you'll debug it successfully.
I remember my first breadboard attempt at a fuzz face well. It was very confusing, took forever, and I had no idea "why" anything connected anywhere.
Now, I can picture schematics in my head, and I "know" what to put where just like you learn the notes and scales on the guitar... in the beginning your head is spinning from looking up at something (schematic or layout/sheet music) and then down at something else (guitar/breadboard).

You're trying to build and debug a compressor? That's an audio amp with some kind of variable gain element... an audio to dc rectifier... that feeds the variable gain... that's 3-4x more complex than a newbie should be at. Get comfortable with building just audio amps... then get fancy.

My question: when building a pedal/stompbox, as you build it, do you go along and make measurements (measuring voltage/resistance/etc....) as you go along so that you don't complete the pedal before seeing if it works (like I've done)?


Do I measure? Yes. Constantly... no. Depends on the build too. A nice PCB from a reputable kit maker? I probably won't make any measurements during stuffing, and I'll take voltage measurements at the active devices just as a final check. A perfboard build? I'll be checking continuity (low resistance check) as I go if I have a questionable joint or whatever.
If debugging something, then measuring is the first and last thing I do.

Can this be done with someone with little experience, a lot of desire, and measuring box (measures voltage, resistance, etc....the name escapes me at the moment)?


The "measuring box" you must have is a good digital multimeter, or DMM for short. If you don't have one, get it immediately. Even the cheapest one is better than none. It is a basic skill, more basic than soldering, and it is expected of people with zero experience. Electronics 101 = multimeter use.

How would you know what the values should be?


Resistance checks should be made between things you want connected (should read near zero), and things you don't want connected (should read OL for over limit, or some kind of megaohm reading). Check resistors to match the value on the color code.
You'll not need to check current in the beginning.
Power supply voltage is one of the first steps in debugging. Check your 9V battery for >9V... and check that the circuit is getting the 9V everywhere it says so on the schematic.
Check that 0V (ground) nodes are really at 0V.
You'll have to learn about voltage division (google it) and how the active devices (transistors, opamps) react to voltages to get a grip on the voltages "in the middle."

I have all the components, the schematic and a breadboard. What do I do?


Buy a multimeter. Build a dirt simple amplifying/boosting/distorting pedal. Build another simple pedal, and another. Then hit the books again and explain to yourself why it all works. Then move on to compressors and other complex effects.

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Re: checking as you go...

Postby fireflyva » 29 Dec 2013, 19:15

thanks for taking the time to reply. Good advice. Perhaps I was trying to go "too big" with my first build. Thanks again to all who replied.
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