troubleshooting a boost pedal

[cgibsong002]

just built my first boost pedal from a schematic. i'd previously built my first pedal using the GGG BMP kit. this boost was the first one i built simply following a schematic.

its a simple boost with a pot, switch, and led. problem i'm having is that, while the pot is at 12 o'clock, there is a volume drop when the effect is switch on. when the pot is set to max, there is only a very, very, slight volume boost, if any at all. there is also a noticeable treble roll-off or presence cut.

this is the boost circuit:

this is the switch layout i used:

I substituted R1 with 330 ohms. I substituted R3 with 820K ohms. Everything else is hopefully as it should. The effect seems to function exactly as it should except for the lack of volume and tone cut. I'm not sure if this is due to a circuit problem or due to the substitutions that I made.

IF it helps... I originally had the positive circuit supply attached to one of the positive lugs of the DC jacks, and the led hooked up to the other positive lug. when i had it hooked up this way, i was only getting 9 volts from ground to the positive lug that had the led was attached to. there were no volts to the other positive lug. when it was wired like this, everything functioned as it should, except there was an extreme volume cut when the effect was on. i then moved the positive power line (to the circuit), to the same lug that the LED was attached to, which I knew was getting 9 volts. This is the configuration it is in now, which improved my volume, but still seems to be lacking.


and FINALLY  hi, my name is C.J., and I plan to be here often. sorry for the lengthy first post!

[MikeH]

Hello and welcome to the forum!

I originally had the positive circuit supply attached to one of the positive lugs of the DC jacks, and the led hooked up to the other positive lug. when i had it hooked up this way, i was only getting 9 volts from ground to the positive lug that had the led was attached to.

FYI -  on most of the DC jacks we use there are 2 positive lugs as you mentioned; the interior one is for the batter snap connection.  When there is no plug plugged into the DC jack they are jumpered together, but when you insert a plug into the DC jack it disconnects the battery connection.  Otherwise bad things would likely happen.  So always use the outer lug, the inner one is for the battery.

As far as your other issue, I'd double check for any solder bridges between tracks (vero is notoriously easy to get solder bridges on).  Double check all component values.  Also double check the pinout of your transistor. 

Do you have a volt meter or a multimeter?  I'd suggest getting one if you don't.  It's almost impossible to debug without: a) a voltmeter, b) a continuity tester (a common feature on most multimeters) and c) an audio probe- which you can make easily... if you do a google search you can find a diagram.  It will also be easier for people to help you if you can post voltages from your build.

And last but not at all least, look at this:  http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Good luck!

[cgibsong002]

thanks! i did take a look at that thread, forgot to mention i do have a multi-meter. not sure what type of values i can expect however. could you guys possibly run me through some measurements that might lead me to an indication of where my problem might lie? it might also be likely that my two cuts (as described in the schematic) in the board might not have been clean cuts. i used a screwdriver to just etch away at the copper strip at those two holes until the copper was gone. i'm fairly sure theres a solid gap, but i figured i'd at least mention if it helps.

also, about the dc jack, i was kind of thinking the same thing, that the other lug is only for the battery snap. i am, by the way, powering the pedal with a one spot dc adapter, with no battery snap connected.

[Quackzed]

not sure about voltage readings , but i'd look at that cut under r4, as well as reheat / resolder the volume pot connections... my money is on the r4 cut tho....

[MikeH]

Your multimeter should have a setting that looks like a diode:  -->|--  Sort of like that.  On mine, when I have it on this setting it beeps when the two probes come into contact.  So you can use it to make sure that a trace cut is indeed cut, and also to make sure that 2 traces that are adjacent aren't connected in some way.  In short, you can use it to make sure that things that shouldn't be connected aren't and vice versa.  If you don't have the diode thingy or some other continuity checker, you could use the setting that measures resistance.  0 ohms means there is a connection.

The best thing to do is follow the protocol in that Debugging thread and post your findings here.  You are most likely to get help that way.  You've already posted the layout you used and some general info about your build, which is really great, but now we need other info like voltages off of your transistor, etc.

[cgibsong002]

that setting is actually a big help! i never knew what that was for. unfortunately, since this was my first real build, i didn't plan the layout so well. i have the circuit buried underneath all the wiring with the electrical contacts face down. so i've pretty much got to unsolder a whole bunch to be able to pull the circuit out. hopefully i'll have a chance to take a look tonight and report back.

[MikeH]

Whenever I build a pedal I first solder up the circuit board with the pots attached, and with in, out, V+ and ground wires and that's it.  I leave jacks, footswitches and the enclosure out of it until I know the circuit works.  I take my board and hook up the ins and outs and power etc to some jacks and test it out before wiring it into an enclosure- just for that reason; it's often very hard to work on the circuit board once it's all wired up and crammed into a box.

[cgibsong002]

yup, should've done that. was going to do that actually, but then i started looking at the diagram with the footswitch and saw so many wires i didn't know where to begin. i eventually just decided, screw it, just start soldering stuff and eventually you'll finish it. which worked, except for the fact that it doesn't work. i guess i didn't realize it's quite simple to just leave out the footswitch and all the extra wires associated with it.

[petemoore]

  You'll have to divide to conqueor the entire kingdom for your pathway and power.
  The cable must be mono sleeve if input power trick-off jack is assigned [plug pull cuts power].
  The guitar side tip of the cable must connect to the tip lug of the input jack.
  Skipping for luck test, or stopping to stompswitch study to determine if 1/4 turn before soldering is necessary, then continuing continuity tests through to input of circuit board pad.
  I always start with the non-V+/Gnd continuity test, as close as I can get to power supply [for no-short condition of power supply].
  Passes ?...then voltage test the circuit pins.
  Debugging, what to do when it doesn't work...read and follow, learn and debug electronics.
  Eventually, all the paths are opened, the power supply is there, amplification occurs. It is conditional, a matter of determining what they are, and setting up certain conditions.
  Sometimes the switch rotation is 1/4 turn off, requiring de and re soldering.
  A 'Full Wrapper' box...with the full set of variables is host to many a conditions some of which are difficult to explain, this is why determining the source of the problem should be the 1rst order of preponderance.
  An insulated testjig platform with 2 jacks three testclips [other clip-on or quick- to solder components like volume control are optional] makes it easy to put a battery clip on a circuit board and test it, tweek it, take it out of the debugging equation or fix it before it's 'embedded in the box/wrapper components with all their variables for problems.   

[cgibsong002]

ok. trying to make some progress here. got my circuit back out. my diode function seems to work differently. if i read my manual correctly, it seems to give me a voltage reading across the two points. so if there's a short, it would be 0. if theres a resistance, there should be a numerical value. one of my soldered points was bent towards the parallel contact strip and may have been making a connection. i fixed that. now i don't have any 0 readings across the two cuts or across any two parallel strips. i get some readings across some of the strips, but if i'm understanding the function correctly, that's simply telling me that those two strips are connected by a component, but not shorted together or else it'd read 0.

i didn't fully take out the circuit, but just disconnected enough wires to allow me to bring it to the top to work on. is there anything else i should look at or take readings of before testing it out again?

[cgibsong002]

hoped everything was fixed, cleaned everything over and double checked everything, still same results. i'm going to try to switch out the 330 ohm resistor with a 390. it's still not the 360 that's called for, but I don't have one of those, and i have a 390 laying around, so hopefully that should at least indicate whether my problem is components or circuit issues.

edit: no dice. switched out the resistor, no noticeable difference. can't figure out the problem. anyone real good with either multisim or labview 2009? I have both and am fairly good with each, but don't know how i could simulate a guitar type input signal. I've built the circuit in multisim, but I've also heard it's possible to get a realistic input signal into labview and then import that into multisim.

[blooze_man]

Maybe a picture would help if you have one.

[cgibsong002]

my camera isn't too good with closeups.. but maybe someone will notice something blatantly obvious that i assumed was obviously correct... i can take more if it helps

[Quackzed]

are the in and out jack's sleeves connected to the circuit board ground? can't tell.

[MikeH]

We need voltages off your transistor

[cgibsong002]

are the in and out jack's sleeves connected to the circuit board ground? can't tell.

yes, i have those grounds and all other grounds attached to that extra little strip board

We need voltages off your transistor

across the outer legs (Drain to source? is this a mosfet?) is 9.15 V. across the two bottom connections is .54V and across the two top is 8.55V

sorry for my lack of knowledge... we learn about this stuff in circuits classes, but we don't learn much in terms of practicality and real life applications.

[blooze_man]

I would cut those long leads off that are just hanging off the board. It's probably not be the problem but it could cause other ones.

[cgibsong002]

I would cut those long leads off that are just hanging off the board. It's probably not be the problem but it could cause other ones.

yep, those two are just from the resistor that i just switched out. i didn't cut them because i was just testing to see if the different resistor would affect it. obviously it'll all be cleaned up much better once i figure this thing out.

[Johan]

I like to always run a screwdriver down between the traces on those stripboards...it's an easy way of ensuring there are no hairline bridges between the tracks after soldering..
J

[Cardboard Tube Samurai]

It might just be me but the resistor (R1?... lowest in pic 2) doesn't look to be connected to the same strip as the others which should be the ground yeah? Also, I can't make out a wire link between this ground and the offboard grounds on the other piece of stripboard. That might just be the pics though. Also, get yourself a magnifier of some sort and look for solder bridges