troubleshooting a boost pedal

[cgibsong002]

lol, yeah, i really need a magnifying glass. and that resistor is in the right place, it's just bent under so it looks like it's going in the wrong strip (just a weird pic angle). i spent a good half hour going in between the grooves with a flathead and making sure there were no bridges. i'm really confused now as to whether this is a problem with my circuit, how the circuit is just supposed to sound, or i dunno. the guy that gave me the circuit originally designed it as a circuit to use as a booster into another circuit, with no controls or anything. so i'm thinking it's likely that this thing wasn't designed to give me the huge volume boost that i'm expecting. barring any other random thoughts or solutions you guys might have, i might just take the circuit out and replace it with something a bit different.

do you guys know of any other circuits i might be able to build using mostly the same components? i have a decent amount of extra resistors and caps of different values, but this transistor is the only one i have.

[Cardboard Tube Samurai]

Triple check the pinout of the transistor too

[cgibsong002]

Triple check the pinout of the transistor too

i assumed that the layout schematic was just set up to have it go in the same way it's facing in the layout.

if anyone can tell me what kind of current an electric guitar puts out, i already have my circuit made in multisim, i should be able to get theoretical voltage readings.

[Quackzed]

i took a look at the 5088 pinout as well as the lpb schem...looks ok to me.. are you sure that the 360r r1 is in fact just a 360r and not a 360k or something...?

heres the schem , looks like its correct to the schematic...
?!? double check the battery?!?

[blooze_man]

360r(ohms) is correct.

[cgibsong002]

i took a look at the 5088 pinout as well as the lpb schem...looks ok to me.. are you sure that the 360r r1 is in fact just a 360r and not a 360k or something...?
heres the schem , looks like its correct to the schematic...
?!? double check the battery?!?

yep, R1 is correct (well, it's 390 not 360, also tried 330). Power source is good as it's not a battery, run off my 1 spot getting 9.48 or so volts.

So this is the original circuit, huh? Are any of you guys good enough to tell me how exactly these minor changes in the circuit will change the tone? I see the original circuit uses pretty much the exact same components as the circuit I was building, so I'm curious to know the differences. Today I'm just going to unsolder the whole circuit board and re-do it. If I'm going to do that, I'd like to know the differences in the two circuits so I can build the better one for me.

edit: i also just listened to a clip of the lpb-1. mine is definitely not working like that at all, that thing sounds just like what i'm looking for. i'd like to know the differences between the two if you guys could help out.

thanks!

[Quackzed]

390 vs 360 is insignificant, i don't believe there would be any difference 1 or the other... same with 820k vs 830k no significant difference...
generally you can imagine if your resistors are 10% tolerance, meaning they are the printed resistance +/- 10%, then changing one for another of less than 10% difference shouldn't matter...
as far as a .1 cap vs. a .15 cap... the .15 cap will cut slightly less bass but just slightly, so it shouldn't affect anything other than that...
all in all, your slight changes shouldn't add up to much difference at all. at least not enough to alter the function of the circuit..
btw you can get npn transistors at radio shack 2n3904 2n2222 2n5088  etc... are all good candidates for this circuit, i think they sell them in a 'npn transistors' package with 10 or 20 transistors in it.. just in case you have a rat shack near by...
sure , just make a new board, it's a small low parts circuit, probably easier than debugging anyway...
hopefully it will go smoothly and work for you.
let us know.

[cgibsong002]

sorry, wasn't quite clear. i was wondering the differences between the original schematic i posted in my first post, compared to the actual lpb-1 booster schematic that was just linked to on this page. but, i was also curious about the differences, if any, that would've arisen from the minor changes i made to the resistor values, so thanks for clearing that up.

[Quackzed]

oh, ok - yes, i believe they are the same exact circuit.

[cgibsong002]

they aren't exactly the same. Brad's version has an extra resistor and different caps i believe. Unless I drew up his schematic wrong, here are the two side by side:

[Quackzed]

well, yeah, (i believe c1 should be .15uf rather than 15uf tho), which IS different than the lpb's .1uf - a minor difference to me, and the extra resistor is a 1m 'pop' prevention resistor, used to leak any dc to ground when wired as true bypass and in bypass... sort of a modern addition, but it's still an lpb.

[cgibsong002]

yup, the 15uf was just a mistake by me making the schematic. so they're more or less just the same circuit aside from the .1uf compared to the .15f? if the .15uf cuts less bass, why would you want a .1uf? i'm trying to keep my tone as unaltered as possible, i just want to drive my amp harder to get better sustain and harmonics.

[Quackzed]

.1uf vs .15uf ..... they'll still both cut a bit of bass, to prevent the transistor from getting 'flabby' or distorted... so basically, the orig. probably played it safe and used a .1 rather than anything bigger, though a .15 is probably fine... if you felt the circuit was too bassy you could use a .1 as well, but i doubt you'd hear a difference either way.. were talking about (estimating here) rolling off bass 6 db per octave below say 40hz vs say 50hz, both  below a guitars low end output  either way... it may or may not matter, but if you get a bit of distortion in the low end try the .1 if not don't worry about it.

[cgibsong002]

well unfortunately a case of severe food poisoning has kept me out this weekend, but i plan on rebuilding this soon and reporting back.

Does anyone have any suggestions for cutting the stripboard? I've had some ok success using wire cutters parallel to the copper strips, but I haven't figured out a way to cleanly cut perpendicular to them.

[Cardboard Tube Samurai]

To cut the vero, I score mine deeply with a craft knife  then cut it with side cutters

[deadastronaut]

well unfortunately a case of severe food poisoning has kept me out this weekend, but i plan on rebuilding this soon and reporting back.

Does anyone have any suggestions for cutting the stripboard? I've had some ok success using wire cutters parallel to the copper strips, but I haven't figured out a way to cleanly cut perpendicular to them.

I use a 5 mm drill , a few twists by hand of course , and its gone....watch for tiny burrs though ok...but it removes it nice.,.

[MikeH]

*Post removed, because apparently, I can't read  

- This is a CBE situation, not a DSG. 

[cgibsong002]

perfect, thanks guys.

Also, I ran my simulation with a fake 100mV sine wave as the input and a 9.48V DC power source. Some interesting results. (hopefully I put this schematic together correctly)

Circuit with input signal, DC power source, recording the decibel gain from input to output. Additionally, the lower the load resistor on the transistor, the greater the gain. Using a 330 ohm instead of the 390 ohm gave me just under an extra decibel.





Then this picture should be what kind of DC readings I should be getting when taking measurements with no input. It appears I should be getting a 6-7V approximate drop across the 10K ohm resistor, with most of the remaining voltage going through the transistor. So it appears like my 10K ohm resistor in my actual circuit is somehow being bypassed since nearly all my voltage is going straight through the transistor.




EDIT:

Measure from each leg (Drain, Gate & Source) to ground.  It's explained in the debugging thread, but it might talk about CBE for Collector, Base & Emitter.  But the method is the same.

Post those voltages.

I was still in multisim when i noticed you posted that, so I did this real quick. Let me check my actual data now.

[cgibsong002]

Now, correct me if I'm wrong here. But I'm getting almost the full input voltage appearing across my transistor, when most of it should be going across the 10K and only a few volts across the transistor. The Drain of the transistor is only connected to the 10K and the .15uF. If I'm getting full voltage across the transistor, it appears my 10K is being bypassed and the power signal is going straight to the .15uF. Now, if you're looking at the stripboard layout rather than the schematic, it would be very obvious that my problem is caused by lack of a cut in the first strip, correct? If there's no cut, the 9 volts would follow least resistance and bypass both of those resistors, go straight to the cap, which will then shoot the full voltage across the transistor.

Does this sound correct?

EDIT again: it appears I'm correct, at least somewhat. I just checked, and I'm getting barely any voltage across the 10K, and over 8 volts across the capacitor. But I can't see how I possibly have a jump in my cut... is there another explanation for this?

EDIT again again (I'm just talking to myself now  ): GIANT mind@#$%. for me at least. I just re-ran my simulation with a short from power to the .15uF, which would be the same as if my cut was not actually a cut. I achieved results more or less identical to the actual readings I just took. Is there another way there could be a short here even if the strip is properly cut?

[cgibsong002]

triple post... i know, i know, i apologize. but... Problem solved!! mostly.

If you can believe it... we all missed it. The transistor was backwards! I redid the whole circuit board on a new piece of stripboard, and triple checked the cuts and continuities before any soldering. everything was fine, so i redid the circuit. plugged in, and identical results. i got incredibly confused, and figured the only possible thing was the transistor. in multisim, i flipped it around just to check, and what do you know, i got the same results as i did on my actual pedal. i then flipped the transistor, and the pedal works now!

only problem i'm getting is crackling which is only really noticeable through the gain channel. i think it's my pot, the input wire to the pot (output from the circuit), was cutting in and out before. i resoldered it and now it works, but cuts in and out. i've resoldered that connection many times as it kept giving me trouble seemingly. did i possibly burn a connection, or is it maybe just dirty from having solder resin melting and possibly getting inside?