Stupid Box help.

[vigorandkandor]

i found this schematic for the stupid box:



i know pin 1= output
pin 2 = -
pin3 = +

do i need to use any other pins of this op-amp (tl072) to make it work?

[Jaicen_solo]

You don't need to use the remaining pins, you can just tie them to ground if you want. I'd personally use the other half of the opamp to make a second Stupid box which you can switch between. Perhaps make one with Ge diodes or one with with four diodes (two sets of two in series) for less clipping. 

[vigorandkandor]

so pin 8 doesnt need +V for the op amp to work?

pin 8= Vcc
and pin 4= Vee

i made this pedal, actually first pedal i have tried to make from scratch. i noticed in other schematic's with simalar op-amps the Vcc gets positive voltage, and the Vee is connected to ground. i bread boarded this schematic and my signal doesnt get past the op-amp. i just wanted to make sure that the op-amp is getting all the power needed.

[Jaicen_solo]

Yeah, pin 8 definitely needs to go to the +'ve power supply (usually +9v), and pin 4 will need to be grounded for anything to work.
You can't run a car without petrol, you can't run an op-amp without power!

[vigorandkandor]

just to be sure, if i just connect +V (9v) to pin 8 and pin 4 to ground it should work.


thats what i thought. thanks for your help.

[vigorandkandor]

yeah it did work! awesome. thanks for the help. sorry for being a noob kinda. all i have done in the past is mod circuits.

i thinking i might use the other half of the chip for a Microamp type boost circuit. hmmm....

[Jaicen_solo]

Hey no problems, everyone has to start somewhere! Glad you got it going.
Like I said earlier, i'd definitely consider building a copy of the circuit using the un-used portion of op-amp. If you use the same diodes as the first, but put a pair of Ge diodes in series with them you'll have softer clipping around 0.5v higher (most common Ge diodes turn on at 500mV, I use OA90 & OA91's) than the first that will give you more boost and slightly less distortion.

[LyleCaldwell]

If you don't use the second half of the opamp, ground pin 5 and tie pins 6 and 7 together.

[vigorandkandor]

i added an LED in series with one of the existing diode, and i really like what it did.
when i get an enclosure bigger than the MXR sized ones i will see about using the second half of the opamp. when i tested the circuit i used a carbon battery and it sounded fuzzy and good, when i use a power supply it doesnt sound as fuzzy anymore. could the battery really have that much of an affect on the circuit. i didnt leave any room for a bettery inside. if it turns out it does makes a difference than i guess i have to move some stuff around.

[Jaicen_solo]

It's possible that effect could have been caused by low voltage lowering the clipping threshold, or conversely a high voltage from a fresh carbon battery, who knows! Carbon batteries especially have quite significant internal resistance, so perhaps that adds some 'sag' maybe?

I was wondering if you could record some sound samples of this thing at clean, low and medium gain for me? I've just done a layout for Tim's Q&D VCF and i've got a half op-amp spare, I was thinking of putting this in front to add some harmonic interest.

[vigorandkandor]

i have played around with the diodes quite a bit in this little thing. even without diodes it will drive quite a bit. i didnt build this pedal thinkning i would love it as much as i do! it has an overdrive feel, with a hint of fuzz on top. after all is said and done i like mine with the LED in series with one of the existing diodes. i will try to get some clips recorded maybe today. if i do record it will be on a clean solid state amp, so the pedal will be doing all of the driving. the only other thing i did was i used a .15uf cap for the input.

if you go to www.subdecay.com you can hear some clips of the circuit. click on the Stupid Box link.