#1
Okay, I`ve been working on this OD distortion pedal and I don`t know why but I can`t get it working....

http://www.montagar.com/~patj/dodoverd.gif

Basically the problem is the 741 IC Before the signal comes into it I can get the output and it works great, after the signal goes through it I get nothing not even static. What am I doing wrong>? Any Ideas?
#3
it's difficult to suggest anything without seeing wiring, but are you sure the opamp is the right way round? Sounds obv but as i say pics would be useful.
EH


"Show me war; show me pestilence; show me the blood-red hands of retribution..."
#4
i dont understand the description of your problem, doesnt make sense to me. sounds like the IC is your issue though. make sure it is wired up correctly (ie correct pin layout and connections) and make sure it is in the right way (if socketed). then see if you have any electrolytic caps in backwards. um, cant really think of anything else without some more info/pics.
#5
Yes, pics, pics, pics.
Lefty Strat Copy w/ GFS Lil' killer rails + Crazy wiring
Lefty Kona Thinline Acoustic/Electric
Righty-to-Lefty Silvertone Bass
Righty-to-Lefty Memphis Short Scale Bass
Vox AD30VT-XL

Tascam US-428 USB Interface Mixer
Guitar Rig 3
#6
Make sure your part values are correct. That schemy looks like it can hide a decimal point somewhere. Find another schematic of the pedal and make sure the part values match.
Dot>Jekyll & Hyde>Turbo Tuner>DD-3>DD-7>DRRI
#7
Some DC levels for each of your 741 pins would help.

Looking at that circuit, all input and output pins (2,3 & 6) should be in or around +4.5V DC.
Last edited by HankMcSpank at Dec 10, 2009,
#8
Are you sure the Schematic is even correct? I mean has it been tested?
MY GEAR!
Amp
-Peavey Classic 30
Guitars
-Silverburst Epiphone Les Paul Custom
-Squier Stratocaster
Pedals
-Ibanez TS9DX Turbo Tube Screamer
-Fender PT-100
-MXR Phase 90
-Fuzz Face Clone
-MXR Carbon Copy
#9
Quote by fender4482
Are you sure the Schematic is even correct? I mean has it been tested?



surley?
EH


"Show me war; show me pestilence; show me the blood-red hands of retribution..."
#11
Quote by blandguitar
a picture of the brand name pedal doesn't mean that scheme was drawn correctly.


no but it does say at the bottom that it's a pretty common unit so i'm sure it must be a pretty well known schematic. Well here's another schematic of the same unit:



now to me that looks pretty much the same as the first pic.
EH


"Show me war; show me pestilence; show me the blood-red hands of retribution..."
Last edited by eddiehimself at Dec 11, 2009,
#12
Nobody is focusing on the obvious...most opamp probs are related to incorrect biasing. Both those circuits above are using a single rail/virtual earth arrangement, so with a 9V supply, the input & output pins should be sitting at about 4.5V DC (give our take a couple of hundred millivolts) ....we can all pontificate until the cows come home, but without some DC readings taken at those input & output pins, all we're gonnna do is guess.

It's get your multimeter out time!

BTW...for what it's worth...the distortion sound from that circuit is gonna suck canal water thru its butt - I can't believe people still bother making such circuits! It the distortion equivalent of us all still sitting around with kipper ties, droopy 'taches & massive flares, singing "Everybody was King Fu fighting". Yeah, yeah...in a digital age, a lot of folks hanker back to good old analogue (indeed I prefer some of my stuff to be analogue too)...but simple analogue doesn't necessarily = great. (roughly translated....an opamp amp & two diodes does not make a pleasing sound)
Last edited by HankMcSpank at Dec 11, 2009,
#13
Quote by HankMcSpank


BTW...for what it's worth...the distortion sound from that circuit is gonna suck canal water thru its butt - I can't believe people still bother making such circuits! It the distortion equivalent of us all still sitting around with kipper ties, droopy 'taches & massive flares, singing "Everybody was King Fu fighting". Yeah, yeah...in a digital age, a lot of folks hanker back to good old analogue (indeed I prefer some of my stuff to be analogue too)...but simple analogue doesn't necessarily = great. (roughly translated....an opamp amp & two diodes does not make a pleasing sound)


I agree. A big muff would have been much better :p
EH


"Show me war; show me pestilence; show me the blood-red hands of retribution..."
#14
Quote by HankMcSpank
...sitting around with kipper ties, droopy 'taches & massive flares, singing "Everybody was King Fu fighting"...


That sounds...


AWESOME.

And yes, either give us pics to check wiring or take readings from the IC.
#15
What are you using to power it? A battery or an adapter? A lot of wall wart adapters you find may say 9V on them but with zero load, they put out 12-14V and only put out 9V at their full rating, say 500mA, so if your circuit is only using 50mA, its probably getting 10-11V. Thats if you're using a wall wart style plug.

As others said, it could be a biasing problem. Following schematics and putting stuff together doesn't always work out part for part. Different IC's, different transistors, all have different ratings and power. One circuit I was working on took me forever until I looked up the obscure datasheet for the transistor I was using and found out it was like BEC instead of the standard EBC pinout. Another, although the IC I was using was 'compatible' with what the circuit called for, I had to bias the resistors to it in order to make it, and those values were way off the values on the schematic and its because the IC I was using expected different resistor values for its gain, etc. A breadboard helps alot when doing circuits and you can swap out resistors, caps, etc to tweak it to work.

For something that should be all science, its not an 'exact science' when you build things. lol.

And again, lets see some PICS. lol. It would help people alot.
Lefty Strat Copy w/ GFS Lil' killer rails + Crazy wiring
Lefty Kona Thinline Acoustic/Electric
Righty-to-Lefty Silvertone Bass
Righty-to-Lefty Memphis Short Scale Bass
Vox AD30VT-XL

Tascam US-428 USB Interface Mixer
Guitar Rig 3
#16
Quote by HankMcSpank
BTW...for what it's worth...the distortion sound from that circuit is gonna suck canal water thru its butt - I can't believe people still bother making such circuits! It the distortion equivalent of us all still sitting around with kipper ties, droopy 'taches & massive flares, singing "Everybody was King Fu fighting". Yeah, yeah...in a digital age, a lot of folks hanker back to good old analogue (indeed I prefer some of my stuff to be analogue too)...but simple analogue doesn't necessarily = great. (roughly translated....an opamp amp & two diodes does not make a pleasing sound)



yea, I kinda agree. I built the 250+ from BYOC and I used the distortion plus parts... it wasn't really that great. but then I swapped out a resistor and put it after a booster and it sounds a lot better. still not up to what I hoped it would give me, but I'll probably still use it for bluesy type stuff. It was the first pedal I built other than the confidence booster and I just wanted something simple, and it was... but then I added in a diode switching mods and had hell getting it in the enclosure lol.