First breadboard project, and having problems.

[Tranin]

Alright, I've been trying to build an MXR Dist+ as my second project, and I have rebuilt this thing 3 or 4 times with no success...that being said, I still want to get it working, but I have a few questions.

Trying to breadboard it, its quite possible I'm doing something wrong there, but, I don't think so...but then again, I've thought that before, and been wrong. I can always snap pictures later if need be, but for now, I'm just curious about a few things, just wanted to throw out this is on perfboard so people don't worry about my soldering and what not.

First question: I ordered my parts from smallbear, I ordered the two pots necessary, but I'm unsure if he sent me the right parts. The volume pot I ordered was a single gang, but he sent me a double gang, no big deal, its just big, but it's the right value, and it works. I ordered the rev log pot for the gain, that I have had issues with. What I'm wondering is if he maybe sent me a regular 500k log pot instead of the rev log pot, but I am unsure how to check. As I'm typing this, I'm thinking using the multimeter in some way would probably work...but unsure how...

Question two: The IC...OK, the first two times I built it, I was being dumb, and counted the pins clockwise, not counterclockwise. After I figured out I was doing that wrong and fixed that, I got sound through it, the vol pot worked, the gain pot didn't do anything until it got to like...98%, and then I would get REALLY bassy distortion. I think I got the pinout on the ic right that time, that was build number 3. However, just last night, I took it all apart, and back together, and again I get sound through it, volume pot works, but the other pot does nothing now, and its a lot quieter then its should be(if I take the cable out of input and plug directly into amp, it gets a lot louder.) Just to make sure, I've created the crappy image below, this is how I'm counting the pins, please let me know if I've got this wrong



Other than that, I'll do some checking on voltages, but does anyone know what I should expect to find for each pin? I'll also put the schematic I'm using on here. I've verified I have the correct values for caps and resistors 4 times now, so I'm fairly confident in saying they are all correct. The only question I have on the schematic is the dotted line for C5..not sure if thats just a line that didn't come out right, or if that means something special. I have just put them on the board in parallel(I think.) Enough for now, hopefully I'll get some ideas from whats already been asked.


Thanks Again,
Tranin

[GibsonGM]

Hi Tranin,

To check the pot with a meter, measure the resistance at about 1/2 rotation...if it's obviously not 1/2 the pot value, it's log taper.  By turning it in either direction, you can then determine whether it's reverse log or standard log...watch which direction the values change in (look up The Secret Life of Pots at GeoFX for a better explanation).  I've never had a prob. with Smallbear, and if you tell Steve about the pot mixup you'll probably get a good explanation - he's a nice guy and good to buy from.

To test if the trouble is with your drive control....replace that pot (R7) with a low value R, such as 1K or even 500 ohms or so. See if you get a dirty output.  Then try 68K or so, see if it cleans up.  Remembering that pots are just variable resistors, we can remove them & 'hardwire' a resistor on the breadboard to test their function.  As long as R6 is there, you can even just jumper the pot and get max drive!  R6 is a limiting resistor so when the pot's at zero there is minimum resistance in the ckt.

If this doesn't clear things up, I'd try audio probing the ckt. to see where the trouble lies.  Your pin sequence is correct, BTW. 

To get you going, pin 4= 0V, pin 7 = battery V+
at R2/R3, you should have the bias voltage, about 1/2 V+
At pin 2 and 3, about 1/2 V+

The cap in dashed lines is a bypass cap, to slightly tame the really high end this thing delivers on max gain (freq increases as you turn up the gain).  It's optional, and yes is in parallel.

There's always a chance you zapped the 741, so if you have another you might sub that in there to be sure, until you get it working!  1 less thing to worry about.  Keep working on it, and post back - others will pitch in - gotta run, I am late for an appt!

Later

[Tranin]

Always with a fast reply! I wont get a chance to mess with it until tomorrow, at work, and after working, going to jam with some coworkers. I'm not too worried about the bigger pot being sent, like I said, as long as its the right value, I'll make it work, although, it would be nice if I could snap the bottom gang off, just nto sure if thats possible without breaking the top one...I'd order from him again, I just thought if he sent me one wrong pot, maybe the other one could be wrong too, but I'll check out that Secret Life of Pots as you suggested and meter it tomorrow.

I still need to make me an audio probe...maybe I'll stop at radio crap, er...I mean, radio shack and pick up something to make one out of.

You said another thing I was wondering about too, the possiblity of frying the 741...I hope not, I only ordered one, although, I think that is one thing that radio shack *MIGHT* have had...but I'd have to check again.

I'll let you know how it turns out manana!

[mattpocket]

you made sure the IC is not connected across the middle didnt you? You need to straddle it over one of the central columns so there is no continuity between pins 1-8, 2-7, 3-6, etc...

Matt

[Tranin]

The IC is indeed straddled over the central column, I could see how that would be an easy mistake to made, but lucky for me, not one that I made. I'll get this thing working tomorrow, or, maybe have more questions, we shall see, but right now I'm beat, just got home from jamming for about 4 hours, so I'm going to bed.

[FisTheGoon]

Maybe the Ic is dead.Try to change it if you got the spare.My 5cent of advice.

[mattpocket]

It will probably be something really simple... how do you have it wired off board?

[Tranin]

To get you going, pin 4= 0V, pin 7 = battery V+
at R2/R3, you should have the bias voltage, about 1/2 V+
At pin 2 and 3, about 1/2 V+

I just measured voltages, right now, battery is at 9.1VI measured as following:
pin 4: 0V
pin 7: 9.1V
pin 2: 4.51V
pin 3: 1.82V
pin 6: 4.51V
R2/R3: 3.02V

Sounds like I might have something messed up in the R2/R3 area(I'm not sure, but I'm guessing that even C3 could be part of the problem here, so I'll check that whole first part of the circuit), so I'm gonna recheck my values there, but I gotta do a little running with da wife before she goes to work, so I'll get back in an hour or two with what I find...if anything.

[Tranin]

Alright, I just got home from radio shack, bought a couple new 741's, put one of the in, and that did not help, and I am getting similar values when I read voltages(a little lower because I left it plugged in while I was gone.) I just went through all the resistors and caps in front of the ic, and cannot find any that are incorrect. I could take a picture, but I'm not sure if it would help...I replaced the gain pot with a 1K resistor, and its completely clean and still much quieter than it should be. I'm just not sure if I should be looking at the beginning of the circuit, or maybe something between pin 2 and where it meets with output from pin 6. Any thoughts on where I should check next would be appreciated.

Tranin

[Tranin]

Well, we have good news...and...stupid news...

Good news: It works

Stupid news: I got R8 and R9 switched around...so apparently, the values on the ic are fine, I might plug the old IC back in just to make sure it works...Still have that 1K resistor in for the gain pot, but I can deal with that, now that I know it works...kinda buzzy, but I have a feeling it will be better when not sitting right in front of my monitor(yep, just turned it off and much quieter  )

Thing sounds pretty nice too...I'll be making this on a pcb for sure! I bought an etchant kit today, so we'll see if I can get that done correctly.

Heres what it looks like if anyone cares...



Cheers,
Tranin

[GibsonGM]

Glad you figured it out, bud 
We usually do figure out our own mistakes, it just takes prodding from other forum members!!

Look into the audio probe - you only need 1 cap (I used something like .22uF) and some old wire.  Using a big cap (1uF etc) will allow the signal you hear to be basically unchanged from what's really there - smaller values can make things tinny due to their highpass nature....