no distortion

[swal]

i am building a mxr dist. plus using the ggg setup. http://www.generalguitargadgets.com/diagrams/dist_plus_sc.gif
 It is all built everthing works fine except there is no distortion.   I have checked all the connections over and everthing is ok. so i used my audio scope and there is almost no change in sound through the whole circuit, now my question is at what point in the circuit should i hear the distortion. should it be when it goes out of ic pin 2 to  the caps and res. going to the gain pot ( which is working as a volume/ tone control) ?  Or should it just be after the diodes going to the volume knob. This will help me pin down the problem. Anyone had this problem before pls help! thnkx

[petemoore]

Opamp in DIST+ distorts.
 Much more distortion is achieved when the diodes clip the signal output from the OA, anything past these diodes should sound clipped.
 Gain Knob, and guitar volume knob attenuate' clipping, I usually turn them uup, does the gain knob have influence on the circuit?
 Take Voltage measurements of the Opamp Pins from ground, include battery supply voltage and post them here.

[swal]

the gain knob changes the volume and also the tone of the pedal.  the battery is 9.18

1= 0        8= 0
2= 4.27    7= 9.18
3= 1.8     6= 4.57
4= 0        5= 0

I guess this is telling me there is a problem at pin 3 since ggg is telling me it should be 3.6v. And just to let u know the opamp works fine I just plugged it into my tube reamer and it works fine, it is one of the LM741 from radio shack.  What would be problem causeing it to only have 1.8v instead of 3.6v?

[swal]

i dont know that much about electronics so forgive if i am wrong. but, if pin 3 is only showing half the voltage that means:
There is not enough power to cause it to clip?
And the most likely problem is in the r2 r3 r4 and c1 input before the 3rd pin?
Pls help and correct me if I am wrong. I am just guessing here :?

[axr]

did you use reverse audio pots for gain??

[swal]

no but that just effects how distortion is dialed in (ie. all the distortion at the end or spread out evenly.) so there should still be some distortion. the pedal is completely clean no distortion at all.

[swal]

pls help anyone know why i would have only half of volts i need on pin 3 pls help thnx

[niftydog]

What is the voltage across C1?

should it be when it goes out of ic pin 2

it won't be going "out" of pin2 at all. Signal will go out of pin 6, and you should see distortion there or at the level pot.

the gain pot ( which is working as a volume/ tone control)

that's bad. There's something not connected properly around that area of the circuit. Check again, but remember "ASSUME NOTHING!" Be absolutely sure of the connections, don't just think to yourself "oh yes, I connected that to that, it will be working properly" you must check your own work!

Considering that you have the wrong voltage at pin 3, and the gain control isn't working as it should be, your problem(s) is(are) very likely in that area of the circuit. (R2,R3 & R4 as well as R6,R7 & R8 plus the capacitors around these resistors.)

[swal]

voltage across c1 is at 3.25

[RLBJR65]

This is what I would do, but I'm not always 100% right.

Assuming you have rechecked all the wiring and solder conections first,
then yes, look at C1, R2, R3 & R4 they are a voltage devider, If you check out some other schematics you'll notice that most opamp circuits will have similar arangements.

First check C1 it's a polorized cap make sure it's in the right way - side to ground. If it is try lifting 1 side of R2, R3 & R4 check them with an ohm meter. I've bought new resistors that were bad before so I test every one before putting them in to make sure they are within tolerances.

If they test ok you may try a trim pot in place of R4 so you can dial in the right voltage to pin 3.

[niftydog]

voltage across c1 is at 3.25

disconnect one lead of R4 and measure the voltage across C1 again.

[swal]

still comes up as 3.25 with r4 lead disconnected

[niftydog]

then there is something wrong with R2 or R3 (or both) or possibly even C1 is giving trouble as well. Dissconnect R2 and R3 and measure them.

R2 and R3 should both be 1Mohm. This configuration of resistors should result in very close to half the supply voltage across C1.

[swal]

ok i'll take that whole section of the pedal apart and measure everthing. thnk u so much for u help !!!!!

[swal]

ok took it all apart r2 r3 r4 are all 1m working fine and i put in a  brand new 1 uf cap triple checked the polarity. and i remeasured everthing.
before r2 = 9.86
after r2 = 3.28
after r4 and at 3pin on ic = 1.95
the only way i can get anything close to 3.6v at pin 3 is if i disconnect r3.  but then pin 6 jumps to 9.28 v.  
my question is what should the volts be after r2?
and what is going on? :evil:  :evil:  :evil:
i cant believe i cant get this thing working sos, fuzz face, ts, bazz fuzz, npn boost, no problem.  But this stupid dist + is driving me crazy :evil:
HELP

[niftydog]

my question is what should the volts be after r2?

R2 and R3 should both be 1Mohm. This configuration of resistors should result in very close to half the supply voltage across C1.

hint; the voltage across C1 is equal to the voltage accross R3.

- you've disconnected C1 and R4
- R2 and R3 are definately 1Mohm
- you're still getting 3.28V across R2?

That is rather strange as it defys the laws of physics.

It's begining to look like a wiring error or a measurement error.

measure DIRECTLY across R2; that is, put the multimeter leads directly on the pins of R2. Do the same for R3. The two voltages should add up exactly to the battery voltage (assuming C1 and R4 are still disconnected.)

[swal]

disconnected r4 and c1 and r2 is still getting 3.28 and across r3 I am getting 3.26. when i measure from the input of r2 to the output to ground on r3 i get 9.78.

[niftydog]

R2 = 3.28
R3 = 3.26

across both R2 and R3 = 9.78.

This is not possible. The sum of the voltages across R2 and R3 should equal the voltage across both resistors.

3.28 + 3.26 = 6.54

This leaves 3.24V unaccounted for.

Either you're measuring this incorrectly or there is something else inadvertently connected to this circuit that is dissipating the remainder of the voltage. If the circuit was as shown below, there is only one possible result, and that is that you have roughly 4.5VDC across both resistors.

Code Select Expand

  9VDC
   |
   o
   |
  .-.
  | |1M
  | |
  '-'
   |
   o-----------4.5VDC
   |
  .-.
  | |1M
  | |
  '-'
   |
   o
   |
  ===
  GND

[swal]

sorry the volt over r2 and r3 was not 9.+, it was 6.54 sorry

now when i disconnected everthing except just r2 attached to the battery clip so it was 9v battery to r2 (1m) it read as 3.28. should this be reading as 4.5 because its not? and also also tried with a another 1m and it also reads 3.3. and i double checked to make sure it was a 1m res

[niftydog]

the volt over r2 and r3 was not 9.+, it was 6.54

ok, but the voltage across those two resistors should be equal to the battery voltage. If you've only got 6.54 volts, then you either have a very dead battery or there's something incorrectly wired.

i disconnected everthing except just r2 attached to the battery clip so it was 9v battery to r2 (1m) it read as 3.28.

ok, you need a "circuit" first. a 9V battery connected to a 1M resistor isn't a circuit, the other end of the resistor must be connected back to something to close the circuit. Can you be more specific?

I'm concerned about your measurement techniques. Here's some tips.

- Take the black lead of your multimeter and connect it to the negative of the battery. Now, LEAVE IT THERE - Do NOT move it! All of your measurements should now be made by using the read lead only.

- Measure the batterys voltage while it's connected to the circuit. Measuring the battery out of circuit is not useful.

Now;
- measure the voltage at the "input" to R2 (should equal the battery voltage)
- measure the voltage at the "input" to R3. (should be half of the battery voltage)
- measure the voltage at pin 3 of the op amp. (should be very close to half the battery voltage)