Audio Probing Help

[einziger76]

I am building an MXR Distortion Plus.  After having problems I built an audio probe.  I have my IPod Plugged into the input of the pedal and the audio probe plugged to my amp.  I am hearing music all the way to pin three of my op amp.  A question I have is should I hear music when I touch the probe to the output of the op amp, pin 6?  And where should I not hear music?  The negative side of the input doesnt play music but when I touch the resistors or caps it clears the signal I am hearing.  I have my amp on very low gain and volume on just enough to hear the music so when I say it clears the signal I mean it takes the hum out.

[DavenPaget]

Are using a single opamp or dual opamp ?

[einziger76]

Using a 741.

[electrosonic]

What are you using for an audio probe? Does it have a blocking cap? Pin 6 is biased to 1/2 the supply voltage, which might throw off your audio probe.

Andrew.

[einziger76]

I am using the same setup as the one found in the debugging section.  I have an output jack with a chord going to my amp.  I have the sleeve lug of the jack going to the ground of the 9V battery that is hooked to the circuit.  I have the tip lug of the jack with a lead wire connected to one lug of a 1uF 50V non polarized capacitor.  I am using the remaining lug of the capacitor to probe the board.

[DavenPaget]

It's a 0.1uf or 1uf ? But it doesn't make any difference anyway since it's a high pass .
Have you tried another opamp ? It seems like you have
1) floating ground
2) unconnected supply
3) nonfunctional opamp

[einziger76]

Its a 1uF.  Yes I have tried two different op amps.  I dont know what the problem is but it is becoming a very big head ache.  I used the schematic from here drawn by R.G. Keen.  I feel like I have everything wired 100% correctly.  I have made different things using schematics and have never had a problem with following them before so I feel comfortable in that area.  The only thing that concerns me is the diode part.  Will the pedal work with the diodes completely off the board?  I feel like this is where my problem is.  I want to run LED's but i have diodes configured in right now.    I understand it is hard to track a problem when I give you nothing to look at.  But my question still is with the audio probe where should I have sound and where should I not?  Should I hear music when I probe pin 6 of the op amp?  If not what should I hear?  And Is there any where I can find a verified board layout of this pedal so I can see how the diodes are supposed to be?  Right now this is what i have as far as diode layout.  Following the schematic leaving pin 6 i have a 1uF 35V Tantalum Capacitor with the positive side sharing the row with pin 6.  I have the negative side going to a new row. I then have a 10k resistor with one lug sharing a row with the negative side of the 1uF 35v.  I have the other lug of the resistor going to the top hole of a new row. I will call this hole one in the new row.  In hole 2 i have a wire going to the pot.  In hole three I have a wire going to a new row where the diodes are.  its Is in the center of the row.  I have the diodes sharing this row with a diode on each side of the jump wire.  I have the I have the diodes as to where one diode has the cathode end sharing the row and the other diode has the anode end sharing the row with the jump wire.  I have the other ends of the diodes sharing a row with a wire in the center or the row.  The wire in the center of this row goes to the ground row.  Does this sound correct?

[Le québécois]

You should have sound at pin 2, 3 and 6. 7 is Vcc and 4 is ground the other (5 and are not connected in theory.
It should work with and without the diode or led but without, there won't be distortion or little.

Best to strat debugging with a multimeter. IMO the audio probe can help when all the voltage are correct and the error was not obvious with the DMM.

good luck

[einziger76]

I have two multi meters and have no idea how to use them on a circuit board.  Lol. Ill try taking the diodes out completely and see if i can anything.  I works when the switch is on the bypass side.   

[Le québécois]

One will be enough

You put the multimeter in DC mode (select 20 v or any value close). Then you put the black wire of the DMM to the ground of your circuit (anywhere) and leave it there. then with the red wire you move around and touch opamp pin 1 by one. To test if it work just try to measure the +9v (it should +9!, if it's negative, you invert the plus and minus wire in the dmm).

[einziger76]

I took it all off the perf board and went back to the bread board.  I have signal through both the bypass and overdrive side.  It seems to be working on the bread board as it was before i started soldering.   And it has distortion.  But I am getting no difference in tone when i put the LED's in.  It sounds the same with the LED's on or off the board.  Which leads me to think the same thing as i have.  I dont have the LED's wired the way they are supposed to be.  Is there a way to add a picture to this post?  I will post a pic of how I have them on the board.

[Le québécois]

Well, LED vs SI diode or GE do not always give stunning differences. Expect something but not too much (other may disagree).

You can post picture on this site but you need and external server for your file (I use dropbox) but there is other options.

[einziger76]

I meant if I have no diodes or LED's in the board it sounds the same with them out completely.   I have no difference in tone with diodes/LED's in the circuit or out of this circuit completely.

[DavenPaget]

I meant if I have no diodes or LED's in the board it sounds the same with them out completely.   I have no difference in tone with diodes/LED's in the circuit or out of this circuit completely.

Something tells me that your gain isn't set properly (i.e resistor not touching ground or simply not touching something)

[einziger76]

I have completed the pedal and it is in working condition. Thanks to everyone for the help.   This was my first build!