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[Audioguru]

Here are the input and output of your circuit:

 

[SparkyCal]

Hi guys...I hate to say it, but I need your help again .

As you know, I have been building this circuit rather successfully and have recently installed the stomp switch in prototype mode, successfully.

So I moved on to regular build on a PCB.

This happened twice now:

I get the circuit built and test the pins. Pins have the expected readings.

I then install the stomp box switch.

Now, my Pin 1 has a reading of 7.82 and Pin 2 has a reading of 7.78. Pin 3 has no reading at all.

I installed the stompbox switch according to this instruction (see attached pics)

The only part I have yet to install is the LED because I figured I want to make sure the circuit works before doing so.

Why would I, all of a sudden go from perfect readings to a reading of 7.82 and Pin 2 has a reading of 7.78. Pin 3 has no reading at all.

It may or may not be due to the switch wiring, so I am wondering what are the possible causes for this?

Thank-you

 

[bertus]

Hello,

The switch has 2 position, in wich each time 3 connections are made:


The following page will give you more details on the 3pdt switch:
https://www.diystompboxes.com/smfforum/index.php?topic=110805.0

Bertus

 

[VenomBallistics]

round actuator .... symmetrical pin grid ......
Seems to me these switches carry the potential of being rotated 90 degrees and confusing you.

 

[bertus]

Hello,

As @VenomBallistics said, is the orientation of the switch correct?
You could measure the switch with the diagram I posted and measure the pairs that are linked.

Bertus

 

[Audioguru]

Pin 3 on a single or dual opamp is the + input that must be fed the half supply voltage produced by the 2-resistors voltage divider then fed it through the 1M resistor.

The switch has nothing to do with it since the input capacitor blocks any DC from the switch.

 

[SparkyCal]

Thanks. I wil start by checking the switches orientation. Bertus, thanks for the link. @AG- I’m with you and as I said, my pin readings have been perfect, which means I am wiring the pins correctly.

How stupid of me. I think I have the switch 90 degrees off. I took a quick look. I am building a new BBQ today so probably won't have time to look further in to thus until later. Will report back.

If I had the switch wired wrong, could I have fried the op amp or any other components, or should they be ok?

 

[VenomBallistics]

If I had the switch wired wrong, could I have fried the op amp or any other components, or should they be ok?

likely not.
most of these things are rated to have their outputs shorted to ground indefinitely. About the only way to kill them is reverse power

 

[SparkyCal]

So, this is interesting.

One end of the 1M resistor (the end that connects to the two 100K restores to make the voltage divider, measure at 3.8V - whihc is normal.

BUT..the other end of the 1M resistor- the end that goes to Pin3, measures 0 volts coming out- which is a problem. Does this mean that the 1M resistor is no good?

 

[VenomBallistics]

So, this is interesting.

One end of the 1M resistor (the end that connects to the two 100K restores to make the voltage divider, measure at 3.8V - whihc is normal.

BUT..the other end of the 1M resistor- the end that goes to Pin3, measures 0 volts coming out- which is a problem. Does this mean that the 1M resistor is no good?

Probably not.
Set to ohms mode and test across said 1M to be sure, but I'm betting that it's fine, and your volt meter has an impedance low enough to sink the remaining current

 

[Audioguru]

1) If the voltage divider measures only 3.8V then your 9V battery is almost dead at only 3.8V x 2= 7.6V and its voltage will continue dropping. Maybe the opamp is defective and is drawing a high battery current?
2) If pin 3 reduces the voltage at the end of the 1M resistor to 0V then either the resistor is bad or the pin 3 of the opamp is bad.

Be certain that the multimeter is set to measure voltage, not current or resistance.
Also be certain that the marked pin 1 on the opamp is at the pin 1 on the circuit.

 

[SparkyCal]

I replaced the 1m resistor. When I tested the circuit, it worked for about 5 seconds. and then went dead. I may do a rebuild. Something is quirky. Maybe a faulty component.

 

[bertus]

Hello,

Are you buiding on a breadboard or PCB?
Are you using IC sockets?
If so wich type?
The dual leaf sockets are not as stable as the turned ones:

https://www.petervis.com/electronics/DIP_IC_Sockets/IC_Sockets.html

Bertus

 

[SparkyCal]

Hi Bertus: Yes I am. I have both kinds, but on this build, I am using the Turned Pin type.

I just built the new voltage divider part of ther circuit. Before the 1M, my volt reading is 4.7. After the 1M, the volt reading is 4.2. I am using a new battery now. I think those readings are good- right?

 

[bertus]

Hello,

When your multimeter has an input impedance of 10 MOhms, a voltage divider will be made.
You will measure about 10/11 X 4.7 Volts = 4.27 Volts.
It can be a little lower due to the input impedance of the opamp in parallel with the multimeter.

Bertus

 

[SparkyCal]

Thanks Bertus.
Here is a pic of my new build this far. The voltage divider has been built and I just fastened the socket for the op amp. Nothing else has been done yet beyond that.

Question>

The circuit calls for a 10nF capacitor just after the input (this is a change AG recommended- the original had a very high capacitor value that he thought was too big).

My question is this: I am running out of 10nF film capacitors. When I do, can I use a 6.8 nF or 15nF capacitor instead? Or are these values too far off?

 

[bertus]

Hello,

For the capacitor, look back in one of your other threads what AG said about the capacitor.
The 15 nF will have a longer settling time and more low responce.

Bertus

 

[SparkyCal]

Hello,

For the capacitor, look back in one of your other threads what AG said about the capacitor.
The 15 nF will have a longer settling time and more low responce.

Bertus

Thanks Bertus. Yes, I remember that. But the original schematic had a 470nF capacitor- whihc, as AG said, was way too big. So. given that it started with a 470nF, just wondering if it would work with a 15nF even though it may take a little more time that a 10nF. Far better than 470-nF I would assume.

 

[SparkyCal]

I bought some 1uf capacitors. They only had 50volt ones, so I bought those. I didn’t realize that their cap size is bigger. Aside from the size inconvenience, there is no reason they wouldn’t worth in this circuit right?

 

[bertus]

Hello,

The 15 nF will be much better as the 470 nF.
The 1 uF capacitors are in the signal line.
They will be fine.

Your schematic can be found here:
https://www.wamplerpedals.com/blog/...ow-to-design-a-basic-overdrive-pedal-circuit/

Bertus