Am I missing a secret - any circuit with an Opamp fails

[Sacorus]

I searched before I posted this new topic - hoping I could find an answer...

Pedals I build with Transistors work fine - be it either designed from building blocks or the occasional clone

Pedals with an Opamp in them - zero success

I use Eagle for schematics and layouts

I have tried on breadboard (just tried the Intro IC based OD before I posted this)

And build on Perf and strip board (and occasionally a bought PCB)

I have multiple choices for ICs - 741 4558 TL072etc

I have a good multimeter (Fluke) a good solder station and plenty of parts

I have had pedals with CMOS chips work and also successful builds with PT2399

Is there something that I am missing???

[Rob Strand]

Probably something simple.

Get a simple opamp buffer circuit working on a breadboard and take it from there.

Maybe there's something wrong with the way you are interpreting pinouts for IC's?

Are you wiring the power pins?    You need to wire those even when the circuit doesn't show them, it's kind of understood (although some circuits can be ambiguous).

If you can't get it to work, measure the voltages on each pin of the IC and post them.  Post a pic of your board.

There's plenty of people on the forum to give you a push.

[Sacorus]

Not just the one board

Anything I try

example on a dual op

V+ on pin 8
GND pin4

Set up a voltage divider for Bias (virtual ground)

all checked and measured with the multimeter

[Sacorus]

[Sacorus]

Passes no sound

I checked the signal path from the opamp side of the input cap - signal is gone at that point

[GibsonGM]

I'd try a simple buffer as suggested, Sacorus.   Many SINGLE opamps like 741, TL071....V+ is pin 7. That's an easy place to make a mistake.

Try measuring right on the chip's pins (but don't short it out!) could be a bad connection at the breadboard fooling you. 

It's easy to screw up pin numbers in the feedback area, too, and have R's etc going back to the wrong input...

HTH!


*****saw your last reply - check for continuity with input pin &  the input cap's leg on the opamp side. Could be breadboard...pressing on the back of them sometimes re-seats the metal clips inside...or else something is grounding out your input signal (?)

[antonis]

Something weird happens here..

Does white aligator clip bring input signal on non-inverting input (pin 3)..??
If yes, I can't see any feedback resistor between inverting input (pin 2) and output (pin 1)..
(or I can't trace well the combination of 3 blue body resistors around left side of the green cap..)

[ElectricDruid]

+1 agree with Antonis. I think something is weird in the feedback network.

I'd pull those bits off the breadboard and stick a simple wire loop from pin1 to pin 2 (e.g. turn it into a voltage follower/buffer). Once you've proved that works, you can add the non-inverting gain feedback components back in.

Also start with just the bare essentials for gain - two resistors, or one resistor and a pot. When that's working, you can start adding in extra resistors to adjust the pot range and caps to change the frequency response etc. etc. For starters, keep it simple.

[Rob Strand]

You should check pin 1, the opamp output, is at about 4.5V.
If that isn't true the whole thing will fall in a heap.

[duck_arse]

Not just the one board

Anything I try

example on a dual op

V+ on pin 8
GND pin4

Set up a voltage divider for Bias (virtual ground)

all checked and measured with the multimeter

this is not a circuit diagram. please, PLEASE!!! like james brown said, please - draw a circuit diagram, and then show it to us. please?

[Sacorus]

Apologies on the delay getting this up

(Had to get some enclosures finished)

[GibsonGM]

Took a quick look...As drawn, the power supply appears short to ground at the 100r resistor...which also is not necessary.  But I'm sure that ground symbol there isn't real, correct?  If this is for simulation, it will cause an error.

I would change R4 to 1M.  As it stands, the gain ratio is not working in your favor.   You might take a look at this for a better understanding, in the part about voltage gain:
https://www.electrosmash.com/mxr-distortion-plus-analysis

R9, 470r...seems too low.     HTH!

[ElectricDruid]

Gibson, I think that 'ground symbol' thing is a +9V port - it's labelled.

If you're going to use the 100R resistor, you need a decent size electro cap across the power rails, fro your +9V to ground. Then you'll have a proper lowpass filter to reduce noise and/or hum on the supply. Otherwise, get rid of the 100R because it doesn't do anything on its own.

The rest of the circuit looks fine, but there's a lot of bits I wouldn't put in initially. I already mentioned the feedback network. I'd build it minimally first, get that working, and then add the other bits. If it *stops* working, then you know it's something you've just done and you can take a step back. If you go straight in, you know there's a problem, but it could be *anywhere*.

[ElectricDruid]

I suggest you start with this:

[antonis]

I suggest you start with this:

Just green line short is enough..
(no reason to delete that magnificent broken elbow wiper of GAIN pot..)

@Sacorus: GAIN pot C stands for reverse-log taper mark and should come after its value..
(or else, it could be easily confused with capacitors numbering..)

[deadastronaut]

do you have continuity across your + and - rails...?

most breadboards have a split in the rails.....and need jumpers to connect them.


also add jumpers to the top and bottom rails. +/-

[bluebunny]

I assuming that the floaty unused half of the 4558 isn't actually left unconnected.  (Connect - to OUT and V_REF to +.)

[Sacorus]

I appreciate the help -
i will try without the additional parts

and I normally use a 100u Electro across past the 100ohm on the supply

And breadboard rails where joined - I also checked with my multimeter

[antonis]

i will try without the additional parts

As you like..

But Electric Druid suggestion for shorting Out and inverting pins release you form checking individual items & combinations..
(it converts op-amp configuration into a unity gain buffer so you don't have to deal with NFB/Gain loops for the moment..)

[Rob Strand]

Checking all the DC voltages on the opamp pins would be a big help.