Help with IC circuit fundamentals

[eightsevenzero]

I’m a little ashamed to admit this but I cannot for the life of me get any IC based schematic to work! I’ve built quite a number of non-IC pedals and they all make complete sense but any time I go to logically follow a schematic for an IC design it passes unamplified signal but never works farther than that. My supply voltage tests correctly and I try to check my wiring but it seems correct.

Is there an absolutely dead simple TL072 boost circuit someone can link that could allow me to diagnose if this is a breadboard issue or something? I’m looking to eliminate the most margin of error and use the most limited amount of parts. I feel like a complete idiot!!
Thanks!

[ElectricDruid]

Have you tried breadboarding some basic op-amp circuits? Simplest I suppose is a single op-amp like a TL071 (or 741 if you were born back in the day!...).

Here's a link for a straightforward op-amp input buffer:

https://electricdruid.net/wp-content/uploads/2018/12/StompboxElements.jpg



I use one of these on the front of pretty much all my pedal designs. Note that it uses the "Virtual Ground" bias shown in the bottom right. This is shown as half a TL072, but you could do it with a TL071 if you adjust the pin numbers accordingly.

HTH

[iainpunk]

maybe try a MXR DIST+ or a Blue Clipper or a DOD250. it uses only one of the opamps, you can ''deactivate'' the other opamp by linking the output and the (-) input directly and ground the (+) input.

cheers

[eightsevenzero]

Just tried the buffer circuit you posted and I'm more confused. It won't pass a signal at all. Gets 3.5v to pin 3. I know I must be doing something stupid wrong, but I cannot figure it out.

[iainpunk]

Just tried the buffer circuit you posted and I'm more confused. It won't pass a signal at all. Gets 3.5v to pin 3. I know I must be doing something stupid wrong, but I cannot figure it out.

what are the voltages on the other pins of chip?

cheer

[niektb]

I may have overlooked something but did you connect power to the IC?

[FiveseveN]

Well, can you blame him? There's no power on the schematic either

[eightsevenzero]

Attached is another pic of how I have it wired. I'm sure I'm missing something in the fundamentals, I hope you all can be gracious with me. I have power coming in on pin 3 which is how I understood it to be wired via the schematic. There's 3.5v at pin three but no other pin is outputting meaningful voltage.

[edvard]

For an Op-amp circuit, you need 3 connections to power; Positive voltage, Negative voltage, and a point between them called Ground.  Most circuits only need Positive Voltage and Ground, but Op-amps are different.  The breadboard circuit you have only has one connection; without Negative voltage and a Ground to bias the input, your circuit isn't going anywhere.  Give me a few and I'll whip up something you can follow, or somebody else will jump in before I can fire up a graphics program.  Either way, that's what I'm seeing.

EDIT: I just looked up the pinout for a single Op-amp, and you have positive voltage going to the +input, that's not going to have anything happening.  Your -voltage needs to go to Pin 4, and +voltage to pin 7.



If you're using a dual Op-amp, +voltage goes to pin 8

[BJM]

Is there an absolutely dead simple TL072 boost circuit someone can link that could allow me to diagnose if this is a breadboard issue or something?

AMZ has some simple op-amp booster schematics, the three last schematics on this page:
http://www.muzique.com/lab/boost.htm

Note the power supply is not included in the schematics.

[antonis]

[eightsevenzero]

Now it's starting to make sense, thank you!! Hooked up 9V to pin 8 and G to 4 and lit up.

[ElectricDruid]

Well, can you blame him? There's no power on the schematic either

Absolutely my fault! I agree!

There's a serious point in here somewhere about the assumptions that experienced people make and the shortcuts they assume and the problems that gives people who don't know those rules yet.

Anyway, very glad it's working for you now, eightsevenzero. Welcome to the wonderful world of op-amps! There's a *lot* of circuits now available to you!

[PRR]

Go back to days of vacuum tubes.

Heaters are rarely 'wired' on schematics but the darn tubes won't work until they are connected.

And remember ALL power needs an IN and an OUT. 2 wires (at least).

[edvard]

OK, here's how I'd do it; your layout may vary, but the basic ideas should be the same.  I will assume that your power strips (the dual rows on either side of the breadboard) are continuous all the way down.  The outside left will be the Negative, outside right will be Positive, and the inside tracks of either side will be the virtual ground (+4.5v really, but it works out).
- The two 100k resistors and 22µF Cap make the virtual ground.
- The second op-amp is properly disabled by grounding the +Input and shorting Output to -Input. 
- The 10k/47k pair gives the Op-amp a gain of 5 (ish).  If you want more, increase the 47k, if you want less, decrease it.
- Capacitors on Input and Output make sure that the 4.5v bias doesn't show up as DC at the jacks.

[antonis]

- Move 22μF positive plate on 100k/100k junction and negative plate to battery (-)..
- Make 100k/100k voltage divider values 10k to 22k ..
- Move INPUT jack tip wire in series with 10nF cap (where sleeve wire goes) and INPUT jack sleeve wire to battery (-) column..

[iainpunk]

Go back to days of vacuum tubes.

Heaters are rarely 'wired' on schematics but the darn tubes won't work until they are connected.

And remember ALL power needs an IN and an OUT. 2 wires (at least).

reminds me of the first Matsumin Valve Caster i tried to build.

cheers