Opamp noise, sound cut off

[duck_arse]

Phew. Finally worked. Didn't have a 10uF so I used a 1uF for the power supply and a 47uF and 1uF in series for the output (resulting in ~9uF), worked out nicely. Thanks for the help yall (and sorry for throwing a bit of a fit earlier, bad temper and no sleep don't mix, I'm afraid :/)

see? yer a natural, what with the subbing values and all.

one thing tho - when you put caps in series, the overall capacitance is always less than the lowest value cap. 1uF in series with 47uf will be less than 1uF of capacitance. so 979nF, not 9u7. and as that series string works for you, you can just use the 1uF instead. you have proved that value yourself.

[amz-fx]

Last schematic is prone to noise, due to big supply resistors..
(with all respect to Jack..)

No offense taken since the examples posted on that page are just building blocks that a designer would use to then create a final design by adding other elements as required. However, I have seen (at least) two commercial buffer pedals that use that example exactly as it is shown on the page without change. It will be okay with a battery but there are no pulldown resistors or power supply filtering, for example.

regards, Jack

[anotherjim]

Does anyone know where there is a one-stop article for newbies explaining why we do things differently with op-amps compared to what the standard & educational sources show?

[amz-fx]

Are you talking about how most op amp source material shows dual power supplies?

Historically, the 9v battery has been the power source of choice for pedals, so some engineering is required to configure the op amp for a single supply - I believe that Analog or Burr-Brown had an app note about running op amps on single supplies.

regards, Jack

[antonis]

Does anyone know where there is a one-stop article for newbies explaining why we do things differently with op-amps compared to what the standard & educational sources show?

Right aside the article explaining differences between Real ground, Mains ground, DC ground, AC ground, Virtual ground, etc.. 

[PRR]

> for newbies explaining why we do things differently

http://www.geofex.com/circuits/what_are_all_those_parts_for.htm

[Tim Age]

So since it all worked out yesterday, I moved the power supply from breadboard to perfboard today, soldered it all together - boom, same issue as initially. I swapped the cap values as recommended (47uF for power supply, 1uF for output), wired a 741 up on the breadboard, connected the power supply I'd just built - noise, hum, stutter. Just added a diode to protect against reverse polarity.

Wired the 741 for unity gain, input and output caps are the same that did the job yesterday, all grounds connected... doesn't work.

[GibsonGM]

1) I don't like the diode that way, tho it will work. You will lose about 1/2 volt with it in series.   Best way (only IMHO) is to use it parallel, so it would be cathode TO 9V, with anode to ground.     If you're having trouble, take it out, take your output from the 9V behind it. 

2) use your meter to be sure you have ground on the left, 9V on the right, and about 4.5V in the middle, oriented as your pic is.     THEN connect it to the rest of the circuit.   This will assure you DON'T fry anything from reverse polarity.

Did you connect your chip's "+" and ground connections?    All the grounds to one spot on the board, the in/out jack grounds too?  Is your IC in a SOCKET?  If not, you probably 'bridged' 2 pins with solder, which can be bad.

If it worked when on breadboard, it'll work now, just that you made a small error somewhere.   Does the cap have its " - " symbol facing ground? Can't see it; guess it seems to be.


If still nothing after that, you should post front and back pics of both boards!  You might have a bad solder connection or something.

[Tim Age]

1) I don't like the diode that way, tho it will work. You will lose about 1/2 volt with it in series.   Best way (only IMHO) is to use it parallel, so it would be cathode TO 9V, with anode to ground.     If you're having trouble, take it out, take your output from the 9V behind it.

Okay.

2) use your meter to be sure you have ground on the left, 9V on the right, and about 4.5V in the middle, oriented as your pic is.     THEN connect it to the rest of the circuit.   This will assure you DON'T fry anything from reverse polarity.

Should be this way, will check that tho.

Did you connect your chip's "+" and ground connections?    All the grounds to one spot on the board, the in/out jack grounds too?  Is your IC in a SOCKET?  If not, you probably 'bridged' 2 pins with solder, which can be bad.

IC is on the breadboard so no accidentally bridging, in/out grounds, power supply ground and IC ground are connected (+ rail on the breadboard has +9, - rail on the breadboard has GND)

Does the cap have its " - " symbol facing ground? Can't see it; guess it seems to be.

Yup.

[GibsonGM]

Well, you want to make sure the little board you just made WORKS, so testing the voltage there will do that.  If anything is fried, you'll get no output (like, if the diode was dead...no likely at all, but hey it could happen).   The fact it worked the other way tells us something you changed (or DIDN'T change) is to blame, most likely.


Just to be clear...you had it working on the + and - voltage, by the original 2 cap splitter?  Or you got it going this way, with the bias voltage, and now it won't work since you made this little board?  Sorry, lots of things demanding my attention.   

If you are moving from the "split supply" we originally talked about, to the one using the bias voltage, make sure each ground is going to where it actually needs to; that the chip has + and - ;  that your board is outputting the 9V and 4.5V, and they are going where they are supposed to.    Remember,   pin 4 (gnd) on the IC needs to go to GROUND here....before, it went to 'minus 4.5'.    These are things we just have to check over and over, and then we find ONE small thing got knocked or something, making it not work!    Gotta be methodical, altho it's hard.