opamplifying signals

[Squeal]

So I want to boost my guitar signal up to about +/- 8 volts. I'm trying to use one side of a jrc4558d to do it and I can't seem to make it go. I have tried the inverting and noninverting amp schematics from an electronics book, and I am getting zero output from both. I tried setting it up like the first stage of the big muff opamp version and also no output. I'm wondering if the chip is blown. Shouldn't any opamp work when set up in the 2 resistor inverting/noninverting amp circuit? Does anyone have a schematic that would work?

THis is my 1st post ever so if there is a more appropriate way to get this info please let me know. Thanks.

[niftydog]

+/- 8 volts

Welcome Squeal!

There's a lot of things that could be to blame here, I'm sure the schematics are fine so it's just something else that's up.

Have you got a multimeter? Have you done the basic checks like supply voltages, continuity checks etc etc?

There are a lot of beginner oriented threads here, like "What to do when it doesn't work" - which would be a good place to get some other pointers.

[R.G.]

Hi, Squeal. here are some pointers.

All amplifiers should first be thought of as warts on the outside of a power supply. Only when the power supply is correct can you expect anything at all from the amplifier. What kind of power supply are you using, and what opamp.

The power supply limits things many ways, but the most primal one is the available voltage. If you want an output signal as large as + and - 8V (peak?) then the power supply must be more than 16V total, probably about 20V for most opamps. You can not get +/-8V peak signals out of a 9V battery without a step up transformer following the amplifier. Opamps were developed for bipolar power supplies - equal positive and negative supplies with ground in the middle. Many opamp chips are still specified that way. For a given opamp, the output may simply not swing closer than within 2V of the power supply rail, positive or negative. That's why I say you need 20V total for +/-8V peaks. Some opamps will swing within millivolts of the power rails, but not all by any means.

And then there's the reference voltage. The positive input of an opamp simply must be attached to some reference voltage within the power supply limits, and preferably close to the middle. If it's not near the middle, the output will bang into the power supply voltage limit earlier on one side than the other.

Pinout is another common problem. If you're new to experimenting with opamps, DOWNLOAD THE DATASHEET FROM THE INTERNET, PRINT IT OUT AND CHECK YOUR CIRCUIT AGAINST IT. Getting the pinout wrong, especially after having checked the circuit fifty times, is the single most common mistake that people new to opamps make.

Print out your circuit, and then using your DMM, trace out the connection with the ohmmeter setting. Mark connections on the printed circuit as you verify them.

If you don't own a DMM, get one before you do anything else. They're cheap, widely available, and so useful that it's silly to do anything else.

Finally, When you've done the stuff above, use your DMM to measure every single pin voltage on the opamp, and post your circuit and the voltages here. One of us can tell you pretty much instantly what's wrong.

[Squeal]

Thank you.

[Ge_Whiz]

Most common mistake I've made - and I've made it many times - is use a voltage divider to get the +/- voltages, then earth the circuit to the -ve rail without thinking... D'oh!

[Squeal]

I'm not sure what the -ve rail is; I finally got mine working last night by volage dividing the battery, powerring the opamp with 0 and +9 volts, and thinking of the 4.5 volts from the divider as my new "ground". Hopefully this is correct. I guess that's probably what you're saying. Anyway thanks again to R.G. for dumping that knowledge on me. It all comes somewhat clearer now.