[sdiy] a bit frustrated

[Rob B.]

Well, no, now your next problem is that you have to make a virtual ground
reference for your unused opamp inputs.

Take two 20k resistors, one from the unused input going to +V, and another
going from the unused input to gnd. This references the unused input
properly so it operates between +V and gnd.

You *can* get any project that runs off of +/- rails to run off of a single
supply. I have proven this time again ;)
It doesn't always work exactly as well as it would otherwise though, and
sometimes you will have other problems, but it general you can get it
working. TL082s prlly aren't the best to use for this sort of circuit.
Perhaps a LM324 would be better because of the narrow operation voltage? In
normal opamps, you lose the last .7 to 1 volt or so near the rails,
something which you can't afford to do when your rail-to-rail voltage is a
mere 9v. I *think* the LM324 is a rail-to-rail design.

Read some of the Forrest Mims books on opamps. They explain a lot of that.

Rob

----- Original Message -----
From: <ElmacacoX at aol.com>
To: <xoxos at earthlink.net>; <synth-diy at node12b53.a2000.nl>
Sent: Wednesday, May 09, 2001 9:27 PM
Subject: Re: [sdiy] a bit frustrated


> OK, I'm new at this too, but I think I know what's wrong.  Op amps need a
> symetrical powersupply,  you need, say 9v+ on the + of the TL082, and 9V-
on
> the negtive input, not ground.  this is why it isn't working I reckon.
now
> you'll need the other guy's with the EE degrees to tell you how to build a
> symetrical psu that runs off 9v batteries.
>
> don't dispair, it is worth the effort and frustration in the end.... I
> think....
>
> eduardo