6 Band EQ problem

[Radamus]

I just completed the GGG 6 band EQ. I wired up a TL071 to make it seven band EQ, but I can't even tell if that worked yet.

This has been like all of my projects in that it didn't work the first time I turned it on. Then I put all of the IC's in their sockets and tried again. Still no luck. I spent a couple minutes with my audio probe and I think I found where the problem is. The first op-amp isn't amplifying. I haven't had a chance to run the DMM on this, but I suspect that I'm not getting any current to the opamp. At the same time, the battery was getting really hot.

I think my problem is probably in that ABC power thing. I'm using a single battery, mostly so I can also put a 9v socket in with it, so I'm not really using the C part, other than where it connects to ground. I made it with those parts included though.

So I have 20k (2 ten k) of resistance between hot and ground. I don't think that's enough and I'm not sure why that's there. Granted, I know very little about this stuff, so if anyone can explain it, that would be great. Also, does anyone know from experience whether or not you have to take any parts out to make this work with just one battery?

My theory, here, is that there is something unique about having the two batteries together that makes this work, and without the second battery, I'm just draining the first into ground. I am prepared for that statement to be completely wrong.

Any ideas? If I need to be more specific, just let me know.

Also, what does having the 10uf capacitor in parallel with the first opamp do?

Thanks

[George Giblet]

> Also, what does having the 10uf capacitor in parallel with the first opamp do?

The capacitor in series with the 250k gain pot is a major design flaw.  You should not design opamp stages with no DC feedbac -the 10uF cap removes the DC feedback!!  I'm assuming that's the 10uF cap yoo are talking about.

The simple option is to short out the 10uF cap.  I suspect that should work perfectly OK.

As far as debugging goes.   If you have a multimeter the outputs of each opamp should be very close to zero volts.

[Radamus]

but what about the ABC power stages? IS all of that fine? Like I said, the battery was getting pretty hot.

I can take that capacitor out, or short it. That's not hard. Are there any other problems I should fix?

I'll check everything with the DMM/ I wish I had more to test, but the problem is really right there at the beginning, so there's not much else to check right now.

Can anyone explain to me what the ABC power does? It looks like the b is -, the a +, and c is ground, but I got confused because b is ground. SHould I connect the two? Then what should I do about the capacitors and resistors in between A and B?

This really isn't the clearest design, probably because I'm not familiar with its type.

Thanks.

[George Giblet]

The circuit shows two options:

- the first uses a single battery.  You connect the battery + to A and the battery - to B, C is left unconnected.

- the second uses two batteries.  You connect the battery + of the top battery to A, the battery - of the bottom battery to B, C is the connects to the battery- of the top battery and battery+ of the bottom battery.

With this circuit you cannot use the socket switches to turn the power off and on.

If your battery is getting hot check:

- you have to battery the right way around
- the 1N4003 diode is the right way around
- all electrolytic is in the right way.