lm386 amp

[heisenberg]

I know this forum is for pedals, but this is the same sorta.

I've biult a few lm386 amps, bridged, in packs of smokes, trilogy VHS boxes, old amps and stuff. But whenever I've tried to put something else before it in the same circuit, I get wailing. I tried to biult the ruby with the fetzer valve in it instead of the buffer, like in the runoffgroove FAQ, but I just got wailing. I built it a buncha times and it didn't work. I breadboarded it and it was fine.

But here's my question, I'm trying to build this amp now from generalguitargadgets.com: http://www.generalguitargadgets.com/richardo/practiceamp/practiceman.pdf

I breadboarded it and it just wails non-stop. I took the amp out and just played the rest of the circuit into my MS-2 and it worked fine. But when I put the lm386 after it and an 8 ohm speaker it just wails! I wasn't using tantalium caps like in the schem, and i was running it off a 9v battery, instead of the wierdness he says to use. I tried 6v, still same deal.

Another question about the schem, there are 3 op amps. But couldn't I just use two?

Also, U3 is just one op amp,  but the schem is drawn so it looks like it's two. It has it's own power, and bias thingy goin on. And it's own ground. WTF?!

But it all works, it's just I cant get it to be it's own self contained amp!!

[heisenberg]

I mean, it seems like there's this strange voodoo going on and I can't figure anything out!

[doc_drop]

What is your power supply? If it is an adaptor, is it filtered and regulated? I have stopped my squeeling circuits by using a Godlyke PowerAll adaptor. The 1 Spot is similar.

I have built a couple of modded Ruby amps, and I haven't had the same problem, but now that I wrote that I probably will...

[tiges_ tendres]

I know this forum is for pedals, but this is the same sorta.

I've biult a few lm386 amps, bridged, in packs of smokes, trilogy VHS boxes, old amps and stuff. But whenever I've tried to put something else before it in the same circuit, I get wailing. I tried to biult the ruby with the fetzer valve in it instead of the buffer, like in the runoffgroove FAQ, but I just got wailing. I built it a buncha times and it didn't work. I breadboarded it and it was fine.

But here's my question, I'm trying to build this amp now from generalguitargadgets.com: http://www.generalguitargadgets.com/richardo/practiceamp/practiceman.pdf

I breadboarded it and it just wails non-stop. I took the amp out and just played the rest of the circuit into my MS-2 and it worked fine. But when I put the lm386 after it and an 8 ohm speaker it just wails! I wasn't using tantalium caps like in the schem, and i was running it off a 9v battery, instead of the wierdness he says to use. I tried 6v, still same deal.

Another question about the schem, there are 3 op amps. But couldn't I just use two?

Also, U3 is just one op amp,  but the schem is drawn so it looks like it's two. It has it's own power, and bias thingy goin on. And it's own ground. WTF?!

But it all works, it's just I cant get it to be it's own self contained amp!!

The way opamps are drawn schematically is in two halfs.  Each half representing 4 pins (or less if the pins arent needed) of the chip.

As for your squealing, that could be any number of things.

If you use the search function you will see that there are a number of common cures for this problem.  One is using shielded wire, another is to use as shorter wire as possible to connect ins and outs.  Hi gain pedals often create this kind of whine or squeal.

If you breadboarded this, are you sure you laid it out to avoid problems like noise?

[heisenberg]

Im using a 9v battery

I breaboarde it so i dunno how it could be wiring issue. I know th lm386 enough to
Not screw up the circuit. Its all there on thebreaboard. I didnt know there was a certain way to
Breadboard.

About the op amps, i know how they are drawn. But look at the schematic. U3s power and bias pins are DOUBLED. Also, only one of the amps are used in two cases. Coulnt you just combine these and use one?? Im not a total beginner ive biult 15+ pedals so if i run into a problem its not something stupid. I know how to de bug, i built an audio probe and all that. I have bo idea what the wailing is. Ive tried different lm386s. I was actually using jrc386

[heisenberg]

Its like a staticy, trashy loud noise. High pitched but loud. I connect the input directly into thr power amp stge and it works fine! The pre amp section works alone. Th amp works alone. Connect em with the wire and "SHKEEEEOOOOOOQWWWWWKKIWWWOWWWLK..."!!

[tiges_ tendres]

ive biult 15+ pedals so if i run into a problem its not something stupid.

Famous last words!

Perhaps post your voltages and see if you get any bites from that.

[mdh]

Three things:

1. On the oscillation issue, have you tried a cap to ground from the bypass pin of the 386 (pin 7)?  IIRC, 100n should do it, and sometimes tames oscillations.

2. On the schematic issue, yes, it looks like the schem is somewhat in error in suggesting that you use three dual op-amps, but only use half of two of them.  Most people building from a schem would probably just ignore the part designations, and use two duals.  Since none of the op-amps is being used as an oscillator (at least, not intentionally), I don't see why it would matter which physical package each one is in.  I would just choose based on the most convenient layout.  Likewise, yeah, it's a little weird that the Vcc pin is indicated more than once for U3, but the fact that each op-amp has a Vbias connection is completely correct, and there's nothing weird about that at all.

3. Regarding your statement, "I breaboarde it so i dunno how it could be wiring issue," are you insane?  Breadboarded circuits are (a) very likely to be miswired in some way, just because it's so easy to connect things up on a breadboard, and (b) rife with stray capacitance and bad layout (long wires flying all over the place, etc.).  I'm not sure if the considerations in (b) could cause the oscillation, but incorrect wiring certainly can, and it's no knock on your breadboarding skills to suggest that this might be the problem.  Everybody screws up at some point when breadboarding.

[heisenberg]

Yea but i checked before posting this. Ive also taken it apart and rebiult it twice. I tried the cap from pin 7 already. Also the rc network or wutever its called.

I was just wondering about the weird schematic. I knew how to put it together, cus it works fine without the power amp section. The amp section also works alone. So i know its not breadboard error. Im tellin ya it only when i hook the two up. I litterally just move one wire to another hole and cray noize.

About pin voltage: just check if im getting 4.5 and 9 on the pins? Im not sure what im sposed to look for.   

[heisenberg]

Bump

[tiges_ tendres]

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[heisenberg]

Its not a problem with the build, its the schematic. It doesnt work on the breadboard. The anp section works, the pre amp works, litetally move onr wire to connect them and the its just endless screaming. This doesnt make sense! I swear to god this is not a stupi problem like i put the caps in backwards or missed a ground connection, i swear i know better than that. Is there anythin else it could be?

[slacker]

First thing I'd do is make sure C15 is as close to the power pin of the 386 as possible. I've had oscillation problems with 386s before even using an already well filtered and regulated supply and that solved it.
The other thing I'd try is use the inverting input of the 386 instead of the non inverting one and see if that makes any difference.

[jacobyjd]

you really should follow the debugging procedure.

[heisenberg]

I read what was on there and its stuff i already know how to do. Common sense stuff.

Ive tried the negativr input of the amp instead, that was one of the first things i tried. Nothin

[heisenberg]

To anyone who is goin to tell me to follow the debugging procedure, if you read my posts youll see i already have.

[heisenberg]

First thing I'd do is make sure C15 is as close to the power pin of the 386 as possible. I've had oscillation problems with 386s before even using an already well filtered and regulated supply and that solved it.
The other thing I'd try is use the inverting input of the 386 instead of the non inverting one and see if that makes any difference.

This looks like it might be closest to the problem im having. I tried moving it close. I used to same rail on the breadboard that pin 6 of the 386 is in. I put the negative lead right into the rail that the fourth ground pin is in and nothing. Thisnis weird!

[slacker]

Where are you connecting the ground wire for the speaker? Depending on where it's connected you could be pumping crap into the ground line that could cause oscillation.
If you haven't already try connecting it straight to you DC or battery negative, not to any of the ground lines on the breadboard.

Also what happens if you ground the input?

[snap]

sounds like the same issue: http://www.diystompboxes.com/smfforum/index.php?topic=75530.0