Experts needed: Crazy phase issue with Inverted Gainclone

[PaulHilgeman]

I only get .015 VDC across the output, and I can see no change on the woofer cones when I turn it on.

-Paul

[Steve Eddy]

Are you running both amplifiers off the same power supply?

se

[PaulHilgeman]

Yes

[Steve Eddy]

Ok. Scratch that anyway. I was thinking at the wrong end of the problem.

If you're truly getting significantly less bass with the speakers wired in opposite polarity, then I can't think of anything being the cause other than one of your amplifier channels being non-inverting, one of the channel outputs being wired opposite the other, or one of your speakers wired in opposite polarity either internally or externally.

se

[PaulHilgeman]

Originally posted by Steve Eddy
Ok. Scratch that anyway. I was thinking at the wrong end of the problem.

If you're truly getting significantly less bass with the speakers wired in opposite polarity, then I can't think of anything being the cause other than one of your amplifier channels being non-inverting, one of the channel outputs being wired opposite the other, or one of your speakers wired in opposite polarity either internally or externally.

se

Hey, I think we might be a bit unclear on the problem here. I'll try again, forgive my poor descriptions.

In Phase with eachother:
-No bass, imaging is decent, not good, just barely decent. I can tell that somthing is wrong for sure though with the mid and trebble.

Out of phase with eachother:
-Bass has more presence, but still not where it is with other amps. Imaging is wacky, and spacy, there is that suckout feeling that you get when you wire them out of phase.

-Overall, bass is always better (deeper and louder) with one speaker hooked up.

It seems as though I am getting a phase shift in one channel, and I have no idea why.

I know that my wiring is correct, here is a pic. I have corrected the problem with the potentiometer (the middle pins sticking through) and the feedback resistor is on the rear side of the PCB. The twisted wires are the RCA inputs, and the straing ones go to the speakers. The caps are on the reverse side of the PCB as well.

-Paul

[PaulHilgeman]

I just tried adding input caps. Didnt do anything. No change in sound.

-Paul

[PaulHilgeman]

I changed chips, the problem still persists.

I will use a scope on it tomorrow.

-Paul

[Steve Eddy]

Sorry, took a break to whip up some snackage.

Originally posted by PaulHilgeman
Hey, I think we might be a bit unclear on the problem here. I'll try again, forgive my poor descriptions.

I'm pretty clear on what the symptoms are.

In Phase with eachother:
-No bass, imaging is decent, not good, just barely decent. I can tell that somthing is wrong for sure though with the mid and trebble.

Out of phase with eachother:
-Bass has more presence, but still not where it is with other amps. Imaging is wacky, and spacy, there is that suckout feeling that you get when you wire them out of phase.

Except that this is a classic symptom of one speaker being wired with the opposite polarity of the other.

-Overall, bass is always better (deeper and louder) with one speaker hooked up.

This doesn't make much sense. Driving both speakers together could load down your power supply considerably more (seeing as you're just using 1,000uF reservoir caps) than driving one speaker, but that would tend to manifest itself by the amplifier's clipping sooner rather than playing louder or softer.

It seems as though I am getting a phase shift in one channel, and I have no idea why.

And I can't see any reason why such a drastic change in phase would take place in the chips themselves.

Color me stumped.

se

[PaulHilgeman]

I am completely stumped as well. I am going to take it in to a lab to measure right now, i should have results by midnight or so CST. It seems as though the bass is partially out of phase, when the speakers are wired normaly. Then when I reverse the phase of one speaker, the phase alignment of the speakers is better, but not great, and the mid and treble is completely out of phase, creating the suck out effect.

-Paul

[Anthony Dockril]

Hi,

Why do you have no cap across the chip? Place 0.22-1uf across the + and - supply pins. It may not fix your problem but it will make the amp more stable.

Also be aware that the kind of cap you put there can change the character of the amp.

Cheers,
Anthony