phase relationships between 2 amps

[Recycled_Brains]

ryan,
thanks for the help. i guess i should have been more clear in my pedal situation: i have a pedal that splits my signal (a chorus pedal) then after that 2 pedals go to 1 amp and 1 pedal goes to another. judging from what you posted earlier, that could be the issue.

Ah... I see. I wonder if the polarity inversion is happening at one of the outputs of the chorus pedal.

[JustinHedrick]

i actually think part of it is the amps and part of it is the pedals. the reason that i say that is whenever i turn on the delay pedal that is after the chorus, not only does it sound delayed, but it sounds noticeably better than when it is off.

[ashcat_lt]

It would be easy enough to run your two chains to two tracks in a DAW. Run some form of test signal through. A long sustaining note would be ideal, but about anything will work. Switch each pedal on and off independently and then look at the two waveforms side-by-side and look for places where the polarity is reversed. You'll probably hear it, too, but you'll definitely see it. This will help you track down your culprit.

The big problem with a pedal that inverts your signal will be if you switch it on and off during performance. The idea of the inverting switch box in the above quote is a good one, thought I think you could probably hack an inverting buffer stage into the existing pedal almost as easily.

A lot of stereo effects do invert the effect portion of the signal on one of their outputs, but I think the clean sound would remain right-side up.


Now, just for fun: There are quite certainly several electronic filters in various places along both sides of your chain. These generally introduce frequency-dependent phase shift around their cutoff frequencies. So there probably will be significant difference in phase (not polarity) between the two sides in certain areas of the spectrum. I don't think this is the problem in this case, just throwing it out there to confuse things even further.

[ashcat_lt]

i actually think part of it is the amps and part of it is the pedals. the reason that i say that is whenever i turn on the delay pedal that is after the chorus, not only does it sound delayed, but it sounds noticeably better than when it is off.

Is that delay set 100% wet?

[JustinHedrick]

i actually think part of it is the amps and part of it is the pedals. the reason that i say that is whenever i turn on the delay pedal that is after the chorus, not only does it sound delayed, but it sounds noticeably better than when it is off.

Is that delay set 100% wet?

no.

[JustinHedrick]

so on saturday i took a tuner pedal and split my signal and ran into both amps: no polarity issues, so i went back and rewired my pedalboard so it is a mono signal, split with a tuner right before the amps. hope this solves it.

[???????]

Each stage of gain in a tube amp inverts polarity.

A stage of gain is half a dual-triode tube or one single triode or pentode tube.

It sounds like your two amps are set up with inverse polarity of one another.

This is simple to remedy.

Switch the "+" and "-" of the speaker load on one amp.

If multiple-speaker cabs, then you do this by making a speaker cable that inverts polarity (i.e. the conductors are reversed on ONE end of the cable). Then you're done.

If the amp is a combo, switch the + and - connections to whichever speaker directly connects to the amp. If the speakers are in series as opposed to the more typical parallel, you have to switch everything.

[Electro-Voice 664]

If the amp is a combo, switch the + and - connections to whichever speaker directly connects to the amp. If the speakers are in series as opposed to the more typical parallel, you have to switch everything.

Should you first determine which one of the two amps has the correct polarity, and adjust the other amp to that, or???? If a speaker has the + where the - should go, doesn't the speaker cone pull instead of push or something?

[Z-Plane]

If there is only one speaker in the cab, polarity is kinda arbitrary, or at least unlikely to become an issue. Push and pull is exactly right, you can use this method with a fig 8 mic to open up some stunning recording possibilities. For this you need two cabinets opposite and equidistant from the mic with inverted polarities (relative to each other). Its a great way to blend speaker tones and would also instantly reveal any polarity questions you might have about the two.

[Electro-Voice 664]

Cool, I guess it's the arbitrary +&- that has me confused.

[ashcat_lt]

There are some people who claim to be able to hear a difference. The idea being that the initial attack should push the speaker outward first. I think that's all hooey, but some people's kids...

The OP seems to have proven that his amps are not of opposite polarity, and it must be something in his split signal chain causing the problem.

Justin - your solution will work, but you said you had different pedals on each side of the split, and I don't see any reason you should give up on that if it's what you really want. Take a minute to find out exactly which of your pedals is causing the trouble and lets fix it. We've laid out a couple of possible (relatively easy) fixes already.

[JustinHedrick]

There are some people who claim to be able to hear a difference. The idea being that the initial attack should push the speaker outward first. I think that's all hooey, but some people's kids...

The OP seems to have proven that his amps are not of opposite polarity, and it must be something in his split signal chain causing the problem.

Justin - your solution will work, but you said you had different pedals on each side of the split, and I don't see any reason you should give up on that if it's what you really want. Take a minute to find out exactly which of your pedals is causing the trouble and lets fix it. We've laid out a couple of possible (relatively easy) fixes already.

thanks for the help. i re-ordered my pedals and now it sounds amazingly better. but, in the back of my head, i STILL want to switch the leads on one of the cabs because of the whole pre amp tube thing (one of the amps has 1 more pre amp tube than the other) . . . thoughts?

[???????]

depends on what the preamp tubes are doing.

Not all tubes do the same thing.

It's not about counting tubes... it's about counting stages of gain.

Have a look at the schematics for your two amps and count the stages of gain.

Something like a tremolo oscillator is not a stage of gain and will not invert polarity. A reverb driver will invert polarity... for the reverb only. And the reverb recovery will flip it back!

A cathodyne phase inverter uses half a tube to do its job, and a Schmitt PI will use a whole tube to do the same job plus will provide gain... but its JOB is to split the signal into two of opposite polarity... confused yet?

Vintage Jensen speakers and I think vintage JBL speakers have "+" and "-" marked the opposite of modern convention-- for the long time there was no standard.

It's not as simple as counting tubes. You have to listen!!

[ashcat_lt]

If your pedals are set up in a config you can live with, and it sounds good, then you're done. Defintely won't hurt anything to reverse the speaker wires, and it might be educational.

[JustinHedrick]

depends on what the preamp tubes are doing.

Not all tubes do the same thing.

It's not about counting tubes... it's about counting stages of gain.

Have a look at the schematics for your two amps and count the stages of gain.

Something like a tremolo oscillator is not a stage of gain and will not invert polarity. A reverb driver will invert polarity... for the reverb only. And the reverb recovery will flip it back!

A cathodyne phase inverter uses half a tube to do its job, and a Schmitt PI will use a whole tube to do the same job plus will provide gain... but its JOB is to split the signal into two of opposite polarity... confused yet?

Vintage Jensen speakers and I think vintage JBL speakers have "+" and "-" marked the opposite of modern convention-- for the long time there was no standard.

It's not as simple as counting tubes. You have to listen!!

the amp doesn't have reverb or trem. it does have an FX loop. maybe it coudl be for that?