Simple phase switch anyone??

[jubjub]

Hello people. I'm using two amps combined at the moment. Fender and Marshall. When I blend them together I get a wierd phase cancellation at certain frequencies and I was wondering if there was a simple phase reversing switch you know about that I could use on one amp to see if it fixes the problem. I see them on acoustic pre-amps alot. Is this a common problem??

[R.G.]

Swap the speaker leads.

[jubjub]

Ok, will do. Perhaps you can help my understanding of this a little. I thought that if you swap the speaker leads that the speaker will actualy push air backwards instead of forwards? I'm obviously wrong. Maybe someone can point me in the direction of some literature.

[RDV]

What R.G. means is that one of your two amps speaker(s) is pushing backwards, or "out of phase". It would do to have a good look in the back of your amp & see if you can tell which one is wrong. Oftentimes a speaker will have a red dot(indicating+), or a + or - sign.

HTH

RDV

[Rodgre]

well no, the speakers could all be fine.... it could be A) one of the amp's circuits has an inverted stage (the channels on some Fender and Vox amps are inverted from eachother sometimes!) or B) the amps are at odd distances from your ears and you're hearing the sound hit you out of phase.

I would actually be more interested in a phase switching box as well. Swapping the speaker leads on one (doesn't matter which) amp will probably solve the problem as well.

To answer your question about the speaker pushing or pulling, the cones are vibrating at a high frequency... back and forth. What you're doing by switching the leads is making the "forth" part be a "back" part and vice-versa.

Roger

[RDV]

Some peoples amps are always out of phase with everyone else's in the world. That would be me.

VDR

[Elektrojänis]

No books come to mind, but swapping the speaker leads around should make just what you want. (Swap only in one amp of the two ofcource.)

Speakers are actually always pushing and pulling the air. The direction changes at the frequency of your signal (generally from 20 to 20000 times per second). If it would be only pushing or pulling then there would be a DC component in the signal. (Actually most real world speakkers are incabable of doing that.)

So... Like a guitar string, a speaker cone swings to both directions of its resting position.

Actually there should be no tonal difference when you change the polarity of the signal in case of one speaker. In theory that is... Some people say that they can hear it with some signals, but the difference is small and it is questionable that it is the phase that causes the difference and not some other nonlinearity in the testing systems.

Edit: I'm way too slow...  :?

[jubjub]

I guess then a simple answer would be DPDT switch on the speaker lead wired so that you can choose the polarity of the speaker signal. That should work shouldn't it?

[Transmogrifox]

I guess then a simple answer would be DPDT switch on the speaker lead wired so that you can choose the polarity of the speaker signal. That should work shouldn't it?

I would agree that's the most simple solution.

If it were me I'd forget about the DPDT switch thing and just solder them in reverse.  It's an easy job to repeat if you ever want to switch it the other way for whatever reason.  I suppose the DPDT would be nice if in the future you end up using a different amp than what you have now, and it's phase is different.

[Hal]

if you really wanna switch phase electroniclly, which it sounds like, an op-amp will to the trick.  Just wire for inverting input and unity gain.  but everyone else is right, switching the speaker connectors will work.

[jubjub]

Thanks to everyone for there input on this. I've just made another speaker lead for the marshall that's wired out of phase which has solved the problem. How one wired properly can be out of phase with the other is wierd. I've also discovered that my original 1974 pro reverb which I've been using happily for the last three years and which has been used for the last thirty years has been wired up wrong from the factory! It's a 4 OHM output going into 2x8 OHM speakers wired in SERIES giving me a 16 OHM load. How did this not blow by output transformer ? And here's a curly one, why did it sound better using a 16 OHM load as opposed to the matched 4 OHM load? (the speakers aren't out of phase, I've checked)

[R.G.]

I would actually be more interested in a phase switching box as well.

One has been up at GEO since January 2001.
http://geofex.com/Article_Folders/polarity_reverser/polarity_reverser.htm

[niftydog]

Phase in arbitary, there's no "correct" way around.  So having two amps from different manufacturers that are out of phase is not at all surprising.

Swapping on set of speaker leads will cause both amps to push at the same time and pull at the same time.  Rather than one pushing while the other is pulling.

Be wary of installing a switch on the speaker leads, there's a lot of energy going to those speakers, a switch may not withstand the punishment!  Best to make a new speaker lead out of hefty cable.

It's a 4 OHM output going into 2x8 OHM speakers wired in SERIES giving me a 16 OHM load. How did this not blow by output transformer ? And here's a curly one, why did it sound better using a 16 OHM load as opposed to the matched 4 OHM load?

Are you sure they're wired in series and not parallel?  Either way, it's not a problem.  The 4 ohm output is quite capable of driving a 16 ohm load.  In fact, the output is living on easy street!  It's driving a load that is far less demanding than that which it was designed for!  That is why it may sound better than with a 4 ohm load.

A 16 ohm output driving a 4 ohm load... now that's a whole different story!  Don't try it!

[jubjub]

Definately series and it's the original wiring for sure. I asked a freind who bought an early 70's pro reverb very cheap because it sounded awful and when he looked at the speakers he saw that one of the speakers was marked with the wrong polarity. He changed the wires around and hey presto!  Sounds like working for Fender in the 70's would have been a doddle with vey long tea breaks.

[niftydog]

Sounds like working for Fender in the 70's would have been a doddle with vey long tea breaks.

Yeah, and from my experience, working for Mesa Boogie these days is much the same.  :shock: