Checking the phase of an amp

[Mr. Foxen]

As in is the output in phase with the input. Thinking if I run a fleet of valve amps, some might be out of phase. Polarity is easy to flip, but can they be other than 180deg out of phase? Also, how do you type a degree symbol easily?

[essexbasscat]

Not sure I have a good understanding about the nature of the problem you are describing.

Would you be splitting one input signal into;

- Several complete amps (a fleet of amps) comprised of pre -amp and amp i.e. as in a handful of combos

- several different pre - amps into one power amp

- etc, etc

If you clarify the question some, it may be easier to offer something.


Just my 2p's worth

T

[EdwardHimself]

Yeah not sure about how you phrased your question either. As for the other question:

[url="http://www.starr.net/is/type/altnum.htm"]http://www.starr.net/is/type/altnum.htm[/url]

It tells us that the º sign can be created from holding alt and pressing the number keys 0186 on the number pad. If you want to make things easier then bookmark this page.

[Stewart]

A dual-trace oscilloscope would be my first choice...

[Mr. Foxen]

Signal split at pedal board level, into several amps and cabs. I just know it isn't necessarily true that the output of an amp is in phase with the output, the polarity could be flipped anywhere along the line, so if I run a bunch of amps, some could be out of phase with others.

[obbm]

It would depend on the number of amplification stages in each amp. Each gain stage will give a phase reversal, whereas a cathode follower stage will not, plus there will be a phase shift due to RC networks.

As already mentioned a scope is a good starting point.

[Mr. Foxen]

Umph, get back inside my amps and get counting those gain stages.

[geoffbyrne]

Surely the only thing that matters here is the phase/polarity of the speaker wiring?

Use the old 9V battery trick & ferkle the wiring so they are all going in & out at the same time & phase.

G.

[Mr. Foxen]

[quote name='geoffbyrne' post='987169' date='Oct 13 2010, 05:24 PM']Surely the only thing that matters here is the phase/polarity of the speaker wiring?

Use the old 9V battery trick & ferkle the wiring so they are all going in & out at the same time & phase.

G.[/quote]

9v battery trick won't work into the amp, they don't pass DC unless they are breaking. The issue is the amp can reverse the phase of the signal, so if some amps do, and some don't, it will put them out of phase with each other.

[obbm]

[quote name='geoffbyrne' post='987169' date='Oct 13 2010, 05:24 PM']Surely the only thing that matters here is the phase/polarity of the speaker wiring?

Use the old 9V battery trick & ferkle the wiring so they are all going in & out at the same time & phase.

G.[/quote]

Not really. If you have 2 amps with different numbers of gain stages but with the same input signal, then the outputs will out-of-phase going to the speakers. You can bodge it by changing the speaker wiring but you need to see the signals on a scope to be certain of exactly how far they are out-of-phase.

[geoffbyrne]

[quote name='obbm' post='987193' date='Oct 13 2010, 05:38 PM']Not really. If you have 2 amps with different numbers of gain stages but with the same input signal, then the outputs will out-of-phase going to the speakers. You can bodge it by changing the speaker wiring but you need to see the signals on a scope to be certain of exactly how far they are out-of-phase.[/quote]

That's really what I was trying to say above - providing the speakers are all in phase that should work.

G.

[Phil Starr]

The simple way to do this is to use your ears. If you have two amps and they are out of phase by 180 degrees you will lose some bass and if not you won't so just do two at a time and reverse the polarity of the input lead. Make sure you keep everything earthed though.

The battery trick will give you a momentary movement of the speaker but obviously you won't want to put 9V into an input jack. Use 1.5V and a line level input if you want to try this way.

I don't think you need to worry too much. You are going to get cancellation and reinforcement due to the different path lengths from spaced cabs anyway as well as those due to reflections off the floor and walls. Any phase lag of a few degrees will change the sound a little but whether this will be audible will depend upon the exact position of the listener and the room acoustics.

Hope this helps