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Old 13th November 2009, 09:34 PM   #1
wicked1 is offline wicked1  United States
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Default Phase help

I'm having a difficult time figuring out the phase of my amps. I know what they should be, but what I'm hearing is telling me something else.

Would it be safe to hook up a 1.5 volt battery to my amps, and look at which way the speaker goes?
Well, better maybe to put it through a pot and slowly bring the voltage up, but still, is it safe to put that DC on my amps and speakers for a minute?

Thanks!
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Old 13th November 2009, 09:43 PM   #2
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You can use a 1.5V battery on the speakers but I wouldn't put that in the amp. Even if the input is AC coupled the gain of the amp will make one almightly pop.

A good trick for amps is to put the same signal in both channels and look at the AC volts across L & R output +ve terminals. If the amp is correctly phased then there'll be zero volts across the speakers +ve to +ve but some volts across each speaker +ve to -ve.
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Old 13th November 2009, 10:08 PM   #3
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play some bass ( turn down the treble and up the bass ) put your ears between the speakers while playing music. listen for a little bit. Play the same music again but this time reverse one of the speaker terminals on one of the speakers. The base should either disappear or come back. The difference is very obvious and not subtle at all. IF the base comes back the speakers were wired out of phase, if it disappears the speakers were wired in phase. If you are using multiple amplifiers of different brands it is possible that a rising signal input in amplifier A will produce a rising output at the speaker terminals, while amplifier B with a rising input signal will produce a negative signal at the speaker terminals. This will cause problems if you use the amplifiers at the same time. IF you have multiple speakers and multiple amplifiers, start with one amplifier and one pair of speakers. Do the phase test as I mentioned above at the beginning then add one more amplifier using only one channel of the amplifiers and do the test. Continue from there. IF you use a sine wave test tone from a computer program be careful not to use a high volume level especially at mid or high frequencies if you do say good by to your mids and tweeters.

If you are worrying about absolute phase when the recording was made, don't. The music has passed thru many processors, preamps transformers amplifiers only the engineers know for sure, maybe
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Old 13th November 2009, 10:45 PM   #4
wicked1 is offline wicked1  United States
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Thanks, I've been trying to tell by just listening to it, but the different amps are connected to different speakers. I'm using music which has too many frequencies, some overlap, some don't.. Well, basically, there are far too many variables right now, and I can't hear a clear winner.
A test tone is a good idea.. Good excuse to get my modular synth out of the basement, too .

The trouble is I'm 80% sure one of my amps, which is the only one I'm using that I didn't build, is out of phase. I just don't fully trust myself/hearing. I've asked other people to listen, and the results are mixed 50/50!
Well, I'll do some testing w/ my synth over the weekend.

Testing the voltage is a good idea, too. I think by testing between amps I'd get some voltage when in phase, but probably more when out of phase. I may try that too. (If that's a bad idea for some reason, let me know)
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Old 14th November 2009, 01:34 AM   #5
chrish is offline chrish  Australia
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Do you have a scope? That would be the easiest way to check.
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Old 14th November 2009, 03:28 AM   #6
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Wicked, you must ask more specifically about what it exactly is you would like to know.

What you are talking about is absolute polarity, not phase, which is something different. Do you want to know if the two channels of your amp are outputting in the same polarity, given input signals of the same polarity? Do you want to know if your amp preserves the absolute polarity seen on its input on the output? Something else?

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Old 14th November 2009, 03:28 AM   #7
wicked1 is offline wicked1  United States
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It's just an old single trace scope.
Maybe a good time for a new scope.

I think I've got this particular one sorted, tho.. I'm about positive this one amp is reversed. It shouldn't be.. but it is.
I hooked the questionable amp, plus another to a pair of the same speakers, and got the volume equal as best I could, and followed multisync's advice.. basically did a listening test under slightly more controlled conditions.

Poindexter,
Have been playing with multi-amping. different amps for different frequencies, different speakers.. Only because I've built more amps and speakers than I need now

Last edited by wicked1; 14th November 2009 at 03:30 AM.
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Old 14th November 2009, 03:56 AM   #8
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Quote:
Would it be safe to hook up a 1.5 volt battery to my amps, and look at which way the speaker goes?
Not a good idea. I assume that we are talking about tube amps. A DC step function applied to the input will turn into a transient due to the inevitable coupling cap. Tube amps usually have OPT's, which really dislike this type of transient.

At least with my small Yamaha speakers I can watch the woofer cone with some loud kick drum hits. The cone should move outward when the drum is stomped, and yes you can hear the difference. I did a bunch of experiments when my daughter still lived at home. She played the drums. I did some recording and playback experiments using Cakewalk software and a PC. I also learned that putting a diaphram type mic inside the bass drum will ruin its day.

Quote:
I'm about positive this one amp is reversed. It shouldn't be.. but it is.
The wild card in many tube amps is the OPT, especially SE OPT's. I have found about an equal number that invert the signal as those that don't, when hooked up according to the manufacturers diagram.
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Old 14th November 2009, 04:04 AM   #9
wicked1 is offline wicked1  United States
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Of course! Coupling cap, or DC blocking cap.... I obviously didn't think that one through
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