Bronal Posted January 29, 2019 Posted January 29, 2019 Can someone please explain how to test the phase of an amp using a multimeter? 'Cat sat on the mat' language please!
andyr Posted January 29, 2019 Posted January 29, 2019 (edited) What do you mean by "the phase of an amp", Alan? If you mean "does it invert phase or not" ... a multimeter won't help you - you need a sig-gen and a CRO. But you can determine whether it inverts phase or not if you have the cct diagram. AIUI, each gain stage inverts phase - so if the amp has: 1 gain stage ... phase is inverted 2 gain stages ... phase is not. Andy Edited January 29, 2019 by andyr
Addicted to music Posted January 29, 2019 Posted January 29, 2019 (edited) I’m guessing that what you’re trying to determined is when a + ve cycle is applied to the input, is it a +ve cycle on the output of the speaker terminal of the amp? Just to clarify, multimeters are used for measuring such as voltage, currents and resistance, not for testing. Most will have a continuity mode that’s used for testing continuity: to ensure there is a connection. If you want to see if an output is in phase with the input, then a multimeter is not the tool. As the above post points out, you need a scope to see the actual waveform. Edited January 29, 2019 by Addicted to music
Bronal Posted January 29, 2019 Author Posted January 29, 2019 I bought a pair of monoblocks and one of them inverts the phase. I know this because they failed my stereo test disc routine (L-R channels OK, but no real balance and phase reversed). I reversed the connections on one speaker and all is OK. I spoke to Bill Crampton today and he told me I could test the phase on the amps using a multimeter. I didn't ask him to explain further as I would probably have got confused. That's why I asked here.
Zaphod Beeblebrox Posted January 29, 2019 Posted January 29, 2019 8 hours ago, Bronal said: I bought a pair of monoblocks and one of them inverts the phase. I know this because they failed my stereo test disc routine (L-R channels OK, but no real balance and phase reversed). I reversed the connections on one speaker and all is OK. I spoke to Bill Crampton today and he told me I could test the phase on the amps using a multimeter. I didn't ask him to explain further as I would probably have got confused. That's why I asked here. Why would one (presumably identical) amplifier of a pair, invert phase? What does the manufacturer say?
Bronal Posted January 30, 2019 Author Posted January 30, 2019 4 hours ago, Zaphod Beeblebrox said: Why would one (presumably identical) amplifier of a pair, invert phase? What does the manufacturer say? Your post is of absolutely no help at all. I've described my situation as best and clearly as I can. My best guess is that one of the amps has received attention in the past and the positive and negative outputs have become reversed. This seems to be proved by the fact that they are in phase when I reverse the inputs on one of the speakers. I'm going to let Bill have a look at them, which I was going to do anyway. 1
Zaphod Beeblebrox Posted January 30, 2019 Posted January 30, 2019 4 minutes ago, Bronal said: Your post is of absolutely no help at all. I've described my situation as best and clearly as I can. Well, not quite. You made no mention of what amps you had, nor that you (apparently) acquired them second hand. So, you should have made those facts known first, doncha think? 4 minutes ago, Bronal said: My best guess is that one of the amps has received attention in the past and the positive and negative outputs have become reversed. This seems to be proved by the fact that they are in phase when I reverse the inputs on one of the speakers. I'm going to let Bill have a look at them, which I was going to do anyway. Well, again, it would be helpful if we knew what you were dealing with. Depending on the amplifiers, it could be that the input has been reversed. It could be that the amps are designed deliberately to operate that way. Who knows? Without more information, it is difficult to advise you further.
Bronal Posted January 30, 2019 Author Posted January 30, 2019 (edited) OK, the amps are Musical Fidelity monoblocks. Does that help? Which amps are designed to be out of phase and why? Edited January 30, 2019 by Bronal
Zaphod Beeblebrox Posted January 30, 2019 Posted January 30, 2019 1 minute ago, Bronal said: OK, the amps are Musical Fidelity monoblocks. Does that help? Not in the slightest. WHICH MF monoblocks? 1 minute ago, Bronal said: Which amps are designed to be out of phase and why? Some amplifiers use internal switching, or links, to enable out of phase operation, to facilitate bridged operation. VERY common in stereo amps. Less common in mono amps.
Bronal Posted January 30, 2019 Author Posted January 30, 2019 They are 550K Superchargers. They run in 'hot' mode (like a bridged stereo amp).
Zaphod Beeblebrox Posted January 30, 2019 Posted January 30, 2019 8 minutes ago, Bronal said: They are 550K Superchargers. They run in 'hot' mode (like a bridged stereo amp). Indeed they are internally bridged amps. I've never had one on my bench, but my reading of what the amp does reveals some curiosities: * High level inputs operate as non-inverting ones. * Line level inputs operate as inverting ones. Beyond that, you will need to hand it to a tech for evaluation. 1
davewantsmoore Posted January 30, 2019 Posted January 30, 2019 21 hours ago, Bronal said: please explain how to test the phase of an amp It's easy to work out that one amp is reversing the phase (as you have done). To work out which amplifier is flipping the phase? .... You don't. It's hard. Wait for your tech.
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