What's the impedance like up to 100k+ range? If it appears to be inductive then the model is not really accurate.
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Complex Load for Power Amplifier torture testing
- Thread starter pma
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- dummy load testing
- Thread Starter
- #82
You may make almost any impedance load you want and need to test. You just use same parts as for speaker crossovers - big coils, big MKT foil capacitors (like the one in post #1).
You may also use coils with non-linear core to simulate speaker's non-linear impedance partly.
Please stop excuses. There are designers who want their designs to be able to drive speakers including Martin Logans, without excuses for their "incompetent" impedance. BTW, Martin Logan speakers have very nice sound so you might consider ability to drive them - might be good even from business point of view
No. They are bad designs. Perhaps you should stop excusing them?
Who says Hypex or Purifi can't drive them? I am happy that they can.
Business POV? It's a tiny part of the market. You have it the wrong way round, it's actually ML that are limiting their market by requiring special amp consideration.
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The thing is, if capacitive load is that important, insert a coil after the output to isolate the high frequencies then it will be stable.
Low impedance in general is a current output and internal output impedance voltage drop issue rather than capacitive load. If it's capacitive load then it's easy.
Low impedance in general is a current output and internal output impedance voltage drop issue rather than capacitive load. If it's capacitive load then it's easy.
D
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PowerCube Elac Alchemy DPA-2 amp
restorer-john
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It's always been a horses for courses game we have played with HiFi with respect to amplifiers and speakers. Everything in the 50s through to the 70s was 16ohms to 8ohms nominal and not terribly hard to drive.
Ribbons and large array speakers, along with inefficient smaller speakers and some real idealistic designs (apogee, ML etc). They needed arc welders and the market built them. Now 4 ohms nominal is pretty much the standard.
Personally, I think super low impedances at high frequencies are a dreadful thing to subject an amplifier to, but we have to accept the fact there are some magnificent sounding speakers that people will want to use, that will tax/stress or destroy many amplifiers. We can't all rush out and buy a Krell FPB (much as we'd like to). They are the ultimate F.U. to any speaker.
@March Audio is right in his ascertion that super low impedance speakers are an aberration and arguably a faulty design- but only if you decide that all consumer speakers need to fit to a recognized standard. There isn't one, and as such, some amplifiers will collapse in a heap with certain speakers like that. MLs are out on the edge, but universally appreciated in one way or another and I'm thankful that I can go to the only HiFi store around me and I know they will have some on display to listen to.
That's OK. Buy the amplifier that suits your speakers, not the other way around.
Ribbons and large array speakers, along with inefficient smaller speakers and some real idealistic designs (apogee, ML etc). They needed arc welders and the market built them. Now 4 ohms nominal is pretty much the standard.
Personally, I think super low impedances at high frequencies are a dreadful thing to subject an amplifier to, but we have to accept the fact there are some magnificent sounding speakers that people will want to use, that will tax/stress or destroy many amplifiers. We can't all rush out and buy a Krell FPB (much as we'd like to). They are the ultimate F.U. to any speaker.
@March Audio is right in his ascertion that super low impedance speakers are an aberration and arguably a faulty design- but only if you decide that all consumer speakers need to fit to a recognized standard. There isn't one, and as such, some amplifiers will collapse in a heap with certain speakers like that. MLs are out on the edge, but universally appreciated in one way or another and I'm thankful that I can go to the only HiFi store around me and I know they will have some on display to listen to.
That's OK. Buy the amplifier that suits your speakers, not the other way around.
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- Thread Starter
- #91
None of the loads shown here are capacitive above 20kHz. Even the load in post #1 is inductive above 20kHz - as a result of both small R2 in series with C1 and load lead (inlet) wire inductance. And real speakers are also inductive above 20kHz.
- Thread Starter
- #93
Sorry, your assumption is wrong. Because resistive load 1,2,4 ohm or whatever has 0° phase angle of impedance and no imaginary component. You seem to share same misunderstanding of amplifiers stability with @amirm . The load in post #1 has capacitive impedance from 200Hz up to 20kHz and may result in amp instability, depending on amplifier loopgain amplitude and phase plots. Depending on C1 value as well. This is the routine for us analog circuit designers to investigate amplifier's loopgain plots and also response to voltage step with different loads and we know possible issues and how to cure them. It may not be so clear to those who just make an assembly from OEM modules designed and produced by other manufacturers.
To check stability, just use capacitor, pure capacitance. Open dc load and test 1nFto 1uF to see at what point the amplifier becomes unstable.
For power amp, I use 2.2nF as necessity, 10nF as good, and use 100nF+ to be robust.
For power amp, I use 2.2nF as necessity, 10nF as good, and use 100nF+ to be robust.
@pma @restorer-john
OK, I went rummaging in my box of crazy crap and it turns out I had the parts to try this test so threw it together on the bench. Slight variation, 30uF and 0.56 ohms.
Purifi amp running 4 ohms resistive at 5 watts
Purifi reactive load. HF 0.5 ohms
No issues at all.
OK, I went rummaging in my box of crazy crap and it turns out I had the parts to try this test so threw it together on the bench. Slight variation, 30uF and 0.56 ohms.
Purifi amp running 4 ohms resistive at 5 watts
Purifi reactive load. HF 0.5 ohms
No issues at all.
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Of course double blind tested, as I have known your requirements to others
Only when differences not supported by measurements are being claimed.
Well, there IS one difference here (besides heat, power output, and power consumption) and that's noise. If you want me to DBT that to demonstrate that I can hear differences in noise level, I'd be happy to do so. Or post recordings of the noise differences between the Class D setup I'm currently (temporarily, alas!) using and the AB amps I usually use.
Was that a serious request or sarcasm?
Offensive to Amir and me in one post. Its disappointing you feel the need.
Its quite clear, understood, and always has been thank you. The same with Amir no doubt.
I have actually tested my amps previously for precisely this, just not with quite such a pathological load. When you see no issues with challenging but sensible loads, you dont bother wasting time chasing ghosts.
I do however recommend people buy quality speakers that dont have serious design flaws.
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