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Complex Load for Power Amplifier torture testing

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pma

pma

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Yes, expected, just bits that were to hand.

So as you can see above just a very small resistance in series with a 30uF cap and the amp is stable.

Your test, putting a high value cap straight across the output is not correct. This will never happen. There will always be some series resistance and inductance.

If you have been testing amps this way Im afraid you have been misleading yourself and drawing false conclusions about stability.
Look - I know all of that. You know that in post #1 there is a small resistor. However, I have been in analog design since 1980 as a professional, graduated in electroacoustics in 1979, and having amp design as a hobby since about 1970. And I want for my amps to be stable even under such conditions that I have shown. Why? Because you never know. You may expect that 20 speakers will never get you into the trouble and then the 21st will, because you just didn't know. I understand your point, but you do not need to protect your business so. There is no problem, no danger. We are talking different things, different language. I am interested in worst case conditions, even if they are improbable, but they are not impossible. My approach is not a business approach. If you fulfil worst case conditions, you have it all. If not, then just maybe.
 

amirm

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If you fulfil worst case conditions, you have it all.
Worst case requires continuous operation into 0.1 ohm resistive load without a protection circuit triggering. Is this what you are advocating regardless of amplifier output power?
 

March Audio

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Look - I know all of that. You know that in post #1 there is a small resistor. However, I have been in analog design since 1980 as a professional, graduated in electroacoustics in 1979, and having amp design as a hobby since about 1970. And I want for my amps to be stable even under such conditions that I have shown. Why? Because you never know. You may expect that 20 speakers will never get you into the trouble and then the 21st will, because you just didn't know. I understand your point, but you do not need to protect your business so. There is no problem, no danger. We are talking different things, different language. I am interested in worst case conditions, even if they are improbable, but they are not impossible. My approach is not a business approach. If you fulfil worst case conditions, you have it all. If not, then just maybe.
Sorry but clearly you don't. You don't understand that there never is a pure highly capacitive load placed across an amp. This is extremely surprising considering your experience.

What you have done with the high value cap only test is beyond worst case and it is a situation that will never happen. Its not just improbable, its actually impossible.

This isn't a case of "you never know". We really do know what represents the most difficult of speaker loads, even if they are bad designs.

This has nothing to do with my business, this is about your lack of technical thought plus some, to be frank, obsessiveness, which is creating totally erroneous FUD. This isn't just regarding my amps, but all amps. I have no idea why you are blowing this rare problem out of all proportion.

This is Audio Science Review, not throw your amp out a 10 storey window and expect it to work after hitting the ground review.

We can see above that we can put a 30uF cap with a very low resistance, a 0.5 ohm impedance and my P701 and the Purifi are happy, stable and remarkably low distortion - distortion that's actually out of the audible band. That's close to as extreme a load as you will find in the real world. Your Kenwood is happy too. I don't have a problem with that, even though it is still probably less than 0.00001 % of the speakers out there, and badly designed ones at that. Dumping big caps straight across amp outputs is just dumb however. It informs us of nothing.

Reactive load testing is useful, but, you need to get some perspective. Otherwise you are misinforming not informing
 
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March Audio

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Worst case requires continuous operation into 0.1 ohm resistive load without a protection circuit triggering. Is this what you are advocating regardless of amplifier output power?
It's actually 0.1 ohms impedance with +-90 deg phase angle swings. ;) :facepalm:
 
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restorer-john

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Worst case requires continuous operation into 0.1 ohm resistive load without a protection circuit triggering. Is this what you are advocating regardless of amplifier output power?
I don't think that is a situation Pavel is advocating.

Amplifiers have been driven into purely capacitive loads for decades as an indicator of stability and recovery. It was always a burst test at low power, not continuous and I would expect competently designed amplifiers with adequate protection would trigger their over-current protection at high outputs in such a continuous situation.

Based on Pavel's pictures and schematic of his Kenwood clone, the only protection is rail fuses for each amplifier and a primary fuse. It doesn't appear to have any 'smart' protection, DC protection, or over-current/SOAR protection (the original Kenwood design had all of that) and with a single pair of output transistors his amplifier may well self destruct with high power low impedance loads, whereas a fully monitored class D would survive and protect itself. At the least, you'd be removing the cover to replace fuses. But, it's a proof of concept design, not a commercial product.

I would argue a shorted speaker terminal at full power is the best test of all, as that frequently occurs in the real world. People trip over speaker cables at parties, have poorly stripped and terminated cables and accidents happen. We know the Class Ds can survive that as I've tested that myself. Many traditional amplifiers will not and the results aren't pretty...
 
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Thread Starter #166
Back to complex load in post #1
https://www.audiosciencereview.com/...r-amplifier-torture-testing.10298/post-282912

Yamaha AX-396 integrated amplifier is unable to pass the test at 4.6Vrms output voltage. The protection circuit triggered off the amplifier at 3400 Hz frequency, where the impedance is 1.275 ohm and -53°. This is a typical commercial amplifier with only one pair of output devices, which is very little regarding output devices SOA limitations for complex load. This amplifier will not be able to drive speakers with difficult complex impedance. Review coming very soon.

ax396_complexload.png

Output voltage + distortion vs. frequency

ax396_complexload_dist.png

Distortion in % vs. frequency, 4.6Vrms
 

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I would argue a shorted speaker terminal at full power is the best test of all, as that frequently occurs in the real world.
Such amplifiers exist. But they are massively over-designed to be able to handle a full short circuit and not shut down. Clearly we don't want to make that the criteria for every amplifier. So his notion that an amp should be designed for worst case scenario is non sequitur. If his amps have fuses, he hasn't designed for this either.
 

DonH56

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Soundlab A-1 -- about as bad as I've seen. I thought they were a pretty hard load based on decades-old memories but someone recently linked an old review that had this in it:

1576534539279.png


Note the A-1's spec sheet just says "8 ohms nominal".
 
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blueone

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I heard a pair of well set-up Sound Lab A-1PX a couple of years ago. Huge, and hugely expensive, but totally awesome-sounding. The area they need to sound best in a room, both laterally, out from the back and side walls, and from the listening seats, would make for a modest bedroom or office. String instruments and horns are practically a religious experience.
 
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restorer-john

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Soundlab A-1 -- about as bad as I've seen.
From the review: "Allowing LMS to subtract the cable impedance from the speaker impedance curve produced a graph whose minimum was essentially a short circuit above 20kHz."
 

RayDunzl

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Whatever you guys come up with...

... I'm not gonna try it.
 

RayDunzl

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Krell don't care, they enjoy spot-welding plate steel together in their spare time.
Mine have too many parts...

http://pages.cs.wisc.edu/~timc/e/krell-cap/index.html

I learned during my work years not to tempt fate.

Mistakes would stop the Phones from working. All over town. (cell phones were still a slightly distant fantasy).

Besides, my current activity of above average importance is to see if Code P0420 returns on the '09 Civic the Little Woman drives.
 
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DonH56

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When Perreaux brought their first shipment of amps to the store I worked they dropped one off the truck (about six feet) to show how rugged they are. It worked.

Unfortunately, a few years earlier a Sencore rep showing off their new ruggedized meter pushed it off a bench to show how it held up to shop abuse. It did not work.
 

restorer-john

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When Perreaux brought their first shipment of amps to the store I worked they dropped one off the truck (about six feet) to show how rugged they are. It worked.
Perreaux amplifiers were tough alright. Practically the only part to fail was the power switch from arcing/surge.

The 2150b and the 5150b were incredible amps. Chock full of HItachi MOSFETs straight off the application notes. Their only downfall in my opinion was residual noise. I could always hear a low level buzz in any Perreaux. I've got a 2150b in the storeroom awaiting repair (had to source original MOSFETs)

Here's a scan for you @DonH56, straight from an original brochure I picked up as a young bloke at the Australian HiFi show, around 1986 ish.
5150b02 (Medium).jpg

Real specifications. No pussy specs here. Makes me feel all warm and fuzzy inside... ;)
5150b01 (Medium).jpg
 

Blumlein 88

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Krell don't care, they enjoy spot-welding plate steel together in their spare time. ;)
Hey it was the Mark Levinson that Audio magazine actually used to weld with. Shot 1 khz through it at max power and welded two pieces of steel together. An ML 3 I believe.
 

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Does anyone have an up to date opinion on the more modern Quad ESL incarnations that came out of IAG?
I have directly compared the 2905 with some restored 63s with integrated subs - I chose the 63s with subs. John Hall (Quad ESL repairer) also had the 2905s, he told me that they are basically the same design as the 63s, but with extra bass panels and a slightly different aspect ratio to the panels (not as wide but higher on the 2905). He also told me that IAG had some quality and consistency issues for a while, but it had been fixed at the time we last spoke. Hope that helps! (BTW, I still have the 63s with subs at home, if you are ever in Melb you can pop in for a listen.)

To keep this on-topic, I have driven the Quads with a number of amplifiers and never noticed any problems with stability.
 

DonH56

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Perreaux amplifiers were tough alright. Practically the only part to fail was the power switch from arcing/surge.

The 2150b and the 5150b were incredible amps. Chock full of HItachi MOSFETs straight off the application notes. Their only downfall in my opinion was residual noise. I could always hear a low level buzz in any Perreaux. I've got a 2150b in the storeroom awaiting repair (had to source original MOSFETs)

Here's a scan for you @DonH56, straight from an original brochure I picked up as a young bloke at the Australian HiFi show, around 1986 ish.
View attachment 42788
Real specifications. No pussy specs here. Makes me feel all warm and fuzzy inside... ;)
View attachment 42787
Yup, that one! Heckuva' beast... I think these were among the first of the MOSFET designs, and were among the group of "super high power" and ultra-wideband amplifiers for the time. They didn't seem to get the sales traction of other companies but I think are still around (?) But, I thought they were from New Zealand, not Australia, senility...
 

PaulD

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Yup, that one! Heckuva' beast... I think these were among the first of the MOSFET designs, and were among the group of "super high power" and ultra-wideband amplifiers for the time. They didn't seem to get the sales traction of other companies but I think are still around (?) But, I thought they were from New Zealand, not Australia, senility...
They are still around and they certainly are from NZ - that must have been an Australian brochure...
See https://www.perreaux.com/about/perreaux-history
 
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