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Complex Load for Power Amplifier torture testing

restorer-john

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Were those the amps that Kenwood made which used remote sensing for the feedback? It was a clever idea in theory. In theory.

No @SIY That was the early 1980s with their "Sigma Drive" where they ran a second set of speaker cable to the speakers and an additional NFB path.

It was an unmitigated disaster as people couldn't wire them up properly, especially as the rear panel markings were not exactly clear to mums and dads. If they had used a plug/socket for the sigma drive cables and pre-wired speaker cables it could have been a real success.

They also combined sigma drive with rail switching amplifiers and they went up like flashbulbs. I have some in the storeroom as parts donors...
 

ajawamnet

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Absolutely. I've had so many of those amplifiers through my hands it's amazing. The Mk2s have 600KHz bandwidth and turn into oscillators in their old age (compensation cap issues). In fact, I just helped a friend with my last set of 6 original outputs. I sold my last pair about 5 years ago. Had 9 at one point (mix of 07s and 07mk2s).

And they are unconditionally stable with any resistive dummy load you can throw at them. Current limiting is clean. Difficult load however...

This was my last pair, I kept for a most of a decade in storage, then decided they need to go to someone who would use them. Had the original unused 12M directional (!) cables and the 12M trigger cables too.

View attachment 42078

View attachment 42079

Here is six of them at my place back in 2007. The pair above is the pair on the left.

View attachment 42080
The outputs in the mk1.
View attachment 42081


Yep - replaced lot of those
And you had some of the black ones too... cool.

Here's something that I've kept around for a long time - no idea why:

IMG_20190807_114300.jpg

IMG_20190807_114317.jpg
 

amirm

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Amir can't be bothered with extensive amplifier testing- that is quite clear.
I already perform extensive amplifier testing. This graphs don't just materialize out of thin air.

What I don't have time for is chasing people's individual ideas of what I should be doing across every review I am performing.

Now, you are welcome to make this task easy for me to implement. I priced the Audiograph Powercube and it costs US $15,000 for a stereo unit with up to 500 watts capacity. Raise the funds for me and I will subject every amplifier to that.

Until then, I recall you wanting to make this load as a community project but then didn't follow up. So I am assuming your actual interest level and motivation is quite low.
 

SIY

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The more I read, the more I move away from class D

Opposite for me. I have an all class D setup running my speakers at the moment (biamped) and I can't ever remember it sounding better. And my electric bills are lower. :cool:
 

restorer-john

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Here's something that I've kept around for a long time - no idea why:

Here's a few of mine, the older manuals are the best for vintage, particularly the data and the separate sub manuals. I've even still got the first few Towers International Transistor Selectors I bought as a kid. Full of germaniums which comes in handy for the 60s stuff.
sub manual.jpeg
 
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DDF

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Big mistake.... Try a low distortion powerful one and it will change your mind forever.

My NC400s are "end game" for me. Truly effortless, powerful and transparent. OTOH I design my own speakers and know enough not to ask an amp to deliver into -60 deg phase angles or 1 ohm loads. Little thing called system design.

That doesn't detract from the importance of properly designed, stable amps that can't be stimulated into oscillation by RF, or input disconnects. I've yet to see anything remotely like this with the Ncores (and I live in an RF cesspool with bad AC).
 

ajawamnet

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Here's a few of mine, the older manuals are the best for vintage, particularly the data and the separate sub manuals. I've ven still got the first few Towers I bought as a kid. Full of germaniums which comes in handy for the 60s stuff.
Now all you need are your old ECG and NTE cross books. We had shelves of those little yellow boxes
 

DonH56

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ESL's and wideband amps were a mess in the late 20th century. I have not been in the business since then so no data.

I forgot about the Hill Plasmatronics tweeter, another amp-buster. For that matter, IIRC all the early Quad ESLs (do not know about the current models) self-protected by shorting the amp inputs and a fair number of amplifiers became quite unhappy about that.

The original Apogee ribbon speaker was mostly resistive but at 1 ohm caused more than one high-end amplifier to overheat (or worse).

The Magnepan ribbon is below 3 ohms but again almost purely resistive.

Are you sure that's correct about most being sub 1 ohm. It's not been on the searches I have performed.

I guess we can debate "most". Most of the ESLs I have known/recall from over the years dip below 2 ohms at 20 kHz, varying from just below 2 ohms to about 0.2 ohms depending on maker and panel size. I did not do an exhaustive search and, while I was looking at a 0.2-ohm ESL yesterday or whenever, I didn't bookmark it. Here are some current ML models (below).

Martin Logan ESLs
Neolith: 4 ohms, 0.43 ohms @ 20 kHz. Compatible with 4, 6, or 8 Ohm rated amplifiers
CLX: 6 Ohms, 0.7 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers
15A: 4 Ohms, 0.5 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers
13A: 4 Ohms, 0.7 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers
11A: 4 Ohms, 0.6 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers
9A: 4 Ohms, 0.8 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers

I could not find an impedance for Sanders. Sound Lab only listed "8 ohms nominal". Acoustat spec'd "4 ohms nominal". I don't remember early Quads (57); Stereophile tested the 2912 and it dipped to about 3.3 ohms. I know Levinson targeted the 57 in his HQD (a system I heard several times back then) and they taxed his amplifiers. Quads after the original model or two have a network to control dispersion that also increased HF impedance so they are by and large an easier load than most ESLs (again if memory serves). Don't recall KLH, ServoStatik, Beveridge, etc. impedances and too lazy to dig (and I need to quit this and get practicing -- performance in a couple of weeks). When I read through the ML specs they didn't strike me as odd so I never really thought about it.
 
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restorer-john

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Now all you need are your old ECG and NTE cross books. We had shelves of those little yellow boxes

I've got plenty of these little b#stards. The glue binding fails and the pages go everywhere if you are not careful. And I need a magnifying glass these days to read them.

sub (Small).jpeg
 

restorer-john

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IIRC all the early Quad ESLs (do not know about the current models) self-protected by shorting the amp inputs and a fair number of amplifiers became quite unhappy about that.

An SCR/Crowbar IIRC. Nasty.

Some old Quad amps did the same IIRC. Plenty of big PA power amps would take DC to ground in a DC event (to break the relay contact arc), figuring the amp is already toast, might as well finish it off.
 
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March Audio

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ESL's and wideband amps were a mess in the late 20th century. I have not been in the business since then so no data.

I forgot about the Hill Plasmatronics tweeter, another amp-buster. For that matter, IIRC all the early Quad ESLs (do not know about the current models) self-protected by shorting the amp inputs and a fair number of amplifiers became quite unhappy about that.

The original Apogee ribbon speaker was mostly resistive but at 1 ohm caused more than one high-end amplifier to overheat (or worse).

The Magnepan ribbon is below 3 ohms but again almost purely resistive.



I guess we can debate "most". Most of the ESLs I have known/recall from over the years dip below 2 ohms at 20 kHz, varying from just below 2 ohms to about 0.2 ohms depending on maker and panel size. I did not do an exhaustive search and, while I was looking at a 0.2-ohm ESL yesterday or whenever, I didn't bookmark it. Here are some current ML models (below).

Martin Logan ESLs
Neolith: 4 ohms, 0.43 ohms @ 20 kHz. Compatible with 4, 6, or 8 Ohm rated amplifiers
CLX: 6 Ohms, 0.7 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers
15A: 4 Ohms, 0.5 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers
13A: 4 Ohms, 0.7 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers
11A: 4 Ohms, 0.6 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers
9A: 4 Ohms, 0.8 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers

I could not find an impedance for Sanders. Sound Lab only listed "8 ohms nominal". Acoustat spec'd "4 ohms nominal". I don't remember early Quads (57); Stereophile tested the 2912 and it dipped to about 3.3 ohms. I know Levinson targeted the 57 in his HQD (a system I heard several times back then) and they taxed his amplifiers. Quads after the original model or two have a network to control dispersion that also increased HF impedance so they are by and large an easier load than most ESLs (again if memory serves). Don't recall KLH, ServoStatik, Beveridge, etc. impedances and too lazy to dig (and I need to quit this and get practicing -- performance in a couple of weeks). When I read through the ML specs they didn't strike me as odd so I never really thought about it.
So it seems that Martin Logan ESLs all have similar design issues. I'm not sure why any designer would think thats not an issue, or acceptable to have impedances that low. It's clearly possible to design that out to sensible levels.
 
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RayDunzl

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So it seems that Martin Logan ESLs all have similar design issues. I'm not sure why any designer would think thats not an issue, or acceptable to have impedances that low. It's clearly possible to design that out to sensible levels.

What would you do about it?

1576050538197.png
 
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pma

pma

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Opposite for me. I have an all class D setup running my speakers at the moment (biamped) and I can't ever remember it sounding better. And my electric bills are lower. :cool:

I can't ever remember it sounding better.
Of course double blind tested, as I have known your requirements to others :D
 
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pma

pma

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So it seems that Martin Logan ESLs all have similar design issues. I'm not sure why any designer would think thats not an issue, or acceptable to have impedances that low. It's clearly possible to design that out to sensible levels.

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 ;).
 
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pma

pma

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Do you feel one can only call a design succesfull if it passes this particular load ?
Is the load representative of the vast majority of speakers out there and/or worst case ?

Never said that. Never said it is the one and only that should be tested. However, it is one of the load types that any good amplifier should be able to drive.
I am also using more conventional RLC loads to simulate speaker impedance, but never found problem with them in case that the amp has reasonably low output impedance.

dummy_RLC_imp.png
 

JohnYang1997

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Never said that. Never said it is the one and only that should be tested. However, it is one of the load types that any good amplifier should be able to drive.
I am also using more conventional RLC loads to simulate speaker impedance, but never found problem with them in case that the amp has reasonably low output impedance.

View attachment 42159
So still. Not able to drive the load = bad amp right? Isn't it what he asked?
 
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pma

pma

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So still. Not able to drive the load = bad amp right? Isn't it what he asked?

Not a universal amp. Martin Logan's are not unusual and they are not the only ones with similarly low HF impedance. Strictly said, bad amp, if I want the amp to be universal.
 
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