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Audio Research D300 Power Amplifier Review

tkr

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Another point - to me measurements to 8ohm load are close to useless. Almost no speaker impedance stays at 8ohm. Even 8ohm nominal impedance usually goes to 4ohm. Dips to 2 ohm or even below are not unusual. So, to me, this is much more informative

In Germany (and iirc with IEC standards as well) it is required that speakers not dip below 80% of their nominal impedance. I.e. a 4ohm speaker should always stay above 3.2ohm over its whole frequency range. That is not to say that all speakers sold actually fulfill this requirements or are labeled correctly.

Besides low impedance not all amplifiers work well when confronted with a complex load. German magazine "Audio" thus measures the power at different combinations of impedance and phase of the speaker load. They publish the results in a way that is easy enough to understand and gives an indication whether the amp delivers stable power. An ideal amp would simply show a flat plane with its height corresponding to the power output and no dips in the delivered output voltage, regardless of the speaker load. To illustrate have a look at the results of five different integrated amps (full review in german: https://www.in-akustik.de/fileadmin...11_2015_.pdf?c5414814307e0e2738aba30edb90bbba). The separate diagram is only included as I can scale it to a size where the descriptions are actually readable (taken from https://www.audio-components.de/assets/Uploads/PASS-100.8-Audio.pdf). However, with the price of the Pass amp more than 10 times higher than the ones in the other test it is not a fair comparison.

1575301048170.png
1575301914189.png

Phase = phase
Impedanz = impedance
Spannung = voltage
 

maty

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I remember seeing it when I was looking for information on the new Marantz SR8006, which I discarded.
 

Putter

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What is clear looking at those specs is that there are NO distortion specs although Amir's tests put it somewhere around 0.3% THD for 150 wpc@8 ohm and 250 wpc@4 ohm. This is below their specs of 160 wpc and 300 wpc (the 'magic' doubling into 4 ohm loads that I have NEVER seen on a tested amp). It is a little frightening the lack of distortion specs, but high end was/is all about listening not silly stuff like measurements.:rolleyes:

Despite this, it certainly would do a decent job of amplification given that even 1% THD is the threshold of audibility for music and would therefore likely pass a blind test.
 

maty

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maty

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anmpr1

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German magazine "Audio" thus measures the power at different combinations of impedance and phase of the speaker load. They publish the results in a way that is easy enough to understand and gives an indication whether the amp delivers stable power.
The Power Cube has always seemed to me a very intuitive method of visualizing amplifier performance. Few reviewers use the device, which I've heard is very expensive.
 

tkr

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The Power Cube has always seemed to me a very intuitive method of visualizing amplifier performance. Few reviewers use the device, which I've heard is very expensive.

Measurements will take up more time as 35 instead of just 2 data points are needed. I can only assume that the neccessary dummy loads capable of high power are the expensive parts?
 

pma

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In Germany (and iirc with IEC standards as well) it is required that speakers not dip below 80% of their nominal impedance. I.e. a 4ohm speaker should always stay above 3.2ohm over its whole frequency range. That is not to say that all speakers sold actually fulfill this requirements or are labeled correctly.

Besides low impedance not all amplifiers work well when confronted with a complex load. German magazine "Audio" thus measures the power at different combinations of impedance and phase of the speaker load

I think you know that hi-end speaker manufacturers do not care about standars of impedance at all.

616BW802fig1.jpg


Maxfig01.jpg


1008Avafig1.jpg


Re power cube, I know measurements of Audio magazine, good method. And I understand German ;). BTW, your examples of power cube measurements are instructive, especially at ASR forum. Pass amplifier has not any low distortion, but is capable to drive almost any load, which counts. Harmonic distortion below some limit is in fact not very important sonically, though it seems to be main concern here.

I use a dummy load and I often measure with real speakers (at lower power)

1575312168395.png

Distortion vs. frequency into dummy load
 
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tkr

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I think you know that hi-end speaker manufacturers do not care about standars of impedance at all

Yes, I am aware that some speakers are rather demanding on the amp. I think that some electrostatic ones do go as low as 1ohm if I remembered it correctly.

One can just hope that persons buying high end stuff think about it before spending all that money. But then again other factors than (measurable) sound quality are at play at these levels. I had the opportunity to listen to a stereo system from Dynaudio (Arbiter Pre + Power Amp, Consequence stereo speakers, CD transport plus DAC) which cost about the same as a house with proper. Being a student at that time I could not understand someone spending that much on a stereo system.
 

DonH56

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Audio Precision offers an automated Power Cube capability but I think Amir said it was very expensive thus he did not buy it. The cube itself is made by AudioGraph: https://www.audiograph.se/ -- I did not see a price (I found one several years ago but do not remember the cost).
 

SIY

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It is quite expensive, like $20k or so if memory serves. I can jigger the APx1701 (under $10k) to do something similar, but it’s limited to 100 watts.
 

pma

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Maybe a kind of own thinking and creativity would make it similar and much cheaper. You do not need to spend same money as for a car for every new SW option. AP prices are crazy, it is same as for prices of High End so often criticised here.
 

tkr

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I did not know that this was available of the self, albeit at a hefty price. No wonder not many magazines own that type of equipment.
 

DonH56

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I had $30k in mind for the automated package plus Power Cube for the AP but was hoping I was wrong.. I know @amirm looked into it and it was way beyond what donations from ASR would provide. Of course, we are bigger now... ;)

I keep thinking we could build something reasonable using air or oil cooled RLC networks to create just a couple of "nasty" loads. I had in mind a conventional design with typical (wild) excursions (maybe a low bass point plus another one or two higher up with high phase angles) and one that emulated an ESL with falling impedance at high frequency.
 

anmpr1

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I did not know that this was available of the self, albeit at a hefty price. No wonder not many magazines own that type of equipment.
Audio Critic owned one, but evidently it broke (!) and then Peter retired, so I don't know what became of it. From the Audiograph Website, it looks like their market is geared toward manufacturer R&D work. Nevertheless, I'd much rather a magazine plot out an amp's Power Cube and print it out, than tell me about liquid mids, lower end slam, and front to back depth.
 
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SIY

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Audio Critic owned one, but evidently it broke (!) and then Peter retired, so I don't know what became of it. From the Audiograph Website, it looks like their market is geared toward manufacturer R&D work. Nevertheless, I'd much rather a magazine plot out an amp's Power Cube and print it out, than tell me about liquid mids, lower end slam, and front to back depth.

100% agreed. After frequency response, this is the single most important power amp measurement- and hardly anyone (including me) has them as part of the review process.
 
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