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Audio Research D300 Power Amplifier Review

amirm

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#1
This is a review and detailed measurements of the vintage Audio Research D300 Power Amplifier. It is on kind loan from a local member. The D300 came out circa 1995 and initially cost US $3,500 but then price rose to US $4,000. Quick search shows used ones going for US $1,500.

The D300 is built like a tank:

Audio Research D300 Stereo Power Amplifier Review.jpg

I am confident you could drive over it and nothing will happen to it. Even the handles are massive which is a blessing as an ultra heavy transformer sits vertically behind the front panel. I could carry the D300 by myself so it is not too heavy to be unmanageable.

The back panel is as you expect:
Audio Research D300 Stereo Power back panel connectors Amplifier Review.png

With one exception: the non-detachable power cord. What is there though seems amply sufficient as it is supple yet quite thick.

Heatsinks are very thick gauge and in use, they got warm but not hot. The rest of the case got warm as well. The amp never complained no matter what I did to it in testing.

Overall, if you want an understated but high quality feel, that is what you have in D300.

Amplifier Audio Measurements
As usual, we start with a 1 kHz tone at 5 watts into 4 ohm load:

Audio Research D300 Stereo Power Amplifier XLR Audio Measurements.png


Ouch. Lots of second harmonic causing SINAD which is the sum of distortion and noise to be rather poor. As such the D300 lands well below average in our list of some 62 amplifiers tested to date:
Best stereo amplifier tested.png


Noise performance was quite good though so it is the distortion that is the problem:
Audio Research D300 Stereo Power Amplifier XLR SNR Audio Measurements.png


32-tone test signal representing "music" showed what we already know as far as rather high distortion levels:
Audio Research D300 Stereo Power Amplifier XLR Multitone Audio Measurements.png


Frequency response was excellent:
Audio Research D300 Stereo Power Amplifier XLR Frequency Response Audio Measurements.png


As was crosstalk (one channel bleeding into the other):
Audio Research D300 Stereo Power Amplifier XLR Crosstalk Audio Measurements.png


Let's get into the meat of the measurements with power vs THD+N starting at 4 ohm:
Audio Research D300 Stereo Power Amplifier XLR Power Into 4 Ohm Audio Measurements.png


Boy, this is worse than the dashboard indicated. Almost immediately, distortion takes over and keeps climbing. While the D300 is much more quiet, it quickly loses to an integrated home theater receiver (NAD T758)! Not good.

Same story repeats for 8 ohm load:

Audio Research D300 Stereo Power Amplifier XLR Power Into 8 Ohm Audio Measurements.png


Distortion is so high at higher power levels that if we set a limit of 0.1% for THD+N, we only get 60 watts out of each channel!
Audio Research D300 Stereo Power Amplifier XLR Regulated 4 Ohm Audio Measurements.png


Relaxing that to 0.2% though gave us a lot more power and no indication of frequency mattering. This was proven yet again in our multiple sweeps:
Audio Research D300 Stereo Power Amplifier XLR THD+N vs Frequency vs Level Audio Measurements.png


All the lines fall on top of each other indicating the amp just doesn't care what frequency you feed it. It amplifies it, adds a heap of distortion and that is that. Makes you want to cry and celebrate at the same time!

Conclusions
There is clear excellence in the engineering in Audio Research D300. Build quality is superb as well. There must have been a conscious decision to use low amount of feedback which translated into rising distortion with power. It is a shame that capable designers follow audiophile myths to build non-performant amplifiers when they could do so much better.

In this day and age, this type of performance is not competitive so I really can't recommend the D300. Then again if you want something with high build quality and can get the unit on the cheap, it makes for a decent option.

--------
As always, questions, comments, corrections, etc. are welcome.

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maty

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pma

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Thanks for this review and let me add some technical information and experience. This was a nice series of ARC amplifiers, D200-300-400, differing in output power and number of output devices. Very well built. Parameters are as good as not to make audible distortion, so though they would not excel in Amir's SINAD chart, distortion is inaudible. Amplifiers were very good sounding and capable to drive difficult loads. And remained operating till now. Hats off! No disrespect needed. The designers made their choice in the way that does not reduce perceived sound quality.

Some technical info, click on thumbnails. (manuals downloadable from ARC archive)

ARC_D200_D300_D400MKII_flyer4.jpg D400_inpstage.jpg D400_outstage.jpg
 
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#6
Interesting. While some of the old amps were very good, this one seems rather pedestrian.
And not very powerful either. Great review as always!!!
 

maty

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#7
H2 at -70 dB. H3 at -98 dB.



With this intentional harmonic profile (to emulate SET tubes sound) the question is how complex recordings like electronic or orchestral sound. Maybe H2 about 84 dB would be the good compromise to ALL recordings, better than 70 - 73 dB.

 

pma

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Boy, this is worse than the dashboard indicated. Almost immediately, distortion takes over and keeps climbing. While the D300 is much more quiet, it quickly loses to an integrated home theater receiver (NAD T758)! Not good.
Put it into real test with some speaker with impedance falling below 2 ohm, against that NAD T758 AVR.
 

Blumlein 88

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#9
Interesting. While some of the old amps were very good, this one seems rather pedestrian.
And not very powerful either. Great review as always!!!
Actually I don't think so. If you go and look at some measures at Stereophile from that era, this was typical of large amps. Quiet and low noise. Wide bandwidth. Lots of power and not bothered by supplying a ton of current into a reactive speaker load, and claimed specs ranging from about -60 to -75 db THD. This one seems a little short at high power on that. This was usual for Krell, Threshold, Mark Levinson, Spectral, Classe, C-J solid state and other amps of the day.

I second @pma about hanging this and the NAD AVR on a tough speaker load. This is one reason that while @amirm can't yet get his Klippel for measuring speakers, it is within reach I think to get some sort of setup to put genuine speaker loads at high power on some of this gear and see what happens. That is the next most useful thing this forum could offer after speaker measurements.

Having owned tough speaker loads and such amps as well as seeing others try such things, an amp like this probably won't let you down on much of anything. Some of these AVR's would let the smoke out trying.

This also gives you an indication of how terrific some modern amps like a Benchmark or Hypex or Purifi amps are vs the best of yesteryear.

I also believe this was the other amp in the Swedish AES series amp tests which nearly passed their transparency gauntlet. Only the Bryston managed it in all ways. This one managed it sighted, but failed during blind testing.
 
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I
Actually I don't think so. If you go and look at some measures at Stereophile from that era, this was typical of large amps. Quiet and low noise. Wide bandwidth. Lots of power and not bothered by supplying a ton of current into a reactive speaker load, and claimed specs ranging from about -60 to -75 db THD. This one seems a little short at high power on that. This was usual for Krell, Threshold, Mark Levinson, Spectral, Classe, C-J solid state and other amps of the day.

I second @pma about hanging this and the NAD AVR on a tough speaker load. This is one reason that while @amirm can't yet get his Klippel for measuring speakers, it is within reach I think to get some sort of setup to put genuine speaker loads at high power on some of this gear and see what happens. That is the next most useful thing this forum could offer after speaker measurements.

Having owned tough speaker loads and such amps as well as seeing others try such things, an amp like this probably won't let you down on much of anything. Some of these AVR's would let the smoke out trying.

This also gives you an indication of how terrific some modern amps like a Benchmark or Hypex or Purifi amps are vs the best of yesteryear.

I also believe this was the other amp in the Swedish AES series amp tests which nearly passed their transparency gauntlet. Only the Bryston managed it in all ways. This one managed it sighted, but failed during blind testing.
It has a lot of distortion...ability to drive reactive loads notwithstanding. There were better amps available earlier than this one.
Which is why I call it pedestrian.
 

Blumlein 88

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#11
I


It has a lot of distortion...ability to drive reactive loads notwithstanding. There were better amps available earlier than this one.
Which is why I call it pedestrian.
I would not call this amp SOTA for the time.

So which amps would you list as better?
 

maty

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maty

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#14
To finish, tube amps have traditionally specified the max power with THD+N of 1% = -40 dB. Probably it is right with small groups with acoustic instruments and modern commercial (so bad, with DR < or << 10 dB) but complex recordings... You know, many have two amplifiers in the audio system, depending on the type of music.
 

restorer-john

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#15
There were better amps available earlier than this one.
He's right. late 80s to early 90s there were a ton of Japanese amplifiers with performance well in excess of what this has shown. But Audio Research have always done their own thing, not bowing to fashion or style and they have a loyal following to this day. Personally, I'm glad they have survived and are still in business.

So which amps would you list as better?
Shall I start at A for Accuphase and go through the alphabet? Pretty much every power amp they produced from the late 1980s onwards would outperform by a wide margin this Audio Research.

There's plenty of Denons, Onkyos, Sonys, Pioneers, Luxmans, JVCs, Kenwoods, Technics and Yamahas that could drive <1ohm loads at stupendous powers and low THD with DC-Daylight responses. Remember, the Japanese were building the fast silicon high powered dedicated audio transistors and MOSFETs (Hitachi/Toshiba/Sanken/Fujitsu etc) Their premium models were often home market or EU and didn't make it to the US.

Here's a few random (early 90s) Accuphase THD vs Po plots I posted in another thread:

1575102890410.jpeg

P-360 btl.JPG

P-800.JPG
 
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Blumlein 88

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#16
He's right. late 80s to early 90s there were a ton of Japanese amplifiers with performance well in excess of what this has shown. But Audio Research have always done their own thing, not bowing to fashion or style and they have a loyal following to this day.



Shall I start at A for Accuphase and go through the alphabet? Pretty much every power amp they produced from the late 1980s onwards would outperform by a wide margin this Audio Research.

There's plenty of Denons, Onkyos, Sonys, Pioneers, Luxmans, JVCs, Kenwoods, Technics and Yamahas that could drive <1ohm loads at stupendous powers and low THD with DC-Daylight responses. Remember, the Japanese were building the fast silicon high powered dedicated audio transistors and MOSFETs (Hitachi/Toshiba/Sanken/Fujitsu etc) Their premium models were often home market or EU and didn't make it to the US.
The only amps I knew of at the time were the Yamaha that did make it here. Actually have one with matching pre I'll be selling soon. It did power speakers as well as the better known brands. The others you describe weren't here then. Doesn't mean they didn't exist of course. That is why I said the AR wasn't sota. It was not very atypical for what was in the USA. And I would take it over an AVR.
 

maty

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He's right. late 80s to early 90s there were a ton of Japanese amplifiers with performance well in excess of what this has shown. But Audio Research have always done their own thing, not bowing to fashion or style and they have a loyal following to this day. Personally, I'm glad they have survived and are still in business.



Shall I start at A for Accuphase and go through the alphabet? Pretty much every power amp they produced from the late 1980s onwards would outperform by a wide margin this Audio Research.

There's plenty of Denons, Onkyos, Sonys, Pioneers, Luxmans, JVCs, Kenwoods, Technics and Yamahas that could drive <1ohm loads at stupendous powers and low THD with DC-Daylight responses. Remember, the Japanese were building the fast silicon high powered dedicated audio transistors and MOSFETs (Hitachi/Toshiba/Sanken/Fujitsu etc) Their premium models were often home market or EU and didn't make it to the US.

Here's a few random (early 90s) Accuphase THD vs Po plots I posted in another thread:

View attachment 40824
View attachment 40825
View attachment 40826

With tons of GNFB -> very good specs. But sound, emotion, 3-D... ?
 
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restorer-john

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The others you describe weren't here then. Doesn't mean they didn't exist of course.
The US had a very healthy high end, big iron amplifier industry (a bit like their V8s..) and the Japanese had a lot of success in Europe and particularly Germany. They made the decision to stay out of the US with their premium stuff unfortunately. In Australia, we really only got to tap into the EU models, the world models and the military (PX) models as they were multi voltage.

What's your Yamaha? A CX600/800/1000- MX600/800/1000, C-60/80 M-60/80/85?

Or have you got a pair of these CX-10000 and MX-10000 Centennial Series? I sold one preamplifier. $10,000. A whole system including NS-10000 speakers went to Western Australia. The rumour was, it was Alan Bond. (An entrepenuer that collapsed with debts over a billion dollars)

1575104073607.png


Inside:

1575104304601.png


1575104104061.png


Inside:

1575104248750.png


1575104837344.png


12 Sanken LAPT MT200 transistors per channel. Insane.
 
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maty

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#19
BTW, small round holes to avoid that they work like an array of RF antennas :)
 

DKT88

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Could you just change the components in the global feedback network to add more feedback in an amp like this? If you increased the feedback it would reduce the output, right? Would there be unintended consequences?
 
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