• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Audio Research 100.2 Power Amplifier Review

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
44,370
Likes
234,396
Location
Seattle Area
This is a review and detailed measurements of the Audio Research Corporation (ARC) 100.2 stereo power amplifier. It is on kind loan from a member. The 100.2 came out in year 1998 at a cost of US $2,995. It was later raised to US $3,495. If I remember correctly, the owner told me this the last solid state amplifier ARC produces before going to all tube route.

The 100.2 is as solid as a rock:

Audio Research Corporation ARC 100-2 Stereo Power Amplifier Audio Review.jpg

The back panel is as you expect with the exception of (custom?) speaker binding posts:

Audio Research Corporation ARC 100-2 Stereo Power Amplifier Back Panel Audio Review.jpg

In use the 100.2 cooked and cooked good. I measured 45 to 47 degrees C on the heatsinks. The internal temps are likely much higher. I read that it uses unobtanium output MOSFET transistors so if they go, you likely have a giant door stop. :) In use though the 100.2 did not complain one bit and ran through all of my tests.

Strangely when you power the unit down, it takes it a while to do that. What it is doing, I don't know.

The design of the unit is based on low feedback factor of just 6 dB. Based on that alone I can tell you it is not going to perform well.

Amplifier Audio Measurements

Audio Research Corporation ARC 100-2 Stereo Power Amplifier Audio Measurements.png


We have huge power supply peaks, like due to poor power supply rejection ratio of low feedback design. Second and third harmonic dominate the distortion profile resulting in lackluster SINAD of just 65 dB. That lands the ARC 100.2 near the bottom of some 72 amplifiers tested so far:

Best Power Amplifier Review 2020.png


Frequency response is excellent:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Frequency Response Audio Measureme...png


Response changes some with a simulated 2-way speaker load but nothing to cry over:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Frequency Response Speaker Simulat...png


Multitone test shows the high distortion products of the power supply:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Multitone Audio Measurements.png


And rather high noise floor which we can directly measure using signal to noise ratio:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Dynamic Range Audio Measurements.png


Crosstalk shape is odd but not an audible concern:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Crosstalk Audio Measurements.png


Amplifier Power Measurements
The sins of low feedback factor stare at you in the face with our 4 ohm load:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Power into 4 ohm Audio Measurements.png


Yes, distortion gradually increases but then it clips anyway. So why not have clean power until clipping???

Same deal into 8 ohms:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Power into 8 ohm Audio Measurements.png


At least it slightly exceeds its power specifications.

Strangely burst power (momentary peaks) doesn't generate much more power:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Peak and Burst Power Audio Measure...png


Keeping THD+N constant at 0.1% gives us incredibly low and strange amount of power:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Regulated Power vs Frequency Audio...png


There is so much distortion and noise in the output of this amp that you don't get much power if you set your goal at 0.1% THD (likely threshold of audibility for some people). FYI I ran the above at 0.2% THD+N (not shown) and it produced about 80 watts with a straight line. Anyway, who says only class D amps have trouble with this test?

Amplifier Thermal stability
I powered the unit cold and let it run nearly half hour while recording distortion and noise. This is what I got:
Audio Research Corporation ARC 100-2 Stereo Power Amplifier Warm up Audio Measurements.png


That is very high degree of improvement. Again, low feedback means that it is more sensitive to operating temperature. Given the high heat dissipation, it is a tough deal to have to also keep the unit on for a while to get the best performance.

Conclusions
Sigh. The best analogy I can think of here is if car owners said, "you know, a car should have more square tires" and manufacturers running to build cars that way. Yes, audio folklore says feedback is a bad thing. Well, I have news for you: distortion is really, really bad thing. As is noise. It surely doesn't give you "blacker background" if it has higher noise, does it?

I read some place that it has less feedback so it can deliver less phase shift. Do folks not know that you have reflections in your room, every one of which arrives at your ears with a different delay and hence phase? That they all mix up and as a result, the brain discards that info? If it did not, we would go crazy trying to make sense of people talking to us in indoor situations. Anyway, we digress.

Needless to say, I cannot recommend the ARC 100.2. Serviceability will be poor and so will the performance.

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

Been working on a project morning to evening every day and spending the last two hours before midnight on reviews. Even the panthers are feeling sorry for me. If you do too, please donate using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

VintageFlanker

Major Contributor
Forum Donor
Joined
Sep 20, 2018
Messages
4,940
Likes
19,692
Location
Paris
The 100.2 is as solid as a rock:

index.php
The back panel is as you expect with the exception of (custom?) speaker binding posts:

index.php
Many thanks and happy New Year, @amirm.

Very cool industrial design for a 22 years old unit! It could has been released yesterday.

Sad the performance seems clearly broken.
 
Last edited:

Cahudson42

Major Contributor
Joined
Sep 21, 2019
Messages
1,083
Likes
1,556
Thanks @amirm . Interesting to see a really bad class AB from that era. Warns us 'all is not golden' (like the RX-596) from back then...
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,201
Likes
16,983
Location
Riverview FL
Strangely when you power the unit down, it takes it a while to do that. What it is doing, I don't know.

Draining the main reservoir capacitors.

I have two amps that will play on after the AC is cut. The higher the volume, the faster they die. Low volume, maybe 30 seconds or so until the rails meet the output swing, then they sizzle (clipping) until silent.

I suppose I should drag them out and do a few measurements, since the big ones didn't embarass themselves too badly.

http://www.krellonline.com/archive_pdfs/KAV250/KAV250A_V000_MAN.pdf

http://www.hifi-review.com/153494-acurus-a250.html

"To gain some idea of the energy storage capacity of its power supply, we switched it off while playing music at a normal room level. For almost 30 seconds, the volume and quality of the sound did not diminish."
 
Last edited:
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
44,370
Likes
234,396
Location
Seattle Area
Hi Amir, can you ask the member who loaned the amp if the PS supply caps have been replaced or are they still the originals from 1998?
I peaked in there and they are rated at 63 volts. I read some place that the original caps were 50 volts so I am assuming they are replaced.
 

Koeitje

Major Contributor
Joined
Oct 10, 2019
Messages
2,292
Likes
3,880
These kind of reviews make me wonder how my 1996 $2000 MSRP Marantz PM16 integrated would do. Would that also be bad nineties tech?
 

bigx5murf

Addicted to Fun and Learning
Joined
Nov 6, 2018
Messages
522
Likes
343
Almost not surprised considering they left the distortion spec blank. Then instead of listing SNR they listed a made up spec,
"Hum & noise 150 microvolts RMS (105dB below rated output IHF A-weighted)"
 

Attachments

  • Screenshot_20200103-014142.png
    Screenshot_20200103-014142.png
    348.2 KB · Views: 290

milosz

Addicted to Fun and Learning
Forum Donor
Joined
Mar 27, 2019
Messages
584
Likes
1,643
Location
Chicago
Some people probably actually LIKE this kind of sound. It seems it would sound a little different from amps with proper amounts of negative feedback; and so I bet that certain listeners have convinced themselves that this difference means it's better.

I wonder - would it approach a "tubelike" sound? Has high-ish source impedance, and so some level of response coloration when connected to speakers- just like most tube amps. Adds harmonics and noise to the signal - is this the "richness" some like in tube amps?

But, you know, even though it's measurements rise almost to mediocrity, I would guess that for most listeners, under ordinary listening with typical ~87 dB efficient speakers, this thing would be hard to tell apart at reasonable listening levels from an amp of similar power levels that measures really well. Probably in a critical A/B comparison some listeners MIGHT be able to reliably tell the difference, but I bet that even under such controlled circumstances most of us would throw up our hands and say "sounds pretty much the same to me."

But now, if you pair a crap DAC and noisy preamp with this thing, all the sonic crud will start to add up and start to mask the sound of the recording. So, if you get a DAC that is clean, and let's say you feed it directly to a very clean amp- well then it would seem like there is little chance for equipment flaws to mess up the sound. And when you can buy a DAC and power amp that measure very close to SOTA for not TOO much money- well then there's really no reason whatsoever to use an amp like this unless you find it laying in the alley.
 

Matias

Master Contributor
Forum Donor
Joined
Jan 1, 2019
Messages
5,029
Likes
10,799
Location
São Paulo, Brazil
Hiss and hum fest...
 

Addicted to music

Active Member
Joined
Sep 3, 2018
Messages
113
Likes
111
Anyone know what the make and model of those “unobtanium” output Mosfets are?
 
Last edited:

Thomas_A

Major Contributor
Forum Donor
Joined
Jun 20, 2019
Messages
3,422
Likes
2,407
Location
Sweden
A general question regarding the measurements: How doesl the SNR numbers compare to a standard reference level e.g. 2.83V, unweighted, audio band weighted and A-weighted?
 

JRG

Member
Joined
Oct 2, 2019
Messages
48
Likes
91
Location
La Rioja, Spain
I think they should have retired the "High Definition" slogan from this product. It is not "high definition" at all.
And the name of the company "Audio Research"? What Research is about? Unobtanium silicon devices?
Putting a product in the late 90s with a SINAD of about 60dB don't seem to involve a lot of audio research. May be in the 60s
 

Francis Vaughan

Addicted to Fun and Learning
Forum Donor
Joined
Dec 6, 2018
Messages
933
Likes
4,697
Location
Adelaide Australia
In fairness to AR they could hardly demand that Toshiba keep manufacturing an obsolete part just so that people could repair 20 year old amplifiers. (Toshiba 2SA1303 and 2SC3281)
Where they are annoying is in carefully sandpapering the manufacture's markings off all the low power semiconductors and marking them with painted on colour bands. If you need to replace anything in the voltage gain stage you need to order a colour coded part from AR. They won't tell you what it actually is. Some if these are almost certainly hand selected parts, matched to a specific parameter value, not just random parts off the production line. Even so, it seems a bit mean.
 

Xulonn

Major Contributor
Forum Donor
Joined
Jun 27, 2018
Messages
1,828
Likes
6,311
Location
Boquete, Chiriqui, Panama
Jeez, Amir - you've done it again. I can't wait until you are able to test one of their revered tube amplifiers

Sacred Cow.jpg


From Stereophile reader comments:

November 7, 2016 - 3:16pm

mrkaic wrote:
Colleagues, does anybody known which tube amps (both power and integrated) have very low distortion and measure well in general? I am aware of only two : McIntosh MC275 and Quad II Classic Integrated.
I am sure that there are more out there. Could someone please let me know of other low distortion tube amps.
Many thanks.​
Reply:

Audio Research has several tube amplifiers that are currently in production, and has made many other model over the years that are available used. Virtually all of them have extremely low distortion. Many experts consider them to be the very best ones that are currently available.
The Audio Research Reference 75SE and Reference 150SE will possibly be of great interest to you...

...I suggest that you look at the Audio Research website for the current models, and that you also look at the ARCDB website, which is a database of every Audio Research product ever made, including current ones, with complete specs and pictures.
 

anmpr1

Major Contributor
Forum Donor
Joined
Oct 11, 2018
Messages
3,722
Likes
6,406
... the owner told me this the last solid state amplifier ARC produces before going to all tube route.
By the late '70s ARC was seriously considering getting out of the tube business. Their 'high end' street cred was mostly based upon the many SP3 preamplifier versions, which because of their accessability were taking the Dyna mod route--i.e. cottage designers like Paoli were modding the preamps, adding that special magic only they could provide.

Perhaps in order to stop this sort of thing, ARC came out with their 'Analog Module' scheme, which as near as I remember were ICs or opamps potted in thick goo, so a third party couldn't 'fix' what they didn't like. The upside was that all repairs had to go through ARC dealers. The downside was that after a few years you couldn't get Analog Modules anymore, making your preamp or amp pretty useless if it broke. Of course this sort of thing wasn't endemic to ARC... recall Hitachi MOSFETS (Acoustat) and Sony V-FETS, et al.

s-l1600.jpg
 
Last edited:
Top Bottom