Integrated Amplifiers

Harman Kardon HK 990 Stereo Integrated Amplifier with Digital Room Correction and Dual Subwoofer Bass Management – Part III


Overall Conclusions About the HK 990

For those who started with Tyler's review and worked their way through this three-parter, 20,000 words have passed your eyes. Only a very special product requires that level of analysis. There is no comparable for the HK990. One could say that an equivalent could be crafted with three or more boxes. Unfortunately, this is not a viable option because many different functional blocks inside the HK990 interface with each other in ways that cannot be replicated with RCA cables running between multiple external boxes.

As with any debut product, the HK990 has some glitches. The front panel controls are very difficult to manipulate and the room-correction system has some software bugs. Putting these issues aside, the HK990 is a revolutionary product that will be on the list of the 100 most important audio components ten years from now.

















The Nationally Recognized Testing Laboratory safety mark on the HK990
Written by David Rich , November 03, 2011

In my discussion of the protection system for the power amp I neglected to mention the ETL safety mark at the rear of the HK990. ETL is a Nationally Recognized Testing Laboratory (NRTL), certified by OSHA (Occupational Safety & Health Administration) to assess equipment safety. Underwriters Laboratories (UL) is also an NRTL and uses the same tests as all other NRTL's. The NRTL mark is found on most products sold at Best Buy, but high-end equipment is more likely to display a CE mark, referring to standards, including safety, required for sale in the EU. CE testing is undertaken by the manufacturer, not a third-party. CE certification is less comprehensive and less expensive to achieve since the tests are done internally.

The absence of replaceable fuses or resettable circuit breakers illustrates an enhanced safety element of the HK990. When the Amp Fault line goes high (see block diagram of power amp above), the power to the transformers driving the power amplifier is cut off by a relay in series with the transformer. This is done under the command of a protection circuit that monitors for faults. The protection circuit also commands another set of relays to open the connection of the amplifier to the speakers. This removes a fault that could be caused by a short in the speaker cable and protects the speaker from a large voltage at the amplifier's output when the fault is inside the amp. A third transformer supplies power to the protection circuit and remains connected to the AC line.

A user-induced fault might be a shorted speaker terminal or an overdriven amplifier input. The amplifier will recover after it is switched off provided the user removes the cause of the fault before turning the unit on again. If the amplifier is internally damaged, the fault signal status returns and the relays at the speaker and AC line again open. Now the amp most go for service. For the HK 990, it is never incumbent upon the user to change a fuse or reset a breaker as would happen if the amplifier did not have internal relays. That's to the good because a user might substitute a higher amperage fuse, which would be quite dangerous were the unit to remain on when an internal fault produces a potential safety hazard.

Circuit-breaker values cannot be change by the user, but the fault must be significant enough for the current flowing in the power line to exceed the breaker's pre-set level after damage has occurred. The HK 990's fault status line activates well before the line current reaches the maximum level. Some amps have many sub-fuses that activate when one amplifier draws too much current. The user must remove the cover and identify the tripped fuse. NRTL-tested equipment is affixed with a label that warns against opening the cabinet (for good reason).

When fuses and breakers are present, no relay may be in series with the speaker's output terminals. Your speaker could be damaged before the fuse or circuit breaker activates. The HK990 does have a couple of hidden fuses that trip if the protection circuit is defective and fails to act. Any component in the category of the HK990, including a home theater in a box, is vetted similarly by an NRTL and has a similar protection system. The website below identifies the marks that should appear on your amplifier after passing a safety inspection by a third-party NRTL.


Congratulations with an Exceptional Review!
Written by Igor Khachaturyan , November 04, 2011

I would like to thank and thank you for the most comprehensive and informative review that i have read in many years!

Once could only wish that all audio reviewers had your competence and willingness to provide facts instead of based opinions.



Re: Congratulations with an Exceptional Review!
Written by David Rich , November 05, 2011


Your support of my work is appreciated and I am glad you found it useful.

Nothing like his would be possible without the support of the editor-in-Chief, managing editor, and the site manager. Besides the process of editing the document, the staff prepared the piece for on-line publication, then split it to improve ease of navigation. Also, many figures were modified to enhance readability.

It would have been impossible to present this in printed form, and I am heartened by the team's commitment to ready my work for the site.

Your feedback validates everyone's effort.

David Rich


    Written by Nick , November 06, 2011

    Bummer that there is no HDMI. I have a two channel system, but several sources that only output over HDMI.


    Written by Pere Barceló , December 05, 2011

    Dear David,

    Congratulations on something that some could call a review but it seems to border on a research paper. I have never seen such and in-depth technical analysis like this one.

    Thank you for you work on this piece.

    I must also admit that having considered buying this unit, your work brings more doubts as it points out to some clear software mistakes in most of the room correction programs.

    As such, I'd like to ask if you have any additional info on the manufacturer as far as if they are willing to to into theses issues and provide a fix through a firmware update down the road.

    My other question would be, software aside, if there is any other implementation mistake that warrants consideration. I could live without the room correction but not if the DAC, preamp or power stage has a major fault.

    If you prefer to privately respond as this is a personal request I'd be delighted. Sorry but I'm not an engineer and some stuff has proven hard for me to follow or understand.

    Many thanks in advance and again a most enthusiastic congratulations!


    Thank You!
    Written by jkasch , January 16, 2012

    Probably the most informative review I've ever read. I've had my HK 990 about 18 months now and love it more than ever.

    Three points I'd like to add/question:

    I believe EQ1 works without subs. I'm running floorstanders that have no trouble getting down to 30hz. EQ1's effect is obvious in my room. It kills the room-boom, nicely. EQ2 and 3 are very similar in my setup and sound a bit thin on all but the most bass-heavy recordings.

    HK has always listed 4 ohm power output in the literature I've seen. It's stated as 300wpc, 20-20K, but with


    Power Cube measurement
    Written by Ian MacLeod , January 29, 2012

    Dr. Rich,

    I spent a day with your review, and came to appreciate my HK990 so much more. It is driving my JBL Array 1000 speakers now, and I consistently have goosebumps when listening. I do not use the room corrections with the Array 1000 speakers, so these weaknesses are not an issue with me, though perhaps I would use it if it worked better.

    I case you or anyone wants to see the Power Cube measurements, you can find them here (they look pretty good to me): - HK Insight 2009 (English EU).pdf

    One question I do have. I use balanced cables to connect the HD990 CD player to the HK990, which then runs analog, Direct path. This is using the player's DAC, which is also dual AD1955. However, after reading your article, it seems to me that it would be better to run the player over the HRS-link and use the HK990 DAC. This not only saves the expensive balanced wires for something else (I may return them), but removes this extra wire from the circuit as the dual HK990 DACs provide balanced output directly to the amp. What is your view?

    Thanks again for a superlative review. I hope you share more.



    EQ1 works without subs?
    Written by David Rich , February 03, 2012


    Thanks for your kind words on this work.

    I tested many speakers full range and do not recall seeing EQ1 do anything in the frequency response plots as I toggled to all the possible modes. The instructions say:

    "This preset processes the subwoofer channels only"

    Unfortunately the unit has gone back so I cannot check to be absolutely sure. Going from direct to any EQ mode can introduce a significant level difference (1 - 2dB).

    You are correct the instructions have a 4 ohm FTC specification:

    Continuous average power per channel (FTC), 20Hz – 20kHz, both channels driven: 300 watts @


    Go with the HRS-link
    Written by David Rich , February 03, 2012


    I do not know how you could have possible found that power cube in the fine print of some HK brochure on an EU site.

    The balanced inputs on the HK990 use good opamps but not as good as what is in the rest of the direct path or the DAC output circuits.

    I do not have the HD990 schematic but from looking at the board it appeared to have discrete buffers driving the balanced outs.

    David Rich


    Ian - a subjective opinion
    Written by Tyler S , February 07, 2012

    From my time using the HK990/HD990 combo, I agree with David - stick with the HRS-Link. While the RCA and balanced analogs certainly sounded very good, the HRS-Link was still noticeably better to my ears. The biggest difference was how individual notes just seemed to resonate more naturally and decay beautifully into the background. Sound via HRS-Link was just more life-like to me, more like what you hear with live performances. I also preferred to keep the equalizers OFF for all of my listening.

    Best idea is to try out the different options for yourself and see what you like the best.

    Tyler Stripko


    HRS-link it is
    Written by ian macleod , February 15, 2012

    Dr. Rich and Tyler,

    In the end I did let my ears decide. HRS-link it is, and I returned the balanced cables.

    I can't recall how I found that Power Cube reference, but I'm sure Google helped...

    Thanks for responding.