I cannot recommend this amplifier enough. I had 3 of them including an original prototype. I was also a friend of James so let me share a couple things he said. First off he always claimed the output was 75wpc. Also the opamp in this is a special order higher voltage custom LF353 and not a stock IC. The power supply is rather special and referred to as the cyclotron by my electronics guru. I believe I have had this amp, a silver faced rack-mount model since about 1999. I sold the ugly prototype and standard black model a few years ago and so glad I hung on to this one.
The tweak upgrade IMHO is to replace the opamp with an AD823 which I have done as well as replace the captive refrigerator power cord with an IEC socket. I've also replaced the rca input jacks with Cardas and the speaker binding posts with Eichmanns. In direct comparison this amp made a Krell Integrated amp sound broken. The difference in the mids and highs was stupefying. Adding Hifi Tuning Fuses for the AC and DC rails took this even farther. Quite surprised how loud this drives my 89db Induction Dynamics ID1s but my ears are more sensitive than most; 100db is painful.
The fan is a big issue however and I am about to replace it with a 26dba modern model; fingers crossed. James told me that not a single one of these models ever came back to the factory for warranty repair. It was the lease expensive amp they produced yet the quality is superb.
I actually preferred it compared to the Sumo Gold. It blew away my Andromeda as well which disgraced a Macintosh, Audionics, and Yamaha amps I had. However I also got to compare it to a Sumo The Power which knocked me out of my seat but good luck finding one.
Others are right in recommending a tube preamp to drive this. the combination is staggering if you have the source, speakers, and cables to match. Loves Stealth Audio power cords but I also had wonderful results with DIY DH Labs cord kept as short as possible. The chassis is a bit live and I use some mass loading on top and good cones underneath. Absolutely scary real and completely enveloping sound field which is my thing as I do record a local symphony here. I believe the SRP was only $600 and of course the 650W push-pull description is way way off. Class A all the way!

Have owned the Sumo The Nine amplifier for decades. Purchased used at The Listening Room, Westchester Cty, NY. Actually I purchased 2 of them. Has played reliably and beautifully for many, many years. Had it recapped about 15 years ago. Really didn't need the new caps.
Drove Dalquists DQ 10s, Quad 63s, Quad 57s, Sound Dynamics 300ti.
And has been submerged in my flooded basement more than once.
Still playing my 63s as I write this note.

I origionally purchased the Sumo Nine in 1984 along with the Sumo Electra preamplifier. I was initially driving a pair of Tannoy Windsors which gave way to a pair of Acoustat 2+2 electrostatic panels which I still have. I still use the Nine and just replaced the preamp with a Blue Circle BC3. The BC3 really works well with the Nine - very musical combo. The BC3 took my system to a new musical level and the Nine shines more. The Nine is very capable and deserves a fine preamp. I also have a sub which you need with panels. The Nine is very easy to listen to hours on end. There are better amps out there but for the money ($1400 new) there is nothing that can touch it. It is a class A design with 65 watts into 8 ohms and 120 into 4. It does run hot and the only drawback is the noisy fan. It is the class A design that makes the sonic differene. Other class A amps have the same beautiful sound as the Nine but cost far more and are somewhat better. The Nine will sound close to a tube amp just not as sweet. I have yet to do any service work on it and have been running it for 26 years. Don't know what I'll do should it ever bite the dust. If you find one, seriously consider it. Anyone can get great music out of $5000.00 amps. You will get close with a used Nine at the fraction of the price (spend the difference on a tube preamp - I should have swapped preamps years ago). The thing to remember is the Nine is only 65 watts into 8 ohms. If you have inefficient speakers, the Nine might not have the omph to drive them if you like loud.

Open, airy, floating mids and highs. Great low, tight bass too.

Fan noise. See above. I remedied that problem. I figured at the price I paid, I'd remove the fan and chance the overheating problem. So far, 4 years later it still works flawlessly.

Might not have the power needed for big inefficient speakers if you are into turning them up loud and running them full range. It has more than enough muscle for my setup.

Just keep the drunk at your party away from the volume control if you have inefficient speakers.

I've been using a SUMO Model Nine amp for my main system for about 4 years now. It is a fabulous sounding little amp! I think solid state "class A" is the way to go if you want a somewhat tube sound without the eventual maintenance issues.

I orig. used a Sumo Andromeda II amp for the mains. Great amp, but overkill on the powerfor my efficient speakers. Now I go thru an active crossover and use the Nine amp down to about 65 HZ . The Andromeda II is now running a homemade NHT driver (#1259?) subwoofer. I quit tinkering after this setup. It sounds great!

FYI, I feed the amps via an AVA "Audio by Van Alstine" hybrid SS/ tube pre amp, then an Audio Control active crossover that I bought about 10 or 12 yrs ago. I think those were the last pieces of gear that I bought new. After that I got addicted to good deals on used vintage stuff.

As far as the fan..... It drove me crazy. I like zero background noise when I 'm listening, so I took the fan and top off and made a new cover. I bought a piece of heavy expanded steel mesh at Lowes. (available in 2 x 2 ft sheets and has 1/2 inch diamond shaped openings). I shaped it perfectly, painted black to match and bolted it on. It looks great and has max open air flow. It gets very hot, but so far it's been fine. The up side with a class A amp is that they make great space heaters in the winter months....:-)

BTW, It's 60 wpc "class A", not 650 wpc, as the above heading states.

Jeff

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A bunch of toys over the years.

Great sound stage and imaging. Very smooth sound (Class A?.)

Would like a bit more power occasionally. Always hot because I leave them on all the time (helps heat the room in the winter.

Bought 2 Sumo Nines when they were first produced (early 80s?). Have been using since then driving Dahlquist DQ10s, Magnapans, and now Sound Dynamics 300ti. Amps were stored for a time in basement that flooded. Cleaned them up, still operating! Only problem was tendency to blow the power rail fuses. Fan was noisey. I removed the fan and the case. Amps have been operating like this for years without a problem and no overheating. Keep children and cats away!

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Ampzilla

Airy/transparent, delicate

Didn't have the low end punch you would expect from SS. Could someone send me the Power ratings on this thing?

I am really quite surprised at that I found any reviews on this product at all! I know that Sumo's been out of business but could still have some of the Bongiorno descendants out there; most notable of his products would have to be the Sumo Nine and 9+. Technically, I could not dare to axplain what Class A really means. I saw this unit on the shelf collecting dust for more than a year at a friends shop and got a bit curious. Started surfing for reviews: Ditto. Except some impression that the amp has quite a cult-like following. How does it sound? After taking the unit home for auditioning matched with music reference RM5 Tube pre and Soliloquy 5.0 speakers. The result was impressive. It seem to cough up a bit and sounded steely at first (probably the result of being in storage too long) but later bloomed and opened up after a few hours. Definitely an excellent performer. After a few hours details seemed crisper and the amp started to breathe. Despite it's heavy looks, the sound seems airy and transparent resulting in less fatigued listening. The sound stage was also better than expected from an SS. Would recommend this Amp for anyone who wants to get into hi-end sound. Don't let looks and age fool you.

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AMPS: Ambient Tech Tube Amp(40wpc EL34 Ultralinear), QUAD 405-2, Adcom 545, Hafler XL600, DH220, P230, NAD 3020B, Ambient SET (RCA 6AS7 Single Ended Parallel) Speakers: Soliloquy 5.0, Magnepan SMGC, B&W 604, Epos ES14, Systym 935, Tannoy M2,B&W 201 Prism

Extremely smooth from botttom to top. Great ability to recover from clipping. Excelent soundstaging. Very musical.

Absolutely none. The most reliable amp you could ever want.

My Sumo Model Nine Class A amplifier has given me more than 20 years of high performance. It has also been reliable beyond belief. James Bongiorno says he never had an output transistor fail in a Sumo Nine, and I believe him. How many amps can remain this trouble free over more than 20 years? I do not intend to replace this beauty. It delivers 120 watts into the 4 ohm load presented by my Dynaudio Audience 42s. What more would you ever want when driving a pair of Audience 42s? The sound is both sweet and extremely coherent. Smooth. The greatness of the Sumo Nine revolves around its ability to recovery gracefully whenever it is overdriven. Your ears never hear any clipping distortion, because the amp is so effortless in its reovery. It never loses a step. There is no way i can buy a better amp for the Dynaudios. The soundstaging is phenomenal also. This amp may be the all time champ in terms of bang for the buck. System includes Rega Planar 2 with Blue Point, Arcam Diva 62T CD, Adcom GTA 500 preamp and tuner.

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Had a Yamaha CA 1000 decades ago. Nice integrated. And many of the infamous Quatre Gain Cells. Blowup champions of all time.

Clear, sweet, articulate sound

The fan which is bothersome even after replacing the stock unit with a superior quality (lower db) ball-bearing fan

I read a number of glowing reviews of this amp and jumped at the chance to purchased the Nine Plus when it appeared in the local classifieds. Compared to the NAD 208THX and Harman Kardon PA2200 I owned previously, the Sumo delivers delivers improved definition between instruments, and is sweeter sounding. A number of recordings I considered harsh sounding prior to buying the Sumo became listenable & enjoyable. Considering that the amp can drive a pair of Magnepan's to reasonable sound levels I don't think anything used compares in this price range. My low budget system: *Sumo Nine Plus Amplifer *Modified PAS 3 tube pre amp *Musical Fidelity X24 DAC *Yamaha 555 CD Player *Magnepan SMG's *Energy XL8 Sub

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None

Coherence of sound, power, value.

Fan noise, heat, banana plugs only, feet are cheesy and fall off.

I agree with most of the comments below (except Mr. Lee - WTF is this guy thinking about?). This amp is a bargain! It is built incredibly well, has a HUGE toroidal transformer (that will trip circuit breakers when turned on) and is very durable. How many 13 yo Class A amps are still out there, never having required so much as a output device replacement? Mine sounds as great as it did when I first put it into my system in 1988, and it's been moved about every couple of years.
Unfortunately, it eventually was relegated to the rear channel or backup duty by the above amps (only the Krell was in improvement - at triple the $$), for which the fan and heat thrown off (I live in a small apartment now) caused it to lose out to a PS Audio 100C. The fan could probably be easily replaced with a more modern, ball bearing computer fan that would be both more efficient and quieter. The only clearly better amps I've heard at length have been the Krell (better at everything) and the Atma-sphere M60's (marginally better mids and top end, more powerful, but hotter). The Bryston 3B (another great used deal) is more powerful and has better bass.
If you can find one, they're a great used deal and a reasonable way to get high end sound in a modest system. I'd recommend between speaker placement (gets the heat and noise away form the listening position), a stand and a few mods. Replace the fan, replace the inputs (originals not gold plated - and if you can find someone smart, I'll bet you can rig balanced inputs - the amp is a fully differential balanced design) and possibly the speaker taps.
After thinking about it, maybe I'll keep mine and do some bench work.....
Highly recommended. 5 stars for value, 4 because there are better amps out there. Would be a Stereophile Class C/borderline B (because of relatively low power and non-state of the art inputs/outputs).

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NEW A20.1, Krell KSA-80, Atma-sphere Mk60 II, Bryston 3B, PS Audio 100C and 2C+

Sumo Nine Plus Class A Power Amplifier and Electra Plus Preamplifier
It may seem irrelevant to submit a review about two products that have long been discontinued, (actually, they have been superseded) however, in the context of reproduced sound, I feel these components deserve serious consideration. As do all of the products offered by this not so well known company. Readers of this website would be wise to investigate Sumo's own website for further information about their current products at www.sumo.com.

It was these two components that would forever change the way I listened to music, some twelve years ago. Prior to their purchase, I hadn't considered myself an audiophile, a mere audio enthusiast at best, but no more. But the day I inserted these two components behind my Technics SBG-710 speakers, I became an audiophile. Before you laugh at my speaker choice, there's a lesson to be learned from all this.

I had been using a Carver amp/preamp combination with the Technics, and never really thought much about the sounds being produced. The Carver's served their purpose, they drove my speakers. However, when the Sumo's were hooked up, things began to happen. These inexpensive, typically mid-fi speakers bloomed into something not so distant from an expensive mini-monitor design.

Most noteable, was the way individual instruments could be clearly picked out of the mix and followed. There was a sense of air around the performers. Gone was the muddy, hollow bass that distorted the soundfield. It was replaced with a deep, full, defined bass that integrated into the rest of the spectrum, providing a firm foundation for the whole soundstage. Where the highs once sizzled and rang with a screeching bite, a sweet, detailed, and natural treble emerged giving life and immediacy to the sound. I'm telling you, everything was there. In spades.

This is clearly a testimony that good ancillary equipment makes all the difference in the world, and that the Sumo combination was a match made in heaven. Eventually, I replaced my faithfull Technics speakers with a number of different brands; Infinity kappa 9's, Bose Am-5's, and Magneplanar MG-IIa's. All of which exhibited superior sound with the Sumo's.

To describe their sound is a complicated affair. It wasen't so much a sound as it was an emotional experience. No other components have left such an impressionable mark on my music appreciation as the Sumo's have. Then, or now. Notice I speak of the Sumo's in the past tense. I no longer have them anymore, and yes, it was the biggest mistake I made in my audio life to replace them. I have yet to capture the emotion and musical pleasure with any other combination I have tried. Not even my current Arcam Alpha 6 plus amp, Alpha 5 plus CD player, and Magneplanar 2.7 combination comes close.

Two things to remember: One, never search any further for the sound that you are enjoying now. Two, If you're are even considering Krells, Mark Levinsons, and the likes as your next amp/preamp purchase, or Rotels, Adcoms, and Arcams for that matter, do yourself a favor, listen to the Sumo's. You will be amazed.

As it is, now, I am saving my money to buy the current Sumo Class-A incarnations and return to that magic my system had twelve years ago when music was enjoyment, not an endless chase.