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Sumo Polaris Power Amplifier - What a Surprise!

Connor G

Connor G

Ear conditioned
Subscriber
Transitioning from some of the best amplifiers to come out of the 70's, I ran across this little gem. I've had it stored for about a month in my closet after I scored it in a package deal.
I hooked this tiny power amplifier up to my daily drivers - the Canton Ergo 70's - and my jaw immediately dropped! To the best of my knowledge, the inside of this amplifier hasn't seen the light of day, let alone had an overhaul, yet his thing sings! Almost everything I'm hearing is superb! Total control over the speakers in my system - A damping factor of 525 (!!!), A S/N ratio of 103db, and a THD of 0.05%. Plus the ability of driving loads down to 2 ohms with ease, straight from the manufacturer. This thing is a total sleeper and it's blowing my mind! Anyone else have experience with Sumo gear?

Here are a couple snippets from their brochure:
hfe_sumo_catalogue-page-004 (1).jpg hfe_sumo_catalogue-page-009.jpg
 
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I forgot to mention... No protection circuit! They wanted to mitigate the distortion caused by protection circuits so they didn't incorporate one into the amplifiers design!
 
Sumo Polaris II power amplifier Specifications





Sidebar 2: Specifications
Description: MOSFET stereo amplifier. Power output: 120Wpc into 8 ohms (20.8dBW), both channels driven, from 20Hz–20kHz with less than 0.05% THD; 200Wpc into 4 ohms (20dBW), both channels driven, from 20Hz–20kHz with less than 0.1% THD. SMPTE IM distortion: less than 0.05% (0.25W–120W, 8 ohms). TIM: unmeasurable. Hum and noise: 105dB below rated output, 90dB below 1W. Frequency response: –0.1dB from 20Hz–20kHz, –3dB from 1Hz–200kHz. Input sensitivity for rated output: 1.3V; for 1W: 130mV. Input impedance: 47k ohms. Damping factor: greater than 500. Risetime: less than 2µs. Separation: greater than 80dB.
Dimensions: 19" W by 5.25" H by 11.5" D. Weight: 30 lbs.
Serial numbers of review samples: none (first sample), 3200166 (second sample).
Price: $799. Approximate number of dealers: 100.
Manufacturer: SUMO-Music Communications Systems Inc., Chatsworth, CA 91311 (1991); company no longer trading (2007).
 
I've got one but it it was "requisitioned" by my son. I also have the matching Sumo Athena pre. I like them a lot and would liken them to my old B&K Pro10MC pre and ST-140 power (which I prefer).

Both of these were from the remnants of Sumo after Mr. Bongiorno left.
 
Looking into the Polaris, it seems to be very similar to the Hafler DH-200/220 amps in overall look. Sure it has some nice rack handles bolted to the heat sink but other than that the parts are in the same places. Heavier wiring it seems in the Sumo. I can't find a review of the amp from when it was new but the Hafler, another MOSFET amp of 100 wpc was very highly rated. I sure wouldn't mind having my Haflers look like the Polaris.
 
HackWhite said:
I forgot to mention... No protection circuit! They wanted to mitigate the distortion caused by protection circuits so they didn't incorporate one into the amplifiers design!
Click to expand...


My electronic knowledge is very limited but that is the the one thing that stood out to me in the article.
Some other amps (Adcom maybe?) now have ways to add protection to the circuitry available through online search.
Can those "fixes" be used on the Sumo's, or have other protection methods been made possible for them?
 
Sorta funny story, I purchased a new Polaris II and Athena pre, along with Klipsch Chorus IIs while assigned in Germany in the 80s. I was quite enamored with the sound and looks. So my German landlords son came up to hear them and when he cranked it up I heard a pop and immediately lost a channel, so the demo was quickly over. I took it back to the PX Sound and Vision at Mainz-Kastel and they couldn’t replace it but asked if I would allow them to have it repaired, unhappily I agreed. After waiting for several months and being put off I insisted they refund my money, and I bought a Soundcraftsmen A2801 amp and DX3000 pre amp. When the landlords son came back again he said I thought you was going to get something hi fidelity, I just laughed. I still use the stuff to this day, all recently recapped and rebuilt with various mods I’ve learned over the years. Kinda wish I could’ve hung onto the Sumo too though.
 
Has to be one of the finest looking power amps of that period, especially paired with the Athena pre. They were well reviewed at the time as well.
 
Schmidlapper said:
. After waiting for several months and being put off I insisted they refund my money, and I bought a Soundcraftsmen A2801 amp and DX3000 pre amp. When the landlords son came back again he said I thought you was going to get something hi fidelity, I just laughed. I still use the stuff to this day, all recently recapped and rebuilt with various mods I’ve learned over the years.
Click to expand...

I have a Soundcraftsmen 300x4 that has a minor hum and probably needs a recap. Can you go into detail about what you did and replaced? Thanks.
 
Thanks. Mine produces a minor hum that gets a bit louder when things are attached to it. Did yours exhibit this trait?

I understand the concept of using larger filter caps to better suppress noise and reduce distortion when the system comes under a load. But there comes a point where the caps become too big such that it causes too much draw on the transformer when they charge up.

My 300x4 also uses +- 70 volt rails and 11,000 mfd caps. It is actually two stereo amps in one cabinet so I need to buy twice as many parts. I note that you went to 15,000 mfd. Did you note any problems with the power supply or make any other modifications to the power supply to compensate (e.g., inrush suppressor) other than recap?
 
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