Sumo Polaris, Aurora, Athena in the house

[Bauhausler]

Below is a photo of a Sumo Polaris 310 power amp, an Athena MM/MC preamp and an Aurora tuner. I received these pieces in semi-working condition with the recent purchase of a Transcriptors turntable. They are all working now and I'm leaving them to cook in my bedroom system for a week to see if they blow up before selling them off.
I got two of the power amps, both of which were said to be dead. There is no, repeat NO documentation available on these. Luckily, each of the stereo power amps had one dead channel and one live one. Removing 2 screws detaches the channel and its heat sink from teh side of the chassis. It was a moment's work to shuffle the modules and produce one working stereo amp and one entirely dead one.
The power amp clips at 120WPC simultaneous into 8 Ohms and 175W into 4. It's a very beefy common power supply with a large PT and a pair of 15,000uf 80V caps. It's a MOSFET design with 2 pairs of output devices/channel.
I listened to the power amp in my main system for 2 days. The bass amazed me. It is very solid and palpable with great pitch and control. That's compared to my favorite vintage amp, the great Accuphase P-300. I was amazed at how good the Polaris was. The highs were more recessed than the Accuphase, with a distinct 'sweet' presentation. Maybe a little detail missing, but super listenable.
The preamp gave me fits. I immediately found there was a fault in the power supply's regulator section. The bipolar regulator circuit uses 8 transistors, 9 diodes, 8 caps and a batch of resistors. After several nights of fooling around I found a shorted 15V zener and replaced it, but not until I had already replaced 4 transistors (twice each), 3 caps and 2 resistors. The circuit board for this is the size of a legal pad and has over 70 transistors plus associated components. There are traces on both sides and plated through holes transferring signals and current from one side to the other. The component lead holes are plated through, with solder on both sides. This makes it impossible to neatly remove a sensitive component. much less without destroying it. You just can't heat three transistor leads sufficiently and simultaneously to melt solder on both sides of the board. I was one the verge of making a discus out of it when I gave it one last try and fixed it.
I like the tuner. It has worked since I got it. Great sensitivity, and I immediately liked the sound.
The ergonomics are so so. I like the LEDs that indicate the function selected, but the tiny dark gold printing on black requires good light and close squinting to read.
These would be keepers if they were not irreparable orphan pieces. I like the sound a lot, but I don't want to be the owner when they quit.

[cableguy]

Really beefy looking gear....I always loved the styling, or lack there of their gear...cool stuff.

[EchoWars]

Beefy-looking, for sure.

Should have taken some internal pics.

[Bauhausler]

Originally Posted by cableguy

Really beefy looking gear....I always loved the styling, or lack there of their gear...cool stuff.

They are stoutly built, especially the power amp. Styling isn't the number one factor for me, but I do like to be able to read the front panel when it has something it needs me to know. The big, deep knobs on this gear obscure the lettering, which is small and low contrast to begin with.
This is my major beef with my current favorite SS pre, the Yamaha C-2x that's staying in my system. The selector knobs are big flat slabs so you can see at a glance what direction they're pointing, but if you have to actually read something, bring a miner's lamp and a magnifying glass.

[Bauhausler]

Originally Posted by EchoWars

Beefy-looking, for sure.

Should have taken some internal pics.

Okay. I snapped some shots of the inside of the Dead/Dead unit. This reminds me of a Hafler or a Son of Ampzilla somewhat in layout.
The dead one presents a dilemma. No opportunities for repair present them selves. The PSU is +/- 60VDC dropping to 54V at full current load. That's a good supply for one of the 150W MOSFET amp modules from Aussie Amps. Two of them would fit, too. I'm just not sure I want to spend $300+ to make a hybrid oddball out of it.

[Bauhausler]

This is a link to the amp modules that I found tha twould fit. There may be others. They're $AU 160.00 each plus shipping halfway around the world. Not exactly an impulse buy.

http://www.aussieamplifiers.com/index3.htm


NX150

Specifications

+-56vdc Voltage Rails (Idle, No Signal)

146 Watts RMS into 8 Ohms

230 Watts RMS into 4 Ohms

+-63vdc Voltage Rails (Idle, No Signal)

185 Watts RMS into 8 Ohms

275 Watts RMS into 4 Ohms

Frequency Response: 2hz to 160khz (Input Filter Limited)

Power Bandwidth 2Hz - 500khz -3dB Filter Limited

THD Typically 0.005% @ 8 Ohms 1khz

Damping Factor 400

Input Impedance 34k Ohms

Input sensitivity for full power out into 8 Ohm load 900mv







Features of the New NX150 Amplifier are....

*

Fully Symmetrical Double Differential Input Stage
*

All Hexfet Differential Input Stage
*

Fully Symmetrical Topology
*

Bipolar VAS HEXFET Cascoded Driver Stage
*

4 x Single or Dual Die Lateral MOSFET O/P Stage
*

HEXFET Constant Current Sources
*

Very Low Distortion
*

Compact PCB measures only 100mm x 50mm
*

Plated Through Holes, Solder Masked
*

Double Sided and Screen Printed PCB
*

3 Ounce Copper Foil on both sides of the PCB
*

No Cross Conduction Problems
*

(Zero Cross Conduction @ 100khz)

[Beobloke]

Lovely amps! Never knew they did a matching tuner, though.....

[SteveP]

Bauhausler,

There is a tech on the diyAudio forums with a Polaris 310. He traced the circuit board to come up with a schematic. You can find a thread linked below where he and several others go through it. Read all the way through the thread as the original schematic posted undergoes a few corrections.

Good luck,
Steve.

http://www.diyaudio.com/forums/showt...hlight=polaris

[Bauhausler]

Originally Posted by SteveP

Bauhausler,

There is a tech on the diyAudio forums with a Polaris 310. He traced the circuit board to come up with a schematic. You can find a thread linked below where he and several others go through it. Read all the way through the thread as the original schematic posted undergoes a few corrections.

Good luck,
Steve.

http://www.diyaudio.com/forums/showt...hlight=polaris

Steve;
Thanks for reminding me of that. I found it a while ago. It only lets logged in members view attachments. I have long since forgotten my login. It won't let me re-register because I registered once under my only email address. Requests for my login information go unanswered. I'm in a catch 22 here. Maybe I can eventually get in there and see the schematic.

[SteveP]

Here's the schematic, with one more correction shown on the attached jpeg image. It may be worth getting a new 'hotmail' type of account so you can re-register on diyaudio and read the thread. 'jackinnj' repaired his amp and still has it I believe.

Steve.

[Bauhausler]

Originally Posted by SteveP

Here's the schematic, with one more correction shown on the attached jpeg image. It may be worth getting a new 'hotmail' type of account so you can re-register on diyaudio and read the thread. 'jackinnj' repaired his amp and still has it I believe.

Steve.

Thanks for the info. I actually just created a GMAIL account and re-registered on that site. It was my only option since multiple requests for my login info have not been answered.
I doubt I'll be attempt to repair this myself. It's beyond my skills. Maybe with the schematic I can find someone to tackle it for me.

[Robie]

I have both a Polaris and Athena. I like both very much. I would love to get the matching tuner.

Tangentially, they are pretty similar to my B&K ST-140 and Pro10MC (both mosfet amps, passive pre settings, MC phono input setting, similar power, etc.). They sound pretty similar too. In the end I like the B&K slightly better but use and enjoy both as main systems in two different locations. Both are on the warmer, richer and listenable end of the spectrum. I agree the Polaris has better bass and often too much bass with my old Spendor SA2s depending on room placement. IMO, slightly less detail than the ST-140 too but very solid and listenable.

FWIW, there is a brief comparison by Sam Tellig of the ST-140 vs. the Polaris on the Stereophile website that said both were worth considering.

It is my understanding that Sumo's founder (James Bongiorno) disavows any involvement in the Athena and Polaris. Evidently they were designed and built by the entity that bought Sumo from Mr. B. Regardless, they are nice sounding IMO.

Lastly, I discovered a tech in San Diego (Mike Zaccaro (sp?)) who told me he produced a circuit diagram for his own use in repairing several Polaris and Athena units. I discovered him on the Yahoo, SAE forum. I contacted him to repair my Athena when he was recommended by Mr. B. for his understanding of the design of earlier Sumo models. Seems to me I recall another guy in Mn. that Mr. B. recommends (on the Yahoo SAE forum) but I have not used either because they are so far away.

Enjoy them.

[Bauhausler]

Originally Posted by Beobloke

Lovely amps! Never knew they did a matching tuner, though.....

Here's what the tuner nerds say about them: (copied from Tuner Info Center)

Sumo Aurora (1987, $750, photo) search eBay
Beats us. The Charlie is the Sumo tuner that all the James Bongiorno groupies rave about, but one of our audiophile contributors liked the Aurora better. The Aurora only shows up a few times a year on eBay and usually sells for $110-215, with a high of $280 in 1/06.

Sumo Charlie (1982, $500, gold, black, closeup, schematic) search eBay
The Sumo Charlie ("Charlie the Tuna," get it? har, har) was a black or gold digital tuner that was also known as the Sumo Model 700. Some audiophiles praise the Charlie's sound, and its designer, James Bongiorno, proclaims its eminence above all other tuners except the Marantz 10B (but see our writeup) and Sequerra Model 1. While any 20+ year old tuner is likely to require alignment in order to perform up to its capabilities, the Charlies with rack handles (3,500 of the total 5,000 made) were personally aligned by Bongiorno before he left Sumo and may be better bets than the handle-less ones if you must buy a Charlie. We at TIC tested two Charlies with handles and found it to be an extremely quiet tuner on strong signals, and the electronic equivalent of 6 gangs gives it good overload rejection. However, its sensitivity is remarkably poor; it uses lots of filters, yet its adjacent channel selectivity is way below average (a narrower ceramic filter or two would probably help); its ergonomics are perplexing; and its build quality is somewhere between Kenwood's bottom-of-the-line KT-5300 and a typical NAD tuner. Our Ricochets panelist David "A" faults the Charlie's "Mitsumi front-end, lack of correct alignment and poor standard of construction." Former Stereophile reviewer Don Scott was not impressed with its weak-signal pulling ability: in 1989, he "did a test of 9 tuners at WFME's [94.7-NJ] site on South Mountain in the Oranges trying to receive sister-station WKDN (106.9), Camden, NJ. By far, the Charlie had the worst IF and RF rejection of the group." Our contributor David Rich notes that the Charlie has a double-tuned filter at the antenna and is double-tuned after the RF amp. Click here for a whole page on the Charlie, pro and con, and here to see how one Charlie sounded compared to many top tuners. When three Charlies sold for over $500 on eBay in 1-2/02 (one for $610), four of our panelists agreed that the Charlie was a contender for the title of "Worst Value in a Used Tuner," but over the past few years they've generally sold for just $165-255, with a recent high of $306 in 11/05 (but as low as $125-130 with minor cosmetic issues). [BF][EF][JR]

[Blue Meanie]

Originally Posted by Bauhausler

Okay. I snapped some shots of the inside of the Dead/Dead unit. This reminds me of a Hafler or a Son of Ampzilla somewhat in layout.

Maybe a stupid question, but wasn't James Bongiorno the designer of both Ampzilla and Sumo? Maybe that's why they are somewhat similar?

Jeff

EDIT: My question was answered by reading a later post in this thread (DUH!). Sorry!

[Bauhausler]

Originally Posted by Blue Meanie

Maybe a stupid question, but wasn't James Bongiorno the designer of both Ampzilla and Sumo? Maybe that's why they are somewhat similar?

Jeff

Yes, and no. He designed some of the Sumo stuff, but not this amp. I have several Ampzillas and Sons around here. I hear he prefers BJTs to FETs.