Very smooth sound
Extremely wide frequency range (1Hz to 100,000 Hz, +/- .75 dB)
Very low distortion ( 0.003% )
High S/N ratio ( 120 dB )
Wide range of accepted speaker resistances ( 2 to 8 Ohm -- 525x2 to 165x2 respectively)
Fantastic constuction
Good price (it has decreased in price over time)

Voltage Meter lights burn out over time ( it took 6 years for the first one to burn out :) ) But is this really a weakness?

OK, I probably have the oldest M-504 reviewed here, so keep in mind that the M-504 that sells today might be slightly different than the one that I own. I feel that it is a testiment to the quality of the design of this power amp (and the P-504 pre-amp) that the same design has been sold for at least 12 years. A note to all of the present day purchasers: All of you are very lucky. When I bought mine, I got a GREAT deal on the unit. The price was only $859! I think that MSRP at the time was $1099. Over the last decade, the price has slowly decreased. This has conversely increased my desire to purchase 2 more to flesh out a home theater system.

I purchased mine in 1988. During the last 12 years the unit has been used on a daily basis. The sound quality has been perfect every that I have used it and time has not decreased the quality of the sound. The construction is tank-like, as its 49.5 lb. weight powerfully backs this thought. Additionally, the amp can handle 2-8 ohm speaker loads. Moreover, the amp scales nicely with the lower impedance, topping out 525W into EACH channel at 2 Ohms. (An aside note, Onkyo used to sell line of products called Grand Integra (the 504s are in the Integra series), perhaps 506 designation. With balanced inputs, and a 205W (?) output they were supposedly much better than the 504s, but their price was over double.)

My setup consists of the P-504 / M-504 duo, various other audio equipment and some custom fabricated speakers. Since my setup does not exist anywhere else, I never really had anything to compare the amp to...until very recently. I had given up on Onkyo years ago to produce a surround sound aware pre-amp to complement the M-504. All the while I'd secretly lusted after the Sony digital pre-amps (starting with the 1000 in 1991-2, then the 2000 and now the 9000...but I digress).

In any event, a fantastic deal came up on a Pioneer VSX-908S receiver. It has pre-outs for all channels, so I knew that I could fall back on the M-504 if I didn't like the sound. The 908S couldn't compare the P-304's 0.0003% THD (yes that is correct 3/10,000s of a percent), but sometimes compromises must be made. The difference in sonic quality was quite suprising. The M-504 was noticibly better in the mid-high and up frequency range. CDs that I had recently played now had a harsh almost crystaline sound (just try to imagine, it's hard to explain). What can you expect from the Pioneer when it has 30 times the distortion of the M-504? :)

So in summary, what am I trying to say? If you are looking for seperates, BUY THIS AMP!!! The price is right to pick up 3 for a home theater system. The unit will last you a decade or two, providing you with 10s of 1000s of hours of audio nirvana. There may be better amps out there, I haven't listened to them all, but from my personal experience, I could not expect to be more pleased with any other design.

For people who are interested in getting a receiver with M-504 qualities, Onkyo recently released the TX-DS989 receiver. Its power output is 165Wx7 (6 Ohm, 130W at 8 Ohms) with 1Hz to 100,000 Hz output. Sound familiar? Obviously they cannot house 3.5 M-504s in the 989s chassis but it will get you as close to the M-504's audio quality as you are going to find.

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Auditioned many in stores. Only direct comparison is a Pioneer VSX-908S receiver

Looks real nice; sounds even nicer...very neutral with good air/soundstage. Almost sounds tubelike.

Fake wood sides. Looks kind of plastic up close. Real wood would have been nicer.

I've had this amp for several years, and it has been faithfully working flawlessly all that time. The sound is quite warm and neutral, with good detail and air. I have been running this into Soliloquy monitors on stands, and am amazed at the control and power this amp has. All in all, a steal if you can even find one. I don't know if Onkyo still makes these, or where you can find one.

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Yamaha, NAD, Proton

Warm, involving, unfatiguing sound, priced well

None for the $

I bought this amp since I wanted to hook up a secondary system (in my home office) with separates without spending a king's ransom. I got this amp for about $599, which, considering what you get, is an excellent price. This amp, firstly, looks absolutely GORGEOUS! The large twin meters look beautiful and serious, and the green backlighting, and thin needles are perfect. In fact, you cannot readily see the twin needles moving from a middle distance away. So there is not much to 'distract' you, as opponents of meters on amps usually claim. Secondly, this amp sounds very sweet and warm for a Japanese mid-end, mid-high end amp! In fact, with a good set of speakers (I drive Magneplanar MG12's), the sound is neutral and draws you in. There really is no brightness or harshness whatsoever with the 504. In fact, this amp sounds like one that costs 3-4 times the price!!! Lastly, the design is great. This amp has 2 independent circuits and signal paths (dual mono) as well as real aluminum cast cooling fins (unlike the cheap, thin pliable fins many manufacturers use these days in mid end equipment). Evident is the excellent engineering that went into this design. Again, all these praises are considering its sound and price. Sure this is no Accuphase, but for about $600-700 street price, this amp is a total winner, and it sounds high end with a good preamp, interconnects, and speakers. You will be surprised.

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Adcom, NAD, Hafler

Superb sound. Highly detailed, and transparent.

Remove the imitation wood side panels. I understand you can purchase genuine wood panels from Onkyo at $212 a pair (OUCH!).

It is not often one encounters a true bargain. But such is readily the case with the Onkyo M-504. I purchased this unit from J&R Music World at $550, and am most impressed with the sound quality. For some music, I find the sonics warmer, and more detailed than my Parasound 1000As, and definitely superior to the three amps I previously owned. Currently, I have the M-504 connected to a Parasound PLD-1100 preamp and Advent Legacy I speakers. Coupled with a Pioneer Elite CD player, the results are nothing less than stunning.
As mentioned, my only complaint is with the ersatz wood panels. Onkyo should have either used real wood, or made the cabinet all metal. This however, is a minor cosmetic detail. A highly recommended amplifier for anyone seeking outstanding quality at a very reasonable cost.

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Phase Linear 400, SAE 2400L, Adcom GFA 555 Mk II, Parasound 1000A (Two, in half-stereo mode.)

Good detail, good power reserve

minor weakness- base circular feet should have been solid aluminum, not plastic (this is a 50 pound amp)

This is one sweet sounding and detailed amp for the money. It sounds warm with no listener fatigue, and drives even 4 ohm speakers (like my Magneplanars) with no problem whatsoever. The large twin analog power meters look like they 'mean business' as well. This amp is visually gorgeous too. If you can still find one of these, go for it. You won't regret it.

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Harman Kardon, NAD

Tubelike sound, very good construction, gorgeous level meters

Not yet!

I own this wonderfull amp since 1989 and it's still workin' hard. I got a pair of Polk Audio SDA-1C, speakers whose impedance load goes almost below 3.5 ohms at low frequencies, but incredibly, this amp always sounds good. Well builded and engineered, still don't cease to wonder me with its smooth and warm sound. The best audio affair of my life. Best wishes to ya all

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Several amps

tight

smokin uh

this is nojoke if money aint a thang bangan

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yours

I have had an Onkyo M-504 since I purchased it new back in 1986 or 87 (don't remember exactly). My system consists of a Sound Valves SV-100 audiophile preamp, the 504, and Polk Audio studio 10B monitors on stands (bought the Polks back in '86 when in my opinion, their speakers sounded better and were built better as well). I have had no problems with the amp, and it has performed flawlessly for over 12 years or so, and has given me countless hours of warm sounding, fairly detailed music. I would define the sound as being in the bottom echelon of true high end quality... in other words, good detail, fair amount of warmth, and fair transients. I am happy with the sound, considering my system's total cost. The 504 seems to have a fair amount of punch and reserve, but if I could fault it for one thing, it would have to be for its lack of high current capability. It should be more powerful. We hooked this amp up to my friend's pair of 'Carver Amazing' speakers, and it clearly fell short in the areas of dynamic power and 'punch'. We then hooked up a 'high current' Harmon Kardon amp (similar to the 504, less meters...I forget the model #), and the HK blew the 504 away. It was able to keep up with the musical transients much better than the 504. Nonetheless, given it's good overall sound and appearance, I would honestly rate this amp a 4 out of 5. It's sound reeks of quality, for the most part. The right speakers paired to a 504 will give you great sound.

P.S. please disregard the model year indicated as 1995. This is actually an older model 504 as described above, but the system did not allow me to enter anything less than 1995

I bought a Onkyo 504 mainly because of its looks and power.I had at the time Nelson Reed 804c's loudspeakers and a Sony 608es cd player running directly into the 504 to get the cleanest sound possible and upon listening to the 1st cd I played thru the 504 I could tell something was not right. It turned out to be a lifeless sounding amp,dry on top no midrange presence and the bass was thin and lean.If you like the looks of the 504 try to find a Onkyo M588f or even a M508 as they are superior sounding amplifiers.

I PURCHASED THE M-504 ABOUT 5 MONTHS AGO IT WAS THE DISPLAY MODEL ,WHICH MEANS IT HAS BEEN THRASHED BY COUNTLESS CONSUMERS. SINCE INSTALLING THE AMP IN MY SYSTEM IT HAS PERFORMED FLAWLESSLY,GREAT HIGHS,POUNDING BASS,SMOOTH MIDRANGE.MY ONLY REGRET IS THAT THERE WAS ONLY ONE AVAILABLE.SYSTEM INCLUDES;ONKYO TXDS838,ONKYO DXC606,SONY DVPS300,BOSTON VR40,PARADIGM CC350,BOSTON HD8,PARADIGM PS1200.