Price Paid:  $0.00

Summary:
I got this amplifier with matching preamplifier P-304 from a well funded foreign student who finished his Ph.D. program and went back to his country of origin. I consider myself as a music aficionado, not a snobby audiophile and I listen to all kinds of music depends on my mood. I have been using 10 year old Yamaha integrated amplifier which sounded natural yet somewhat lacked detail and sounded overly warm. My speakers are PSB 6T which are relatively good full range speakers and my listening/hobby room is medium sized with high ceilings.
After I got the M-504, I was surprised how heavy it was and I could see two massive transformers through the top vent slits. I was mesmerized by the beauty of the amplifier. The lighted dual meters looked really charming and professional.
After initial hook up, I played some rock music, mainly Led Zeppelin and Metallica stuff. They sounded very clean, holographic, and smoothly powerful. The base was tight and well controlled.
The voices were clean and natural and highs were crisp and sweet. My old Yamaha amp sounded lack luster and inferiorly detailed.
I listened to Nadja Salerno Sonnenberg's violin stuff. It sounded just sweet, detailed and airy vibration of strings just gave me terrible goose bumps. Full orchestra sounded just magnificent.
I do not know exact benefit of dual mono design, but engineers put two independent transformers to achieve something otherwise no cost efficient Japanese engineers put in two energy guzzling transformers. Segovia's Bach suite on guitar sounded more defined, detailed, and sweet. I could smell (?) sweet aroma of Segovia's Ramirez guitar through my PSB 6T.
Finally, I listened to liquid child's "diving faces", which is a heavy electric techno club piece. The bass output was awesome as my woofers moved back and forth and my house was shaking.
The M-504's dual meter danced harmoniously with PSB's woofers. The amp never lost its composure and remained neutral supplying clean, controllable power. M-504 played music quite well and it would be a killer amp for main home theater setups. I am glad and lucky to acquire this amplifier and it woke up my old PSB 6Ts as if they took some Viagra (?).

Strengths:
Clean, neutral, and detailed power output. Good looks. Good Sound staging.

Weaknesses:
heavy and big.

Similar Products Used:
Yamaha, Rotel, Marantz

Price Paid:  $350.00 from audiogon

Summary:
This is a quality amplifier for the money. For the $350 you can find this amplifier for on the used market, you'd be very hard pressed to find a similar amplifier value.

Dual mono design. 160w rms.

The sound itself isn't as refined as more expensive amplifiers. Thus, my 3 star overall rating.

However, this amplifier provides an excellent value. It would be an excellent amplification upgrade for someone with a mid-fi receiver or preamp.

The overall character of the sound is a bit on the warm side. Also, unlike more expensive monster amplifiers, this amplifier won't be comfortable with under a 4ohm load. Don't try.

Oh, and the wattmeters are neat.

Fantastic value.

Strengths:
+Dual Mono Design
+Value
+Watts for the Money
+Warm smooth sound

Weaknesses:
- Less refined than more expensive amplifiers

Price Paid:  $500.00 from Stereo shoppe inc

Summary:
Without drifting away from the subject matter right from the start I will say that as with anything it is not how something is done but how well it is done. The M-504 is a shining example of that. All other factors being equal such as a quality pre-amp and speakers this power amp will deliver the goods as far as being free from irritating intermodulation distortion, has clean power for any respectable speaker,and used properly will give your ears many enjoyable hours of listening enjoyment. Fire and finesse is my rating on this wonderful piece of gear. Now before getting bashed I need to point out that I am looking at the total picture,price vs build vs performance. Is the M-504 perfect? NO far from it, but many others aren't either..and for a lot more money.2 transformer dual mono designs are far and few and to get 1 at this price point is a find. Sorry to say I wish Onkyo would have taken it a little further with better connections and a better lamp set, but the foundation for a truly good power is already there, so what's a few bulbs and a little upgrading? nothing considering what you get.

Strengths:
Great looks good basic design.... tried and true dual mono constuction. Good with low impedance loads.

Weaknesses:
Input and binding posts could be better..but can't complain at this price point.

Price Paid:  $550.00 from Sydney

Summary:
What can i say more to what's been said already. Seeing this unit in action about 5 yrs ago, decided this is the amp for my system. Though this is not for everyone.

My system consists of:-
Tjoeb 4000 Valve CD player
Bottlehead Foreplay Preamp (plus Anticipation kit)
Onkyo Integra M-504 Power Amp
Mission 752 speakers (Rewired)
Chris VenHaus Power & IC Silver Cables
DH Labs Q10 Cable

Initially installing the Onkyo M-504 there wasn't much difference between this and the Onkyo TX-777 Integrated HT Amp and was dissapointed.

Then i decided to mod the Onkyo as far as i could ,the changes I made in order was.

- Organized a replacement of a large number of audio caps (due to ageing).(7)
- Installed an IEC Socket for a proper power cable (7)
- Build a Chris Venhaus Power Cable (7)
- Build the CVH Silver Interconnect Cable (7)
- Replace the RCA's with the M-508 Gold RCA's (6)
- Wire the Speaker cable directly to the speaker cable board (8)

The numbers represent what value i place on the change 10 being the highest. What do I think now ! Now it sings ! It is quite a different beast to the original. Not still a lamborghini , but turned a BMW into a racehouse on steroids (legally).

The soundstage is open and quite wide, dynamics completely changed, with a nice openness about the sound.

I always ask would i do it all over again, the answer is absolutely it was worth all the effort.

I still think without and changes it's a good power amp. I realize that the changes are not for everyone and is dependant on the system, but for me, I am very content .. at least for now !

Strengths:
Clean Power and lots of it. Lovely from LED's , Bargain for the money .

Weaknesses:
Terrible binding posts, actually all the connections from the rear.

Similar Products Used:
Onkyo HT amplifiers

Price Paid:  $350.00 from Japan

Summary:
I read a large portion of these reviews and have 1 thing to say. Anyone who does not LOVE this amp is either tone deaf or has a poor set of speakers. Remember, it doesn't matter how good your system is if your speakers don't justify it. Having said that I see alot of unnecessary componants being used as well as inferior speakers. The way Onkyo was designed is best complimented by Klipch Speakers. Back when I bought my M504/P304's (85'), the reference line for Amp to Speaker combo's was Onkyo/Klipch. You can't beat this combo. These are the BEST AMPS for the money!!!

Strengths:
Incredible power. Great design!!!

Weaknesses:
Speaker jacks

Similar Products Used:
Everything from Kenwood to Sumo (anyone remember Sumo Class A Amps)? If so your showing your age.