I bought my DH-500 about 15-years ago. It is by far the oldest piece of audio equipment that I own. Everything else has been replaced several times but I have never had a reason to replace this amp.
It is simply a work horse ampifier. Sure... it's big and heavy. There are amps out there that have better specs. But this thing works flawlessly for me since the day I bought it.

Right now I'm using it to drive a massive array of sub-woofers. Hell, this thing has enough gumption to drive a washing machine. This is one great amplifier!

Well, I have to set the record straight. I've occasionally ranted in these parts about problems I've had in the past with my DH-500, specifically with respect to driving PSB Goldi speakers, blaming them for the amp tripping due to (what I thought) was their under 3-ohm load they can present at lower frequencies. First I thought it was bass frequency-induced vibration interpreted as DC by the amp's internal protection circuit (as described in the manual), but having finally found the problem it is time to clear its good name.
Under the heat sink assembly--getting to which is a nice trick the way it is put together--I found I had an oxidized and subsequently burned solder connection on one terminal of one of the Thermal Breakers in the AC circuit driving the primary of the power transformer. I guess it would heat up and get intermittent and trip the breaker. A new pair--always replace a pair when there is a pair--and things are fabulous again. And while taking this troubleshooting trek I learned a few things that every DH-500 owner should know:

1. Hafler (a.k.a. Rockford-Fosgate, or whatever, in Arizona) HAS A TON OF OUTPUT DEVICES IN STOCK FOR THE DH-500. That's right, those twelve MOSFETs on the heatsink, six per channel, are IN STOCK if you need them. Only thing is, nobody ever does, except club owners that use them for P.A. systems and mount them in poorly ventilated racks. Thermal Sensors (for the fan) are gone, however, and Thermal Breakers (like I needed) are going fast.

2. The amp has a congenital defect in its design that makes it all-too-prone to parasitic oscillations that can cause unusual overheating and strange behavior that is hard to detect--without a Spectrum Analyzer--but easily cured. Basically, pull up the heatsink assembly, scrape the paint away from the mounting holes where it contacts the enclosure bottom, and reassemble it with external-tooth star washers between the heatsink and the case. Also, install new input jacks--pre-wire them before assembly--and be sure to scrape the paint from where their single grounding lug attaches to the case, too. And do a better job dressing all supply and ground wiring in general (mine needed it and it was factory assembled)--pay particular attention to the single #14 solid wire between the caps to which all returns are connected, and consider doubling it and using beefier spade lugs on the caps. I also stuck a 1.0 mfd @ 630vdc Solens FastCap across each big-mother electrolytic cap, but who knows what that accomplishes? Hey, I had them. (Should have also stuck another 5 mfd on there as well, but hey, I didn't have them.)

3. I also installed a #14 gauge 3-wire line cord with .01mfd @ 2KV bypass caps from both Hot and Neutral to chassis ground at the point of entry (actually at the front panel switch--there's a hole in the chassis already there for you), which provides better immunity from line noise and inadvertant shock hazards.

4. Somehow, during all of this activity, my speaker protection relay coil opened up, and I had to find a 48-volt, 1.2-watt DPDT relay, which it turns out Hafler has in stock, too. Thing is, I had already crossed it to a current-production Potter & Brumfield (a.k.a. Siemens) that has 10A contacts instead of the stock relay's 5A contacts. Had to go to Newark Electronics to get it, but it eventually came in. Dropped right in there.

In the end, anything beyond these changes is simply gravy. I left everything else alone, feed it with a PAS-3X completely recapped with 716P Orange Drops, and it sounds just awesome. The Hafler 500 remains one of the most bulletproof, great-sounding amps of all time, and you don't have to pay Musical Concepts $279 or Frank Van Alstine $599 to update it.

Five Long-Term Stars.

Support Presumed Consent for Organ Donation in the United States. Thanks.

Excellent resolution of detail, spatiousness of sound, there is great warmth and vitality to the music, and the soundstage is HUGE

none other than they are getting difficult to find!

Best value in amplifiers in my opinion

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Note that model year is not accurate-this item dates back to the mid 1980s and the data entry field would not permit me to ignore a date so I chose the closest date

Tons of clean, RELIABLE power.

Fan noise under certain conditions.

I built my first DH-500 in 1982 and still use it to this day in my main system. I remember taking it to a NAD-sponsored amplifier clinic in the late 80's to have it bench tested. The guy was actually reluctant to test it, I think because it might show up his NAD amps. (no offense to you NAD owners) Anyway, it put out a continuous 310 Wpc at 0.01%. He wouldn't test it into 4 ohms because he said his dummy load wouldn't handle it! I felt like a proud father whose son just hit a homer in a little league game, and wanted to say "See, now that's a REAL amp!"

I've never had a problem with this amp and think highly enough of it that I recently picked up two more and an XL-280; all for use in a home theater setup.

Great amp - get one if you still can!

With multiple amps at my disposal, both SS and tube, my 15 year old Hafler DH-500 is one of my favorite. It's certainly not sonically perfect,
but it's still is a very musical amp. The true beauty of this amp is it's
simplicity and unmatched reliability. It simply won't die! I have had water
blowing out the exhaust port when I used it to supply music at a outdoor
party; It started to rain heavily and the area where the equipment was
placed had a small flash flood. I opened the Hafler, dumped in some alcohol
and hit it with a hair drier; 20 minutes later it resumed playing music after
I relocated the gear. Even with water being blown around by the cooling fan,
it never skipped a beat until I pulled the plug when I noticed the amp was
submersed in three inches of water.

I've used the Hafler in multiple systems with some really hairy impedance
loads. I've used it powered by a portable generator! It's even been used
as a guitar and bass amp for emergency sound reinforcement applications.
I think you could drive this amp into clipping with pink noise, hook up some
welding cables and repair a broken truck frame and never worry about damaging
the thing. The protection circuits have been tripped MANY times when the amp
has been stressed thermally, or running into a dead short. But it's NEVER failed.

If you ever get a chance to pick up one of these amps used, DO IT!!! Chances are it will outlive you and your kids will be enjoying for years.
Kudos to David Hafler for an engineering job well done.
Oh yeah, it sounds pretty darn good, too.

i've now owned my amp for over 15 years.i built it from a kit and it's rocked ever since.it's out lasted one pair of 901's(foam rot)and had the police banging on my door on many occasions.needless to say my neighbors don't appreciate it as much as i!it's always been super clean,super powerful,bulletproof,the sound is amazing at all levels ,you want to here live performance this is it!i don't know what direction they've gone in,but they're old stuff kicks a**!!!!i also have the matching pre-amp,equalizer and tuner,all from kit ,all high quality,all very nice.the specs still blow anything away you can get now!i've got them you don't too baad!!i'll give them the max any day of the week five chiles+++++

Crazy power, very reliable, helped me sniff out a bad audio dealer

Heavy as F#$k, not pretty, doesn't get nice writeups in much of anything

I bought this amp from Cherokee Studios in Hollywood, CA. It was used to power the subs for The Police's Synchronicity album as well as a couple Motley Crue records and most everything else that came out of that studio for the last ten years. I picked it up for $250 and mistakenly tried to have it "improved." Never again. The only thing these hacks did is keep it for way too long. There's a couple shops that flat refused to do anything to it since there's really nothing to do to it that makes it that much better.

It's a solid performer. I don't know if I'd buy another one to try to build a home theater out of it since I'd have to get my hands on three more to do it. I don't think there's three people out there that want to part with theirs!

I'm very satisfied with mine. It's outlasted a Nakamichi tape deck (soon to be replaced by a DR-10), four cars, six addresses, one girlfriend, two receivers, a TV, and two 2,000 mile moves.

The bad audio dealer screwed up my speakers, by the way. he's Van L of Van L Speakerworks in Chicago. He's a drunken fool and he TOTALLY miswired my Tannoys. Nice job, meathead. I had to have them completely redone once I moved away from Chicago. Next time, use the same wire on BOTH speakers and remember to connect POSITIVE to POSITIVE!!! Last time I get anything tweaked at a shop. Anyway, Van kept telling me the problem was with the amp. It never was. Once I finally took my speakers to somebody with a clue they opened the speakers up and showed me how badly Van butchered them. The amp just kept revealing the problems inherent in the bad speaker wiring job.

This is the only Hafler piece I have and I'm keepin' it.

Oh, one downside -- it drinks huge amounts of electricity. And I live in California, so that's kind of a big deal right now.

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Cheap japanese receivers, Denon integrated amp, couple amps my friends had

This is the best piece of euipment I have bought. In fact all my Hafler equipment has run near to perfect for nearly 15 years now. The DH-500 amp besides getting warm enough to fry an egg on it, is one solid amp. My DCM Time Windows which they power are also about 15 years old, blow away most systems that are manufactured today. (in it class of course) It just goes to show you that before these companys where "bought out by big business", the engineers who manufactured this stuff in "mom and pop factories" really took pride in american manufacturning.

I have had the DH-500 since 1981 when I bought it new. I am still using the amp today! It never has failed. On occasion, the thermal breaker would kick in after listening to hours of music at concert volume levels. I have a pro system with EAW FL-103 speakers and am now planning to bi-amp them using the Hafler as the high & mid amp. I just got a QSC 3002 at 600 watts per channel to power the woofers. They are rated to handle 800 watts per channel. (Along with a seperate powered JBL 15 inch subwoofer). This arraingement will give the Hafler some R&R as well as to bring the roof down!

Everything

none

This amp is extraordinary. In use since 4/7/84 it has had thousands of hours of use and the only thing I've had to do is replace the power switch and the input jacks in back. Thats it.It drives JBL LSR-32s with its brother, another DH-500 driving another pair of LSR-32s with an HGS-18 SUB. The sound is phenominal in the surround theater scene. I'm through upgrading forever. However, hopefully parts will be available indefintely because I've had poor luck with some manufacturers(Mitsubishi) keeping parts for various components past 7 years. Its already 16 years old but it just keeps going. I couldn't recommend this product enough.

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