HAFLER P500 - DH500 difference

[avionic]

12 x MOSfet,

Hitachi Lateral MOSFET's...

 

[wingzam]

I


The P500's were often used in PA rigs so you may want to check with a local music shop tech. If you don't happen to find a local tech, I'm in Cleveland, Ohio. I don't market myself as a repair service since I typically install QUA-CO Audio's PC-1 upgrade kits in DH Series amps, but I routinely adjust these. It's not a job for an inexperienced individual as there are lethal voltages involved. The design engineer at QUA-CO, Ed Fantasia, was Hafler's Amplifier Project Manager for 25+ years, but he no longer does bench work. He has been mentoring me for the past 3 yrs.. I do all his install work. So I know these pretty well. If you get stuck, reach out to me. I usually have a waiting list for amp upgrades since I do this work on the side from my TV Engineering job, so you would have to get on my list. I know these are very heavy(50lbs.), but if double boxed & packed properly, they travel well via UPS ground. Average shipping costs are about $40-$70 each way. Suggestion: If you don't need the balanced Inputs or Input level controls of the P500, you may want to sell that one off and buy another DH500 especially for home use. Its a much simple circuit and more stable. There are LOTS of DH500's on eBay that can be had from $300-500. And if you want an upgraded 'High-end Audiophile' version, I'm your guy. I have lots of very positive testimonials. Hope this info helps.

I had to put my 500 in storage and just now got it out.
It works but the fan comes on when it powers up and at low volume levels the fan will run faster and faster until it hits max rpm, then I shut it off.
Anyone know what that problem could be?

 

[loudnoises]

I had to put my 500 in storage and just now got it out.
It works but the fan comes on when it powers up and at low volume levels the fan will run faster and faster until it hits max rpm, then I shut it off.
Anyone know what that problem could be?

The fan itself rarely goes. There's a temp probe under the heat sink. They can go bad, but it seems less common. The fan will run faster as it gets hotter. Replacing the probe is a big job, look elsewhere first so you don't waste the time.

Start by cleaning. My sink had developed a coating of film, cleaning it and the fan blades solved my speed issues. if there's no improvement then look at electrical causes. Those massive caps will pack a punch, so be very careful.


There are virtually no more mosfets for these. Treat them with utmost caution. A new matched set is worth more than your amp... (unless somebody unearthed more? Last I heard we were working off a box of rejects)

 

[wingzam]

The fan itself rarely goes. There's a temp probe under the heat sink. They can go bad, but it seems less common. The fan will run faster as it gets hotter. Replacing the probe is a big job, look elsewhere first so you don't waste the time.

Start by cleaning. My sink had developed a coating of film, cleaning it and the fan blades solved my speed issues. if there's no improvement then look at electrical causes. Those massive caps will pack a punch, so be very careful.


There are virtually no more mosfets for these. Treat them with utmost caution. A new matched set is worth more than your amp... (unless somebody unearthed more? Last I heard we were working off a box of rejects)

Thanks for that

 

[loudnoises]

Happy to help. I'm just the entry level guy tho, you've had the real experts pass through already.

I love my hafler, it's going nowhere eve .

 

[wingzam]

Happy to help. I'm just the entry level guy tho, you've had the real experts pass through already.

I love my hafler, it's going nowhere eve .

Yes, I was excited when I got this amp because of the reviews and that there's a lot of upgrades for it but I wasn't aware of the rarity of the MOSFETS..There's always something..

 

[loudnoises]

It's the case with a lot of old amps. The power parts are generally not made anymore. The hafler is especially tough because it requires so damn many.

Sometimes people do find stuff though, nos is out there, lost in the attics. I keep my fingers crossed that folks who find that stuff don't just throw it away. This spring I stumbled on a guy selling a huge horde of old electronics parts, way too many dozens of boxes for him to comprehend. Hopefully he found a good outlet.

 

[jsettecase]

I had to put my 500 in storage and just now got it out.
It works but the fan comes on when it powers up and at low volume levels the fan will run faster and faster until it hits max rpm, then I shut it off.
Anyone know what that problem could be?

Just saw your post. Is the Fan just running fast or is the exhaust air temp getting hotter too? The good news is that the Thermal Fan Speed Sensors are doing their job. 2 Thermal Sensors close at 50 & 65 deg. C and activate the 2nd and 3rd Fan Speeds. Then if the cooling isn't enough, There are 2 Thermal Breakers that shut the amp Off at 70 deg. C. Then Power Switch Lamp will 'flash' to indicate an 'Over-Temp' has occurred. I don't suspect the Thermal Sensors. They usually will not 'close' if they are bad and then the higher Fan speeds will not engage. But I suppose that the opposite could be possible. Yes, They are a pain to change and require major disassembly to access them. If the fan is running at the higher/highest speeds early on, that means that the MOSFET's are running much hotter than they should. Bias can drift UP over the years as things age causing them to run hot. Bias should be 350mA +/- 10mA with < +/-50mV of DC Offset(ideally '0'). And as Bias drifts, so will Offset. Hopefully, readjusting these will solve the problem. If yours is an early DH500 version with the PC-10 Driver bds., there are no DC Offset Pots on those. To correct High Offset in these, the transistors in the Front end will need to be replaced with freshly 'matched' pairs(I install these Front end kits), then the Bias can be corrected as well with the Bias Pot. If you have any version of the PC-19 Driver bds., they have a pot for each. These two adjustments interact and should be adjusted after the amp has warmed up for about 15 minutes so that the Bias & MOSFET Temps settle in. Its not likely that you have a failed MOSFET(s). It takes quite a bit to kill one and they either short or open,not partially fail. Yes, cleaning the Heatsink fins will help it shed heat better. Cleaning the Fan Blades will unload the motor and help balance the spin. Let me know if I can help further. Jim

 

[sirianni]

Until I bought my McIntosh equipment I ran for 4 P505s that I had modified with the QUA-CO mod, which is excellent. I’m still running two P505s for my subwoofers Hafler has always been noted for a great solid-state amp that sounds like vacuum tubes.

 

[jsettecase]

Thanks, I think I'll go ahead and replace it. I thought it was as it was performing as it was supposed to be until I got the DH-500. Any recommendations on what fan to use to replace it?

I have not been able to find complete documentation for the 'P' version (and there were several versions of the 'P') and the only schematic I have been able to find had errors in it. But I recently had a P500 to upgrade which I avoid BECAUSE of the lack of info & no written upgrade instructions from QUA-Co as yet. It takes almost twice the labor to do an upgrade on these which would make it extremely pricey. But I noticed that the Fan Motors between the DH & P versions have different Part Numbers on them and in the manuals. Ed at QUA-Co confirmed that the P version fan IS, in fact, different & runs faster(more CFM's) & has different drive circuitry. This was done because the 'P' versions were designed for PA application where extra cooling would be required & where fan noise would not be an issue. You are still better off with a DH500 for home use because of its simplicity.

 

[DonP1]

Just saw your post. Is the Fan just running fast or is the exhaust air temp getting hotter too? The good news is that the Thermal Fan Speed Sensors are doing their job. 2 Thermal Sensors close at 50 & 65 deg. C and activate the 2nd and 3rd Fan Speeds. Then if the cooling isn't enough, There are 2 Thermal Breakers that shut the amp Off at 70 deg. C. Then Power Switch Lamp will 'flash' to indicate an 'Over-Temp' has occurred. I don't suspect the Thermal Sensors. They usually will not 'close' if they are bad and then the higher Fan speeds will not engage. But I suppose that the opposite could be possible. Yes, They are a pain to change and require major disassembly to access them. If the fan is running at the higher/highest speeds early on, that means that the MOSFET's are running much hotter than they should. Bias can drift UP over the years as things age causing them to run hot. Bias should be 350mA +/- 10mA with < +/-50mV of DC Offset(ideally '0'). And as Bias drifts, so will Offset. Hopefully, readjusting these will solve the problem. If yours is an early DH500 version with the PC-10 Driver bds., there are no DC Offset Pots on those. To correct High Offset in these, the transistors in the Front end will need to be replaced with freshly 'matched' pairs(I install these Front end kits), then the Bias can be corrected as well with the Bias Pot. If you have any version of the PC-19 Driver bds., they have a pot for each. These two adjustments interact and should be adjusted after the amp has warmed up for about 15 minutes so that the Bias & MOSFET Temps settle in. Its not likely that you have a failed MOSFET(s). It takes quite a bit to kill one and they either short or open,not partially fail. Yes, cleaning the Heatsink fins will help it shed heat better. Cleaning the Fan Blades will unload the motor and help balance the spin. Let me know if I can help further. Jim

My son just picked up a P505. We started it up with the cover off. The fan quickly goes to high speed and the heat sink gets HOT. I'll do some investigating, but it may be a trip up to Cleveland if this is bad. It does play and sound good. He's using it to drive a pair of Polk Audio Monitor 10s.

 

[loudnoises]

Is the fan and sink clean?

These often did club duty, and a film will coat the sink. Mine looked clean, but ran much quieter and cooler after a good cleaning.

Still, they do get warm. It's it evenly hot?

 

[DonP1]

We did a quick cleaning. It wasn't really dirty inside. It heats up really fast. The fan goes to max speed in under a minute.

 

[JB1962]

Got a P500 amplifier as well as the Hafler Model 10 preamp from a local record store (The Corner Record Store), Ritchie of 'The Circuit Shop Loudspeakers' (located upstairs) went through both of them thoroughly, corrected some heating issues and got rid of some hum that I was experiencing in the phono section.

What fantastic piece's of equipment, looking at the specs in the manual for the amplifier, I cannot imagine a set of speakers where this thing would/could possibly fall short. The frequency response is off the charts as far as media and any speakers reproduction capacity goes, in short, I challenge anyone (frequency response wise) to show me a set of speakers that can ask anything of this amplifier that it cannot give, or a CD, LP, etc, that it falls short of being able to reproduce. Love it!

 

[JB1962]

Correct. It's the pro version of the DH-500. The Left/Right gain knobs, and the 1/4" headphone input jacks are the main differences.

We used a P500 where I used to work, in one of our audio studio's. The other studio used a Bryston 4B. The rest of the gear, even the speakers, were identical between the rooms. The 2 studios were the same size as well. We kept it that way, to make mix comparisons easier. So, to me, the Hafler was better than the Bryston. Warmer sounding, more musical. Less dry in the treble too. The high end on the Bryston was really dry, flat, with no air.

Oh yea, just recently read an old review for a DH-500. It bench tested at over 300 watts into 8 Ohms, 450 watts into 4 Ohms, and 390 watts into 2 Ohms. Short term peak output was 792 watts into 4 Ohms. Not too shabby.

http://www.hifi-classic.net/review/hafler-dh-500-287.html

One other thing. eBay seller qua-co, is a former Hafler employee/engineer. He sells spare parts and rebuild kits for Hafler gear. Good prices too. Worth looking at if you ever need to do a rebuild on the amp. I'll use him whenever I rebuild my DH-500. qua-co sells mod kits also, including newly designed driver boards. They seem to get good reviews. Another company doing mods is Musical Designs. They offer many different mods and upgrades. They've been offering their mods for years, and are well received.

http://www.musicaldesign.com/Haf_pwrmods.html

I walked into my favorite record store one day and found a Hafler 110 Preamp and a Hafler P500 amplifier for sale among other things. I did some quick research on the amplifier, then bought it. Didn't even occur to me to look up the preamp, figured it must be pretty good as well. It is!