Hafler DH-500 Repair

mackdrool

Hey guys!

I've got a Hafler DH-500 with a troubled past and could use some help on how to move forward with it.

My dad bought it in the mid 80s and used it with a set of Acoustats. In 1987 the amplifier failed and sent voltage back the RCA inputs, frying the input components attached to it. Output components were unharmed.

He sent the amplifier to a Halfler certified repair service and they deemed there were no issues with the amplifier and that it was probably a ground loop issue.

He claimed to not have any issues with it after that.

Fast forward to 2008. I hooked it up to a laptop and a pair of 3.1tls and ran it for about 3 hours until it failed. The speakers started to hum quietly but then got louder and then BAM. Amplifier sent current back into the laptop and fried the whole thing. Output components were unharmed.

I just turned it on for the first time since then. I'm feeding it with an old laptop that I won't be upset if it blows it up. The amp in my opinion is running really hot. It will shut down after 15 minutes of white noise. The red light will stay on but I can hear the relays close for about 10 seconds and then they reopen. The amp will also send quiet static occasionally without anything plugged into the inputs.

I'd like to get it repaired if you guys think it's worth repairing. I have no idea where to send it either. I am not skilled enough to even think about tearing into it. Thanks!

TLDR-Hafler DH-500 needs serviced-Where do you recommend I send it?

motorhead43026

http://musicaldesign.com/Haf_pwrmods.html

Start here.

spongebobsquarepants

People seem to love this amp. heres some reviews.

One person on there says "woke up my SDA-SRS Studio 1C like a giant that had been in a long sleep"

That guy also had the amp recapped and loves it.

There's all kinds of upgrade kits and replacement boards for this amp on ebay.
Sounds like a fun project, but terrifying that it may blow up your sources!
I'd be too scared of collateral damage personally.

motorhead43026

The DC offset has run amuck, most likely.

I have an XL600, It is a very capable amp.

[Deleted User]

Sounds like Admiral Yamamoto's supposed comment, “I fear all we have done is to awaken a sleeping giant and fill him with a terrible resolve.”

motorhead43026

I missed the “hooked laptop up to it”...LoL, WTH?

Thought processes have shut down today I fear. Wonder what else I misinterpreted today?

xjghost

I have a Hafler 500 running my 3.1 and it works well. This is the company I plan on using for upgrades. http://musicaldesign.com/Haf_pwrmods.html Someday...

machone

I have a DH500 with Musicalconcepts.com mods. I think it is special. John Hillig at Musicalconcepts.com knows Haflers.

mackdrool

Thanks for the links guys! Much appreciated!

I'll see what Musical Concepts has to offer. I replaced the amplifier with an A21 so there is no rush to get it repaired.

As much as I love this amp I probably wont repair it if the cost is $800+.

I can buy a comparable amplifier for around the $1,000 mark so taking a gamble to save $200 feels a little irresponsible.

dcmeigs

I’m familiar with that amp. At the front end there are a pair of transistors, one on each rail, Q1 and Q2. If either of these old buggers conducts to the gate it would cause a damaging DC offset. I’m going to guess Q1 and I would expect that resistor R4 looks like toast. If R6, R7 or R9 look bad, it’s Q2. It doesn’t really matter, you want to replace them both anyway.

It would cost you just a few bucks at mouser or digi-key to replace those transistors. It’s admittedly a shotgun approach but probably worth a try if you’re handy with a soldering iron.

mackdrool

dcmeigs wrote: »

I’m familiar with that amp. At the front end there are a pair of transistors, one on each rail, Q1 and Q2. If either of these old buggers conducts to the gate it would cause a damaging DC offset. I’m going to guess Q1 and I would expect that resistor R4 looks like toast. If R6, R7 or R9 look bad, it’s Q2. It doesn’t really matter, you want to replace them both anyway.

It would cost you just a few bucks at mouser or digi-key to replace those transistors. It’s admittedly a shotgun approach but probably worth a try if you’re handy with a soldering iron.

Thank you so much for this info! I will absolutely take a look at it and see what I can find. I'm skilled enough with a soldering iron and multimeter to be dangerous. I can handle a few transistors and resistors. I may DM you if I get stumped if that's okay.

Again, THANKS!!

dcmeigs

Sure. I’ll help if I can.