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jdexter 23rd March 2011 08:53 PM

NOOOOOO .... !!!!! Hafler croaking .. ??
Our wonderful Hafler DH200/DH101 amp/preamp has suddenly gotten louder. I was listening to it, when it suddenly ramped up I am really worried it's about to die..

Can't zero volume on the unit and it feels hotter than normal.

Loud on both channels - all sources (radio/turntable/cd).

Tried so far:

Tested all sources in case it was downstream

Tried another power circuit in the house (in case of over-voltage).

Pulled inputs to power amp - still hummed (it always did when it got turned up - but this is now constant).

Have turned it off and am posting here to see if this rings any bells.

Any thoughts/further test suggestions or advise appreciated.

Cheers - Jon

firechief 23rd March 2011 10:35 PM

Good news is that you caught it before it caused serious damage. Do I understand that you have been suffering with hum for some time and it just got louder? If true, it's probably failing power supply electrolydic capacitors. If it is the power supply caps, you don't want to turn it on again until someone has a chance to diagnose the problem. Could be smoke, stink, large cost. Correct me if I have a mis-understanding of the symptoms.

jdexter 24th March 2011 03:16 AM

Thx for reply firechief .. Unexplained change is never good as you clearly appreciate ..

What has happed is that - all - the volume from stack has gotten a lot louder AND it's humming with the pre-amp disconnected from the DH200. When I zero the volumn on the pre-amp, I'm still passing signal to the speakers - can still hear radio/cd/tuner ghosting through.. This behavior is new and alarming ...

When I reconnect the pre-amp and turn up the volumn (no devices turned on) I get old/regular hum that normally came on about 50% - which was never a real problem, as the amp rarely got turned up more than 1/4 .. It's paired with a lovely set of HPM's - which means around %50 - the fluid in everyone's eyes starts to move .. :) ..

Sorry - I digress .. Like I said - much loved Hafler set, more of a friend that an stereo set .. I've got it all powered down and not sure what to do next ..

It replaced a much more modern one that cost a lot more and didn't sound half as good. Well serviced/loved before it came to us .. just dusted out and the bias tuned .. Had it about about 2 years..

If they can spare the time, we would all be really grateful of any thoughts the diyAudio community has on the problem ..


djk 24th March 2011 12:44 PM

Check R39 in both channels, and R45 on the left input jack (PC-6 boards).

Or you may have lost a ground in the preamp.

jdexter 24th March 2011 11:50 PM

Thx djk - what am I looking for exactly?

More than willing to do some basic testing, not shy about picking up a kit and firing up the iron if it's just upgrade time - but will likely hand over to pro for work if we are into the core power parts on this one.

Would anyone mind describing what might be happening in laymen terms for me?

Cheers - Jon

djk 25th March 2011 09:11 AM

When someone tells you to check a part, that's exactly what you do.

If the part is a resistor, you measure the resistance.

Since you don't have a clue, you will take it to someone that owns a meter. He will look at the schematic you give him (you did print did print it out with the parts list, didn't you?) and see that he can check the part numbers I mentioned without even having to remove the top cover. If they are fubar (laymen's term), he will then remove the cover and replace them.

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