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Old 19th February 2010, 03:01 PM   #1
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Default Dh200 hum?

Hi,I have a dh200 that i have been listening to for uite sometime problem free.Last nite it burnt R22 22k ohm resistor on left channel,replaced resistor and now have sever HUM from both channels.If there is anybody out there that could point me in the direction of what could possibly cause this I would greatly appreciate you advice.

Mike Reyes
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Old 20th February 2010, 07:23 AM   #2
djk is offline djk
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Check R45 please.
Candidates for the Darwin Award should not read this author.
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Old 20th February 2010, 11:34 AM   #3
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Are you absolutely certain that was 22k value and not 22Ω ? - 22k W could take the whole rail value of a DH200
Hum likes to have a nice "Noise to Signal" ratio
To "Hum" is to be noticed Quality hum is when it pours out of Electrostatic speakers
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Old 20th February 2010, 03:57 PM   #4
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Thanks for responding,I will check R45,the schematic I downloaded from hafler calls out a 22000 ohm resitor.I am a newbie at this and really appreciate your help.

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Old 20th February 2010, 05:08 PM   #5
jaycee is offline jaycee  United Kingdom
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R22 is the feedback resistor in one channel. If it has blown this it is likely that either there is oscillation or one of the MOSFETs has blown.

Has the amp had it's power supply capacitors renewed, or are they still the originals? If they are the originals they are probably long overdue for replacement.
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Old 20th February 2010, 05:49 PM   #6
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Yes I replaced the two 10,000 uf power supply caps and bridge rectifier sometime back.I replaced them with 33,000uf cornells,also I didn't mention that both channels hum with no inputs connected.I also desoldered each channel from power supply to see if it was one or the other,no change.I only recently installed a 5ohm thermister to help with inrush.Is it possible that it is the tranny and if so how do i test for this.

Thanks again Mike
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Old 20th February 2010, 05:53 PM   #7
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R45 checks good at 2.2 ohms,I replaced to be sure,no change.transformer maybe? Is there a good way to test tranny myself? both tranny secondaries are putting out approx 46 volts.
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