I have a Hafler DH-101 preamp that was working fine but suddenly developed a loud hum in both channels while it was in use.😱
The hum is constant in amplitude and not dependent upon any of the controls or switches -- it remains even with the volume control all the way down. I've checked all external cables and inputs, and have now determined that it is internal to the DH-101.
Are there any Hafler DH-101 experts out there who can point me towards a likely cause? I built this preamp myself from a kit over 30 years ago and applied the DH-106 mods back then by just following instructions, but I don't understand enough about the circuitry to troubleshoot this problem without some guidance.
TIA for any help someone can lend me.
The hum is constant in amplitude and not dependent upon any of the controls or switches -- it remains even with the volume control all the way down. I've checked all external cables and inputs, and have now determined that it is internal to the DH-101.
Are there any Hafler DH-101 experts out there who can point me towards a likely cause? I built this preamp myself from a kit over 30 years ago and applied the DH-106 mods back then by just following instructions, but I don't understand enough about the circuitry to troubleshoot this problem without some guidance.
TIA for any help someone can lend me.
poko said:
replace all electrolytics in power supply , check , and start from here changing all other (even if few bip biggies can be problematic to find new ones);
probably that's only culprit
I was looking at the circuit diagram and being that the hum is on both channels equally, I'm wondering if it could be in the power supply. Could a bad positive or negative voltage regulator cause this?
poko said:
first thing first
change caps , then try further,if needed .
I saw 78xx and 79xx survived shorted cap
Confirm all ground tabs and contacts are good useing a multimeter... have had hum issue this month with corrosion forming...
Thanks Zen Mod and Nordic for your quick replies. I checked the ground contacts and seem to be fine. I have ordered replacement electrolytic caps and voltage regulators for the power supply, and should have them in a few days. I'll let you know if that does the trick. Thanks again!
It is probably those lytics...
Can problematic electrolytics cause an intermittant random scrathing/crackleing sound...
My amp makes this scratchy sound on one channel, which has completely been rebuild (trying to find a cure) appart from the PSU... Thought I had it all fixed... but after standing on for a few hours with no signal, the crackle came back... It is not terribly annoying, can't hear it above... Also it seems to take very long to reach this point... amp was on yesterday for probably 15 hours before it started again...
The quiet channel heatsink was just above ambient, while the noisy channel's sink felt cooler...
Can problematic electrolytics cause an intermittant random scrathing/crackleing sound...
My amp makes this scratchy sound on one channel, which has completely been rebuild (trying to find a cure) appart from the PSU... Thought I had it all fixed... but after standing on for a few hours with no signal, the crackle came back... It is not terribly annoying, can't hear it above... Also it seems to take very long to reach this point... amp was on yesterday for probably 15 hours before it started again...
The quiet channel heatsink was just above ambient, while the noisy channel's sink felt cooler...
Well, I replaced all the electrolytic caps in the power supply, but that didn't fix the hum. So, I replaced both the pos and neg voltage regulators -- nope, still loud hum on both channels. The hum is constant and doesn't change regardless of any controls/switches.
I guess I'll try replacing the diodes as jblmar suggested. There's really nothing else left to replace on this power supply board, so I hope that's it!
I guess I'll try replacing the diodes as jblmar suggested. There's really nothing else left to replace on this power supply board, so I hope that's it!
Bad news... I replaced the 4 rectifier diodes but the hum remains. Since I've replaced all the caps, regulators and diodes on the power supply, the problem is elsewhere.
Anyone have any ideas where I should be looking now? Again, the hum is equal on both channels, remains constant regardless of the volume setting or input selector settings.
Thanks in advance for any help you can give me!
Anyone have any ideas where I should be looking now? Again, the hum is equal on both channels, remains constant regardless of the volume setting or input selector settings.
Thanks in advance for any help you can give me!
Hi poko,
It's time you sat down with a 'scope and a schematic. Normally the advice you were given will fix your problem. You needed those replaced anyway simply due to age.
Do check that you installed them properly, polarity first.
Take a voltmeter and test all the grounding points. What looks good may not be. You could also measure the ground voltages against your common in the power supply board with the unit running.
Look for blown ground traces. Especially in the input area.
-Chris
It's time you sat down with a 'scope and a schematic. Normally the advice you were given will fix your problem. You needed those replaced anyway simply due to age.
Do check that you installed them properly, polarity first.
Take a voltmeter and test all the grounding points. What looks good may not be. You could also measure the ground voltages against your common in the power supply board with the unit running.
Look for blown ground traces. Especially in the input area.
-Chris
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