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A DC Blocker to help stop transformer HUM

Anterantz

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I just connected one of those emotive dc line filter /offset eliminators and it actually did the trick. No more hum from my amp.
i honestly didn’t think it would work but it did. It was not much of a problem but it’s silent now.
What model have you used? I am between the audiolab and ifi
 

littlebigranch

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Thank you to g29 and others who've posted about ATL Hifi. Just received their little DC Blocker, from Bulgaria to our little ranch in Montana. I wasn't expecting perfection, but this thing does really well. I bought a used First Watt J2 about a month ago, and its hum was loud enough to be just audible from our listening sofa. The ATL box doesn't eliminate it, but I have to put my ear to the amp to hear it now. Fantastic!

ATL HiFi DC Blocker Trap Filter – Assembled in Case – v.3
 

Anubis

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Hello ...

Can a run capacitor work as an effective and SAFE dc blocker?
Like this:
Screenshot_20230307-153851.png
 

Anubis

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I got an email that someone replied but there is no new post in the thread.
 

Skeeter

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I’ve done a DC Blocker plus soft start here


I had a YouTube video up showing the effectiveness but took it down since I want to reshoot it.
 
Last edited:

Geert

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I got an email that someone replied but there is no new post in the thread.
Yes, that was me. I noticed my answer was incomplete but I had to run.

You can find the schematics of a DC blocker over here: https://audiosciencereview.com/foru...-to-help-stop-transformer-hum.948/post-226317

Notice that next to capacitors you need diodes, which limit the max voltage over the capacitors. The number of diodes determine the max DC voltage that can be removed from the mains. Full explanation over here https://sound-au.com/articles/xfmr-dc.htm.
 

DonH56

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What is the role of resistor and film cap?
It is discussed in the thread. Helps "bleed" charge off the capacitors when not in use and the capacitor/resistor circuit reduces interference (RFI) if the diodes are switching.
 

Anubis

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So ... Consensus is this particular dc blocker is both effective and above all safe to use?
 

Count Arthur

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solderdude

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Hello ...

Can a run capacitor work as an effective and SAFE dc blocker?
Like this:View attachment 270028
Nope, the capacitance value is too low. At 60Hz the impedance would be 75ohm.

Well...it could only succesfully be used with very, low power transformers (the few Watt max ones) but these usually don't hum audibly so there would be no point in that.
 

solderdude

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https://ibb.co/3dfxkMG
This one

Cant post images for some reason.

It'll be effective IF your problem (occasional hum of a transformer) is really caused by DC on the mains.

These all work on the exact same principle. The only difference between them is the maximum voltage drop in DC they can remove. This depends on the used diodes (or bridge rectifier used as clamping diodes)
 

Anubis

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It'll be effective IF your problem (occasional hum of a transformer) is really caused by DC on the mains.

I believe so ... The buzzing stops when I put a run capacitor on the power cable, but the amp shuts off when I increse the volume.

I thought a stronger cap would work, but it seems it wouldn't.
 

solderdude

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A 'stronger' cap will work. But 'stronger' in this case is a much, much higher capacitance.
As these do not exist in bipolar/non-polar you need 2 of them in 'anti-series'.
Because of the so called CU product these would be enormous in size.
And... because there will be very little voltage across these these caps can be rated just a few Volt.
To ensure that low voltage is never exceeded there are a few diodes in parallel which 'clamp' the voltage (will conduct above their knee voltage).
 

Anubis

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I ment "stronger" run capacitor ...

Ok, thank you all ... I gonna make the ATL blocker, the one with two 47000uf caps and six diodes.
 

jonfitch

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Hmm, I'm having a bit of a humming issue with a Yammy AS-1200. The amp dead silent when playing music and idling at first start, but if it idles for more than about 10-15 mins, it starts humming audibly from a few feet away. The sound doesn't go away unless I power cycle the receiver, or goes away on its own after playing music for a few minutes. I wonder if this is something that would benefit from a DC blocker?
 

HarmonicTHD

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Hmm, I'm having a bit of a humming issue with a Yammy AS-1200. The amp dead silent when playing music and idling at first start, but if it idles for more than about 10-15 mins, it starts humming audibly from a few feet away. The sound doesn't go away unless I power cycle the receiver, or goes away on its own after playing music for a few minutes. I wonder if this is something that would benefit from a DC blocker?
Yes. From what you describe, that’s sound like DC induced hum.
 
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