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 Post subject: Chasing hummmm
PostPosted: 28 Sep 2018, 02:03 
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Joined: 13 Jan 2018, 21:33
Posts: 80
Location: australia
After completing my Chinese ebay 5u4g/6sn7/300b pcb based amplifier I've noticed a humming in both channels audible about from 0.5 metres. I seek help to follow a process to track and fix if possible. Mains voltage is 240v at 50 Hz I think. I do not as yet have a scope.

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 Post subject: Re: Chasing hummmm
PostPosted: 28 Sep 2018, 02:37 
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Joined: 02 Mar 2009, 12:41
Posts: 1065
Location: Vänersborg, Sweden
50Hz hummmmm or 100Hz hummmmm? The latter is propably commmmming from PSU.
50Hz may come from anywhere, bad screening, bad grounding. It amy come from heater voltage.
I could send a very good essay on the matter but it is written in Swedish ...

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 Post subject: Re: Chasing hummmm
PostPosted: 28 Sep 2018, 02:54 
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Joined: 23 Feb 2017, 02:02
Posts: 205
Could be input wires too close to transformers picking up noise, or the pcb inputs too near transfomers


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 Post subject: Re: Chasing hummmm
PostPosted: 28 Sep 2018, 06:19 
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Joined: 13 Jan 2018, 21:33
Posts: 80
Location: australia
thanks guys. i’ll have to check each possibility. i think there’s a bit of the lower freq humming and higher freq buzzing but very low volume. if the swedish article is online googl translate may help me interpret it. i love swedish tv programs/movies Magnus but fortunately they provide the subtitles here.

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 Post subject: Re: Chasing hummmm
PostPosted: 28 Sep 2018, 06:26 
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Joined: 02 Mar 2009, 12:41
Posts: 1065
Location: Vänersborg, Sweden
Sorry it's a pdf-file.

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 Post subject: Re: Chasing hummmm
PostPosted: 28 Sep 2018, 21:52 
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Joined: 04 Jun 2008, 20:59
Posts: 3817
Location: Arizona, USA
Hi, Send some photos of the insides. Sometimes it is possible for us to make suggestions. Also if there is a schematic that would be helpful.

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Bruce

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 Post subject: Re: Chasing hummmm
PostPosted: 28 Sep 2018, 23:07 
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Joined: 13 Jan 2018, 21:33
Posts: 80
Location: australia
Thanks Bruce. Here is a link to the schematic. It will be unconventionally drawn as I tried to trace out the connections from the pcb as well as being a noob at this. The provided circuit was difficult to follow too with missing values and components. download/file.php?id=9645
I will post a pic of the internals as they are now. It's a bit crowded with wires.

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 Post subject: Re: Chasing hummmm
PostPosted: 29 Sep 2018, 04:39 
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Joined: 13 Jan 2018, 21:33
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Location: australia
as promised internal layout.


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 Post subject: Re: Chasing hummmm
PostPosted: 29 Sep 2018, 21:34 
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Joined: 23 Feb 2017, 02:02
Posts: 205
I'm thinking its a poor grounding to mains ground wiering, or its the schematic heaters causing the humm.
Dosen't seem like any plorbem with transfomes postioning


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 Post subject: Re: Chasing hummmm
PostPosted: 01 Oct 2018, 04:25 
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Joined: 13 Jan 2018, 21:33
Posts: 80
Location: australia
thanks ILHF. i tried moving the signal wires a bit and the 5v 300b heater wires to no avail. probably need a scope and to work out how one works to see what it looks like. Also the circuit has fairly basic rectification of voltage for the 300b filaments so possibly i couldn’t expect zero hum anyway. through my relatively inefficient speakers by all accounts i can only hear the hum very close to the speaker with my good ear. the tinnitus is louder with the other almost. at some times hum is louder and is higher freq than a hum. i likely will need a voltage regulator circuit as designed by Suncalc in Mwhouston’s silver dragon once i figure it out. i’m not really sure how i would incorporate it physically though in this pcb design. hopefully from the pic someone might spot some obvious error in my connections or grounding.

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