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Bottlehead Kits => Crack => Topic started by: jimbu on June 07, 2016, 12:28:05 AM

Title: Crack - Standard Build - Loud Buzz [resolved]
Post by: jimbu on June 07, 2016, 12:28:05 AM

Hello,

I finally got around to building my Crack, which I ordered July last year. Yes, it has been a busy 11 months, I got married, and diagnosed with ADD, and those two things probably go a long way in explaining why it took me so long.

So I have completed the build, and there is a loud buzz in both channels, with the following characteristics:
- 55Hz fundamental, with harmonics at every +100Hz (ie. 155Hz, 255Hz, 355Hz, etc) - I did a quick test with an iPhone app by placing the end of my phone inside my headphones.
- Hum is at a low level when I power on and remains like that for around 20-30s, at which point it ramps up fairly quickly to a loud level and remains there.
- Hum is independent of volume control
- Hum is present both with and without a source plugged into the RCA jacks
- I am using Sennheiser HD600 headphones

I've triple checked the connections, re-done most of the solder joints (my soldering is pretty decent), I've tapped/pushed all of the wires, components, lugs, tubes, everything many times with a chopstick , and the hum does not change.

Oh and my voltages and resistances checked out okay.

I should also add, the output tube is a 'special 6080' that was the weekly special at the time of my order. It says "JAN-CAHG-6080WA CHATHAM ELECTRONICS 5933".

I am in Australia, so it is 240V.

I've played music through it, and behind the horrible hum, it sounds great (ie. playback at a high level with music that is dense enough in the low end to drown out the hum) Any ideas?

Cheers,
James

Title: Re: Crack - Standard Build - Loud Buzz
Post by: Doc B. on June 07, 2016, 04:26:20 AM

You have a loose ground connection somewhere. The most common place that happens is where the black wires connect to the headphone jack.

Title: Re: Crack - Standard Build - Loud Buzz
Post by: fullheadofnothing on June 07, 2016, 06:00:39 AM

Incorrectly mounted hardware can also cause hum. Post pictures of your build.

Title: Re: Crack - Standard Build - Loud Buzz
Post by: Doc B. on June 07, 2016, 06:05:11 AM

Yup, good call, Josh. RCA jacks not properly insulated can cause hum too.

Title: Re: Crack - Standard Build - Loud Buzz
Post by: Paul Birkeland on June 07, 2016, 06:16:14 AM

Did you happen to paint the top and bottom of the chassis plate?

Title: Re: Crack - Standard Build - Loud Buzz
Post by: jimbu on June 07, 2016, 01:23:47 PM

Thanks for the feedback, everybody.

I re-soldered all the ground joints this morning, and moved the ground cable that can either go on #14 or #22(?) from #22 to #14. Not sure what did it, but it's quiet as a mouse now.

Cheers,
James