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Old 15th April 2017, 09:31 PM   #1
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Default Peters Mighty Midget tube amp

Hi, I ordered the board (from Peter Millet), the components for the board and Edcors PM-102.
Managed to build a quick set up to see what I bought and hear what I built... :-)
I have alot of hum in da speakers...
When I power up it is there and a lower hum mixes in 3 seconds later...
Where should I start to eliminate da hum?
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Last edited by hifisucks; 17th April 2017 at 01:00 PM.
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Old 16th April 2017, 04:16 PM   #2
Ripcord is offline Ripcord  United States
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Hello Hifi, I built the Mighty Midget a while ago and it's quite as a mouse. Your pictures aren't very big so it's hard to tell but here is a quote from Pete Millett, "Note in the last photo the wire that connects the case to ground. Turns out that this is important - without it the amp was noisy and tended to oscillate. So do ground the chassis!"

Here is the link: The Mighty Midget and a picture.

P.S. Just wanted to add that the amp sounds fantastic!!
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Old 16th April 2017, 04:48 PM   #3
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Thanks for your reply... but I have no chassis... at the moment... :-)
It shouldn't hum even without a chassis... I am not living next to a power plant... :-)
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Old 17th April 2017, 12:50 PM   #4
wfmali is offline wfmali  Europe
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Your pictures do not help much, too small - Pete Millet's board should be out of the question, they are usually very well though through. I would doublecheck part population and grounding and feedback. Relax, have a beer, say "omm" - you'll find the issue :-)
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Old 17th April 2017, 02:46 PM   #5
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Between all the ommmmmmm sessions I had time to check all parts... all ok...
grounding what? The board has fixed all groundings... I guess... AND, I do not have a chassis to ground...
What feedback?
Boy, I am shortly before giving up...
Definitly, this will be my last adventure with tubes...
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Old 17th April 2017, 05:02 PM   #6
TheGimp is offline TheGimp  United States
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One thing I notice in the schematic is the connection from the power receptacle ground to the ground lift diode bridge.

I can not tell from your pictures if you have this connection. Without it you will most likely get hum.
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Old 17th April 2017, 05:05 PM   #7
TheGimp is offline TheGimp  United States
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circled in green.

Is this internal to J3?
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Old 17th April 2017, 05:58 PM   #8
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On the board it has internal contact... I also tried without D1... hums with or without......
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Old 17th April 2017, 06:39 PM   #9
Bone is offline Bone  United Kingdom
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You must have a metal chassis! Preferably put it in a metal box. Tubes are high impedance and will pick lots of ambient crap.
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Old 17th April 2017, 06:48 PM   #10
wfmali is offline wfmali  Europe
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Hums without audio source connected (input open) ?
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