I finished my Chip amp and put it in a chassis, YAY!!!! - diyAudio
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Old 10th February 2007, 10:52 PM   #1
pjpoes is offline pjpoes  United States
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Default I finished my Chip amp and put it in a chassis, YAY!!!!

Now the only problem I have is Hum. I tried many of the techniques suggested, and Peter Daniel is looking at some pics to help me out, hopefully. Anyone else want to take a stab at it. I haven't tried putting a resistor/diode between earth and amp grounds, but when I unplugged the ground to test that, it didn't get any quieter, it actually got slightly worse.

Other than that, the chassis I got is great quality, I'm very happy with it. The amp sounds good generally, other than the hum. I may try changing the power supply caps with something besides the Panasonic FC caps, bypassed by .01uf wima film caps. We shall see I suppose.

I know the Chassis is much too large, but I bought one larger than I needed with the idea that I could add another two modules in order to make a 4 channel amp. Another idea was to wire them in bridged configuration for more power, but I'm unsure if thats really what I want to do.
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Though its hard to tell, the speaker wire and input connections are about 1" above the power wires, and cross at around 90 degrees or so. I'm hoping that is enough not to induce any hum, but that may be an area I need to change. I'm just not a huge fan of shielded wire inside an enclosure, if I can avoid it.

The amps were built up with Caddock and Riken resistors, Panasonic FC caps on the amp board, and Elna Cerafine 10uf caps on the rectifier board, with Black gate .47uf caps bypassing those. The rectifiers are IXYS Schottky FREDS, Kimber Kable wire for the RCA and Speaker cables, teflon insulated copper wire for the power wires.
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Old 10th February 2007, 11:08 PM   #2
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Is your chassis itself grounded to the star ground? You might want to use shielded wire for your source input wires.I've had real good luck with cannabalizing a cheap phono patch cord.This may help eliminate your hum.
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Old 10th February 2007, 11:33 PM   #3
pjpoes is offline pjpoes  United States
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At the moment its not grounded to the Chassis, as Peter Daniel recomended against it. I did have it that way and it didn't really change the sound at all.
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Old 10th February 2007, 11:45 PM   #4
BWRX is offline BWRX  United States
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It's most likely noise being emitted into your input wiring.
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Old 11th February 2007, 12:08 AM   #5
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Quote:
I'm just not a huge fan of shielded wire inside an enclosure, if I can avoid it.

Why? IMHO source input would be manditory shielded and as far away from AC and outputs as possible.





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Old 11th February 2007, 07:42 AM   #6
Nordic is offline Nordic  South Africa
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I Agree with the 2 previous posts...

I always try to organise power, out, and input - in that order, to keep input as far away from power, unscrew the toroidal and check if the hum changes if you move it around a bit...
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Old 11th February 2007, 10:24 AM   #7
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Hi friend,

I see so many loops inside your amp that it would be a miracle if it wouldn't humm.

- AC lines - twist them - and let cables bi evenly long.
- input wire is the only one that is done OK (twisted)
- output to speaker terminal - twiste those wores - you have a huuuge loop there
- DC lines from rectifier board to amp board - again - twist them

I think you'll be close to perfection then
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Old 11th February 2007, 12:02 PM   #8
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Is your chassis itself grounded to the star ground? You might want to use shielded wire for your source input wires.I've had real good luck with cannabalizing a cheap phono patch cord.This may help eliminate your hum.
Good advice from a fellow Iowan.

I use mic line such a Liberty #4340 which is a 22ga twisted pair with shield. I usually have small lengths left in a 1000ft box and this lends itself very nicely to my projects.
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Old 11th February 2007, 02:42 PM   #9
CarlosT is offline CarlosT  United States
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Can we see some closeup of that area in the middle near the rectifier board where all the wires seem to converge? I'm getting a little confused at what I'm seeing...

Also...do you get hum without any input device connected (i.e., CD player, tuner)? Have you tried to use a simple battery powered device like an iPod to see if anything changes?

Did you use Peter's rectifier board? Those normally come with MUR860 diodes as a kit.
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Old 11th February 2007, 02:43 PM   #10
CarlosT is offline CarlosT  United States
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Can we see some closeup of that area in the middle near the rectifier board where all the wires seem to converge? I'm getting a little confused at what I'm seeing...

Also...do you get hum without any input device connected (i.e., CD player, tuner)? Have you tried to use a simple battery powered device like an iPod to see if anything changes?

Did you use Peter's rectifier board? Those normally come with MUR860 diodes as a kit.
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