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Old 6th September 2009, 01:39 AM   #1
gychang is offline gychang  United States
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Default fancy style but picking up hum...

Soldered in Arjen's t-amp clone in a case with cheap volume-pot and input selector switch. The sounds is reasonable and quiet without hum however when I put the amp on top of my Oppo CD player the hum... which gets louder with the vol/pot turnned up. When I disconnect AC to Oppo CD player, hum goes away.

My amp is picking up the stray AC hum from the CD. Another Arjen's amp in a rectangular wooden case with different vol-pot and input selector switch does not pickup hum on the same setup.

Can anyone suggests some ideas on how to minimize hum?, all wires are not shielded..., did not wind the hot input with the ground wires (since 2 hot input with a single black ground).

Would appreciate suggestions for this newbie in electronics.

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thanks,

gychang





Even with a small piece of plywood 1/2" on the bottom of the amp, and hook up the AC on the Oppo CD player (which is resting
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Old 6th September 2009, 02:06 AM   #2
gychang is offline gychang  United States
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this is when the hum is heard.

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gychang
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Old 11th September 2009, 11:21 PM   #3
gychang is offline gychang  United States
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do I need to buy the "shielded" wire to minimize picking up the hum?

can't figure how to wind the wires for 2 separate channels when there is only one ground (seems to be another way rather than rewire the whole input side).

thanks in advance.

gychang
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Old 14th September 2009, 09:53 AM   #4
81bas is offline 81bas  Germany
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Quote:
Originally Posted by gychang View Post
My amp is picking up the stray AC hum from the CD.
Can you lower the hum to zero with the volume pot?
If yes, then I bet that your CD is picking hum from your amp
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Old 14th September 2009, 11:30 AM   #5
gychang is offline gychang  United States
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Quote:
Originally Posted by 81bas View Post
Can you lower the hum to zero with the volume pot?
If yes, then I bet that your CD is picking hum from your amp
that's interesting. Hum definitely is volume dependent, but not sure if goes to zero...

what is the solution then?, I assumedit was my shoddy amp work and most likely it is the problem rather then the CD "problem".

gychang
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Old 14th September 2009, 12:46 PM   #6
Pafi is offline Pafi  Hungary
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gychang!

Hum can arise in three ways: conductive, inductive, and capacitive ways (maybe mixed ways too, but lets neglige this).

- If it is purely capacitive, then shorting input connectors (this is a test) will eliminate it. In this case you should slield your cables, or ground the metal case of your CD player to GND of your amp!

- If it is inductive, then shorting doesn't help, but the volume of hum is strongly dependent on the position of the amp relative to the CD player. In this case twisting the input wires, or magnetic shielding (big iron sheet between the devices) can help.

- In your case conductive way is unprobable, because it is independent from position.
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Old 14th September 2009, 11:01 PM   #7
gychang is offline gychang  United States
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This is a very helpful tip, my guess is capacitive. A novice question, how do I short the input connectors?, from input selector output I have 2 channels (R/L) and third ground.

gychang

Quote:
Originally Posted by Pafi View Post
gychang!

- If it is purely capacitive, then shorting input connectors (this is a test) will eliminate it. In this case you should slield your cables, or ground the metal case of your CD player to GND of your amp!
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Old 14th September 2009, 11:18 PM   #8
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Wooden case, no shielded input wires or shielded cable to input selector.
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Old 15th September 2009, 11:30 AM   #9
Pafi is offline Pafi  Hungary
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Quote:
A novice question, how do I short the input connectors?, from input selector output I have 2 channels (R/L) and third ground.
Connect them all together!
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Old 15th September 2009, 11:50 AM   #10
gychang is offline gychang  United States
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Originally Posted by Pafi View Post
Connect them all together!
thanks, will try it when I get home in 4 weeks (am in Korea now) amp is in USA.

gychang
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