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Old 13th January 2012, 12:06 AM   #2041
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Default No hum

I've got no trouble here. No hum - this amplifier is dead silent.
Look at the input cables path, beside/below the transformers! (sorry for high-sized image)
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Last edited by smartx21; 13th January 2012 at 12:09 AM.
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Old 13th January 2012, 02:58 AM   #2042
bdos is offline bdos  Russian Federation
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Quote:
Originally Posted by linuxworks View Post
bdos: that rca cable line-in goes RIGHT NEXT to the trafo!
that has to be causing hum. it has to be. I would not route it that way if I were you.
Transformer shielded input cable is shielded - no noise. This arrangement of the shortage of space... Thx for a critic ))
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Old 13th January 2012, 03:12 AM   #2043
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Quote:
Originally Posted by bdos View Post
Transformer shielded input cable is shielded - no noise. This arrangement of the shortage of space... Thx for a critic ))
I used the same cable like yours with excellent results.
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Old 13th January 2012, 03:54 AM   #2044
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maybe you don't hear it thru the speakers. but I bet its very measurable on the scope.

of course audible is what counts; but I would never consider wire placement like that. its just asking for trouble even if your current spkr sensitivity hides the hum.
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Old 13th January 2012, 10:13 AM   #2045
AndrewT is offline AndrewT  Scotland
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I use twisted pairs.
I have experimented routing line level twisted pair signal lines next to, on top off and around transformers and mains multi-ganged sockets. I cannot detect mains hum above the 0.1mVac level at the amplifier outputs. With my typical amp gains of 26dB to 31dB and speakers of 86dB to 92dB I have never heard the twisted pair strategy leading to audible hum at the speaker/s.

Hum is usually caused by a wiring error. Not by aerial pickup of a well laid out pair of line level signal and return pair.
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Last edited by AndrewT; 13th January 2012 at 10:16 AM. Reason: Sorry, off topic.
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Old 13th January 2012, 11:51 AM   #2046
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I see andrew .

I will be watching you like a hawk waiting for you to say somthing to someone who posts off topic. After all this is the chipamp photo gallery..

Keep up the good work..

Regards Ian
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Old 13th January 2012, 04:12 PM   #2047
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I don't want to 'chatter' too much in a photo thread (lol) but I've seen my own direct experiences in many amps where placement of trafo MUST be inches and even feet away from input circuits. that includes wiring to inputs. when I make umbilical PSUs, you can pick them up and move them around in-operation and hear the hum come and go. proximity DOES matter. twisted pair helps but power does radiate and wires are nice antennas. shielding and twisting is a 'help' but you cannot fight distance.

my last chip amp was the same thing, I use a trafo box over an umb. cord and the location of the trafo absolutely does affect the audible hum level. goes from no hum to very loud hum. if that was 'wiring error' why would movement of the trafo change things?

its not 'wiring error'. it can be, but that's not the ONLY thing that induces hum. you know that, come on!
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Old 13th January 2012, 04:48 PM   #2048
udailey is offline udailey  United States
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If he doesnt have hum then there is no problem.
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Old 13th January 2012, 05:03 PM   #2049
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in this amp was small hum
401.jpg
402.JPG
one power supply for 2 amp pcb.
P.s. this is tda 7293
on stk amp I dont hear hum, speakers sens 90 db
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Old 13th January 2012, 05:21 PM   #2050
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actually, it can be masked by various sensitivities.

one amp I had (behringer a500) sounded fine on my maggies. any hum was masked by the spkr lack of sensitivity. I changed those spkrs out and put efficient monitors in and the hum was there; had been all along but I didn't notice it until the spkr change.

all I'm saying is that it is likely there. maybe not heard now, but wiring that close to a huge trafo can't be good. its just not good wire placement and that's what I'm trying to get across.

chassis should be laid out with wiring in mind. I dont' see that enough, to be honest. that's what sparked my comment, I guess. lots of diy projects seem to consider wire placement as the last thing and I think that's the wrong way to go about it.
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Last edited by linuxworks; 13th January 2012 at 05:24 PM.
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