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Old 24th August 2010, 09:25 PM   #11
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Originally Posted by Rodeodave View Post
Nice pic, will meditate over it once I'm sober enough. Is there any additional info other than that there's hum? 50Hz?
Yes 50Hz. I am getting a quiet hum from my speakers at the moment and its exactly the same as the transformer
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Old 24th August 2010, 09:34 PM   #12
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Just another idea.
How about rotate the transformer 180 degress so that the secondary wires come out of the transformer near the front of the case right next to the bridge rectifiers (ie right away from any of the other wires)
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Old 24th August 2010, 09:36 PM   #13
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Is the hum coming from the channel that is closest to the ac mains wires (blue and black wires) or is it coming from the other channel?

I don't expect this to help but I would probably twist those blue and black wires together.

I also see those red and black secondary transformer wires going up near the amp channel and crossing wires.
I would shorten those wires or whatever you need to do to route them straight down to the bridge rectifier.

You could also try rotating the transformer.

It might come down to a process of elimination.

Hello again

Its coming from both channels, and is at the same volume.

I'll whip the transformer out tomorrow and see if it helps.

Keep them coming!
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Old 24th August 2010, 09:37 PM   #14
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How sensitive are your speakers?
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Old 24th August 2010, 09:39 PM   #15
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Originally Posted by thanh1973 View Post
How sensitive are your speakers?
Test speakers 89dB, main speaker ~92dB. My various chipamps were silent.
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Old 24th August 2010, 09:48 PM   #16
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Ok you shouldn't have issues because of the speakers.

I would definitely try turning the transformer 180 degress with secondaries coming out near the front of the case right next to the bridge rectifiers.

If you can pick up some galvanised iron sheet (or a tin can) it might be worth making your own magnetic shield to put around the transformer.

Last edited by Melon Head; 24th August 2010 at 09:51 PM.
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Old 25th August 2010, 12:51 AM   #17
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Originally Posted by Tripmaster View Post
...
I'll whip the transformer out tomorrow and see if it helps.
...
Good thinking, take the transformer out of the amp, as far away from signal carrying wires as possible. That's how I diagnosed the problem with my Gainclone.

Twist all AC carrying wires (mains, secondary,...).

I can't really tell from the picture, where do your circuit grounds meet, and are the connected to earth ground? If yes, through a thermistor hopefully?

Are all RCAs and speaker terminals insulated from the case?

I too would suggest to turn the transformer 180. It looks like you're using a power socket/fuse/switch combo, that's fine, but move the screw terminal block to the other end of the chassis, running twisted wires from the switch. Will be very neat once the xformer is turned.

Also, move the bridges to where the 2-port screw terminals are currently, this will result in shorter wires going to the PSU capacitors, which is highly desirable. Possibly you can ditch the secondaries' extensions and run them directly into the bridges. I don't see why not.

In general keep all AC carrying wires as far from any audio circuitry as possible.

And don't give up, hum is almost always curable.
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Old 25th August 2010, 12:17 PM   #18
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Rotate the transformer until the hum is low/equal on both channels .
It works perfectly.
If it is still too much , it need to be moved a bit away.
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Old 25th August 2010, 12:26 PM   #19
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If you disconnect one channel and run the other as a monoblock, does it become hum free?

Where do the speaker leads connect? They both seem to go to the PCB.

Are the brass standoffs isolated from the PCBs?
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Old 25th August 2010, 12:26 PM   #20
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Aluminium actually can provide a magnetic shield. Through lossy magnetic shielding
"Lossy magnetic shielding depends on the eddy-current losses that occur within highly conductive materials (i.e., copper, aluminum, iron, steel, silicon-iron, etc.). When a conductive material is subjected to a time-varying (60 hertz) magnetic field, currents are induced within the material that flow in closed circular paths - perpendicular to the inducing field. According to Lenz's Law, these eddy-currents oppose the changes in the inducing field, so the magnetic fields produced by the circulating eddy- currents attempt to cancel the larger external inducing magnetic fields near the conductive surface, thereby generating a shielding effect."

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