QUAD 405 Clone wiring / ground loop

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PrismX

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Joined 2024
#1
Hi everyone, I have 2 Quad 405 Clone boards which I would like to install in an aluminum housing.
1727615586397.png


I have wired the whole thing as shown in the picture,

1727616031498.jpeg


but I can hear a quiet hum on one channel. It is not loud and you have to get very close to the woofer to hear it, but it is audible.
I use the following switching power supply, it is a +- 40V (I know it is not 50, I will upgrade it later).
1727615693845.png

I have also tried to remove the ground loop breaker and connect PE directly to the GND of the SMPS, same behavior.
I am quite a novice when it comes to amplifier construction, so please point out the mistake.

Thanks
 

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#3
Many thanks for the great tip! It really has improved a lot, now it's just the position of the input cable, which means that when I move it, it gets louder or quieter, almost completely inaudible. And that's only on one channel, the other doesn't hum at all, no matter how I move the input cable. I have now screwed the housing shut, the hum is almost completely gone, but I have the feeling that I have forgotten to connect just one more little thing to make the hum disappear for good.
 
#4
Hi..
Have you ever decided to solder 2x 10 Ohm resistors in ? Between the shield grounding RCA to the two amps. Is such a 10 ohm resistor on board ? I can't believe, its a China Clone....
The problem with rca may be that one rca ground becomes active and building out a potential difference if you use one supply for two boards.

Take a look to the picture...perhaps that way will help.

Greets
Peter
 
#8
Hi...
Dont understand your writing....why remove the ground lift resistors ? I thought about to put them in...
Don't know if such resistors are on the board. Don't think so...
now it's just the position of the input cable, which means that when I move it, it gets louder or quieter, almost completely inaudible.
Click to expand...
What could be the reason for this effect ?

Greets
Peter
 
#9
Basically, you build large ground loops when you place cinch sockets far apart.
It would be better to connect only one RCA socket to ground, and therefore run the earth signal via one RCA line only. This has further advantages: Diameters are reduced, which robs the signal less definition.
 
#11
These boards already have a ground lift resistor as the original Quads do. It is the one in the red square on the photo. They are often 2R7 on these clones. Originally Quad used 10R.

Also check that the Zobel resistor (10 Ohm- green squared) is returned to the power ground on this board, and not the input ground. Some of the Chinese clones have this error.

1727615586397.png
 
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#13
arjen6t8 said:
These boards already have a ground lift resistor as the original Quads do. It is the one in the red square on the photo. They are often 2R7 on these clones. Originally Quad used 10R.

Also check that the Zobel resistor (10 Ohm- green squared) is returned to the power ground on this board, and not the input ground. Some of the Chinese clones have this error.

View attachment 1362635
Click to expand...
Thanks, i'll check that now.
By the way, I just turned on the amp and the hum was louder on the one channel I mentioned. So it's really somehow due to the position of the cable and the device, because yesterday it was almost inaudible.

And another thing, I haven't connected the GNDs of the heat sinks anywhere, as the heat sinks are screwed directly to the heat sinks of the chassi.
1727881063088.png

Does that make any difference?
 
#14
PrismX said:
but I can hear a quiet hum on one channel. It is not loud and you have to get very close to the woofer to hear it, but it is audible.
I use the following switching power supply, it is a +- 40V (I know it is not 50, I will upgrade it later).
Click to expand...
It is a switch power supply, but you heard hum. Hum is usually 50/60Hz(or 100/120Hz). You should not hear hum from a switch power supply.
Do you hear hum when you short the input terminal? It is normal to hum if there is nothing connected to the input.
 
#16
jxdking said:
It is a switch power supply, but you heard hum. Hum is usually 50/60Hz(or 100/120Hz). You should not hear hum from a switch power supply.
Do you hear hum when you short the input terminal? It is normal to hum if there is nothing connected to the input.
Click to expand...
Yes, I knew that if nothing is connected, it can hum.

But I can't explain what has happened now. I switched on the amp as usual to check whether it was humming with short-circuited inputs and it was completely quiet, as usual I had an Android cell phone connected to the input as a source. With short-circuited inputs it was also quiet. But yesterday, with exactly the same setup (cell phone on the input) there was humming... I'm slowly going crazy
 
#17
Try changing the connector wire, it may have a screen come loose inside the plastic housing. I had the same problem with such intermittent hum in my car playing from my phone. I wiggled the wire and it was quiet, then I touched again and it was humming. Changed for a new wire (these things are rubbish) but the hum was gone.
 
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