My Gainclone emits a humming noise at the speakers when I use my laptop connected to is switched mode PSU. It is fine on battery supply.
Could it be DC on the output of the laptop when the PSU is connected, or is it a grounding issue?
Anything I could try to eliminate the problem?
I don't want to modify the inputs on the Gainclone, but I could make up some modified cables (in-line caps) to use with the laptop.
Chris.
Could it be DC on the output of the laptop when the PSU is connected, or is it a grounding issue?
Anything I could try to eliminate the problem?
I don't want to modify the inputs on the Gainclone, but I could make up some modified cables (in-line caps) to use with the laptop.
Chris.
If it is humming then this is due to AC mains noise. So you probably have a ground loop.
Is your gain clones 0v connected to mains ground? If not try a 100R resistor from 0v on the gain clone to mains earth, this sometimes helps with this kind of noise. You can go lower if yuo want to right down to connecting 0v directly to mains earth.
Regards,
Andrew
Is your gain clones 0v connected to mains ground? If not try a 100R resistor from 0v on the gain clone to mains earth, this sometimes helps with this kind of noise. You can go lower if yuo want to right down to connecting 0v directly to mains earth.
Regards,
Andrew
Definitely sounds like a grounding issue. What might be happening is RF hash from the mains coming down the screen of your audio cable into your gainclone. As Andrew says, earthing the 0v might reduce it considerably by providing a preferential path for the noise. If your input signal screen goes to the PCB then try connecting that to the chassis star point instead (assuming you have one).
Every time i've seen this happen it's caused by the power brick of the laptop. Confirm by running the laptop on battery - the hum should go away. Since a laptop doesn't pose an electric shock risk, most of the times the easiest solution is to cheat and plug the laptop in an ungrounded outlet.
you should not need to cheat.
The remote PSU for the Laptop is almost always double insulated and is fed from a two core cable, no earth wire.
All the laptops i've had came with 3-wire cables on their power bricks. On one of them i actually fried the line input when connecting another piece of ungrounded equipment to it, because the laptop was plugged into a grounded outlet, and later i determined that the other equipment was sitting 55 volts above ground...
In what country?
The company I work for is one of the largest resellers of computers/laptops in the world, and there has yet to be a laptop come through our evaluation dept that has a 2 prong plug, they ALL have ground pins.
we do 5 of EVERY HP,Dell,Lenovo/IBM,Toshiba,Panasonic model they make per year.
And they all have 3 pin plugs, that are electrically grounded to the power brick.
I also thought laptops only had a 2 prong connector. then i went to look at one.
Most laptops i have seen use the "for EU plug" in this image.
Nobody has the correct adaptor so basically nobody uses earth on them.
The only time i ever found a problem with buzzing noise on the headphone out was when the laptop went into sleep mode while power supply was plugged in.
three options i see:
1) Disconnect earth and make the problem go away A short on laptop side will propably put the powersupply in safety switch off mode. You are using a dc blocker cap on your amp input?
2) if a friends charger solves the problem get a different charger
3) Only connect amp with power supply plugged out
Most laptops i have seen use the "for EU plug" in this image.
An externally hosted image should be here but it was not working when we last tested it.
Nobody has the correct adaptor so basically nobody uses earth on them.
The only time i ever found a problem with buzzing noise on the headphone out was when the laptop went into sleep mode while power supply was plugged in.
three options i see:
1) Disconnect earth and make the problem go away A short on laptop side will propably put the powersupply in safety switch off mode. You are using a dc blocker cap on your amp input?
2) if a friends charger solves the problem get a different charger
3) Only connect amp with power supply plugged out
to fit a UK socket outlet (to match a BS1363 plug top) one must open the protective shutters over the Live and Neutral receptacles.
This is done with the third prong of the plug top. But that third prong does not need to conduct, it can be all insulating.
The clue is in the cable. Is it a flattish oval with two cores, or a round cable with three cores?
Pics of the cables would be more informative, than pics of the plug tops.
This is done with the third prong of the plug top. But that third prong does not need to conduct, it can be all insulating.
The clue is in the cable. Is it a flattish oval with two cores, or a round cable with three cores?
Pics of the cables would be more informative, than pics of the plug tops.
Yes, sorry should have said. The input ground is connected to the star earth, and I have tried a ground lift in the past, athough I have taken it out.
I think it could just be that the amp doesn't agree with SMPSU's
.Chris.
I think I may have to try something radical such as a USB D/A converter (like this one Behringer UCA202 U-Control USB Audio Interface (GAK)) for use with the laptop.
Chris.
Chris.
Not much. Removing the ground shouldn't have any adverse effects, it's not a computer with exposed metal parts. Anyway, if you haven't tried yet, run the laptop on battery to confirm that the problem is within the laptop PSU.
If removing the ground doesn't work either, most likely the main filter capacitor inside the laptop's power supply has dried and needs replacement.
Buying a USB DAC won't work as they are grounded through the laptop USB port anyway (unless you hooked it up via an optical out on the laptop but it shouldn't be this difficult surely). I'm not quite sure what the deal is with laptop power supplies as I have the same problem on my 2 DIY amps but not with my comercial (Yamaha) amp and only with a laptop that has a grounded power supply. Ones with no ground work fine.
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