Dear builders
Uhm...
My preamp has an annoying buzz. it's not very loud (music overshadows it) but constantly there.
It is not being attenuated (level is constant).
I disappears when I unplug the only input, a USB-dac.
swapping the dac doesn't change, I use a halide DAC HD (usb-powered) or a furutech ADL gt-40, more a preamp than just a dac)
Am I describing a ground-loop?
Many thanks!
Uhm...
My preamp has an annoying buzz. it's not very loud (music overshadows it) but constantly there.
It is not being attenuated (level is constant).
I disappears when I unplug the only input, a USB-dac.
swapping the dac doesn't change, I use a halide DAC HD (usb-powered) or a furutech ADL gt-40, more a preamp than just a dac)
Am I describing a ground-loop?
Many thanks!
Sounds like an earth loop, which means that when the USB input is plugged in the connection joins two grounds together. Most likely the USB source is grounded through its power, and the supply for your preamp is also grounded through the power. When the two are connected together current flows from one noisy ground to the other. Of course current cannot flow without voltage drop. Due to the layout of your system the preamp is amplifying the noise voltage generated by the ground current, because the circuit has no way of knowing what is noise and what is desired signal.
Thanks John.
In the preamp (Wayne’s line stage), I installed a cl60 as groundloopbreak already, as has been recommended in various builds here…
Naresh, I use a Mac mini, which hasn‘t a brick-amps (wether there‘s an amps inside, I don‘t know)
How would I adjust then filter a DAC‘s output?
It is quite possible that even though the power supply to the mac mini is not earthed, some other item plugged in to the mac mini is, and thus causes the an earth loop.
The diagnostic prcedure is to start with nothing but the preamp and headphones connected, i.e. not even the USB connection. Is that clean? If yes connect the USB to the mac mini but without anything else connected to the mac mini. Is it still clean? If yes start to connect the other items to the mac mini, checking for buzz as each one is connected.
The diagnostic prcedure is to start with nothing but the preamp and headphones connected, i.e. not even the USB connection. Is that clean? If yes connect the USB to the mac mini but without anything else connected to the mac mini. Is it still clean? If yes start to connect the other items to the mac mini, checking for buzz as each one is connected.
Where gets the USB the power from? Wall outlet? Plug three pin or two pin? if two pin reverse the power plug.
swapping the dac doesn't change, I use a halide DAC HD (usb-powered) or a furutech ADL gt-40, more a preamp than just a dac)
I think yes.
Yeah, your welcome..
If you can power up that USB using Batteries, and it still makes noise, then it's not a ground loop.
Then remove the ground on the inside of the PREAMP of that DAC input.. If this helps then you find the reason, so make a connection which does not buzz. Sometimes too much GND is too much..
Turn Volume control to left. and check for that buzz..
Hope I could help somehow..
Regards
U na schöne erschte August. (für a räschte)
Hi hpro and all
Today, when I finally got back to the atelier, I swapped the ACA with the big boy F4.
Guess what: no buzz, no hum.
This leaves me a bit puzzled, since it (the buzz) seems to come from the Mac mini/usb-dac (buzz coming from preamp when either dac is connected)…
This is fun but strange. At least to me…
Today, when I finally got back to the atelier, I swapped the ACA with the big boy F4.
Guess what: no buzz, no hum.
This leaves me a bit puzzled, since it (the buzz) seems to come from the Mac mini/usb-dac (buzz coming from preamp when either dac is connected)…
This is fun but strange. At least to me…
Earth loop induced sometimes noise seems like black magic, but the reality is that currents flowing in ground conductors obey Ohm's Law, even though many circuit designers and manufacturers seem to disregard that fact.
The ACA probably has a different input impedance that provides an easy path to ground through the ACA. This is in fact as you say not an issue with the ACA but with the equipment driving it. The ACA gave you the right environment to reveal this issue that was being masked. Whether the sound is better with the loop gone even if you couldn't hear? Can't say; but I can say that having no hidden surprises is a good habit of the craft! Ignoring it will bite you in the *** one day. 
Think of:
Very true! It's easy to forget where all the grounds run and that is why you should use the same circuit for these things.
Think of:
- Video output
- Ethernet
- USB devices that are connected
- Capacitive coupling for big metal things
- Physically touching an earthed thing
- DC offset on something causing current flow
- Anything connected, in theory
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USB has two or more paths for ground, mainly the shield and the power ground.
Edit: try this - plug your usb dac into a powerbank and then into the ACA, no sound playing is needed. If the humming goes, it is related to the power or the connection between the pc and the dac.
I solve this literally by leaving the DAC connected to an external linear supply (though smps would do fine, just no downside to this for me) and the signal lines to the computer that has a root hub using a new chipset. This technically is against the usb spec as the power is there before the negotiation but newer root hubs handle this just fine - it can confuse some older ones though, but we are talking many years old by then.
It is essentially one USB B connector connected to two USB A ends where one only carries Differential Pairs signal (Green-White) and GND and the other one only VCC and GND. I loop the DAC through my DSP box which acts as the power supply for the DAC and then forwards the signal. I have it this way because of future plans unrelated to this power thing.
My primary use for having it completely separate from the computer is so that in the event I forget to shut off the amps, my speakers dont get the huge pop the UMC204HD has. But the spirit is the same.
Attached image is how my situation is, to make it clear that the DSP box does not do anything else than act as a junction box
Edit: try this - plug your usb dac into a powerbank and then into the ACA, no sound playing is needed. If the humming goes, it is related to the power or the connection between the pc and the dac.
I solve this literally by leaving the DAC connected to an external linear supply (though smps would do fine, just no downside to this for me) and the signal lines to the computer that has a root hub using a new chipset. This technically is against the usb spec as the power is there before the negotiation but newer root hubs handle this just fine - it can confuse some older ones though, but we are talking many years old by then.
It is essentially one USB B connector connected to two USB A ends where one only carries Differential Pairs signal (Green-White) and GND and the other one only VCC and GND. I loop the DAC through my DSP box which acts as the power supply for the DAC and then forwards the signal. I have it this way because of future plans unrelated to this power thing.
My primary use for having it completely separate from the computer is so that in the event I forget to shut off the amps, my speakers dont get the huge pop the UMC204HD has. But the spirit is the same.
Attached image is how my situation is, to make it clear that the DSP box does not do anything else than act as a junction box
Attachments
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