Hi all. I am trying out some new DAC's, and am getting a mild hum/buzz. This background noise is in both channels but it more distinct in the left channel. When I connected an old CD player, as well as a relatively new one from a friend (840C) the background is pitch black, but with the two DAC's there is that noise.

It is relatively low level but gets louders as the amp's volume knob is turned up. At normal listening levels (approx. 9 o'clock and above) it is fairly audible, especially with quiet/instrumental music. It also seems as though the left channel (the one where the hum/buzz is a little louder) is slightly lower in volume, as if there is a mild imbalance.

Anyone know what it could be and what can be done to alleviate this? Is this perhaps the dreaded ground loop hum?

Some additional info: tried different IC's and power cables; as well as a different AC outlet. Connecting to DAC using optical Toslink cable. All devices use 3-prong IEC cables.

Cheers
X

Based on what you have already checked, I'd suggest the next possibility is to eliminate ground loop. Other obvious thing to consider is any new appliances or interference nearby - might not be so obvious, perhaps something a neighbor is doing or something you've moved or altered lately? Christmas lights you've been late to take down? Many things can have an impact...

No new appliances in the house. Also, the audio gear is fed from a large medical-grade online UPS putting out a pure sinewave; and it has been like this for a few months without issue. Also, strange thing is that it is there with the DAC's but not with the CDP.

If the DACs are using external power supplies, then I would have a look at those as the source. I had that same problem so I am now using a car battery. Sound is now hum free.

HM

Thanks for the suggestion. Neither use external supplies though; they have internal trannies with an IEC inlet

Then you'll have to do some 'fault finding'.
First of all get hold of a stereo RCA plug to stereo headphone adapter. plug that into the output of each DAC, and have noting else other than the power supply connected to the DAC. Use a set of headphones to listen out for any hum from the DAC. If there is none, connected the DAC input to your source (CD player etc.). Listen again to see if you get any hum when there is no signal present. If there is still no hum, then you know that the hum comes from when you connect the DAC to to amp. Check to see if there is an earth on the mains connection to the DAC. If there is, then that is the cause of your earth loop.

I've been chasing an AC hum for a bit, too. Do you have any dimmer switches in the house? That's one of the issues I'm going to address tonight.

Hi guys. I have tried the following without luck but perhaps it can shed light onto the situation:
- connected the DAC to a different outlet. I tried three in total: a) same power strip as the amp, which is connected to the online UPS; b) different receptable which is connected to the online UPS; c) different receptable connected straight to municipal power.
- different power cables
- different IC's
- moved the equipment away from the amp and/or PC.

Some observations:
- the old Sony CDP (which I use for burn in) has zero noise when connected to the amp.
- the DAC's have a hum/noise. It is predominantly a monotonous hum; but there is intermittent noises, especially when turning the volume up or down.
- the volume of the hum/noise increases with the increase of the amp's volume.
- the noise is virtually entirely on one side (left side). When I swap the IC's around the noise moves to the right side
- I tried with the DAC connected to the amp but with nothing connected to DAC and the hum/noise persists. That is, analog IC's from DAC to amp but no digital/optical cables to DAC, no no input active.

Does the above perhaps point in one direction or another?

Cheers
X

Sounds a bit like a DAC issue....especially if it changes with volume and is only on one channel.
Am I right that you have two dacs connected (you use the plural). If so, does one hum and not the other?
The "crunchiness" in the pot is pretty standard and you may just need to clean it.

I previously tried another DAC in the system - an MHDT Havana. It also had a hum/noise in the same system (though it was much louder), also the left side and increased with volume. I sent it back as I thought it was a faulty DAC. I have now got a new, different DAC exhibiting the same issues. I thought it could mean an amp issue but with the CDP it is silent.

When you touch an exposed metal part on the DAC and/or the amp, does the hum disappear?

Let me try that - what part should I touch on the DAC/amp? (housing, rear panel, front panel)

Also, just touch with my finger?

I have read (scary) suggestions to touch with bare wire either between DAC and amp or between DAC and earth in an AC receptacle

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Hmmmmm, (no pun intended)
I think I'm chasing much the same problem. With my CDP my amp/speakers are silent, when I hook up the desktop computer/DAC, noise. Nasty amounts of noise. When I run the DAC with my laptop plugged in, noise. On the battery, nothing.
When I go home tonite I'm going to try to un plug everythong but the CPU (one at a time) then I'll try to ground the DAC (which is an inline sound card, really). I'll watch this space......

Have you tried disconnecting the UPS completely?
If not unplug it and re-power all your components without the UPS

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Could be that your computer is sending digital noise (clicking) down the line. You might want to try a different outlet, maybe even running and extention cord from another part of your residence to different outlets (to make sure the power lines are not run in series)