Emotiva DC-1 grounding mod - diyAudio
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Old 25th June 2015, 10:41 PM   #1
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Default Emotiva DC-1 grounding mod

Hello,

I have recently purchased an emotiva DC-1 dac/amp/preamp and when used with the headphones I bought it for there is a quiet hum audible - from what I can tell it is somewhere in the -90dBFS range or so. I'm sure with most headphones this is no issue, but I am employing it to drive in-ear monitors rated at 118dB/mW and 22Ohm impedance at 1k with wild variation across 20-20kHz due to the use of 6 balanced armatures in each ear.

From what I can tell, all competing products exhibit similar issues, my phone does not nor does the Objective 2 amp I built.

My listening level is about -50dB on the attenuator or so which provides a volume level somewhere in the 60-75dB range. The hum is equivalent to roughly -80 to -85dB playback but it is tough to tell. It is loud enough to seriously intrude on quiet passages.

I would like to modify the DC-1 to remove this, but I lack the knowledge to do so ideally myself. The hum is made up of a 60Hz tone as well as odd harmonics at greatly reduced volume, so it is certainly a ground issue. I have read from some sources e.g these two:

Basic Troubleshooting for Headphone Amplifiers

NwAvGuy: QRV09 DIY Headphone Amp

that adding resistance to the feedback loop can help resolve this. I especially trust Nwavguy since he designed the O2 which has a truly "black background," though I hate to use such subjectivist terms.

I would be okay with any modification that reduces output level since the unit already has massive headroom with my use cases anyway, but adding resistors to the output directly will unfavorably increase output impedance. I also need to locate if the hum comes from the voltage gain stage, or the output buffers. It could also come from the wire attaching to the headphone outputs, as that appears to run quite close to the large transformer.

Here is a top down view of the unit: https://emotiva.com/sites/default/fi...?itok=P0HzjYRs
Any help with this matter would be greatly appreciated.

Last edited by AiryDiscus; 26th June 2015 at 06:25 PM.
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Old 26th June 2015, 08:48 PM   #2
AndrewT is offline AndrewT  Scotland
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can you measure the output noise?
A DMM set to 199.9Vac will measure down to 0.1mVac over a restricted frequency range.
When it reads 0.0mVac, it means less than 0.05mVac
That is just about inaudible over headphones. Your level must be higher.
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Old 27th June 2015, 07:59 PM   #3
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Unfortunately I don't have access to a multimeter until early august - until then I would like to just gather as much information as possible.
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Old 28th June 2015, 08:20 AM   #4
AndrewT is offline AndrewT  Scotland
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Post2:
missed an "m" from the voltage setting.
It should read set to 199.9mVac, allowing measurements of hum and noise down to 0.1mVac.

Hold off doing any mods until you can measure the before and after output noise.
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