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egglizhen
41
Dec 5, 2018
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Hi fellows, Just joined the drop. Hoping this amp can feed my Elex and HE4XX well. I am hoping to connect my A&K SE100 to the THX 789 via 2.5mm balanced line-out. First I thought all I need is a 2.5 mm male to dual XLR-3 cable. Something like this:
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But then I read an article from Moon Audio suggesting that :"The grounding scheme of portable players have virtual grounds since they can't be tied to an earth ground. When you connect a DAP to a 2 channel stereo system with a true earth ground, some problems can occur...Just doing a 2.5mm TRRS connector to XLRs can often result in a hum issue." Basically they say in order to avoid such humming issue, a A&K PEE11 balanced adapter is needed. Like this:
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They claimed that "The ground from the 3.5mm is used to tie the ground of the Astell & Kern to the ground plane of the preamp. Just doing a 2.5mm TRRS connector to XLRs can often result in a hum issue. Why? There is no ground plane thus why it causes a grounding issue which results in the hum." Has any one used SE100 or any other DAP's 2.5mm balanced out to a desktop amp? Do I really need the balanced adapter to avoid the humming issue? I am pretty new to the amp world. Any comment is greatly appreciated.  Thanks a lot!!!
Dec 5, 2018
Hi @egglizhen Yes there is potential issue that Moon/A&K points out correctly. The 4-pin TRRS doesn't have a ground and was never really intended for balanced audio between equipment as I understand it. So you can end up with massive common mode noise - usually 60 Hz - injecting to your body/player/cable and not being fully rejected by an amplifier input stage, and showing up as hum. You can modify what you have to make your own adapter. I did it myself for a quick demo I had to put together using an A&K player, and it works: Buy your own 3.5mm plug, and connect 2 wires to it's "S" shield part. Leave its Tip and Ring unconnected. Weave/bundle the 2 wires alongside your 4 white wires and connect one each inside of your XLR-3 connectors to pins 1. Don't disturb any existing white wires connections. Then, just like the adapter does, plug both the 2.5mm TRRS and your new 3.5mm TRS into the A&K. It'll pick up ground from your new wires via the 3.5mm sleeve. You've just succeeded in getting balanced audio to your 789!
Dec 6, 2018
egglizhen
41
Dec 6, 2018
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Hey Andrew. Thanks for the explanation~ Much appreciated!! The DIY adapter sounds fairly complicated to me (lol), but I will give it a try with some help from my friends studying EE. Again, THANKS A LOT!!
Dec 6, 2018
mesaone
84
Dec 6, 2018
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Good find. Wish they'd include a pinout image, but the description seems to match what's required. Prices seem more sane than some customs, as well. Thinking about buying an XLR4-to-2x3.5mm TRS cable as a backup, since the canare starquad I have on hand is too thick for a comfortable headphone cable.
Dec 6, 2018
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