This seems so weird. Have to tried using just the XLR inputs and have the switch at the right to auto off instead of pass through?
I did try that, didnât help.
I ended up moving my router away from the amp, which seems to have eliminated the problem. As the router was previously right next to it, my theory is that the RCA cables were acting like antenna that amplified the RF interference. Beats me to hell why only the XLR output seemed to be affected. Perhaps it was just quieter on the SE output. Anyhow, mystery solved for the time being. Thanks all for the help!
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I am glad you solve the problem. I think your theory about RF interference is correct. I guess the XLR output is so much more sensitive the SE that it pick up the interference.
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Which shouldnât be the case as the goal of balanced is to eliminate interference lol (but thatâs mainly for the interconnects)
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LOL I think you are right. My thinking was RF interference came from RCA inputs. But if he selects balance input, the RCA input should be cut off. I am confused now.
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The thx isnât fully balanced, the signal is converted to single ended like halfway though inside
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Thank you for the info. That makes sense. So is this a short cut to make the amp more
cheaper?
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Iâm not sure if it was done for cost or because of the topology not allowing for it, so I canât comment there, but the amp is not fully balanced and is turned into single ended and then back into balanced I think. It doesnât really matter tbh, but perhaps it may have done something in this situation.
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Since its release in 2018, the Drop + THX 789 THX AAA⢠Linear Amplifier has been praised by reviewers and community members alike. Itâs hard to find a âBest Amp Below $1000â thread without a recommendation for the 789 and the incredible value it offers at $399.
Now, two years after the 789âs initial release, weâre excited to announce weâre adjusting the 789âs market position.
As of April 17, 2020, weâre adjusting the 789âs MSRP from $399 to $299.
This price adjustment is made possible via increased production size (thanks to you) and more efficient material sourcing + manufacturing optimization (thanks to our Product Realization team). At $299 MSRP, weâre excited to cement the 789 as a critical part of the Headphone community purchase progression.
Thanks for your continued support and feedback. We wouldnât be here without you.
IMO not the last word on sub $1,000 amps, but it is at a very attractive price now. Competition is a great thing sometimes.
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I think the main thing its not that it is âthe last wordâ, its that its brought up as a good choice for the value. All the THX amps that are around the same price point are a great value for the performance you get, but there is a whole world now out there under $1000 for every taste.
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I just got the 789 yesterday and have been using the Sennheiser 660s on medium gain which surprised me. Before the 789 I had (and still have) the Liquid Spark and didnât have to switch to a higher gain setting to get the 660s to what I considered to be loud or âpowered properlyâ. Does the 789 on lowest gain setting output that much less power compared to the liquid spark? Is it a placebo? Is medium gain harmful to the 660s?
The 1/4" single-ended output of the 789âs (and Monopriceâs 887) provides 0.7W RMS into 50ohms and the Liquid Spark provides 1.3W RMS into 50ohms. So, under the same load, the Liquid Spark outputs more power than the 789âs single-ended output. It is a completely different story when it comes to the 789âs 4-pin XLR âbalancedâ output.
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No gain options will be inherently âharmfulâ whatsoever. Rule of thumb is using the lowest gain setting possible while still maintaining the desired volume. Low on the 789 is meant for low impedance headphones/iems. Medium is meant for a bit harder to drive options usually 150 ohm+. High is meant for just really hard to drive 300-600 ohm. Youâll also get more power at a given gain with the balanced output as well. Think of the volume pot as the brakes in a car. Ideally you want to depend on the brakes/pot as little as possible while maintaining a proper volume. The gains are like gears in a car. You can hit the same speed in any gear, but some gears are better for a given speed. Gears=gains, speed=volume, rpm=distortion/sound quality. This appears to be the case with THX devices at the very least. Using the volume pot to control volume, cause theyâre usually on the cheaper side and just the way theyâre designed, can sound worse than better designed preamp or dac volume controls because the pot acts as a âbrakeâ for amplifiers that are designed for full power output at any given time.
Ok, so gains are irrelevant. Using a lower gain is preferable because of said volume pot behavior. Nothing will be damaged in the way you are using the outputs of the amp unless you blow up the headphones with too much volume.
In conclusion, we need better ways to control our volumes. Most volume pots suck and are cheap af.
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Thanks for the info. Yup, the volume pot my THX AAA 789 (Spring 2018) started to get scratchy (like my Magni 3), and I believe it is outside its 1-year warranty now 
This honestly raises a good question. Iâve recently gotten into custom mechanical keyboards and started using the windows 10 volume system control through my keyboard rather than touching the volume pot hearing about the THX 789âs volume pot issues. Is something like this an actual good fix or is there something iâm missing?
My understanding is the digital software volume control reduces bits when itâs below 100%. So youâre actually losing audio information by lowering the Windows system volume. There are outboard passive potentiometers that you can add to your signal chain. Schiit makes the Sys which is both a switch and potentiometer. If you need balanced, this exists. Iâm not vouching for the quality of that Polsen unit (Iâve never heard it), just letting you know such things exist.
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I saw that Zeos recommended the Magic dac as well for that purpose. Thank you I really appreciate it.
Theoretically there will always be some impact, but your not necessarily losing bits.
If the source is 16 bits and windows is mixing at 24 bits, you donât lose information until volume is as 1/256th of 100%.
If your using exclusive mode, you are losing bits immediately, since your outputting at the same bit rate as the source.
Volume attenuation is just a multiply by a number less than one, if you have bits to waste youâre not technically losing anything.
That does not mean there is no impact.
Passive volume controls are generally a better solution, I use a Creek OBH12 between my DACâs and Amps, though itâs mostly because of the switching functionality and remote volume control.
But a Schiit Sys or similar will work.
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If I were to use my geshelli labs Dac and use one of the lower voltage options then I assume that this would do the trick?
Yeah. Using a lower dac voltage or a dac with volume control will usually yield better results than using the volume pot of the headphone/speaker amp it seems. Controlling the volume with windows/foobar/Spotify etc is fine but you could potentially lose bits of info.