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rajapruk
194
Sep 23, 2018
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For the cabling in my system to be good, I would like an output on the backside of the unit, like this:
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Maybe I can mod the chassis like this. We will see :)
Sep 23, 2018
BurritoJustice
82
Sep 24, 2018
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This would honestly be a godsend, it is unlikely for there to be a change this late however. Plus, they wouldn't mind if you upgraded to the THX-888 HPA4 ($3000) which features XLR passthrough and line-control :D
Sep 24, 2018
rajapruk
194
Sep 24, 2018
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I will not downgrade to something with a ugly screen on it!
Sep 24, 2018
Hi rajapruk. Nice mod proposal! It's too late to implement at the factory right now. However there's plenty of space to add your XLR-4 panel jack where you propose on the rear panel. There aren't any internal conflicts there, except the PCB itself which is fairly low down. Get your tools warmed up :)
Sep 27, 2018
BurritoJustice
82
Sep 27, 2018
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Could you add a bit more detail to the modding required ? Preferably it would be variable lineout for powered monitors using the 789 as a preamp. I am considering a HPA just for this Though obviously not a huge deal as I can just put an externals tepped attenuator in line
Sep 27, 2018
I was thinking @Rajapruk could drill a hole and panel-mount an XLR-4. Then internally use two twisted pair 20 AWG to wire it 1:1 (parallel) with the front panel XLR-4. For you, assuming you want a stereo balanced lineout... there's not enough space to add two XLR-3 outputs on the rear panel. Instead consider using a single custom XLR-5 (e.g. L+, L-, R+, R-, GND). Neutrik makes 5-pin XLRs. Or use two smaller 3-pin connectors. The point is you want a ground connection in there to tie the 789 to the external equipment ground. If you just want RCA L/R outputs, there's plenty of room for that on the rear panel.
Sep 27, 2018
BurritoJustice
82
Sep 28, 2018
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Thanks for your response, I love the 5 pin XLR idea and can source those parts locally. Where should it be wired internally to work as a "passthrough" like the RCA (line-output) and therefore before the amp stage? Additionally, would it be possible to wire it such that it acts as a preamp and the amp volume control controls the output level? I am guessing the answer to the second question is "no" without heavy modification.
I have sourced an external stepped attenuator to work with line-level out of the 789 so I'd love to be able to get passthrough capability.
Sep 28, 2018
Again, this is warranty-voiding off-script stuff... Massdrop and THX are not responsible if following or misinterpreting anything here leads to a damaged unit. Consider wiring your 5 pin XLR internally to the front panel's XLR-4 (4 pins) and to ground (1 pin). It'll be variable output... basically the output of the power amp, routed to the 5-pin XLR. If you want pass-through dual XLR-3 instead, then skip the mods and just buy some XLR y-splitter cables.
Sep 28, 2018
BurritoJustice
82
Sep 28, 2018
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Will using a straight XLR splitter make an appreciable difference to SNR/THD/anything?
Also I'm using pro gear, am I correct in that +19dBu is the clipping point for this amp (standard gain)? Is there any objective difference between the the unbalanced signal or is it treated identically internally? Just trying to decide how to best combine my RME ADI-2 Pro with this to run the 789 at line level and the monitor outs at variable level. There are TS and XLR outputs on the back but they are locked to the same signal so I can't have one be variable and one be line.
Super pumped to hopefully make one of the cleanest and most linear headphone amp setups available.
Edit: I should note, your active participation in the discussion of this product (even outside of specific guidlines) is fantastic and definitely makes me trust THX as a company going forward.
Sep 28, 2018
XLR splitter has 2 similar gotchas, but is otherwise fine 1) un-powered equipment can cause ESD diode clamping on the XLR signals, clipping them for everything that's connected. To workaround, just keep your 789 and your powered monitors both ON whenever listening to either. Or replace the XLR splitter with external XLR 2:1 selector box. 2) Even when powered, 789 input diode clamps will start to clip the INPUT signal on the XLR inputs around +20.5 dBu. So if you're using Y splitter and trying to route +24 dBu to your monitors while the 789 is connected, the 789 presence on the cable can start clipping the input signal to your monitors. Glad to discuss this! Hopefully you get your unit soon. Enjoy, and good luck with the setup/mods!
Sep 28, 2018
AndyMok
34
Sep 29, 2018
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Will you guys do mods w/ additional charge? I don't mind getting mine a bit later XD
Sep 29, 2018
Maybe there's an enterprising community member who can do these mods?
Sep 29, 2018
BurritoJustice
82
Sep 30, 2018
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How much space is there free in the chassis for modification? If I was to add the XLR5 on the back I'd also add an automatic mute relay (when the front outputs are in use). Another option I've thought of is replacing the third gain option (which I see as superfluous for an amp of this capacity) with a preamp option that toggles to rear output. If there is room I'd love to cram a (relay) stepped attenuator in there as well. I believe the THX AAA platform is at the forefront of the market so I'd be nice to get some of the added functionality out of the HPA4 alongside the class topping performance and price of this unit.
Sep 30, 2018
AndyMok
34
Sep 30, 2018
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On boy this is getting more and more interesting. If there's a new iteration in future I hope we get an option to send it back for an upgrade/mod
Sep 30, 2018
rajapruk
194
Oct 13, 2018
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Which connector is used on the front, is it this one? https://www.neutrik.com/en/product/nc4fah-0 I would want to use the exact same model the rear, if I do it.
Oct 13, 2018
pospos
70
Oct 15, 2018
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Why don't you use speakon for your application (compression driver connections)? That would let you use ready-made 4-way speakon cables.
Oct 15, 2018
Hi rajapruk. Yes front XLR-4 is a clone of NC4FAH-0 with same dimensions. For rear you'll want the vertical type so the pins remain above the PCB. Consider Neutrik NC4FAV-0.
Oct 15, 2018
rajapruk
194
Oct 15, 2018
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Yes, it would be best for my application. I wonder if speakon size fits though? 1 Speakon-4 output of the THX-amp into 1 Speakon-4 input into my top-speaker would be nice, only needing one speaker-cable for both UHF and HF. But it is maybe not optimal for crosstalk reasons? (right now I have dual Speakon-2 inputs on my DIY speaker top enclosure, and single Speakon-2 on each of my woofer enclosures).
Oct 15, 2018
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