Massdrop x THX AAA 789

True the Sigma 11 LPS cost more than the 789. But it’s easily available. YBM Audio is a recommended builder on amb’s site. His email is

[email protected]

he’s a great guy to deal with and does excellent, honest work.

The Sigma11 makes the 789 much better but even stock my opinion is the same. Except I didn’t compare it to the ieMsgni stock so I guess that comparison should be taken with a grain of salt. Others said the two were equal in stock form. Mine spanked the ieMagni (though I’m still glad the ieMagni exists)

 

Does the Sigma11 cost just as much as a 789?

 

more. I think I paid 350$ for mine. But my 789 sounds so good with iems. I think it’s worth it if you listen to iems a lot. But of course it depends on what 350$ means to you and how much you care about something like 20-30% better sounding.

 

I definitely don’t want to try to convince people to buy a Sigma 11 LPS for the 789 for iem use. It’s a good investment if you want the best possible desktop iem rig. That’s what I wanted. Otherwise just stick with the stock 789.

 

Has anyone tried lowering the gain on the 789? It’s still uncomfortably high for CA iems. I’m barely passed zero on the volume pot at about 7 o’clock. I can’t help but think it would sound better if the pot was up around 9 o’clock at least. It would also be interesting to put a better pot on the amp.

but this maybe past the limits of this amp.

 

You might look at the THX One. It has lower gain, but it is SE only if that is a concern. I believe it should also take your S11. The HPA-4 might be your endgame IEM amp, but I thought the Pocket Class A from XRK#'s sounded better than almost anything I've heard my Andromeda on. The gain is also too high and it was battery powered.

Funch built one with built-in PS and then next think you know, XRK moved back to the DIY forum and hasn't come back. I just can't join more forums to chase down a little amplifier.

 

Slightly lower gain on THX One and lower volt from RCA inputs should be better for those CA IEMs, if you like the THX sound that is.

 

The 8.8 rear ends on Fox body Mustang is bulletproof til around 450hp. So dill the power back to 400hp and your're spanking 911's well into 2000 on the stock rear end (with a new set of gears).

 

I've upgraded from the THX 789 to a Flux FA-12 and now I can appreciate how in your face and aggressive the THX amp actually is. The 789 has a great black background for all my IEM's though.

 

My THX789 started to make VERY LOUD crispy noisy noises when adjusting the volume. I am pretty sure the volume Pot died and it keeps tripping the protection circuit. I am glad I bought a backup when it went on Sale so no biggie. Is it worth trying to get it fixed out of Warranty?

 

I would love to be wrong but Drop has no repair service of any kind. In warranty gets you a replacement. So I don’t know how you would get it fixed except an audio repair shop which I would love to know of a good one but don’t.

 

One cannot even get a stinking user guide. I was surprised it wasn't available online.

 

I don't know if anyone cares about this amp anymore, but for fun I bought two of the jameco linear regulated power supplies I was going to use with my pi2aes 1.0. At only 12 watts, some might be curious if it's enough for this amp.

I took out my kill-a-watt and measured the power draw from the wall with LCD2F on balanced at deafening volumes and it never went over 5.6 watts. Idle is around 4.8 watts. I think the jameco supply might be a good CHEAP upgrade for IEM use.

https://www.jameco.com/z/DFU240050F...le-Output-24-Volt-0-5-Amp-12-Watt_174879.html

 

IMO said Jameco linear regulated PSU above does seem to improve dynamics and background noise after some extended listening. Unfortunately, the 789 still sucks for headphone use. BA or piezo IEM's are a different story. Worthwhile upgrade for that specific use case.

 

Say hello to a naked Massdrop 789 with the crappy scratchy pot removed.



See also the circled relay. It's too close to the pot location to fit in a bigger nicer stepped attenuator. Does anyone know if I can just use wire to relocate that relay to the side without degradation to quality?

 

Yah, I'm not going to pretend like I spent a lot of time listening to the new pot, cause I didn't. Just two songs. One was Father and Son. Around the 1:30 mark the thx 789 is showing microdynamics and emotion with HD6xx's that it didn't before. This was with an Ares 2 DAC and Pi2AES source. I should point out that I also use a Jameco Linear PSU with my 789. I won't comment more than that cause I'm not done. There appears to be (not sure) missing smoothing caps on the back side of the PCB near the incoming voltage, and I'm tempted to add them if my spares from the building the crack are compatible. I wonder if the lack of filter caps has anything to do with it's slightly fatiguing sound.



So, what value caps do I throw in haha. Can I just run a voltmeter across the two points when it's on to check the voltage across the cap and then put as big a cap in Farads as I can physically fit?

 

Well the input silkscreen says 24V, so the nearest typical voltage is 25V, but for safety 35V (unless all that circuitry is a voltage doubler or rail splitter, so measuring still recommended).

But yeah, lead spacing is your limit. One thing to consider is that a large capacitor right on the output might cause some regulators to oscillate. So I wouldn't put anything huge in there unless you can put a scope on the output.