Massdrop x THX AAA 789

Thought I would update my impressions of this amp after almost two years and upgrading my source (Modi MB to Bifrost 2) and dynamic headphones (HD650, which I still have, but much more headtime for HD800S these days).

I stand by my comments about the cleanliness of the sound and the detail present, but the THX is definitely an inferior pairing with the HD800S, being somewhat bright and strident at times even when coming from Bifrost 2. That led me to purchase a used ZDT Jr. and the improvements on the Sennheisers were obvious: the THX projects a wide-but-ultimately-flat stage compared to the narrower-but-holographic staging of ZDT Jr.; the THX is like watching a HD broadcast of a concert while the ZDT Jr. is like sitting in the auditorium. The tube flavor of ZDT Jr. also greatly compliments HD800S, enriching the sound and making it organic instead of brittle. The THX does still have better extension at both ends, driving my ZMF Ori with a touch more authority than the ZDT Jr. when I want to listen to bass-heavy genres, especially when using the balanced output.

Originally I was considering downsizing my collection to just the HD800S and ZDT Jr. from the Bifrost 2, but I think the THX still has a place in my setup -- Bifrost 2 single-ended output to ZDT Jr. and the Senns, balanced XLR output to THX balanced input to drive the ZMF; also my TV setup runs RCA into THX single-ended for late-night viewing to avoid waking my neighbors. Keeping both amps allows me to keep all sources hooked up at all times in their synergistic pairings.

I still would like to get one of Zach's dynamics one of these days, and at that time I may re-evaluate holding onto the THX. But, for now, the music must flow...

 

I’m getting an intermittent low pitch buzz from what seems to be my 789 amp. Not a hiss or static sound, a real electric sounding buzz like a guitar amp can make when - well I’m not sure when but maybe when the guitar is unplugged? I’ve heard a similar sound from an electric guitar amp anyways.

I comes and goes and I have no idea what could be the culprit. Interestingly adding the Schiit Loki before the 789 made it worse. Before the Loki I’d get little blips of the sound sometimes like interference, usually coming multiple in a row and then nothing for a long time. Adding the Loki turned it into a constant buzz instead of blips but then sometimes it’s gone for long periods. Also when it’s there, if I flip the Loki’s bypass switch the noise goes away completely.

I know it’s related to the 789 because once when it was happening I switched to my lcx which is plugged into the same switcher and DAC and the noise wasn’t there.

my power should be pretty good it was all redone in this room ten years ago and each outlet goes straight to the street so I can plug in a lot of shit without worry.

All my amps/DACs are plugged into one power strip which goes to one power outlet.

I’ve switched out all my interconnects and it has not changed.

any ideas? Thanks!

 

I wonder if this noise could be caused by the power cord/supply. I’ve replaced everything else. Is there a better power cable and power supply I could get that would fit the 789?

 

What you described sounds like the 60 Hz hum. For example, when your fridge start to chill, it emits noise both in the power outlet and in EMF. Your system could pick up noise either way. Changing the power supply may not help much, since SMPS typically don't have 60Hz hum, but cheap ones can still have it... if you really want, you can try to add atomicbob's SMPS nuke. Or a power conditioner like this.

Before buying or making those, you may want to check if the noise is in the signal cable. Try use shorter or balanced cable if you have those on hand. Or untangle the cables, and try to make them as straight as possible, which should reduce noise pick up. The noise could be from the switcher too, so maybe try different output ports. On a side note, try those without Loki. Loki is an active device, which would add noise in its nature. If the noise still persists, then it's reasonable to do those power supply upgrades.

 

Mine does this sometimes too. In my case it seems to come through my DAC which is connected with USB.
It seems to do this when using the XLR output. I have now been using the single ended output and no strange sounds. Worth a try?

 

Thanks for the reply. I’ve ruled out all those. New very good interconnects, only 1.5 ft, the lcx doesn’t make this noise and it’s plugged into the same switcher. The noise was there before I got the Loki, it just changed and got worse with the Loki.

I can’t make that Atomicbob SMPS nuke wish I could. Is the Furman power conditioner really good enough? It seems very cheap compared to every other power conditioner I’ve seen.

how about this, plugged into the wall before the power strip?

https://www.amazon.com/iPurifier-Eliminator-Conditioner-Isolator-Professional/dp/B07835J8XF

then there’s this but it’s f'ing expensive and the outlets are oriented in the wrong direction so a big plug will cover half the outlets.

https://www.amazon.com/iFi-Power-Station-Conditioner-Protector/dp/B07TB9VPWC

 

A series of blips reminds me of when cell phones and other devices would cause my old computer speakers to beep when there was an incoming call or text. This was over a decade ago when things weren't properly shielded and cables or amps were picking up the interference.

 

I browsed a post in ASR, JohnYang has dived deep into this issue. It looks like the noise does come from the SMPS. If that's the case, the Furman and iFi power conditioner wouldn't help much here. Though I've used the Furman one to make my speakers hiss less, they are targeted at fixing ground loops. SMPS still generates noise when fed with clean AC, and they aren't grounded via the outlet. Definitely don't buy the $499 mains bar for THX 789... Directly upgrade the amp makes more sense. If I have time, I can build a state of the art 24 V power supply that absolutely shreds THX 789.

Thus the choice boils down to upgrading the power supply. The Jay's Audio Talema LPS 24V seems decent. There are also plenty of linear power supplies on eBay, but I have no idea how well most of them regulates. (I know there's a good one based on Ti Kan's σ11 design, but purchasing it is supporting plagiarism...) To be honest, atomicbob's SMPS Nuke seems the most effective and bang for the buck. I get it's a headache to make it, because I'm trying to make one for my DIY amp. I collected all the parts months ago, yet drilling steel with a hand drill is the last thing I want to do. I could build one for you, but I don't know when will I conquer my fear of drilling steel. Maybe some of the members here with proper tools can build you one, or they may have extra ones to give away.

 

Thanks for finding this!!!! Finally an answer! It never occurred to me to google it because I assumed there wasn’t such a bad issue with the amp in general. The noise is very bad on mine. Totally unacceptable for a commercial product. I bought a new 789 thinking this one must be broken and they were on sale.

At least I have a solution now. Ahhhhhhh relief!

 

It's ironic that the answer was on ASR, where a Topping representative heavily researched the competition (THX AAA)'s flaws lol. Good on you for sharing @cameng318

 

A couple years ago, I was in the same group chat with JohnYang. (We are the same age, and our hometowns are pretty close) He's actually a pretty cool dude to talk about technicalities. I learned about the IEM world pretty much exclusively from him. I would have been on the same boat with him if I were more fascinated with IEM like he is, but my fascination with full size headphones and bookshelf speakers steered me away. He's a voodoo at modding IEM and 0.000000x amps. Anyway, we both suffer from the young man's curse pretty badly. When we encountered people opposite opinions, I just shut down after a couple of words, because I hadn't figure out how to work with my 97% introvertion; he would turn into a assault riffle (or insult riffle at times) and give people a whole bunch of suggestion to reduce noise and distortion until they are totally pissed off. In the end when we get much more seasoned, I think he'd be a cool folk to hang out with.

 

Does anyone know these for the 789? And if it’s the same for the LCX?

• Current requirement

• Type of DC plug (DC barrel type, but I need the inner and outer diameters)

thanks!

 

THX need 24v/1.8A and LCX need 30v/1.25A

 

awesome thanks! Anyone know the dimensions of the power plug that goes into the amps?

 

The Jays audio one is identical to this LPS on aliexpress, which is from it's mother company LHY.
https://www.aliexpress.com/item/32811516916.html
Now we see the kind of mark up of chi-fi products in overseas market.
btw I suspect 25VA will probably not be enough?

5521 per massdrop discussions.

 

25 VA on a linear power supply should be well more than enough for the 789 unless you try to drive a speaker or max volume max gain on something like Verum One. I'd be hard impressed if it draws more than 100 mA when driving normal headphone loads, since it's a chip based design. Thus 5 VA clean power should be enough for it.

 

I’m having a Sigma 11 linear power supply made for my 789. should clean up this noise and improve the sound hopefully! Going all out!

Does anyone know the polarity of the DC plug? Positive on the inside or outside?

 

99.9% sure it's just standard polarity and not inverted.