Review and Measurements of Massdrop THX AAA 789 Amp

[Jimster480]

Seems like after 3 years, one of my THX 789 capacitors is swelling up and needs replacement. Any idea what is the part number I can use to reorder them? I know it's Rubycon.

Also, the pot seemed to be quite scrathy and was making noises so I put in some WD40 only to find it shouldn't be used . Any idea if the pot can be fixed at all or cleaned?

Thanks

Wew, I might have to open mine up too and check it. I've had it since the first ever batch and use it all the time.

 

[dinglehoser]

Seems like after 3 years, one of my THX 789 capacitors is swelling up and needs replacement. Any idea what is the part number I can use to reorder them? I know it's Rubycon.

Also, the pot seemed to be quite scrathy and was making noises so I put in some WD40 only to find it shouldn't be used . Any idea if the pot can be fixed at all or cleaned?

Thanks

A good dollop of electronics cleaner (to dissolve the WD-40), followed by some Deoxit D (to deoxidize the wiper/element), then Deoxit F (to lube up the same), has worked well for me under similar circumstances.

 

[Dana reed]

A good dollop of electronics cleaner (to dissolve the WD-40), followed by some Deoxit D (to deoxidize the wiper/element), then Deoxit F (to lube up the same), has worked well for me under similar circumstances.

I should give that a try. My 789 hasn't had any scratchy sound, but my Schiit Hel at my work desk has gotten scratchy over time, and maybe cleaning the pot will help.

 

[dsnyder0cnn]

It should be this.
16PX3300MEFCG412.5X20

16PX3300MEFCG412.5X20 Rubycon | Capacitors | DigiKey

Order today, ships today. 16PX3300MEFCG412.5X20 – 3300 µF 16 V Aluminum Electrolytic Capacitors Radial, Can 2000 Hrs @ 105°C from Rubycon. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

Bummer. It's back up to $299, but if something like that happened to mine, I would just purchase a replacement…or save up a bit for the Topping A90 instead.

Drop + THX AAA™ 789 Linear Amplifier | Audiophile Amp

The Drop + THX AAA™ 789 is a linear amplifier. It features THX AAA and feed-forward topology, which reduces distortion by 20 to 40 dB for fatigue-free listening

drop.com

 

[f78fk]

Bummer. It's back up to $299, but if something like that happened to mine, I would just purchase a replacement…or save up a bit for the Topping A90 instead.

Drop + THX AAA™ 789 Linear Amplifier | Audiophile Amp

The Drop + THX AAA™ 789 is a linear amplifier. It features THX AAA and feed-forward topology, which reduces distortion by 20 to 40 dB for fatigue-free listening

drop.com

My drop AAA 789 has been received for 20 days. It sounds very clean. I like it very much and bought a better power supply gst60a24-p1j-24v for it.

 

[Shoaibexpert]

It should be this.
16PX3300MEFCG412.5X20

16PX3300MEFCG412.5X20 Rubycon | Capacitors | DigiKey

Order today, ships today. 16PX3300MEFCG412.5X20 – 3300 µF 16 V Aluminum Electrolytic Capacitors Radial, Can 2000 Hrs @ 105°C from Rubycon. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

Thanks. I have given my 789 to a repair shops locally who is replacing both caps. The thing is I have a LPSU with 24 V and in my experience it seems to give an extra bit of oomph to the lower end with my HD800S that is very pleasing. If I were to change the amp, I'd need to get another LPS unless it has a torroidal transformer inside...which I am not sure which of these Chinese models have...not to mention...the repair costs $50 and the new unit some 3-400 more...

 

[John B]

What LPSU are you using? Curious about this tweak myself and had an eye on the Ifi 24v a while back but never got deep into evaluating these things.

 

[Shoaibexpert]

What LPSU are you using? Curious about this tweak myself and had an eye on the Ifi 24v a while back but never got deep into evaluating these things.

It's a BRZ hifi Chinese LPS, 24V/80W into the 789. Really works well...unless that's what caused the caps to swell up...

 

[trl]

The thing is I have a LPSU with 24 V and in my experience it seems to give an extra bit of oomph to the lower end with my HD800S that is very pleasing.

It might be all in your head, please check Amir's measurements from the first page. Also, the PSU itself cannot alter the bass in any way, unless we're talking about undersized PSU driving really power-hungry headphones at insane levels (not your case), case where THD increases with undersized PSU.

However, feel free to measure the output from your headphones with the original PSU vs. the LPSU and post here results and measurement conditions. Thanks!

 

[John B]

Curious if a benefit could come from running the higher available amperage more than “clean” power from these things? That check out or also iffy because the components only draw down what they need and that amount is tightly ranged?

 

[zepplock]

What LPSU are you using? Curious about this tweak myself and had an eye on the Ifi 24v a while back but never got deep into evaluating these things.

it's highly unlikely different PS will make a difference. Unless someone measures it and it shows better. 789 can power even most hungry headphones, no reason for different PS to make a difference.

 

[Veri]

it's highly unlikely different PS will make a difference. Unless someone measures it and it shows better. 789 can power even most hungry headphones, no reason for different PS to make a difference.

Yup. Not to mention
-the base supply is a well regulated one, think medical grade
-amir's dashboards show ZERO mains noise

 

[John B]

But what of the increase in amperage? To be clear I have no idea how this works and my power supply knowledge is limited to these tutorials.

 

[axtran]

But what of the increase in amperage? To be clear I have no idea how this works and my power supply knowledge is limited to these tutorials.

As long as you have adequate amperage, it isn't a problem. You can go above as much as you'd like to abuse your wallet

Without enough, you can't drive the amp and it'll just not really work.

 

[Dunring]

Quick question here. I have a THX AAA 789 and a pair of OG HD800s which came with unbalanced cable. I see a great deal more power is available through the balanced outputs than the unbalanced, and I'm wondering if I could tap into that by simply using a balanced to unbalanced cable adaptor or whether I would have to buy an actual 4 pin XLR balanced HD800 headphone cable which is obviously quite expensive. Sennheiser is selling its cable for $375 which is more expensive than this amp which as we know has been priced as low as $200.

I've had great luck with several Hart Cables on different Sennheiser models, they cost less than stock and sound great. Also for a real bargain Youkamoo sells them for $42 on Amazon. I've gotten them for the Hifiman to go balanced also and they sound terrific, even on my THX 789 or SMSL SP200 they can handle the power. Factory German anything is going to be way too expensive. The Neomusic and Fantasia is crap though, wires way too thin to handle anything serious. Like was mentioned, an adapter won't work. I have a set of Youkamoo XLR coming Friday for the Sundara, and an XLR to 4.4mm adapter they make for the Sennheiser 660s. Your probably not going to notice the difference though, as you can see from my profile picture, I already tried both and the THX 789 is plenty to power 300ohm headphones like those. The only time I ran out of volume wheel is with the Beyerdynamic DT880 and 990 600ohm, and ONLY when using an Autoeq profile that did a -7.1db preamp reduction, then it was struggling. I'm only getting the balanced stuff to do a bundle for selling them, got a bunch of Amazon gift cards so I grabbed some XLR things. The only difference will be where the volume wheel gets turned to.

 

[mugbot]

I have Hart cables for my HD650 and DCA Aeon 2 Noire's and could not be happier. The interconnects are really handy if you have a variety of amps as the connectors on the cups are pretty fiddly.

 

[John B]

I snagged a beefier linear power supply, mainly because it looked cool. I couldn’t reliably tell the difference on a quick A/B but it did seem to impact tonality. Things seemed more full - but with the qualification that moving my jaw under my headphone changed the sound about as much, so very small changes indeed. Maybe my caps are on their last legs and benefitted from the juice, or placebo effect is working its expensive magic.

 

[jony_m]

$199 again on drop.

 

[hwshi]

Hi all, yowzah just finished reading this thread from the start. So much information and terms go right over my head but what a relief to read straightforward and very advanced advice without all the snake oil involved on most audio sites.
So I turn to you with my very noob questions and confident it won't be littered with suggestions of wood blocks, insane cables, need to spend x amount etc....
I jumped on the Drop deals yesterday before they expired for the Sennheiser hd6xx headphones and THX 789 (179+199!) as they seemed like a great deal and a solid starting/end point in high quality headphones and amplification.

However now that I am doing my research I don't really see much info on how I am planning to use them in my audio system. I am running a 2 channel/vinyl/tape/streaming setup in my living room. I wanted the headphones for when I can't be using my speakers at night or mornings. My Amplifier is a Yamaha a-s801 and I was planning on running RCA from one of the line outs to the THX 789 and using that to power my headphones and bypassing the headphone jack on the Yamaha but leveraging it's built in DAC. Is there an issue I am missing with this setup? I ask because I've not read of anyone using it in this manner?
Secondly I am on my laptop usually and depending on where I am sitting it can be more convenient to use the headphones directly into my laptop rather than a long cable to the Stereo system. Would I be able to use the THX without a dac in that situation ,headphone jack out> THX>headphones ? Or just plug the headphones straight into the laptop and just not have much power to feed them?
I realize this should of been figured out before the purchase but I got it in me that I wanted to up my headphone game and it turns out 2 of the most highly recommended parts of the chain were on sale , so I jumped on them.
Thanks.

 

[mugbot]

Hi all, yowzah just finished reading this thread from the start. So much information and terms go right over my head but what a relief to read straightforward and very advanced advice without all the snake oil involved on most audio sites.
So I turn to you with my very noob questions and confident it won't be littered with suggestions of wood blocks, insane cables, need to spend x amount etc....
I jumped on the Drop deals yesterday before they expired for the Sennheiser hd6xx headphones and THX 789 (179+199!) as they seemed like a great deal and a solid starting/end point in high quality headphones and amplification.

However now that I am doing my research I don't really see much info on how I am planning to use them in my audio system. I am running a 2 channel/vinyl/tape/streaming setup in my living room. I wanted the headphones for when I can't be using my speakers at night or mornings. My Amplifier is a Yamaha a-s801 and I was planning on running RCA from one of the line outs to the THX 789 and using that to power my headphones and bypassing the headphone jack on the Yamaha but leveraging it's built in DAC. Is there an issue I am missing with this setup? I ask because I've not read of anyone using it in this manner?
Secondly I am on my laptop usually and depending on where I am sitting it can be more convenient to use the headphones directly into my laptop rather than a long cable to the Stereo system. Would I be able to use the THX without a dac in that situation ,headphone jack out> THX>headphones ? Or just plug the headphones straight into the laptop and just not have much power to feed them?
I realize this should of been figured out before the purchase but I got it in me that I wanted to up my headphone game and it turns out 2 of the most highly recommended parts of the chain were on sale , so I jumped on them.
Thanks.

Line out from your Yamaha would work fine.

From your laptop this will also work though as you are essentially using the small amp in the laptop in series with the thx there can be a small impact on dynamic range. I doubt you would be able to hear it though.