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Review and Measurements of Massdrop THX AAA 789 Amp

odyo

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Oct 30, 2019
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Gain is very different from power. You can have a 10mW amplifier set with 40db or 60db gain. Yet it's less powerful.
Oh that's interesting. So AE5 outputs more db's with a less power 33ohm: 330mW. THX 33ohm: 1.3W.
I'm going back and forth i noticed some differences but it's not volume matched. AE5 sounds more visceral, thumpy and closer. E30+789 combo sounds more open, distant, less fatiguing, deeper soundstage. I'm getting the feeling of better resolution in the mids and highs but bass is lacking a bit.
 

Marakas

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I have an interesting issue. I have three amps - Stax SRM-353x, Jotunheim R, and the THX 789 - for different types of headphones. I would like to have all three plugged in to my DAC at all times, so I don't have to switch the cables around when listening to different headphones.

So I bought four XLR splitter cables and wired everything up. Since the amp inputs are high-impedance, I figured this would work, and it mostly does. Except, when I'm listening to either the Stax or the Jotunheim and the THX is off, the sound coming from the Stax or Jotunheim is severely distorted. I have to unplug the splitter cable from the THX to make it listenable.

However, I discovered that if I turn the THX on, even if I'm not actually listening to it, the signal recovers and sounds normal again. With the THX on, the other amps sound the same whether or not the THX is connected. Only if the THX is connected and off does it drag down the signal.

Weirdly, only the THX seems to do this. I can listen to the THX while the Stax and Jotunheim are connected and off, and it sounds fine. Likewise, neither the Stax nor the Jotunheim seem to mind the other being connected. But if I listen to one of those two while the THX is connected and off, it sounds horrible.

Anyone know what's different about the THX circuit that makes it do this? I'm thinking maybe an ESD protection diode on the input.

I guess I'll have to get one of those XLR switch boxes, unless someone knows of a better way to fix this.

I have similar issue, with my thx789 and smsl m200.
If both outputs in the dac are connected (xlr thx, espressivo-e rca), sound in rca is heavily distorted if thx is off. When I turn it on, everything's fine.
I already thought it was a m200 fault. Good to know...

T3RIAD what's your dac model?
 
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odyo

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Not super precise but i volume matched the two with a sound meter app.
AE5 low gain %34: 85db pink noise from Ananda
789 mid gain 12 clock: 85db pink noise from Ananda. Switching to low gain it's 75db as it should so i guess it's not totally off.

Still evaluating the sound. Not sure which one is better. There are obvious differences. Slam better on the AE5, smoothness better on the E30+THX789. Now i have first hand experience i can confidently say they sound different but not much. AE5 treble is a bit glary which can hide some detail, 789 treble is calmer and more treble detail is visible. Biggest difference is in the bass punch. 789 is softer here. In the mids i noticed 789 have a bit 3D like sound. With 3D i don't mean it's enveloping surround 3D. I mean sound comes from a flat plane like normal but i can feel the 3d physicality of the instruments.

So basing my opinions from AE5 i can say that THX 789 sound smooth, less fatiguing and deep(soundstage). ''Smooth'' and ''deep'' highlights of the show. It's like a calibrated display. It doesn't have brightness, contrast, gamma, saturation issue which helps showing out more detail.

No difference between E30 filters at first glance. No difference between low, med, high gain settings either.

I've tried using E30 dac with AE5 amp but faced with very nasty ground issues. I will try AE5 dac with THX 789 amp.

Edit: At higher volume THX 789 destroys the AE5. AE5 soundstage completely squashed at high volumes. 789 flawless here. However i don't understand why AE5 have more physical rumble with the bass.

Currently using AE5 dac connected to 789 amp. This is harsher than E30+789 but still closer to E30+789 than AE5 only.

AE5 have no problem at higher volumes with the high impedance Beyer headphones. So i think AE5 have good voltage swing but bad current capability.
 
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I have similar issue, with my thx789 and smsl m200.
If both outputs in the dac are connected (xlr thx, espressivo-e rca), sound in rca is heavily distorted if thx is off. When I turn it on, everything's fine.
I already thought it was a m200 fault. Good to know...

T3RIAD what's your dac model?
My DAC is the SMSL SU-8.

According to another poster some amps just do this. They short the inputs when they're turned off. I'm trying to find the Nobsound MC-103 XLR switch box for sale somewhere to switch between the amps.
 

jahudi

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Hi folks, sorry if this is a stupid question or if this is not the right topic (in which case I'd be happy to be redirected).

I own a THX 789 which is connected to my turntable via RCA (and to my DAC via XLR). Now, for serious listening I use my Aeon Flow Open headphones. But from time to time I would also like to listen to my vinyl records without headphones. I own a Libratone Zipp speaker which has a 3.5mm audio jack. Unfortunately I could not find any specs of this interface and also the Libratone support could not give me any information.

The Zipp has an internal amplifier and my guess is that depending on whether it is active or bypassed when connecting it via the 3.5mm jack it is supposed to be connected to a LINE level output (SE PASS in case of the THX) or could be connected directly to the (amplified) SE headphone output, right? Could it harm my THX or the Zipp if I just tried one or the other? Somewhere I read that in case the impedance of a connected device is too low it could basically hot-wire the SE output, is that right?
 

ZeDestructor

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Hi folks, sorry if this is a stupid question or if this is not the right topic (in which case I'd be happy to be redirected).

I own a THX 789 which is connected to my turntable via RCA (and to my DAC via XLR). Now, for serious listening I use my Aeon Flow Open headphones. But from time to time I would also like to listen to my vinyl records without headphones. I own a Libratone Zipp speaker which has a 3.5mm audio jack. Unfortunately I could not find any specs of this interface and also the Libratone support could not give me any information.

The Zipp has an internal amplifier and my guess is that depending on whether it is active or bypassed when connecting it via the 3.5mm jack it is supposed to be connected to a LINE level output (SE PASS in case of the THX) or could be connected directly to the (amplified) SE headphone output, right? Could it harm my THX or the Zipp if I just tried one or the other? Somewhere I read that in case the impedance of a connected device is too low it could basically hot-wire the SE output, is that right?
Amplifiers generally have quite high input impedances (typically in the 10k-100k ohm range), so you should have no issue regardless of which output you use
 

Jimbob54

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Hi folks, sorry if this is a stupid question or if this is not the right topic (in which case I'd be happy to be redirected).

I own a THX 789 which is connected to my turntable via RCA (and to my DAC via XLR). Now, for serious listening I use my Aeon Flow Open headphones. But from time to time I would also like to listen to my vinyl records without headphones. I own a Libratone Zipp speaker which has a 3.5mm audio jack. Unfortunately I could not find any specs of this interface and also the Libratone support could not give me any information.

The Zipp has an internal amplifier and my guess is that depending on whether it is active or bypassed when connecting it via the 3.5mm jack it is supposed to be connected to a LINE level output (SE PASS in case of the THX) or could be connected directly to the (amplified) SE headphone output, right? Could it harm my THX or the Zipp if I just tried one or the other? Somewhere I read that in case the impedance of a connected device is too low it could basically hot-wire the SE output, is that right?
Not sure why you wouldnt just use the pass thru loop at the back? Why bother trying the headphone out? You're not wanting to listen to the DAC feed on the Zipp?
 

odyo

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@50 ohm SE: 1W, BAL: 3.5W i guess these are high gain numbers. How is low and mid gain ? Also where can i find information about power output and loudness relationship. THX 789 have -10/0/+10 db gains. What would happen if it had less power but same gain settings ?
 

jahudi

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FYI: Both options work. Interestingly the speaker buffers about one second of audio data before playing it. This is noticeable when connecting it to the headphone out and using the amp volume control (it takes about a second to reflect the change). One other positive surprise is that it automatically streams the audio to all other Zipp speakers that are in a wireless group. So everything is as I wished :) Thanks
 
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Given that the dac tool seems to be down, is there any other amp with more power and better ratings than this one anywhere near this price?

This looks like it can drive anything from low ohm headphones to high ohm, whatever. (My dx3 pro is already proving under powered, and I need to fix that)
 

Dana reed

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Given that the dac tool seems to be down, is there any other amp with more power and better ratings than this one anywhere near this price?

This looks like it can drive anything from low ohm headphones to high ohm, whatever. (My dx3 pro is already proving under powered, and I need to fix that)
If you’re mainly talking balanced, the magnius is $100 cheaper and still puts out 5W into 32 Ohm.
 
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If you’re not balanced, then you can save a bunch of money and get an atom or a heresy, and have more power than most headphones need
Going to go look at the pages for them. I am a big fan of buying once. dx3 pro was supposed to be that once, but it's looking like I may need something bigger. Some planars I am looking at supposedly work on the dx3 pro but really shine with more power.
 

Pillars

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I'd still stick to the 789, used it can be had pretty decently priced. If you want shoot me a PM I've got a great condition one and an SU-8 I could part with.
 
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