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Review and Measurements of Massdrop THX AAA 789 Amp

Rottmannash

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I find it hard to let go of a really good amp as it is always possible to fit them in with new gear. I still have my vintage NAD 7125 also. I love the rear mounted heat sink and small form factor still. Also I love my 11 year old THX Select 2 Onkyo 608 receiver that runs cooler than my Denon x3700 that I am pre-outing to it from. My E30 dac can act as a preamp with remote volume also for more flexibility. $300 for an amp as good as the 789 is a worthy investment IMO.
Here's to NAD. I have 2 3140s and will never get rid of them.
 

Aperiodic

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I have an engineering question- is anything with DC-in power by definition a so-called 'virtual ground'? Asking because everything Schiit, JDS and the O2 are all AC-in but amps like this one have to create a negative rail. Is a 'virtual ground' how this is accomplished? Thanks.
 
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Someone can comfirm with measurements if crosstalk decreases in gain I to gain II particularly, is not only affected with SE output for headphones, but even balanced headphones output?
 

Lttlwing16

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Anyone know if the 789 can output from the front balanced headphone output and SE pass on the back simultaneously? Would like to rip vinyl via SE pass while listening from the front.
 

Jimbob54

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Anyone know if the 789 can output from the front balanced headphone output and SE pass on the back simultaneously? Would like to rip vinyl via SE pass while listening from the front.
Yes. If rca is plugged in from source it comes out of the pass thru regardless even if the unit is off. There is no selecting which front output is used, both go at the same time.

The one thing I haven't tested is if the SE pass thru works even if xlr input is selected, but that's not a relevant question in your case.
 

Lttlwing16

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SE pass will only work with SE input, so if that's the case it'll work yes.
Yes. If rca is plugged in from source it comes out of the pass thru regardless even if the unit is off. There is no selecting which front output is used, both go at the same time.

The one thing I haven't tested is if the SE pass thru works even if xlr input is selected, but that's not a relevant question in your case.
Thanks folks.

Yep would look like this: ART DJ PREII RCA OUT>789 SE INPUT>789 SE PASS via RCAto3.5mm>PC input on soundcard

I'd assume the SE PASS follows the volume control, or does it have a set output volume?
 

Jimbob54

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Thanks folks.

Yep would look like this: ART DJ PREII RCA OUT>789 SE INPUT>789 SE PASS via RCAto3.5mm>PC input on soundcard

I'd assume the SE PASS follows the volume control, or does it have a set output volume?

Nooooo- its just a loop out from the RCA input- its not a pre amp - doesnt touch the amplification circuits- same voltage as whatever comes in from your source (and like I say, it still works if the 789 is powered off)
 

Lttlwing16

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Nooooo- its just a loop out from the RCA input- its not a pre amp - doesnt touch the amplification circuits- same voltage as whatever comes in from your source (and like I say, it still works if the 789 is powered off)
Thanks again for the clarification. This would be a perfect fit for my needs then. Now just to find the right DAC..was thinking pairing it with a Modius as it seems the best balanced DAC for the price.
 

raistlin65

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Thanks folks.

Yep would look like this: ART DJ PREII RCA OUT>789 SE INPUT>789 SE PASS via RCAto3.5mm>PC input on soundcard

I'd assume the SE PASS follows the volume control, or does it have a set output volume?
Also, I think normally the idea of a pass through is that does not affect the signal at all. So always double check if you're expecting something described as a pass through to go through the preamp. Usually the manual will describe that kind of thing.

The pass through does work great. That's how I'm using it. And I really like that I don't have to turn it on to use my speakers.
 

Jimbob54

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Thanks again for the clarification. This would be a perfect fit for my needs then. Now just to find the right DAC..was thinking pairing it with a Modius as it seems the best balanced DAC for the price.
Just to be clear, I don't know if the rca signal is passed thru if the xlr inputs are selected. So you may not be able to listen to the modius whilst looping out the rca
 

Veri

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Thanks again for the clarification. This would be a perfect fit for my needs then. Now just to find the right DAC..was thinking pairing it with a Modius as it seems the best balanced DAC for the price.
Balanced DAC will not work with SE pass.
 

Lttlwing16

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Just to be clear, I don't know if the rca signal is passed thru if the xlr inputs are selected. So you may not be able to listen to the modius whilst looping out the rca
Balanced DAC will not work with SE pass.
Thanks again for looking out. I won't need to use the SE pass through with the balanced inputs. I'll only need to use the SE pass with the SE input from my phono preamp, which is what I understand is how it works. I'll be using the balanced connections for the digital inputs (USB and Coax) connections and will only need the headphones for those.

Just ordered the 789 from Amazon, my first purchase towards a reference headphone setup!
 

Jimbob54

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Thanks again for looking out. I won't need to use the SE pass through with the balanced inputs. I'll only need to use the SE pass with the SE input from my phono preamp, which is what I understand is how it works. I'll be using the balanced connections for the digital inputs (USB and Coax) connections and will only need the headphones for those.

Just ordered the 789 from Amazon, my first purchase towards a reference headphone setup!
Enjoy!
 

Lttlwing16

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The 789 arrived today and had a couple question for anyone that owns one:

1) There is an audible buzz, which I assume is a grounding issue, from the turntable SE input. Not noticeable during music, but definitely noticeable before the music starts. FWIW if I place my fingers on the SE inputs around back and my other hand on top of the 789, it essentially eliminates the buzz.

2) The volume knob has an audible rub, and resistance from around 11 - 1, so much so, I can't adjust the volume with 1 finger roll, which I can do outside of the 11 -1 range.

I purchased the 789 "Like New" from Amazon, so I'm wondering if this particular unit was returned for the same reason. I already put in for a return/refund with Amazon, mainly for the volume knob, but thought I'd ask if anyone else experienced the same thing.

Thanks,

David
 

zepplock

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The 789 arrived today and had a couple question for anyone that owns one:

1) There is an audible buzz, which I assume is a grounding issue, from the turntable SE input. Not noticeable during music, but definitely noticeable before the music starts. FWIW if I place my fingers on the SE inputs around back and my other hand on top of the 789, it essentially eliminates the buzz.

2) The volume knob has an audible rub, and resistance from around 11 - 1, so much so, I can't adjust the volume with 1 finger roll, which I can do outside of the 11 -1 range.

I purchased the 789 "Like New" from Amazon, so I'm wondering if this particular unit was returned for the same reason. I already put in for a return/refund with Amazon, mainly for the volume knob, but thought I'd ask if anyone else experienced the same thing.

Thanks,

David
Return it, it's obviously broken. Mine was new from drop and had no issues.
 

Lttlwing16

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Return it, it's obviously broken. Mine was new from drop and had no issues.
I did just that. Brand new one arriving today.

EDIT: Brand New 789 arrived today and volume knob was fully functional. Grounding issue is still there, albeit less noticeable, and really only noticeable on high gain at around 3 o'clock. The manual does mention the included power supply does not have a ground, and relies on the ground of the attached device. This makes me want to upgrade my psu on the art dj preII to a grounded, linear supply.
 
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Hi good folks! I have the Drop THX AAA 789 amp and I have two sets of headphones. A 35 Ω and a 23 Ω that I keep plugged in at all times both in the SE ports. I haven't noticed any volume change when I take one out while listening to the other one. Can the amp effectively drive both at the same time efficiently even when having different impedance? Could there be any issues on the long term if I do this or should I use just one at a time. I've noticed that the amp gets slightly warm. My use case is I work from home and I use one for music and the other one for meetings.
 
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