Review and Measurements of Massdrop THX AAA 789 Amp

[olds1959special]

Have you considered routing the RCA outputs from your DAC to the Monolith as well? And then use the front switch to select between the (a) the higher voltage XLR input when listening to headphones using the 4-pin XLR, and (b) the lower voltage RCA input when you are routing "line-level" output to your amplifier / subwoofers?

That would provide a much greater range on your volume knob when using the THX 789 as pre-amplifier; or even when using it as headphone amp for easier to drive headphones.

Thanks, this works well.

 

[olds1959special]

Have you considered routing the RCA outputs from your DAC to the Monolith as well? And then use the front switch to select between (a) the higher voltage XLR input when listening to headphones using the 4-pin XLR, and (b) the lower voltage RCA input when you are routing "line-level" output to your amplifier / subwoofers?

That would provide a much greater range on your volume knob when using the THX 789 as pre-amplifier; or even when using it as headphone amp for easier to drive headphones.

When doing this (using RCA inputs) I can use the II gain setting as well. I'm not sure if it makes any difference to the sound quality? I guess II is 0dB and I is -10dB. I'm not sure but this might sound better. I'm not going to try III though because that would be too much.

edit: I went back to using the gain I setting.

 

[rcstevensonaz]

When doing this (using RCA inputs) I can use the II gain setting as well. I'm not sure if it makes any difference to the sound quality? I guess II is 0dB and I is -10dB. I'm not sure but this might sound better. I'm not going to try III though because that would be too much.

For an unexpected reason, you will most likely gain stereo sound quality using the RCA inputs.

The reason is that often there is a degree of channel imbalance on analog volume POTS when they are close to zero. When you feed the high voltage input, you were having to turn the volume far towards zero — "It’s a bit hot so I can’t turn it up past 9 or so". By lowering the voltage input so that 12:00 becomes the nominal position (whether that is level I, II, or III gain setting), it allows you to manage the volume POT without having to dip down into the lower range below 9:00".

Further, by gaining a greater range of motion, you are more able to fine tune the volume to the exact level you want it at. That would have a perceptual audio benefit.

But that should be the only audible and perceptual audio quality impact assuming the DAC's balanced and unbalanced amplification stages are both sufficient high quality with undiscernible noise floors. And if the two are not equal, odds are good that the unbalanced audio would be the one with higher sound quality. [Edit: I just looked at the Amir's review of the SMSL DO100, and the XLR output was measured just an (inaudible) smidge above the RCA; so no inaudible penalty either way on this device]

(side note: I have the Monolith THX 887 which is virtually identical to this)

 

[olds1959special]

I stopped using this as a preamp. I'm using it as a headphone amp though, and noticed that I prefer the high gain setting with my DAC set at 80 to avoid distortion.

 

[rcstevensonaz]

I stopped using this as a preamp. I'm using it as a headphone amp though, and noticed that I prefer the high gain setting with my DAC set at 80 to avoid distortion.

Are you using the XLR or RCA interconnect?

 

[olds1959special]

Are you using the XLR or RCA interconnect?

I'm using the XLR but I'm not really sure I'm right about this.

 

[olds1959special]

I’m back to using this as a preamp. My DAC direct to power amps didn’t work so well (ground loop buzz in right channel.) Here’s a pic showing the cables going to my amps and subwoofer. Using the balanced inputs for the DAC seems to work best for me. While I can use the medium gain, the low gain works the best, and there’s enough room to turn the volume. I have my amps and subwoofer on a power strip, so when I want to use headphones, I can just turn them off and plug in my balanced HD650’s into the XLR output, and switch to medium gain. Is there any reason at all this is not desirable as a preamp as well as a headphone amp?

 

[olds1959special]

Using a multi meter I measured the XLR output of my DAC so I could figure out what volume to use to get full output and prevent clipping on high gain (THX AAA 789). I was surprised to find the correct volume setting is 83. This is so good to know because I like listening on the high gain setting to get the full voltage swing. For some reason, while using medium gain the sound feels sterile.