I spent my Sunday afternoon playing with these toys
My main objective was to compare Mojo and Hugo using T51P and HD800 but I threw in the Leckerton UHA-6SMKII as well. To make the comparison simple I only use the USB input on all 3 devices.
The rest of the stuff I used are
1. Audio/Video splitter/switcher
2. Siglent SHS806 Oscilloscope
3. Bunch of cables
4. HD800
5. T51p
6. Chord Hugo
7. Chord Mojo
8. Leckerton UHA-6SMKII (with AD797 as the output opamp)
Music I used for comparison
1. Back in Black - AD/DC
2. Get Lucky - Daft Punk
3. Here Comes the sun - The Beatles
4. Spanish Harlem - Rebecca Pidgeon
5. Lay Lady Lay - Bob Dylan
6. Mmmm - CrashTest Dummies
I setup my test rig by hooking up 2 DAC/Amp to be compared by USB to my Macbook. Then on OSX I setup a "Multi-Output Device" from the Audio MIDI setup utility. This is done so I can send the music stream from my Music Player app(Vox) simultaneously to both DAC/Amp devices. The output of each DAC/amp is connected to one of the input of the AV splitter/switcher and it's only output connected to the headphones I used (either T51p or HD800).
I started comparing Mojo and Hugo using T51p. I tried to match the output volume of both DACs using the app "decibel" and the built-in mic in my iPhone. At this point I started the comparison and quickly noticed that Mojo is somewhat warmer than Hugo. The bass is noticeably punchy than the Hugo when quickly switching back and fort. Cymbal crashes sounded more forward on Mojo than on Hugo. After I finish the first round of listening tests I had made the initial conclusion that mojo is overall warmer with a slight prominence in the treble and the Hugo has a somewhat flat and balance signature on my T51p.
I checked the volume level to make sure it didn't change during the comparison. Then I discover the app I used does not seem to be giving a consistent level especially on Hugo. This prompted me to think that volume level between Hugo and Mojo was not tightly matched. This is when I decide to use the Siglent SHS-806 oscilloscope so I can accurately measure the output voltage and make the level match as close as possible.
When I was satisfied the output voltage is very close (1.10Vpp, +/- 0.06Vpp), I then repeat the same test on T51p. All of a sudden the differences I perceived earlier was completely gone if not very difficult to discern. i kept cycling through the list of the music I use for the test but I can't really identify any differences. There are times I thought i hear a difference but when I repeat the part of the music I thought I heard the difference I can't catch it on successive attempts.
I replaced the Hugo with the UHA-6SMKII so I can compare it with Mojo. I then adjusted the Leckerton to match Mojo's volume level. Leckerton's volume knob needs to be a hair passed 12 o'clock position at high gain to match Mojo. With the Leckerton's analog volume control It can match the Mojo's output voltage more precisely of only +/- 0.02Vpp error/deviation. To my surprise The Lecketon can match Mojo's sound. I also can't pickup any matterial difference that I can constantly perceive just like with the Mojo/Hugo comparison.
Next test is for HD800. With Mojo and Hugo first for comparison I have to raise the output volume to 7.52Vpp on the Hugo and in Mojo at 7.76Vpp (this is the closest I can get them) to reach the volume level I am comfortable to listen (this is a click or 2 louder than my usual listening level). Similar to the T51p comparison, I also can't perceive any difference no matter what I do.
As for Mojo and the Leckerton comparison using HD800, I have to decrease the output of Mojo to 6.5Vpp so it can match the Leckerton which already is at the maximum position of the volume knob at high gain. As expected the volume level is noticeably lower than the Hugo/Mojo comparison but nevertheless still enjoyable level. On this comparison too, I can't perceived any difference.
So what do I learn/get from this experience?
- As you may have guessed, proper volume matching is very important to eliminate imbalance which can easily tip to incorrect perception. I'm not done yet however, and not saying there is no actual/audible difference. If there is I'm pretty sure it's very subtle.
- As long as the amp can deliver the power needed by the headphone at certain volume range the difference is very subtle to non-audible.
- Mojo is indeed a smaller Hugo. They have the exactly same power output (measured) and at least for the headphones I used and using the USB input they sound exactly similar.
- Leckerton showed it's chops which managed to maintain a stable, no-clipping performance even when pushed to it's absolute limits. Although it is nowhere near the output power of what the Mojo/Hugo can deliver (in fact I can only manage half the output of the Mojo/Hugo) it is ab;e less than half the price of Mojo.
At this point, I'm inclined to think that the Mojo is a better value for money than Hugo, especially as a mobile device with it's size and performance matching Hugo. Unless versatility of the output options and bluetooth is worth the premium for you as a desktop amp the Hugo has the upper hand. I find Mojo to fall short a bit as a desktop DAC. It has a shorter battery life. If you use it while charging it can get warm very quickly and depending on your location it can overheat and trigger the overheat protection circuit. I'm in Singapore and my Mojo almost always shutdown when I use it while charging if my room's AC is not running.