Review and Measurements of Massdrop Alex Cavalli Tube Hybrid (CTH) and JDS O2 Headphone Amps

[derp1n]

I sure knew what I was getting when I purchased my O2 - from Mayflower electronics.

I hope your O2 was assembled with better care than this:

 

[amirm]

I hope your O2 was assembled with better care than this:

There must have been a shortage of solder when they assembled that one!

 

[mi-fu]

I hope your O2 was assembled with better care than this:

Your O2 is from Mayflower??

 

[Grave]

The O2 is a great sounding little amp. The number of people bashing it on other forums saddens me. The usual argument by subjectivists is that it sounds bad even though it is easily transparent. :/

 

[amirm]

The O2 is a great sounding little amp. The number of people bashing it on other forums saddens me. The usual argument by subjectivists is that it sounds bad even though it is easily transparent. :/

The really low-budget enclosure sure sets one's expectation that it "can't sound good." Unless a test is done blind or objectively, they will invariably will like fancier boxes and methods.

Someone should build one in a large box with a tube in it that doesn't do anything and see what the feedback is.

 

[tomelex]

Mat at Techmoan pretty much agrees with your opinion about tube headphone amps, although he only did a non-technical review of three really cheap units. (He also has many cool reviews of other off-the-wall tech gadgets on his YouTube channel.)

However, in another review - this one of a tube buffer - Mat liked the subtle changes made to the sound by the Yaqin CD3, a 6SN7 (sorry, no blue LED's lighting up the tubes from the bottom) cathode-follower unit. In fact, Mat liked it enough to keep the Yaqin in his system, and the below review tells that story. The CD3 seems to be a pretty popular system "add-on." and I might get one to get my "fix" of tube nostalgia upon occasion. I like the idea of a relatively inexpensive but good quality tube buffer to let me play with "tube sound" by rolling tubes and perhaps even "upgrading" capacitors!!! (They've even published a schematic for the CD3!)

View attachment 14464

When researched tube tube buffers recently on the internet, if appeared that Yaqin seems to have the only decent good quality unit in the lower price range currently. And the Yaqin actually uses a transformer-based power supply to drive the drive the tubes to "normal" operating levels.

I had to chuckle at the description of the interior components when the bottom plate was removed, and when I saw the below comment in the video...(what could possibly be more meaningful here at ASR that referencing "an extensive scientific study" from a respected university?)

View attachment 14462

the comments at 2:10 to 3:15 should be carefully considered and thought about by audiophiles IMO.

 

[amirm]

OK, this is weird. I ran a test of balanced 50 ohm output on CTH versus previously run unbalanced and get this:

Yup, it actually distorts a bit earlier and definitely does not produce more power!

With similar noise and THD performance, not sure what the benefit of this connector is. In other amps, there is more power in balanced mode. There is nothing here.

 

[Wombat]

The O2 is a great sounding little amp. The number of people bashing it on other forums saddens me. The usual argument by subjectivists is that it sounds bad even though it is easily transparent. :/

It was bad because NwAvGuy kept pricking their subjective belief balloons.

 

[derp1n]

OK, this is weird. I ran a test of balanced 50 ohm output on CTH versus previously run unbalanced and get this:
View attachment 14491

Yup, it actually distorts a bit earlier and definitely does not produce more power!

With similar noise and THD performance, not sure what the benefit of this connector is. In other amps, there is more power in balanced mode. There is nothing here.

CTH is not a balanced amp. XLR does not mean balanced. It's just an alternate connector, in this case.

 

[restorer-john]

There must have been a shortage of solder when they assembled that one!

My 10yo son can solder better than that.

 

[xxie]

It will be very interesting to compare Topping NX4 dsd amp section and O2. NX4 is using 2x opa1688 vs O2 2x NJM4556, they are having similar output capability.

i have both, but I prefer NX4 because it has far longer battery time than O2(when used as amp only, like 40h vs 10h from spec), also O2 low voltage shutdown circuit is bit malfunction at least on my unit.

(I also could not help thinking NWAvGuy is perhaps working for Topping?)

 

[mindbomb]

It will be very interesting to compare Topping NX4 dsd amp section and O2. NX4 is using 2x opa1688 vs O2 2x NJM4556, they are having similar output capability.

i have both, but I prefer NX4 because it has far longer battery time than O2(when used as amp only, like 40h vs 10h from spec), also O2 low voltage shutdown circuit is bit malfunction at least on my unit.

(I also could not help thinking NWAvGuy is perhaps working for Topping?)

and I think the rme adi2 is using 3x or 6x 1688. So those babies can scale.

 

[amirm]

It will be very interesting to compare Topping NX4 dsd amp section and O2. NX4 is using 2x opa1688 vs O2 2x NJM4556, they are having similar output capability.

Unfortunately the NX4 was a loaner and I can't test it anymore. Agree that it may give strong competition to O2 and has a DAC included.

 

[TungstenC]

In contras the JDS O2

on kind loan

Missing a “-t” and an “a”

(Prism Sound dSound analyzer).

You meant dScope?

@amirm was the O2’s gain on 1x or 2.5x(default) during testing?

 

[έχω δίκιο]

My 10yo son can solder better than that.

Move to China and put that boy to work!

 

[έχω δίκιο]

NX4 is using 2x opa1688 vs O2 2x NJM4556, they are having similar output capability.

I looked up the OPA1688 on TI's website and happened to notice the OPA1622 (sorry if I'm late to the party, but I've not been keeping up on high current op amps for driving headphones). While the NJM4556 and OPA1688 have output currents in the 70-75ma range, the OPA1622 is at 145ma. At first glance, it has some very attractive specs. Unfortunately, it's not available as an 8-pin DIP, just as a 10 pin VSON (surface mount). But there are ebay sellers that are offering them pre-mounted them on 8-pin DIP adapters.

See the OPA1622 datasheet.

 

[Vipu]

I wonder, you do listening tests before or after the measurements?

 

[Bhargu]

I looked up the OPA1688 on TI's website and happened to notice the OPA1622 (sorry if I'm late to the party, but I've not been keeping up on high current op amps for driving headphones). While the NJM4556 and OPA1688 have output currents in the 70-75ma range, the OPA1622 is at 145ma. At first glance, it has some very attractive specs. Unfortunately, it's not available as an 8-pin DIP, just as a 10 pin VSON (surface mount). But there are ebay sellers that are offering them pre-mounted them on 8-pin DIP adapters.

See the OPA1688 datasheet.

OPA 1622 has good current capability and PSRR. It was one of the reasons why I was interested in Melokin DA9.1 and Hifime UDA38Pro. Sadly, DA9.1 was a bust. I am waiting to see how UDA38Pro performs.

 

[dc655321]

Unfortunately the NX4 was a loaner and I can't test it anymore. Agree that it may give strong competition to O2 and has a DAC included.

Wait. Did you send the NX4 back to me?
Or, are you talking about opening it up to look under the hood and compare visually?

 

[mindbomb]

@amirm
can you double check the output impedance? my massdrop o2 has almost exactly the specified 0.54 ohms.