Meier-Audio Corda Rock ($240)
Meier Audio of Germany has been a part of the headphone specialty market for a long time. My first really high-end headphone amplifier was Meier's top of the line amp back in 2005, and I was very impressed with the level of transparency and detail it delivered. Since that time, I have probably reviewed, and subsequently purchased, at least a half-dozen Meier amps. And that notable transparency and detail, coupled with just a touch of warmth, has remained the hallmark of Meier designs.
Meier amps are designed in Germany, but built in China by Shanling. This no doubt has contributed to a strong value for the money. And the subject of this review, the "Rock" home headphone amp, is clearly targeted at people who are looking for value--the Rock is the smallest home (non-portable) headphone amp Meier has ever made, and also the least expensive, at $240 USD, or EUR 220 (in the EU). That actually makes it LESS expensive than any of Meier's current line-up of portable headphone amps!
One of the things I immediately liked upon opening the small box that the Rock came in is that there is no dreaded wall wart power supply. The Rock's power supply is on-board, and it has an IEC power cord receptacle, although one cost-saving method is that it does not come with a power cord. It's up to the user to supply one, which is fine with me--I have tons of them. Note, however, that the Rock is small and light enough that a super-crazy-cobra-thick "audiophile" power cord is going to make it tough for the little Rock to remain flat on a desk/table. But I doubt many people will use expensive power cords with a $240 headphone amp.
The Rock is based around the TDA2030 IC, and the relatively few parts it has are of nice quality. Being a non-portable amp, it sports a full-size 1/4" headphone jack, and one pair of RCA jacks on the back. That's pretty much what you get.
We'll talk about the sound quality on the next page.
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Comments
Hi Tyll, one very slight correction: the Rock has 2 inputs (non-switchable). There's the obvious pair of RCA jacks, but also an unlabelled 1/8" next to the RCA.
I understand that gain can also be tweaked via jumpers at the bottom, though for the life of me I haven't figured out how.
You're right about both - I didn't mention these because I didn't use the 1/8" jack, and the amp to me sounded universally better in Hi-Gain mode.
Oops, sorry Skylab! Didn't mean to address you as Tyll.
The Rock is set on hi-gain by default, right?
No worries :). And yes, comes on hi gain mode, and jumpers on the bottom are used to change.
Haven't heard it. Wonder if HeadRoom has one. I'll check.
I've not seen it listed on the HeadRoom site but hope that you can get your hands on one. People who cannot tolerate the W5000 are enamored with the W3000ANV.
Any comments on how it compares to something in the same price range lets say, the Schiit Asgard?
Thanks! Unfortunately I don't have anything else on hand in that price range to compare it to, currently.
Any impressions against the jdslabs O2?
I will be getting an O2 from Tyll to review, so I will have an opinion on that at some point in the near future.
Thats great to hear. Thanks
At this price, can it really compete with something like the Asgard which sells for about the same amount?
Meh, I'll keep my O2. For the money, I see a lot of things I don't like in the Corda Rock. To start with, those two Myrra 47155's. They may look like trafos but they aren't. Those are actually SWITCHING MODE POWER SUPPLIES! This means they work at much higher switching frequencies. This also means that you will need very careful PCB routing and Low ESR capacitors. The "For Audio" caps will not perform very well here. They can not effectively suppress the high frequency ripple caused by the PSU switching elements. You can see all the noise in the plots. Additionally, they are quite expensive (USD12ea from USA distributor Newark) even in bulk, even in China they are not cheap in the quantities Meier must be purchasing at. So, around $24 just in the PS? IMO, waste.
What about that big blue Alps RK27 volume pot? Even with this highly-touted pot it has higher channel imbalance than the O2. 100KΩ = higher Johnson noise than the O2's 10KΩ RK097 pot. IMO, more waste.
The TDA2030 used in the Rock is a LF power amplifier with output stage running in class B or AB. This one has a low quiescent current of about 40mA, hence the lack of heatsink except the front plate. Since Meier is using it to power headphones, not speakers, the Myrra "electronic transformers" may be just fine except for the noise.
With a 4Ω+ output impedance the Rock is 8X higher than the O2. That means on an 80Ω headphone the Rock has a damping factor of 20, while the O2 has 160. For 300Ω cans, it would be 75 versus 600. IMO, meh.
Overlay the graphs for yourself, there isn't any substantial area where the Rock performs better than the O2.
In comparison to the rest of the Meier lineup, this unit isn't particularly handsome either. The O2 can get away with some "ugliness" at it's price point and the fact it was designed as proof-of-concept and to be DIY friendly. But Meier sells the Corda Rock as a finished consumer-ready unnit at $240.00. IMO, just plain not good enough.
" For the money, I see a lot of things I don't like in the Corda Rock. "
Beauty is in the eye of the beholder! 
" those two Myrra 47155's. They may look like trafos but they aren't. Those are actually SWITCHING MODE POWER SUPPLIES! This means they work at much higher switching frequencies. This also means that you will need very careful PCB routing and Low ESR capacitors. "
Within a small enclosure switching mode supplies have big advantages. The magnetic fields of the trafo are much smaller and at frequencies outside the audio-band. Therefore induced hummmmmmmm is much lower.
Of course one has to take care that the high-frequency noise doesn't reach to the powerlines. But that's well possible using inductors between powersupply and buffer-capacitors.
" Additionally, they are quite expensive (USD12ea "
And what do a toroidal transformer, fuse, 110/220V switch, buffer capacitors, rectifiers, voltage regulators, ... cost? They are all replaced by these two power-units!
" big blue Alps RK27 volume pot? Even with this highly-touted pot it has higher channel imbalance than the O2. 100KΩ = higher Johnson noise than the O2's 10KΩ RK097 pot."
The RK27 over most of its range has better channel balance than the RK09 series. Read your specs!
The potentiometer on the ROCK has 10 kOhm!
" The TDA2030 used in the Rock is a LF power amplifier"
Yep, that's why it has so little distortion at high output levels and such a high voltage swing! Actually it's the TDA2030AV, which is better sounding than the TDA2030.
" with output stage running in class B or AB. This one has a low quiescent current of about 40mA"
The quiescent current of the output stage of your beloved O2 is much lower.
Let's say the TDA2030AV runs into class A upto around 30 mA. That means upto 8V with a headphone like the HD800. And even with a 30 Ohm headphone this implies class-A performance upto around 1V. Enough to make your ears bleed!
" hence the lack of heatsink except the front plate."
Without this heatsink the TDA2030 would not survive.
Does the O2 have a heatsink this size, if any at all?
" With a 4Ω+ output impedance the Rock is 8X higher than the O2. "
Can you give me values for some tube-amplifiers?
" there isn't any substantial area where the Rock performs better than the O2. "
Voltage swing!?
Compare Tyll's measurements for the ROCK to those of very well respected amplifiers like the HA160D, the G109, and the EF6 and I think the ROCK does very well, especially considering its size and price.
" this unit isn't particularly handsome either."
Again, beauty is in the eye of the beholder. I know of many people who like the looks of this amp. It's all very personal.
Cheers
Jan
I love reading rebuttals like this.
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