Professional Made-in-USA 24bit/192 ksps USB DAC & Headphone Amp
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The Apogee Groove is a tough and tiny professional USB DAC and headphone amplifier. Just plug it into a USB output from your Mac or PC, select it as your audio output, and you're done. It needs no other power supply or drivers; plug and play.
The Groove is the size of a pack of gum or a large USB flash drive.
It has an all metal case and it's made in the USA. I've known Apogee since the 1980s when they started out making special anti-alias filters to upgrade my Sony PCM-F1, the world's first digital audio recorder that sold for less than a new car. They also made audio filters for upgrading studio recorders that sold for as much as a house.
Thirty years later Apogee is still one of — if not the — top makers of professional digital audio converters. They are probably the world's most popular analog-to-digital converters used to record numerous top Grammy-winning albums — the same music you'll be playing on your own headphones!
This isn't overpriced rubbish thrown together by some well-intentioned but clueless audiophiles in some hacker's garage; Apogee has over thirty years of genius rolled into this little gem. Apogee knows what makes a converter sound great.
It has loads of output; more than 25 times the output power into pro headphones than typical high-end portable consumer junk that people buy today.
It puts out 5 volts into 300Ω and 600Ω headphones, while most consumer and portable equipment can only put out 1 volt. This means that you can play your pro headphones like your DT880s and HD800s as loud as you like.
Low-impedance headphones don't need more power, and for 32Ω headphones it has about the same output as other devices — more than enough to deafen yourself.
As professional equipment goes this is very inexpensive; don't try comparing it to imported plastic consumer rubbish.
It's intended as a headphone amplifier, and it also works great as a DAC to plug into the rest of your system with a 3.5mm to RCA cord.
It only plays from computer USB outputs; you can't plug this into your iPhone.
It should plug-and-play with any PC made since about 2006 or any Mac from OS 10.8.
Box bottom, Apogee Groove.
USB 2.0 (more than enough for audio; of course works swell with USB 3.0).
Micro USB connector.
Short cord included.
Four summed ESS Sabre DACs per channel.
3.5mm stereo jack.
Via USB; no external supply needed.
3.72" (94.5mm) deep by 1.18" (30.0mm) wide by 0.63" (16.0mm) tall, including feet and buttons, measured.
2.059 oz. (58.3 g), measured.
Proudly made in the United States of America.
Solid alloy top and bottom.
Rubber + and − buttons for volume.
$268, February 2016.
You often can find it bundled with great headphones at great prices.
Apogee Groove in its box.
It doesn't have any sound; what's in your music is what comes out the jack on the front. It doesn't make any sound either; it sits on your desk silently with no fans or hums.
As a pro DAC and amplifier it can't color the sound, and it doesn't. What goes in is what comes out. If your recordings are smooth and detailed, that's what you'll hear, and if they're muddy, congested, noisy or harsh, that's also exactly what you'll hear. Consumers rarely realize that most of what they confuse for the quality of their equipment comes down to the quality of the recordings they're trying to enjoy. No matter how good your gear, if the recording isn't magnificent; it's not going to sound magnificent.
The Groove has more than enough output; you won't run out of level even with inefficient headphones.
Remember, the Groove is designed for professional musicians, and they expect to be able to deafen themselves at live studio levels with clean, easy reproduction of whatever they put down.
Bottom, Apogee Groove. bigger.
It sits very well on a desk. It's small, but its solid-alloy body and well-padded bottom keep it from sliding around. The USB cord goes out the back to your computer, and your headphones plug in the front. Done.
There's only one control: the two big buttons that control volume. They're behind rubber so they won't let dirt into your Groove.
They control volume very precisely. Therefore volume doesn't change quickly; you have to keep pressing or hold them — or use your Mac's volume control for fast changes.
I'd prefer a big knob integrated into the case and sticking out the sides (I'm a huge fan of knobs over push buttons), but that's just me. I love the big knob on my Apogee Duet 2, for instance.
It measures well. It has plenty of output and moderate output source impedance.
I measured it worst-case: fed with a sixty-five-foot USB extension cable at 44.1 ksps! I did this to feed it the worst real-world USB signal I could, and it works great. It also works great with only 4.25V feeding it from USB (but I tested it here at 5.0 V).
Clearly this is no prima-donna lab-queen DAC; it easily handles the real world.
Output Source Impedance
I measure a 21.2 Ω output source impedance at 50 Hz, 1 kHz and 20 kHz. It sounded and measured just like every other good amplifier with a 21Ω source impedance.
I didn't hear or measure anything to suggest that it's any different than every other good headphone amplifier; it was not a "constant current source;" it's a voltage source seen through 21Ω.
Frequency response into 300 Ω.
Frequency response is ruler-flat with purely resistive loads as shown here.
This is with a 44.1 ksps input; the HF rolloff you see goes up in frequency as the sample rate increases.
Here are specifics with a 44.1 ksps input:
-0.03 dB @ 17.16 kc
-0.35 dB @ 18.28 kc
-10.6 dB @ 19.44 kc
-8.25 dB at 20 kc
-93 dB @ 20.65 kc
I won't worry about this; Apogee has over 30 years of leadership in knowing exactly how to make anti-alias filters sound great, so I will take this as an example of how it should be done at 44.1. As musicians know, everything above 16 kc is noise, not music, anyway.
Channel balance was always about 0.05 dB off regardless of volume control setting.
This is great.
I tested it into several fixed resistances: 200 kΩ, typical for use as a line DAC to drive a Hi-Fi; 600 Ω, 300 Ω and 37.5 Ω resistors representing various headphone loads, and most importantly I actually I tested it while driving a real 32 Ω set of beyerdynamic T51i headphones. I don't know that anyone else actually tests amplifiers driving real, live loads, and when you do, you see interesting things.
Resolution and Linearity
A 500 Hz tone was still audible and clean at -111.4 dBFS - from a 16-bit dithered source! This is at least 18 effective bits, which is marvelous.
200 kΩ Performance
This is what you'll see using the Groove as a DAC to drive a conventional Hi-Fi with a 3.5mm to RCA cord:
5.35 V at Full-Scale at full volume setting @ 1.0 % THD at 1 kHz.
5.2 V at Full-Scale at slightly reduced volume @ 0.04 % THD at 1 kHz.
Here are measurements at 2V at full-scale, typical for a CD player's line output:
Harmonic distortion components at 31 Hz into 200 kΩ at 2V. 0 dBFS source, Groove volume turned down for 2V output.
Harmonic distortion components at 1 kHz into 200 kΩ at 2V. 0 dBFS source, Groove volume turned down for 2V output.
Harmonic distortion components at 4 kHz into 200 kΩ at 2V. 0 dBFS source, Groove volume turned down for 2V output.
This is only mediocre; any decent CD player has less distortion — not that you'd hear any of this.
The good news is that it's mostly second-order, so tube lovers rejoice!
A 600 Ω resistive load represents the best pro headphones.
5.08 V @ 0.055% THD at 1 kHz.
5.08 V into 600 Ω is 43 mW.
300 Ω Performance
A 300 Ω resistive load represents many pro headphones.
5.0 V @ 0.1 % THD at 1 kHz.
5.03 V @ 0.2% THD at 1 kHz.
5V into 300 Ω is 83 mW.
Harmonic distortion components at 31 Hz into 300 Ω at 1V. 0 dBFS source, Groove volume turned down for 1V output.
Harmonic distortion components at 31 Hz into 300 Ω at 2V. 0 dBFS source, Groove volume turned down for 2V output.
Harmonic distortion components at 31 Hz into 300 Ω at 4V. 0 dBFS source, Groove volume turned down for 4V output.
No worries, but the Groove is distorting more at foolishly high outputs at 31 Hz, most likely due to the larger output source impedance. No worries: it's almost all second-order.
Harmonic distortion components at 1 kHz into 300 Ω at 1V. 0 dBFS source, Groove volume turned down for 1V output.
Harmonic distortion components at 1 kHz into 300 Ω at 4V. 0 dBFS source, Groove volume turned down for 4V output.
Harmonic distortion components at 1 kHz into 300 Ω at 5V. 0 dBFS source, Groove volume up almost all the way.
The Groove is clipping slightly at 5V at 300 Ω as we can see from the even levels of all the harmonics.
Harmonic distortion components at 4 kHz into 300 Ω at 1V. 0 dBFS source, Groove volume turned down for 1V output.
Harmonic distortion components at 4 kHz into 300 Ω at 2V. 0 dBFS source, Groove volume turned down for 2V output.
Harmonic distortion components at 4 kHz into 300 Ω at 4V. 0 dBFS source, Groove volume turned down for 4V output.
High frequency distortion is very low at all levels.
It's perfectly happy driving 300 Ω, as we expect for a headphone amplifier.
37.5 Ω Performance
A 37.5 Ω resistive load represents many portable headphones.
Maximum Output Level was weird driving 37.5Ω. The Groove tries to protect itself and/or your hearing, and cuts out if you try to drive it at above above 1 V continuously for any length of time.
No worries, for actual music it easily puts out one or two volts continuous RMS into 37.5 Ω at below 0.05% THD, which is much more than most portable devices.
Driving the beyerdynamic T51i
These are measured actually driving my 32 Ω beyerdynamic T51i headphones:
Frequency response driving beyerdynamic T51i.
Frequency response driving beyerdynamic T51i, expanded vertical scale.
Aha! The 21.2 Ω source impedance allows the frequency response to be altered by the headphone's typical impedance variation with frequency.
These fractional decibel irregularities are subtle: they won't be obvious if you compare this to other amplifiers. The differences will be barely audible as simple frequency response errors, and these barely perceptible errors make some people imagine the craziest things. This will make most low-impedance headphones sound a little warmer and maybe imperceptibly more detailed than a purer amplifier like the Benchmark DAC 1 HDR; but it's due to the unintended EQ effects, not anything deeper.
Harmonic distortion components driving the beyerdynamic T51i at 100 mV at 31 Hz. 0 dBFS source, Groove volume turned down for 100 mV output.
Harmonic distortion components driving the beyerdynamic T51i at 1 V at 31 Hz. 0 dBFS source, Groove volume turned down for 1 V output.
Busted! Low-frequency distortion is poor when driving a real headphone as expected from the output source impedance.
An iPhone or iPad is better at driving 32 Ω loads; iOS devices have slightly more output and less distortion driving 32 Ω. Headphone amplifiers with lower source impedances, which include iPhones and iPads, have less distortion here.
In defense of the Groove, the headphones were making more distortion of their own at these high levels. This seemingly huge contribution from the amplifier is swamped by the larger among of distortion caused by your headphones; they don't like being hit this hard with this much bass.
It draws about 340 mA at 5V, which is 1.7 watts, which means that of course it's supposed to be warm all the time.
I don't know of any comparable product from anyone.
Consumer brands like the Astel & Kern or Beyer a200p are just plastic from China and have very weak outputs; often inferior to the iPhone's or your Mac's native headphone outputs! They don't compare to this Groove; it's like comparing a disposable 35mm camera to a LEICA. Sure, either will do the job, but there's really no comparison after that.
Compared to professional gear like Apogee's own Duet 2, this Groove is much smaller and has flatter frequency response.
The Apogee One has even flatter frequency response and more power output into 32 Ω, but it's bigger and more expensive. The One also can play, with two AA cells, directly from iOS devices. The One also has a nice, big volume control knob, but remember you're also paying for its built-in mic and mic preamp, 48V phantom supply and ADC for recording.
1.) Plug into computer.
2.) Set your audio preference to output to the Groove.
3.) Plug in headphones and enjoy.
It's only this complicated the first time.
When you unplug the Groove, your computer automatically swaps back to playing however it did before, and when you plug the Groove back in — even a month later — your computer magically starts playing through the Groove again.
It does this on my Mac Pro OS 10.11; I can't vouch for Windows.
It doesn't work from iOS devices; only from computers. Use the Apogee One to play from iOS.
On Mac the operating system simply recognizes the Groove as another available output for you to select, and once you do, it keeps using it.
It's always ON, even if my Mac Pro (OS 10.11.3; late 2013) is asleep.
it draws 1.7 watts and is supposed to run warm sitting on a desk. If you wrap it in a blanket so the heat can't dissipate, it can get very hot. Don't do that.
The volume controls work on your Mac or on the Groove. The Mac's volume control works in big steps as it always does, and the Groove has very fine control.
The system is so brilliant that as you press the volume keys on your Mac keyboard, the Groove changes its internal gain. You aren't attenuating or truncating the digital signal fed from the Mac before it hits the DAC; the Mac and the buttons on the Groove are both changing the analog gain inside the Groove. It's brilliant.
The Mac controls are coarse and don't cover all the quietest settings, but they are fast.
The Groove's push buttons are very precise and cover a huge range, but they're slower if you need to make a big change.
Apogee is brilliant: it has only three variable-color LEDs, and with these three LEDs Apogee can show us just about everything we'd need to know:
A single BLUE LED means that it's on, but nothing's playing. You'll see this when it's idle, music is paused or your Mac is sleeping.
The three GREEN LEDs show the level of the digital audio stream - not the analog output level.
If you get a digital clip, the top GREEN LED turns RED for an instant.
All three GREEN LEDs light above about -3 dBFS.
Two GREEN LEDs light above about -10 to -4 dBFS.
Only one GREEN LED lights above about -30 to -20 dBFS.
The GREEN LEDs are off below about -30 dBFS.
PURPLE LEDs show the level of the volume control as you change it.
I use the Grado Mini Plug Adapter to use my studio headphones with ¼" plugs with the Apogee Groove.
The Groove is a made-in-USA, all-metal professional studio product especially built to excel with professional high-impedance headphones.
For low-impedance (32 Ω) portable headphones, I'd skip it and just plug them into my Mac or iPad, or use the Apogee One which is even better for 32 Ω headphones — but that's just me.
This DAC is much better than consumer products for driving professional high-impedance (150 Ω ~ 600 Ω) headphones.
It is much better than consumer products because of its solid 5 volt RMS audio output into 300 Ω and 600 Ω headphones; more than enough level to drive these headphones as loud as you want. Most consumer and Chinese-made products can't put out more than a volt into any impedance, which isn't enough for high impedance headphones.
This is the best portable DAC and headphone amp there is, especially for higher impedance headphones which usually need an outboard amplifier.
Apogee Groove Box.
This ad-free website's biggest source of support is when you use those or any of these links to approved sources when you get anything, regardless of the country in which you live. Get yours only from the approved sources I use myself for the best prices, service, return policies and selection.
Thanks for helping me help you!
© Ken Rockwell. All rights reserved. Tous droits réservés. Alle Rechte vorbehalten.
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01 February 2016