Firestone Fubar IV headphone amp/DAC in Review – effin’ good!


Firestone have hammered the last studs into their newest audio block just in time for Christmas. The Fubar IV headphone amp/DAC continues the tradition of excellent price/performance for which Firestone are famous and even enjoys a price reduction from last year’s model. This amp sports USB input which makes enjoying high quality music from your computer a breeze and in the same breath, hooks up to SPDIF and digital coaxial input for direct lossless listening from HiFi sources. Finally, it has also wormed its way into my heart with its excellent pre-amp and even-Stephen sound.


  • Amplifier Structure : Coupling capacitor less, Push-Pull with Class-B
  • Linear Output : RCA output 2Vrms, delay time phone out funtion
  • Power Structure : Switching power supply, Soft-Star circuit
  • Gain Control : Low (attenuation 20dB) / High (normal)
  • Volume Control : Series / shunt mode selectable
  • Headphone Impedence : 32 ohm to 600 ohm
  • Circuit Protect : Output short / over current protect
  • Support Format : 16-bit, 32 / 44.1kHz / 48kHz
  • USB Chip : CMedia – CM108
  • Receiver Chip : TI – DIR9001
  • DAC Chip : TI – PCM1754
  • LPF OPAmp : TI – OPA2134
  • Main OPAmp : TI – OPA2604
  • Servo OPAmp : TI – TL072

Build and Packaging
Im typical Firestone fashion, the Fubar IV comes in a strong extruded aluminium chassis which is bolted together into a veritable brick of audio goodness. The amp’s front panel has a single full-size female phono jack and a large analogue volume pot which bares nary more than the Spartan volume indications: + and -. Power is engaged on the rear panel via a horizontal toggle which is a bugger to get at especially when operating in either optical or USB mode. Ergonomic issues aside, the army of audio input and output on the rear panel is spaced just well enough to remain under the radar of annoyance when the amp requires to be moved and unplugged. The Fubar IV is roughly the same size as the Travagan’s Red, so the biggest barrier to perfect ergonomics isn’t the number of connections, it is the size of the amp.

Its volume pot rotates with the slightest of mechanical grinding, but has lots to love; you cannot help but stare no matter how politely you try to ignore it – it is huge. Inside the box is one 1,5 metre USB cable and a fatter-than-Monster RCA to RCA audio cable. Firestone skimped on the power supply, but not much else. The entire package is housed in a cute “Merry Christmas” branded cardboard box. And if you have good eyes, you will find a tiny allen key which after a few grunted twists, will open the Fubar IV up for op-amp swapping.


The Fubar IV really tries to compete in the growing niche of do-it-all audio products. Audio input comes in 3 digital flavours: USB, Coaxial, and Optical SPDIF. Its preamp section passes the message on from sturdy analogue RCA outputs. So how well does it work? Speaking for the pre-amp, outboard connection to other audio equipment is really a table of spades including quality signal which bests thtravae headphone out.


While the Fubar IV features a no-hassle USB input, I generally used the excellent SPDIF optical input. What isn’t advertised in the Fubar’s spec list is that it can also drive low ohm earphones. The spec sheet shows 32-600 ohm, but it easily drives a great frequency response down to balanced sensitive armature earphones which cause many home amps to squeal in pain. Mind you, listening to the Fubar IV through earphones isn’t optimal – we will see this later.

The two gain modes: high and low, work well for a large variety of headphones. When listening to the 600 ohm DT880 in high gain mode, I set the volume to a comfortable 9 o’clock, and to about 12 – 1 o’clock when in low gain mode. And if you’ve had enough with the stock sound signature, the Fubar IV can be disassembled for op-amp swapping.


Audio Performance
There isn’t much to decry. Firstly, even with low ohm headphones, balance is very good at low volumes. On low gain, volume hungry headphone like the 600 ohm DT-800 will reach uncomfortable levels when the volume knob is turned much past 50%. Toward 100%, it will be too much. But, at extremely loud volumes, the Fubar IV distorts heavily past 3 o’clock on the volume pot, leaving the last 30% of the signal a messy affair. Coincidentally, the same is true for the Travagan’s Red which was built by former Firestone engineer, David Lin.

Where the Fubar IV trumps the Red; let me rephrase that: where the Fubar IV smacks the Red around with a frozen fish is in its unadvertised low ohm headphone output. The Red can drive a reasonable signal into 32 ohms, but when faced with balanced armature earphones, it dies in its tracks, losing its otherwise pristine frequency response. The Fubar IV on the other hand, handles the odd impedance swings of balanced armature headphones very well, providing full bass and low distortion even with the hard-to-drive FitEar Private 333. The only casualty is some treble roll off, but then again, who listens to mains-powered headphone amps with inner earphones anyway?


That point leads to the Fubar IV’s biggest output problem. While it sustains pristine response, and as I will venture to praise later, smashing bass, its headphone output is noisy. Even my DJ1Pro can detect a small amount of background noise in one channel regardless of input method. The DT880 of course, is free from hiss at all but the highest of source/amp volume settings. Earphones are another story. Each hisses like an orgy of angry grandmothers, but thankfully, the Fubar IV everything else well.


Let’s drop literal explanations from here on out. This amp sounds good. It has a strong signal, great frequency response, and if I were to apply an adjective to it, it would be something like: square, but that word is often construed negatively. In my terms, ‘square’ means full, resolved, and well-shouldered. It hits the low notes great, rumbling both little and big headphones very well. And, it is full of solid, dry PRaT which errs on neutral side of foot-tapping. Both the Red and the IV sound very good in their price ranges, but the Fubar rolls a drier, stodgier fag between its teeth and puffs a signal which would satisfy a trucker.

Vocal genres maintain throaty resonance, soundtracks smashing stage, and guitars wonderful speed and space. But balance, neutality, and PRaT take precedence over finesse. Cymbals lack a bit of magic sheen, and female vocals that last smidgeon of saliva which flows on spiky treble/mids. Guitars, pianos, strings: natural instruments carry great body and texture. It carries the traditional solid-state signature well, but leaves a bit of beef between headphone speakers for a thick, satisfying sound which has no glaring faults or glorious strengths.

Chart Disclaimer
This review’s RMAA measurements reflect the performance of the Fubar IV when fed optical signal from an Edirol FA-66, and USB from a MacBook Pro. RMAA tests, however, only tell one side of the story: signal quality. They don’t relinquish the finer details: those bits which tickle the ear, which make you blink and go, ‘wow’! These results are applicable to my equipment only and should be used as a reference for general sound quality, not a definitive answer.

Audio Conclusion
The Fubar IV is a massive upgrade to any computer headphone output, and will be a good investment for optical-toting HiFi systems. Another even-Stephen performer, it does bass, mids and treble powerfully, if erring on the side of neutral. It also passes on a pristine signal to external audio equipment. But no matter how well it performs, it isn’t a great mains amp to pair with earphones of any type; more specifically, if hiss concerns you, stay away with highly sensitive headphones. Apart from that, volume is well-balanced and the gain system works well.

But Firestone have to clean up two issues. Firstly, the ON/OFF switch pops loudly when disengaged. I have owned and used many amps at various price points and among all of them, the Fubar IV is the most annoying. I would suggest to keep your headphones unplugged whilst engaging/disengaging its power. And considering the smashing performance for headphones from less than 16 ohms to 600, it is too bad that the amp hisses as much as it does with earphones because its sonic qualities aside from that, are excellent.


Firestone’s sights are set reasonably high. This 220$ amp/pre-amp/DAC combo does most of what I would expect from a much more expensive piece of equipment and it does it well. Many ‘DAC’ toting amps boast USB input, but little else. The Fubar IV manages to squeeze in SPDIF and digital coaxial as well. It also sounds good, so long as your headphones aren’t hiss-prone. It does very well with all of my headphones, providing flat, strong signal in all frequencies, and great space and breath. If Firestone would fix the mains ‘pop’ and the unit’s hiss with low-ohm headphones, they would have a killer audio unit.

Till then, though, this all-in-one will have to settle for a GRAB.


Amp Summary
Title:Fubar IV Headphone amp/DACDeveloper:Firestone Audio
Price:$222Amp Size:
  • Great packaging
  • Good sound
  • Input array is impressive
  • Can drive a lot of headphones
  • Good pre-amp functionality
  • ON/OFF pop is annoying
  • Hiss with sensitive headphones, even DJ1Pro

Headphone amps and DACs help your headphones get the most out of their transducers. Take a look through our headphone section for suggestions of good upgrade/sidegrade options, and our headphone amplifier section for suggestions on how to wring out the best performance from your beloved phones.

  • Dave

    Couldn’t the hiss be caused by that cheap power supply? If you bought a new regulated one it would definitely appear – the Firestone Supplier is also there for that.

  • It is possible, but my review is based solely on the stock product. I did not op-amp roll and will not change power supplies. However, the cheap power supply of the Graham Slee Voyager doesn’t mean that it hisses as much – in fact it does not. I think it is more of a design decision or flaw on Firestone’s part, but I would be happy to be proved wrong. Otherwise (apart from the horrible pop), it is a very good product, especially for the dosh.

  • Dave

    Yep, I understand that. The hissing just makes it seem like a power issue. If I can hear it, I will definitely try out a better one to make sure. Those cheap supplies cause lots of distortion due to unstable output.

  • I look forward to your thoughts, Dave. Cheers!

  • Dave

    Got the device and I am running it through K701s – with the damn hissing present. I also bought a regulated PSU but the plug was too long – I have to get a different one asap. This can’t be a design decision and it has to be a mistake that wasn’t noticed. My soundcard’s internal amplifier plays the same songs without missing – and I tried various tracks as well. Without anything playing the hissing can be heard when the volume is at approximately one o’clock. I need to do more testing and get the regulated PSU. That background hiss is a big downside if one wants to listen to neutral and natural sound.

  • Dave

    Alright, the sound is a lot better now. Got the regulated PSU which boosted the quality of small details by a lot. The hissing is there when the volume knob is at 2-3 o’clock but those volume levels are hazardous to hearing anyway.

    After a burn in, testing and a/b comparison with soundcard’s internal headphone amplifier and Genelecs, the sound is just like you described in the review. Beware, with a good product you start hearing normal recording background sounds better and better. I believe that caused some of my comments above.

  • Dave

    Hi again,

    Could you also try to set the Fubar4 to shunt position by adjusting the DIP switches that are inside. I think that the hiss isn’t as loud at shunt as it used to be at series.

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  • Aubrey

    This amp is super cool which designed like a card.I am using an Amp Sony TAN 5550 with power FETs and ES-820 ebony wood headphones. Can you tell the diference?

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  • Hello Dave, 
    May I know, what brand & type regulated PSU that you use ?

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