[AudioThief]

Hello.

I was looking through a buy & sell "used" webpage here in Norway when I came over an interesting amplifier.

https://www.finn.no/bap/forsale/ad.html?finnkode=57521113

Its 235$ and while I have no idea about amps, some guy at reddit said it looked pretty solid, so I thought I'd run it by the expert over here at head fi and tell me what you think.

Basically its a student from Norway who makes this out of his bedroom I assume, he wrote up a long text describing and explaining the amplifier, which I will try to translate - DISCLAIMER - I will have issues translating some of the words because I don't even understand what they mean in Norwegian. So a lot of the translation will be very awkward, I hope you understand what it means though.

First, the raw numbers:

- Outgoing impedance: 30mOhm
- Frequency Response: 20hz-20000hz - 0,1dB
- Incoming(?) Impedance: 60kOhm
- Output power (8 Ohm): 2x20W
- Output power(16 Ohm): 2x12,5W
- Output power (32 Ohm): 2x7,5W
- Output power (50 Ohm): 2x5,3W
- Output power (150 Ohm): 2x1,9W
- Output power (300 Ohm): 2x1W
- Output power (600 Ohm): 2x500mW
- Offset voltage: <1mV * gain
- Noise floor: 6uV rms (-102dBu) * gain
- Adjustable gain: 1x-3x-10x-24x (0dB-9dB-20dB-28dB) (Utforming av gainbryter kan variere noe)
- Weight: 1,6kg (3lb ish)
- Dimensions: 220x53x189mm (BxHxD)
- Connection: RCA, phono
- Output (?): 6,35mm jack
- Power Supply: 230VAC 50hz

Here is the guys text about the amplifier, translated:

"Atrox V2 is a home made amplifier and is one of the few class A headphone amplifiers on the market that can drive any headphone without breaking a sweat. Every single component is massively overdimensioned to ensure that there are no weak links. Atrox V2 will drive your headphone to its breaking point no matter its impedance. Because it is a class A design, it will be able to do this with an amazingly low degree of distortion. This is the headphone amplifier for those who put sound quality as a top priority.

Making a stereo amplifier for the living room is in many ways easier than making a headphone amplifier, since the impedance of a speaker is normally between 4 and 8 Ohm. Headphones can have an impedance ranging from 16 to 600 Ohm which makes it hard to find an amplifier that does a good job with both extremes. Most headphone amplifiers will do an OK job with low impedance headphones, but run into issues when facing headphones such as the Sennheiser HD800 with a 300 Ohm impedance. There are headphone amplifiers made for high impedance headphones, but these amplifiers might have issues with a headphone such as the Hifiman HE-6 with an impedance of only 50 Ohm. Atrox V2 handles the entire range of impedances and sensitivities. Even if you do not need a lot of output power, thats no issue. Atrox V2 has a gain adjustment which means you can alter the amplification to match your headphones requirements. The gain is controlled by a knob at the back of the amplifier and can be adjusted to 1x, 3x, 10x or 24x.


If the amplifier was given the task to amplify a sine wave, it would be easy to figure out the ideal output power. But since this is music we are amplifying, it becomes more complicated. Music is extremely dynamic and might have short "maximum values" (?) which are many times higher (?) than the average sound level. If the amplifier is asked to give more sound than it is able to, the signal is clipped which leads to distortion and low quality sound. Since music is of such a dynamic nature, the amplifier will only clip the highest tops of the music (often bass hits), which is hard to directly hear. This becomes an issue if it clips a lot/often. It isn't always registered as an error, but rather it gives a feel of the overall sound quality isn't as good as it could've been. Most people are not aware of this phenomena and will just assume that the amplifier has a low sound quality, while its actually the output power thats too low. Atrox V2 gets rid of the entire issue by having high enough output power to ensure that these short but demanding "tops" are amplified without clipping.

On top of the very high output power, I also wanted the distortion of Atrox V2 to be way below what is audible. To achieve this, I chose what's called a "Class A" design. This means that the transistors has continuing current regardless of the output level. This is a very inefficient design and a lot of the effect(?) is lost as heat, but I didn't choose this design for nothing. Class A amplifiers has a very low degree of distortion and practically removes whats called "crossover" distortion in english.

*Technical part, translation massacre begins*

The Atrox V2 amplifier sctructure is sectioned into a "input" and "output", the input being mainly the amplifier OPA551 which is a high quality rail-too-rail operation amplifier, with a THD+N with only a 0.0005%. (??)
The output step is a class AB push-pull transistorjoint which is "biased(??)" into class A with a continuing current of 150mA which gives it a heat loss of 15W. The power supply is a 50VA+-18VAC, ...

Ok **** this I give up, way too much technical jargon lol. Moving on

Its a misunderstanding that a more expensive amplifier will result in better sound. The truth is that a powerful amplfiier will cost more because the components are larger and more expensive, but a headphone amplifier is not very powerful compared to a amplifier meant for floor speakers. The amplification of a sound signal is a very easy task with todays technology, and making an amplifier without audible distortion isn't an issue. If you pay several hundred dollars for a headphone amplifier, you pay for functionality/features, but you will probably not get the insane sound Atrox V2 delivers. Atrox V2 is an amplifier which delivers exactly what an amplifier is supposed to deliver - more than enough sound without audible distortion.

About me:

I work as an engineer in Horten and have for many years been passionate about amplifiers. Since headphone amplifiers are a niche product, a lot of manufacturers has taken the liberty to charge uneccesarily much for their amplifiers. My main intention is to prove that good sound doesn't have to cost a lot, and by doing so I have made an amplifier that is high end when looking at specifications and output power. The feedback I have recieved have been overwhelmingly positive and my amplifier has been tested with a wide range of headphones (Hd600, HD650, HD800, Hifiman HE-7, He-300, a wide range of AKG products ++. The reason the price is so low is because I take minimal profit. My intention behind this product is not to make money. If you are not satisfied, I will give you the money back. "


Sooo.. with all that out of the way.. What do you guys think? Does it look decent? I snooped around and find some mentions of this model on Norwegian forums. Apparantly this is the second ampl this guy has made, and his former amplifier was well recieved as well. It has been described as "a bit dark sounding" but high quality.

 

[Tullebukk]

I just got one today, and it sounds excellent. Upgraded from the Aune x1s and it was a good upgrade from the excisting output, giving more oomph in the low end and a tiny bit smoother in the top. Can't go wrong for that price!

 

[AudioThief]

I just got one today, and it sounds excellent. Upgraded from the Aune x1s and it was a good upgrade from the excisting output, giving more oomph in the low end and a tiny bit smoother in the top. Can't go wrong for that price!

I've read that its on the darker side. Would you say that is correct? How do you find the detail retrieval?

 

[Tullebukk]

I've read that its on the darker side. Would you say that is correct? How do you find the detail retrieval?

Didn't find it dark, just slightly less peaky in the treble. Bass is enormous though, just a very musical amp.

 

[401133]

Didn't find it dark, just slightly less peaky in the treble. Bass is enormous though, just a very musical amp.

Does it help bringing the bass forward on the M1060? I currently have the NFB-11, and might consider purchasing the Astrox as an amp to the M1060 (as DAC), if it improves upon the bass -- which some people with powerful amps have claimed.

 

[daySpring]

It is not dark at all. I'd say, quite flat. Since it doesn't sweat powering the higher impedance lower frequencies of dynamic drivers, the bottom end sounds full bodied on so called bass-lite cans like K702, which may give the illusion of being 'dark'. I find the high ends just as extended on the K702 as on the Magni2. While it is just as detailed and clear (perhaps a hair more) as the Magni2, it keeps the sound from getting too harsh and shouty on certain tracks because of the fullness of the sound.
The headphone out 1/4 female jack isn't the best I've seen on high end amps and it doesn't mute itself while inserting headphones, so if the music was already playing on high volume, the momentary short while grounding the plug may send out a jolt to the drivers. I don't know if it can damage a sensitive headphone in the long run or not, but lowering the sound volume or pausing the music while inserting headphone plug may be a good practice.

The gain knob on the back it fantastic. It doesn't send a jolt up the wires to the drivers while changing gain on the fly. That certainly is a huge upgrade to my magni2, which makes me cringe every time I flick the gain switch at the back.

I like the black background on the quiet parts of the song, even on the highest gain (digital volume close to zero to test out such a setting on a DT880 600 Ohm). Helps illustrate the dynamic nature of a piece of music when the whole orchestra starts playing loudly, giving the feel all hell breaking loose compared to clearly hearing a single pluck of a string a few moments earlier.

The box itself is quite weighty and has a solid high-end feel to it. While it doesn't get too hot, I think having a few vents on the side like the Matrix/M-stage HPA2/4 wouldn't have hurt. It doesn't get as hot as the M-Stage though, after being used for 6/7 hours... but the M-stage is notorious for getting too hot, sometimes even giving out slight 'burning' smell.

I haven't had mine for too long and only time will tell it the Atrox-2 keeps on operating without issues for years to come. Being hand made and all, I am very satisfied with the unit I received in Canada, but quality control may be an issue when a single artisan is making all the units.

Tor-Arne, the designer of Atrox-2 seems like a very nice and helpful guy and answers any questions promptly. He changed the power supply on the unit I ordered from 220V to 110V on request. If you are not worried about geographic distance and not having a big corporation with a lab full of technicians ready to support the product and can trust the quality provided my a one man manufacturing plant, this amp is one of the best bargains in the hi-fi head-amp market right now.

This lets T1-2 keep its 3D immersive sound-stage, make the HD650 sound laid back yet not too veiled, M1060 alive and punchy, let TH-X00 and HD380 shake the head like a subwoofer without muddying up the lower mids. This amp does everything so effortlessly, allowing music to take centre stage and the headphones sound as they are, without drawing attention to itself or it's 'sound signature'.

Does it help bringing the bass forward on the M1060? I currently have the NFB-11, and might consider purchasing the Astrox as an amp to the M1060 (as DAC), if it improves upon the bass -- which some people with powerful amps have claimed.

I didn't notice clear dB boost in the lower bass/sub bass, compared to Magni2. The M1060 is quite accurate and punchy on most amps I tried them on, but have to say, none of the amps I tried on cost a four figure sum.

Atrox 2 is not a fully discrete design amp and I don't know if that plays a part in the so called 'night and day' difference in bass response, especially when the power output capability of the amp is remarkable.

 

[AudioThief]

It is not dark at all. I'd say, quite flat. Since it doesn't sweat powering the higher impedance lower frequencies of dynamic drivers, the bottom end sounds full bodied on so called bass-lite cans like K702, which may give the illusion of being 'dark'. I find the high ends just as extended on the K702 as on the Magni2. While it is just as detailed and clear (perhaps a hair more) as the Magni2, it keeps the sound from getting too harsh and shouty on certain tracks because of the fullness of the sound.
The headphone out 1/4 female jack isn't the best I've seen on high end amps and it doesn't mute itself while inserting headphones, so if the music was already playing on high volume, the momentary short while grounding the plug may send out a jolt to the drivers. I don't know if it can damage a sensitive headphone in the long run or not, but lowering the sound volume or pausing the music while inserting headphone plug may be a good practice.

The gain knob on the back it fantastic. It doesn't send a jolt up the wires to the drivers while changing gain on the fly. That certainly is a huge upgrade to my magni2, which makes me cringe every time I flick the gain switch at the back.
*SNIP*

Awesome post man. I'm placing my order for the AtroxV2 today. I'm from Norway my self and want to support a local artisan, and it seems to fit my next pair of headphones (TH900) perfectly.

 

[AudioThief]

@daySpring

I recieved my unit today. initial impressions via Fostex TH 900, HD650 and JVC HPDX1000 are VERY positive. This amp is no joke! How are you finding yours and what pairings do you have? Oh and how did you find Forsmo Audio ? On ebay?

 

[FastAndClean]

this or magni 3?

 

[AudioThief]

this or magni 3?

I haven't seen much about the magni 3, been busy so not had my head in this industry lately. But I'm going to go ahead and say that the Atrox is probably significantly more powerful at a competitive price. The Atrox outdoes basically all of schiit's current headphone amplifiers in terms of sheer power.

 

[FastAndClean]

yes but i will running oppo pm3 and t50rp mod, they are not hard to drive, but i v read that more power, better control of the driver

 

[FastAndClean]

here in Norway magni 3 is 1500 kr, Atrox is 2000, i am trying to decide between the two, i don't really need that kind of power, but maybe is better to have it, you never know

 

[AudioThief]

here in Norway magni 3 is 1500 kr, Atrox is 2000, i am trying to decide between the two, i don't really need that kind of power, but maybe is better to have it, you never know

Comparing the atrox with the earlier iterations of the magni, I felt the atrox had a more balanced tone overall, more neutral bass but overall warmer, a bit less aggressive highs - a bit dark sounding perhaps. I certaintly prefer the Atrox to the earlier Magnis as far as sound goes.

I think that 500 NOK more for the Atrox is easily worth it considering you get specs that are regularly sold for 1000$++. My unit has worked flawlessly and I am very happy with my unit and my interactions with Tor Arne, the creator.

 

[Stevko]

Comparing the atrox with the earlier iterations of the magni, I felt the atrox had a more balanced tone overall, more neutral bass but overall warmer, a bit less aggressive highs - a bit dark sounding perhaps. I certaintly prefer the Atrox to the earlier Magnis as far as sound goes.

I think that 500 NOK more for the Atrox is easily worth it considering you get specs that are regularly sold for 1000$++. My unit has worked flawlessly and I am very happy with my unit and my interactions with Tor Arne, the creator.

Still own your Atrox? Which DAC are you using it with?

 

[AudioThief]

Still own your Atrox? Which DAC are you using it with?

Hi, sorry for the late reply!

I do not own an Atrox anymore as I sold off my entire dynamic rig and got into estats many years ago. I used a dragonfly red and a Hegel HD12 and both sounded great.