MILTRA OTL-8XT HEADPHONE AMPLIFIER REVIEW

Miltra OTL-8XT Headphone Amplifier is made in Poland, uses an interesting OTL (Output TransformerLess) design and costs €1300. Oscar Stewart warms it up for HiFi PiG.

Miltra are not a brand many of you will be familiar with, they are a small Polish company making a couple of valve-based headphone amplifiers along with a single integrated HiFi amplifier. Each product is handmade and very little is outsourced, meaning the quality of the amplifiers is consistent.

Today we are looking at the OTL-8XT which is the current flagship model in terms of their headphone amplifiers, but it comes in at a very reasonable €1300, proving quality doesn’t always have to cost the earth. 

BUILD QUALITY AND FEATURES OF THE MILTRA OTL-8XT

The main casing of the OTL-8XT is stamped steel I believe; it comes with a solid machined aluminium front plate and there are aluminium trim rings around the valve bases. The volume knob is also aluminium and there are very nice feet on this amp with an aluminium body and rubber feet that prevent it from sliding across your desk. There are 2 pairs of RCA inputs on the back which are of very high quality and a single 6.3mm headphone output on the front. There are 2 buttons on the front of the amp, one for the power and the other for switching between the 2 RCA inputs. I believe the outer casing that houses the transformer is aluminium with an aluminium top cap that has the branding embossed in it. 

The above description doesn’t quite describe how well-built this amp really is though, it feels incredibly solid and the valve sockets are nice and tight. It is also an extremely good-looking amp in person and it came shipped in a wooden crate. Everything feels very well put together, a lot of thought and care has been put into making this amplifier. 

It runs in full Class-A topology and uses high-quality Vishay, WIMA, Nichicon and Alps components, the rear power valve is a soviet made 6N13S which can be replaced by 6AS7G or 6080 valves (6080 valves will need socket savers to bring them up in height). The front driver valves are Soviet-made 6H8C and can be replaced with the common 6SN7 variant. The power transformer is hand-wound in-house by Miltra which is quite impressive too.

There are a couple of little features that stand out on this amplifier, the first is perhaps the delayed warm-up procedure which helps prolong the life of the valves. It takes a couple of minutes to warm up and the LEDs around the volume knob slowly change one by one showing you how far into warming up it is. The second is the volume control itself, the knob is glorious and super smooth due to using a 10mm brass axle mounted on two ball bearings. It uses a relay ladder resistor-based volume control that is microchip controlled, allowing for perfect channel balance at any volume and that distinctive clicky sound when adjusting the volume. The LEDs around the edge of the knob indicate the volume level, this is probably the smoothest volume knob I’ve had the pleasure of using.

SOUND QUALITY

Now, it’s no secret that OTL (Output Transformer Less) valve amps work best with high-impedance dynamic headphones so for this review I mostly used high-impedance dynamic headphones, but I did throw in some planars too as they have flat impedance curves, and my Grado’s for good measure. 

This amp is highly enjoyable to listen to on a subjective level, using the S.M.S.L D6s DAC to feed it a clean audio signal the OTL-8XT then colours the sound in a very pleasant way. This is still a very detailed amp, it will not smear the finer nuances in the tracks you are listening to, but there is an effortlessness and ever-so-slight smoothness to this amp that makes me want to listen for hours on end. Both my German Maestro GMP400 and Beyerdynamic DT880 600Ohm headphones are quite flat and boring-sounding studio headphones that both come alive when used with a good OTL amp. 

Take Linkin Park – Easier to Run, on the GMP400’s through a more linear solid-state amp the bass line gets a little lost, being too controlled and flat, they don’t quite have the impact required for this song. Through this system, you get all the insight with a little more body and articulation in the bass region. These headphones become a lot more enjoyable for music playback when listening through the OTL-8XT, even if they are slightly less accurate.

The Beyerdynamic DT880 600Ohm simply sing through this amp, this is a relatively inexpensive headphone but one that really does scale with good amplification behind them. Spiritbox – Secret Garden is a brilliant song and Courtney LaPlante’s vocals are intimate and detailed, the guitars have excellent power and the driving bass line is controlled yet full without becoming overbearing. There is only a hint of extra warmth from the OTL-8XT which is a good thing in my opinion, but it does take the edge off sharper notes and has a slight fluidity to the sound that works so well with this kind of headphone. I also find that this amp helps with the soundstaging a little, it’s not a huge difference, but the sound does have slightly better width and depth to it.

I also used this amp with the Sennheiser HD660 S2 and found that to be an exceptionally good match, for some reason instead of smoothing out an already smooth headphone, this amp makes them sound a bit more dynamic and punchier with better separation and control. I’ve had this before with the HD650, a headphone I found quite bland until I heard them with a good OTL amp, upon which they really came to life. 

Now, the HiFiMAN Susvara are a headphone that usually use many, many watts of power to make them sing but, the OTL-8XT manages to drive them a lot better than I expected. Planars have a linear impedance curve meaning they don’t usually suffer from the downsides of high-output impedance of OTL valve amps. Yes, at loud volumes I can get the amp to clip, but at my normal listening level the Susvara sound excellent with this amp. They retain the snappiness they are known for, but with a very natural and smooth sound and they don’t lose any impact and spaciousness at the levels I tend to listen at. I’m not going to say run out and grab this amp if you own the Susvara, but it really did surprise me that it drives them well in my setup. Pierce the Veil – Death Of An Executioner has quite a prominent bass guitar line that’s well articulated via the OTL-8XT / Susvara combo, whilst kick drums hit with good punch and depth. This amp manages to portray the treble in a very smooth manner but without making the amp sound dark. There is no doubt that an amp like the iFi iCAN Phantom can push these headphones further, but I found myself enjoying this combo a lot. 

Trying an easier-to-drive planar, the recently released Fiio FT5, this amp handles them without issue and sounds excellent whilst doing so. These are quite a smooth headphone already and this amp might tip them over to being a little too warm for some tastes. There is excellent control and air to the sound and even with the full low end these headphones have this amp seems to work very well with planars… which is good. The OTL-8XT is a little more powerful than some OTL amps, but, as always, finding synergy between your headphones and the amp is key. 

Plugging in the less-than-optimal impedance Grado SR80i does make them sound a little under-damped and the bass becomes a little bit loose, but it does an admirable job at keeping them clean and detailed. This is not an optimal pairing, but then again, this amp is not designed for this kind of load so I cannot complain.

I’m a firm believer that any headphone enthusiast with high-impedance dynamic driver headphones should try an OTL amp with them. Purists might scoff at valves and their distortion, but the reality is that our brains process this distortion as subjectively enjoyable. Now, I’m not saying you should jump right to this particular amp, Miltra do make a slightly more budget-friendly OTL-PCL8, but if you do have a set of headphones that you are enjoying with a valve amp this might be the logical step up for you. 

One of the best features about these amps though, is the ability to roll the valves. I’ve been trying this out a little with the OTL-8XT by fitting some RCA 6AS7G power valves and Hitachi Japan 6SN7GTB valves which is a lovely pairing. There’s a wealth of information on the internet about how different valves sound and it’s easy to get lost in this – try some for yourself and enjoy the subtle differences the different brands and constructions have to offer. In the meantime, you’ll find me with my legs up, sitting back, and enjoying song after song from the OTL-8XT. 

QUIBBLES

As with any OTL headphone amp, it won’t pair well with all headphones, but that’s just how they are. 

CONCLUSION

In the grand scheme of headphone amps €1300 for the OTL-8XT is not a lot of money and this is a fantastic amplifier if you like the sound OTL amps can provide. It’s not a smoothed-over, dark-sounding amp that will make everything sound like it’s behind a blanket, instead, it retains an ease in its detail retrieval and a spacious sound that just sounds effortless. I won’t deny that there is a hint of warmth and smoothness to this amp, however, it won’t drastically change what you are listening to and, instead, I find it to subtly enhance the right headphones. 

Miltra has managed to build an excellent amp for a very reasonable price. It’s not an entry-level amp by any stretch, but it would suit someone who has an entry-level OTL headphone amp and is looking for the next step up. It’s got some excellent features that are backed up by a sound that has all the traits of a very well-designed amp; clarity, depth, and the ability to make you want to listen for hours on end. 

So besides the looks and feel, it also sounds fantastic and has excellent driving capabilities, it will work well with all high-impedance dynamic headphones and also quite a few planar magnetic headphones out there.

AT A GLANCE

Build Quality And Features:

This is an extremely solid amplifier

High-quality components are used throughout

Well-thought-out design

Sound Quality:

Fluid and dynamic

Clean yet smooth-sounding headphone amplifier

Value For Money:

In the grand scheme of things, this isn’t an expensive amplifier for what you get so I think it is very good value for money. 

We Loved:

The looks and build quality are matched with effortless and engaging sound quality. 

We Didn’t Love So Much:

Get the pairing wrong, and it won’t sound all that good at all. 

Elevator Pitch Review: If you’re looking for an OTL headphone amp in this price bracket, do consider the OTL-8XT! It is superbly built and a pleasure to use. The sound is smooth yet detailed, has great depth and, pairs beautifully with high-impedance dynamic driver headphones. Take some time to match this amp with the right headphones and you won’t want to stop listening when this amp gets you lost in the music. 

Price: €1300

Oscar Stewart

SUPPLIED BY MILTA 

SUPPLIED SPECIFICATION

• Output power RMS: sinus 1KHz @ 250Ohm – 550mW per channel
• Frequency range: 10Hz – 60kHz +/-3dB
• Volume control range: -78dB to 0dB with resolution 1dB per step
• Dimensions: 284x170x205mm (LxWxH)
• Weight: 7,5kg