Review - Drop Cavalli Tube Hybrid (CTH)

Review - Sennheiser HD6XX

(si prefieres ver esta review en español, haz click aquí)


The Sennheiser HD6XX are a set of headphones that were one of the first to join my collection and I have not posted a full review of them until now. I will get to the reasons why I haven’t posted my impressions of these headphones in just a moment but first, mainly for those who are reading this in Europe, let me explain what the HD6XX are.

In short, the Sennheiser are the same as the Sennheiser HD650, a headphone that is sort of legendary in its own right. They were introduced almost 20 years ago and are probably one of the most reviewed headphones ever, along with the HD600, another legendary set of headphones that look almost identical to the naked eye.

The HD6XX was released by Massdrop (later renamed as Drop) in 2016 and quickly turned into a huge hit for the company. For those that have never heard of Drop, it is an American company that started out by working as a middleman between many individuals and negotiating “group buy” prices directly with manufacturers. They went on to release Massdrop exclusive models, such as the HD6XX and many others since.

Although (Mass)Drop did have a European base for a while, this was later closed and, as far as I am aware, the only way to purchase in Europe is from the US, with the shipping and import costs that go along with it. In the case of the HD6XX, this is currently available from Drop for $220 but once we account for shipping, import costs and taxes, the price becomes almost the same as purchasing the regular version in Europe, which makes more sense from a warranty point of view, as any warranty claims with Drop involve shipping the product back to the US.

So, if this is a product (the HD6XX) that is difficult to purchase in Europe and also has hundreds (if not thousands) of reviews already, why am I deciding to post this review now?

Well, due to the fact that the HD650/HD6XX is such a widespread headphone that is the first step into high end headphones for a lot of people, they are a very good reference point for getting a feel for a reviewer's tastes and how they interpret what they hear. For this reason, I think it is a reference point that is good for me to include in my reviews.


I said that there were reasons for me not posting a review of these headphones (until now) and the fact is that the Sennheiser HD6XX/HD650 (from now on I’ll just refer to HD6XX) is a headphone that depends very much on what it is connected to. 

Research on the HD6XX will return results speaking about the scalability of these headphones over and over again. Out of the headphones (and IEMs) that I have tried, these are by far the ones that exhibit the most changes when moving between amplifiers. On all of the amps that I currently own (Atom, Heresy, MCTH, L30, P20 and a couple of other options) along with others that I have tried, these headphones sound slightly different on all of them. Don’t get me wrong, they always sound like the HD6XX, but different amplifiers seem to bring out different nuances in the headphones. The same can be said for the tubes in my hybrid amps, while other headphones do react slightly differently with different tubes, the differences are more noticeable (for better or worse) with the HD6XX.

Another issue that has stopped me from reviewing these headphones is the fact that they are also the headphones that are most dependent on my mood. There are days that I can sit for hours listening to the HD6XX, loving every minute, and others when after 2 or 3 tracks I have had enough, no matter the amp or music I am listening to. I have said on many occasions that I am not a huge lover of overly warm headphones and the HD6XX do have a warm signature to them, but I’ll get to the sound in just a moment.


In the case of the HD6XX, the Drop version, these come presented in a rather large box which flips open to reveal the headphones in a sponge cutout along with an overly long cable sitting in a cut out below them.

That’s it, there is nothing else to add, so this bit is nice and short.

Build and aesthetics…

As always, aesthetics is a very personal thing. In my opinion, the HD6XX looks (and feels) cheap. Simple dark blue plastic frames and headband, with very open and simple grilles and velour pads. Others may like the look of them but I am not a fan.

As far as build quality, as I just said, they are made of what appears to be cheap plastic, with a very simple grille that reminds me of a car speaker grille from the 80’s. The only metal parts are the grilles and the extension of the headband, which is just a simple thin metal plate.

Based on all of this, one would expect these to fall apart at any moment but there are people who have been using them for nearly 20 years (even more in the case of the H600 which has identical build) and have had no issues. They are also built in a way that allows you to completely dismantle them and replace any part that may break, without the need for any tools!

So, although my opinion would be cheaply built, they certainly seem to withstand abuse.


The qualities of the HD6XX change depending on the system to which it is hooked up. I am not saying that there are night and day changes and that one day it is a bass cannon and the next it is neutral and detailed, the sound signature of the headphones stays the same, it is the way it presents that sound signature that changes.

While I use these headphones on multiple setups, depending on my mood, the following impressions are while using the JDS Labs Atom which is a common low cost neutral amplifier. My preferred system for the HD6XX is actually with one of my hybrid amps (which I may comment on briefly at the end) but I am choosing the Atom as it is more commonly found and is more neutral. Remember that my intention here is for people to form an opinion on my tastes and how I hear the HD6XX rather than people forming an opinion on the HD6XX, as this headphone has been reviewed by more people than I could count.

The subbass of the HD6XX is not extended at all, in fact, below 100Hz the bass rolls off in quite a steep fashion. I would certainly not choose this headphone for listening to any kind of EDM music, or any other music that depends upon sub-bass rumble. The typical track that I mention, “No Mercy” by Gustavo Santaolalla”, is basically missing half of the information throughout almost all the song. 

As I just mentioned, bass rolls of under 100Hz, which means that the normal bass frequencies are pretty subdued also. However, this doesn’t mean that what bass there is doesn’t sound great. The bass is actually very well controlled and bass guitars can sound great on the HD6XX, as what we mostly focus on with bass guitars are their first harmonic, which starts (in the case of a normally tuned 4 string bass guitar) at 82Hz and moves up. By the time we hit the first harmonic of a G, which is the 4th lowest note on a 4 string bass, we are already at 98Hz and the bass is already at the level it should be. This means that, although the lowest regions of the bass may be rolled off, it is still capable of producing very pleasant bass. The song “No Sanctuary Here” by Marian Herzog & Chris Jones, presents an amount of bass that is by no means lacking for the track.

The frequencies at which the higher bass transitions into the lower mids is one of the most present areas in the frequency response, resulting in a very warm sound signature but it manages to not be muddy nor give the impression of bass bleed at all. Due to the fact that the lower bass notes are rolled off, this takes a lot of work away from the drivers, allowing them to perform much better in the higher bass / lower mids. 

In fact, the mids on the HD6XX are its real power. I am a huge fan of simple songs that are based around acoustic instruments, such as acoustic guitars and basses, with vocals that are smooth and laid back. The HD6XX is a perfect candidate for these kinds of music, specifically the voices. When I am in the mood for the HD6XX sound, and the music flows, I find vocals to be intimate and amazing. I could list endless songs that have vocals that are near perfection on these headphones but to give you an example from my test list, tracks such as “Back It Up” by Caro Emerald sound great. Really, I could probably put together a list of a couple of hundred songs just to listen to on the HD6XX.

Up in the higher regions there is not a lot of shine or air, these are warm headphones that can sound luxurious but will not give a feeling of being at all sparkly. Sibilance is not an issue, nor are there any parts that sound harsh at all. I would usually say that I want more up top, more shine, more air, more breathability, but that really isn’t what the HD6XX is about. 

As far as sound stage, these are very intimate headphones. Something that I would usually complain about also but, again, that is not what I feel these headphones set out to give you. Everything seems closer, more personal. Compared to something like the Ananda which could be a large hall, these are about sitting down in front of someone with a guitar that is only singing to you. The placing of images is not that great either. Things are either to the left, in the centre or off to the right (but never far away). These are not headphones I would pick for sweeping sounds or binaural recordings, they just sit you down in front of the artist.

Detail is decent but they are not detail monsters, however, they never leave you feeling that you are missing anything. Using the same term again, it is like sitting in front of the person in a room and just blending in with the music, not searching for nuances. There are many times that these headphones take me back to my younger days when we would sit around with a couple of guitars, a cajon, and just make music as it came out.

Differences between sources…

As I said, these headphones do show differences when they are swapped from one source to another. Although you feel that you are getting a great deal when you listen to them, you then listen to another source and things change. They get better as the source improves but they never really seem to be bad, as long as the source can power them.

I mostly use these with the Loxjie P20 (running triple mica Reflector OTK 6N3P-E tubes) and also with the (Mass)Drop Cavalli Tube Hybrid. I enjoy both amplifiers but both present them in a different way. With the current tubes in the P20 I find that the bass and lower mids become more focused, whereas with the CTH it is the upper mids that seem to take the spotlight.

Also, in the case of the P20, swapping tubes also changes the focus of the sound. The overall sound never really changes, it just seems to draw your attention to a different part of it. The current tubes are my favourite so far and I would happily just reserve the P20 in its current form for use with the HD6XX. Although, I wouldn’t just reserve the HD6XX for the P20, as I find that the changes brought with different systems are part of what keeps the passion for them alive.


All of what I have just said should give the impression that the HD6XX are a great set of headphones, at least I hope I did, and they are, but as I said at the beginning, they are the most mood dependent headphones I have.

Let me try and put it into context. As I decided to post this review this week, I have spent (almost) all week trying to use the HD6XX as my only headphones for listening, something that I always try to do when I plan on reviewing something. On Monday, I plugged them into the P20 on my desk at work and started listening to some of the music I usually really enjoy on them. Within about 30 minutes I felt that I did not want to listen to them anymore. Everything sounded dull and I just wasn’t enjoying the music. I swapped over to the Atom and it wasn’t any better.

As I actually need to get some work done during the day, the feeling of not enjoying the music does not help my production, so I gave them a break and listened to the Starfields (which I usually have on hand most of the time) which stopped me focusing on the music and let me focus on the task at hand. That afternoon, I again tried the HD6XX, with more or less the same result. On Tuesday, I again set out with the HD6XX on the P20 and everything just sounded great. They were smooth, vocals were great, and they were just generally a delight to listen to all day. 

I am not going to start listing each day but basically, depending on my mood during this week, there have been times when I loved the HD6XX and others when I just could not enjoy them at all, even though the only difference was my mental state, all else was equal (source, music, volume levels, etc.). This is something that happens to me regularly, there are many times when I want to enjoy them and don’t, and others when everything just sounds great.

These are really the only headphones that are so extreme in this regard. For example, the Hifiman Ananda, which is an amazing headphone in my opinion (you can read my review here: Review - Hifiman Ananda), is sometimes not the flavour I want at specific times but I don’t feel the necessity to stop listening to them, I just don’t enjoy them as much as at other times. The same goes for the DT1990, they always just sound the same to me, for better or for worse, and I can just listen to them even if they wouldn’t be my pick at that moment in time. One other example would be the Koss PortaPro, a headphone that I find to have a similar sound signature to the HD6XX (note the word “similar”, not identical). I can use the PortaPro daily for hours every day even though I have other headphones that I much prefer (such as the KSC75). For some reason I just find the HD6XX far more polarizing for my brain, there are days when I love them and days when I would sell them to the first passer by, just to love them again not long after.

I know all of this sounds crazy, and it is, but one of the most important parts of enjoying music (for me) is my state of mind at the time. There are times that I want to listen to all of the nuances and details, others I feel like some extra bass and others I just want to relax in smoothness. 

Now, while this review was meant to be my view of the HD6XX as far as my interpretation of its sound so others can reference my preferences, it seems to have turned into something that should be aimed more towards a psychiatrist than an audio crowd. That is probably my main issue, I just sit down and start talking (or writing) and it just goes where it goes.

So, as a recap, the HD6XX are a very capable headphone that are focused mainly on the midrange, emphasizing vocals and presenting them in a smooth and relaxed fashion. They are also a headphone that reacts differently to each system they are connected to.

I guess that last paragraph would probably have been enough for the review, but where’s the fun in that?