Bottlehead S.E.X. [Review]
The following review refers to the Bottlehead S.E.X. kit amplifier which is the mid-level headphone amplifier in Bottlehead's range. The S.E.X. also happens to drive speakers which is a nice piece of flexibility, but I'll get to that later.
This review refers to the non-C4S modded version of the S.E.X. with a later post being dedicated to the C4S modification (a Bottlehead add-on kit similar to the Speedball for the Crack amp).
The S.E.X. is a step up in price from the Crack and sells for around $600 (incl. shipping) depending on your local currency and shipping costs. For the extra money it offers increased versatility over the Crack and maybe better sound, but I'll save those details for later
Before I discuss the build stages it's worth noting that the S.E.X. is an incrementally harder kit to build than the Crack. The same techniques are used, but there are many more connections, many more wires, some slightly tricky components, and various wiring options. This means you need to keep your wits about you and allow plenty of time. I built the S.E.X. with 2 friends and fellow Head-Fiers, Gikigill and Billymav (1 kit each), and we completed the assembly stage in around 3 hours. It then took us from 11am until 2am to complete the hook-up and soldering stage (including a long lunch and moderate length dinner). That's 15 hours in total, but realistically we were on the tools for about 12-13 hours.
All up, I'd recommend allowing 2 relaxed days worth of work to complete the hook-up and soldering of a S.E.X kit, plus a few hours for assembly and an hour or so for testing (assuming no issues arise).
Parts & Assembly
The carton containing the S.E.X. kit is a heavy beast, and when you open it you quickly discover why. In addition to the aluminium chassis plate, the S.E.X. kit includes a power transformer, two output transformers, and two plate chokes that look a lot like the output transformers so be sure to note which is which (it's easy to tell by the fact that the plate chokes have wires already attached).
As per the Crack (and all Bottlehead kits as I understand it), instructions are provided on a CD so that you can print or view the manual electronically. Once again the instructions are exceptionally clear and well thought out.
Also just like the Crack, the first step for the S.E.X. is to assemble the components such as the chassis plate, terminal strips, RCA terminals, and tube sockets (plus a few other parts). This is just a simple case of following the instructions and wielding a screw driver and pair of long nose pliers from time-to-time.
Once all of the assembly is complete, you'll have something that looks a little like the image to the left except yours will be a silver / aluminium colour, not browny bronze like mine, but I'll get to that.
Now, when you see the image to the left, you might be thinking "Hang on, he said assembly only so far, but I can see wires!" and you'd be right. If you want to stay solder free in stage 1 you could just mount the power transformer only, but if you're happy to include about 5 minutes of simple soldering then you can pre-wire and install the output transformers and plate chokes.
At whichever stage you choose to install the chokes, etc. you need to make a decision. Unless you've ordered the optional impedance switching kit (not reviewed here), the wiring of the output transformers will directly influence what the amplifier is optimised to drive. You can wire the S.E.X. to drive a 4, 8, 16, or 32 ohm load and that basically means you choose to wire it to suit speakers and headphones (4 / 8 ohm) or for more dedicated headphone use (16 / 32 ohm). I chose 8ohm wiring because I'd like to be able to use it with some bookshelf speakers I have, but my main priority is headphones. If using the S.E.X. with particularly power hungry headphones you would probably want to wire for 32ohms or buy the impedance switching kit that allows you to change impedance by simply turning the amp off, lifting the chassis plate and throwing a switch or two (as opposed to rewiring the output transformers which is what I would have to do).
Once again similar to the Crack, the final step of assembly is attacking your chassis plate with a permanent marker to number each terminal for the upcoming hook-up stage. This numbering system is truly a godsend and helps both with wiring and trouble-shooting if needed. For example, when something's wrong with the tube heater power supply it allows one of the gurus from the Bottlehead forum to tell you to check the C-strip (the terminals numbered C1-C5) rather than trying to explain it component-by-component.
When I built the Crack I was too excited to pause for any kind of custom painting or finish (except for staining the wooden base) so the S.E.X. gave me a chance to play.
If it's your first ever kit you may find summoning the patience difficult, but it can be very rewarding. I was fortunate that I had to wait while we found a date that worked for all 3 of us in the build group so I had idle time to play with the looks of my S.E.X.
I really wanted a vintage, art deco look for my S.E.X. so I ended up choosing an bronze colour anodised finish on the aluminium chassis plate (costing around $60) and I painted the visible metal parts on the plate chokes and transformer bell using simple, cheap spray paints from the local hardware store. All up, the customisation cost around $80-90 and a whole lot of patience and prep-work.
If you're painting the metal parts you really need to do the prep well as many of the parts will have resin on them as part of the manufacturing process. The resin doesn't play nicely with primer or paint so take the time to remove it thoroughly first time or you'll have to do what I did and strip back your first attempts (yes, that's multiple attempts - it took me more than one go to get this right) to start again from scratch.
In addition to anodising the chassis plate, other options are to polish the plate or paint it. It all depends on the type of look you're after so don't be afraid to get creative and you can check out the Gallery thread over on the Bottlehead forums for plenty of inspiration.
One final tip: if you choose to paint or anodise the base you'll need to make sure you connect the earth terminal to bare metal by sanding or filing the metal around the screw hole for the earth terminal.
Hook-Up & Soldering
There's not a lot to say here that I haven't already covered in the Crack review above. As already mentioned, the S.E.X. kit has more components and more wires so it is a trickier process than the Crack, but the techniques and steps are essentially the same.
One thing I will mention is that working with the Schottky rectifiers on the power supply is quite tricky because space is limited and the rectifiers have very thick leads which don't easily bend. The only real tip I have for this section is plenty of patience. There are 4 rectifiers to install and not a lot of space so it can get mighty frustrating and a break and a few deep breaths may well come in handy
That said, now is probably a good time to include some general tips which apply to both the Crack and the S.E.X., but which became increasingly important in the more complex S.E.X. kit where space is at a premium and your concentration may fade as the hours go by.
Top Building Tips
- Check and double-check the orientation of all components that have specified directions / alignments. This includes the tube sockets, power switch, diodes, and capacitors. One error here can completely ruin your day and may destroy the component in the case of capacitors. Not only that, but de-soldering is a real pain in the proverbial, especially in cramped spaces with lots of components.
- Measure wire lengths based on the path they will travel. We found a few times that the lengths specified in the manual were a little too generous or a little tight. This might be because we were working with the metric measurements (mm not inches) and a few of these had minor errors. My approach next time will be to check the origin and destination of each wire and trace its path (around obstacles and components) to get a tidier and easier solution.
- Read the instructions carefully. All of the information and guidance is there, but it can be easy to miss a key detail so always read each instruction again before finalising your work.
I'm not going to discuss the testing stage here so please refer to the Crack review for details about testing.
The S.E.X. is a single ended triode design which essentially uses one triode tube per channel in combination with an output transformer. SET designs are simple (i.e. not lots of components in the signal path) and clean, but not particularly efficient in the scheme of things. For our purposes though (driving headphones and sensitive speakers) they appear to be a good choice and knowing the amount of testing and planning conducted by the crew at Bottelehead, the SET design has no doubt been chosen for its combination of performance and affordability (with neither being compromised, just maximised).
By including an output transformer in the S.E.X., Bottlehead have given us an amp that can drive all range of headphones (including lower impedance models) as well as speakers. That's a pretty versatile offering and although I won't be using my S.E.X. for speakers, I love that it can drive them and a brief test proved that it drove my bookshelf speakers admirably (but not set up properly or for long enough that I'm able to effectively review the sound).
The S.E.X. comfortably drives headphones of all different impedances although I'd recommend drawing the line before you get to the sensitivity and impedance of IEMs. I tried my GR07 MkIIs and found the hum to be pretty bad (amp wired for 8ohms) so to me this is a headphone and speaker amp, not an IEM, headphone and speaker amp.
As for using it with various headphones, I've tried 600 ohm Beyerdynamic T1s, 120 ohm Fischer Audio FA-011 LEs, 75 ohm Ultrasone HFI-680s and some old, cheap 32 ohm AKG K-66s. In all cases, the S.E.X. drove the headphones comfortably and well, but I'll get to the sound in a few moments.
The S.E.X. utilises the very utilitarian 6DN7 tube which is apparently an old TV tube and no longer made, but still fairly readily available as new old stock (NOS) it seems.
From everything I've read, there is no benefit to be had with tube rolling on the S.E.X. because all 6DN7s are essentially the same. I'm yet to test this myself, but the overwhelmingly consistent opinions on this topic make my wallet feel a lot more secure than the Crack with it's never-ending range of new, used and ultra-rare tube options.
Back to the 6DN7 tubes... There are some variants floating around where the base is much thinner. These are referred to as coin-base tubes and may look preferable depending on your tastes, but are apparently no different in sound.
So here we are at the part that really matters. I'll start by talking about the S.E.X.'s sound in general terms before comparing it directly with the Crack.
Remember that the following comments are based on the S.E.X. in 100% stock form and without the C4S add-on.
Before I get into the separate aspects of the sound, I wanted to mention that there is a faintly audible hum when you turn on the S.E.X. with any headphones connected. The hum isn't really an issue once the music starts, but I thought it was worth mentioning the hum.
The Bottlehead site states that wiring the S.E.X. in its 32 ohm configuration produces a particularly low noise floor so perhaps the hum I'm experiencing is a result of the 8 ohm configuration. I've PM'ed Doc about this and will update once I have confirmation. I might also re-wire to 32 ohms if that's the case.
One other aside before I break down the sound: when I first went to test the S.E.X. I plugged in my RWAK100 as a source and my old, cheap AKG K-66s as a test headphone. The K-66s were never a particularly inspiring listen (hence why they're my sacrificial test headphone), but I was absolutely gob-smacked when I heard them from the S.E.X. I have literally never heard such an amazing transformation caused by an amplifier.
Now, I'm not suggesting that the S.E.X. will magically transform your crappiest headphones into world-beaters. What the K-66 experience showed me was that the S.E.X. has a great presentation which will lift many headphones to a higher level than other similar-priced amps, and that it synergises really well with the K-66s for some unknown reason. My other headphones still sound clearly better, but where the gap from the NFB-5.2 is exponential between the K-66 and other headphones, the gap becomes much narrower with the S.E.X.
The treble from the S.E.X. is crisp and clean with nice bite. Through the T1s (which can be aggressive with the wrong treble signal), the S.E.X. presents outstanding detail and clarity in the upper registers, but without any fatiguing edge. Where the Crack seemed to offer a slight bump to the lower treble, the S.E.X. seems to be more balanced across the whole treble range. At first I felt it might have had a slight bump to the upper treble, but I think that might be more that I'm used to a little roll-off from the Crack.
The S.E.X. presents some really nice sparkle with the treble. Across a variety of tracks and with all different headphones, the treble presentation is consistently excellent. Somehow the S.E.X. manages to present the treble clarity of a solid state amp combined with the smoothness of a tube amp - very impressive. Cymbals and percussion have really nice energy with the S.E.X., but it's not overdone or in-your-face.
The mids from the S.E.X. are very similar to the treble - crisp and clean. There's a transparency from the S.E.X. that pairs beautifully with the T1s and I'd love to hear what it can do for headphones like the HD650 which are great, but can sound a little opaque at times.
Turning to Sierra by Boz Scaggs, the S.E.X. produces lovely, warm, liquid mids for the vocals and guitars. The presentation is clean and clear with no sense of slowness or blur. Boz's voice has texture and air while still being smooth and lush. Once again I'd describe the presentation of the S.E.X. as akin to the clarity of a solid state amp, but with the smoothness of a tube amp.
One thing I really like about the mid-range from the S.E.X. is the texture it grants to the instruments. I've been flat-out stopped in my tracks a few times while listening to music as I work. I listen to music via headphones for around 4-5 hours per day while I work so I'm used to hearing the detail and clarity that headphones can provide. Having used the T1s with the Crack for some time now, I thought I was hearing everything in my music, but the S.E.X. proves me wrong almost daily, not by showing me any extra details as such, but by revealing the subtle character of those details.
For example, the other day my music was playing on shuffle when a was stopped dead by a piano chord in a track I know really well, but I can't remember the name of as I write this. What stopped me wasn't the detail in the rendition, but the sense of realism conveyed by the texture and resonance I could hear in the piano. As a piano player myself, I find it rare to hear a system truly recreate the proper acoustic sound of a piano with all of its richness and subtlety. What I find amazing about the S.E.X. (especially as a $600 amp) is that it does this really well. I guess it comes back to the transparency I mentioned earlier - if it's in the recording and you have headphones to do it justice, the S.E.X. will let you hear it by simply amplifying the signal and getting out of the way.
If there's one weak spot for the S.E.X. it might be the bass, but not because it does anything wrong per se, just because it is very transparent and therefore may not give some people the "oomph" they're looking for.
I personally like the S.E.X.'s bass presentation because it's clean, tight, quick and punchy, but there's no denying that it doesn't have the body of the Crack (full comparison shortly). If I'm honest, I think that the S.E.X. is probably the more accurate representation of the recording, but some people might want a little more if they're looking for a warm, smooth, tubey sound.
On the plus side, the S.E.X.'s well-controlled and accurate bass is a great foundation for it's brilliant mid-range and treble presentation because there's no bleed between the bass and mids. The bass hits and rumbles when it needs to, but it never blurs the edges of other frequencies. For that reason, it's great with headphones that have a good bass presentation to begin with, but may not pair so well with headphones that people traditionally might use tube-warmth to "fix".
Staging & Imaging
Good golly does this thing image well!
I mentioned the K-66 experience at the beginning of the "Sound" section. It was staging and imaging that I heard with the K-66s that told me I was in for a treat. The S.E.X. presents a soundstage that is both wide and deep. With the T1s the soundstage from the S.E.X. extends beyond each ear by about an inch or two. It also has good forward depth, but I think the key difference I'm noticing is that it extends out diagonally better than anything else I've heard so far with the T1s.
What I mean by that is that the soundstage from the S.E.X. is more semi-circular than triangular. To the left and right of the centre there is equivalent depth to the centre and sides. Other amps I've tried, specifically the NFB-5.2 and Crack as my references from this review, seem to compress the stage at the 45o mark to each side before expanding again at the sides and centre so the result is a kind of triangular stage. The S.E.X. doesn't do this and it makes the stage feel massive and spacious even though it probably doesn't extend much further (if any) in the centre and to each side when compared to the Crack.
Sometimes a large stage can feel too big and the results seems somehow incoherent or unrealistic, but I don't find that at all with the S.E.X. Everything is perfectly placed with space around each sound, but without separating one instrument from the next. As you'll read in the comparison to the Crack. It does everything the Crack does well and a little bit more when it comes to staging and imaging.
Turning to Good Excuse as I did in the Crack review, the checked the S.E.X.'s ability to layer the stage vertically and was pleased to find that it manages the vertical equally as well as the horizontal. John's voice was clearly slightly higher than the cymbals behind him and higher still than the sound of his guitar. Bravo Bottlehead!
While completing this review I got a bit tired of the same songs over and over that I'd selected for these reviews so I switched to a different playlist. One of the tracks that followed was Clint Eastwood by Gorillaz. In the background of the track is a old piano that sounds like it's recorded from an adjacent room (not to be confused with the main synth which is piano-like, but not a piano). Listening on the S.E.X. actually made me double-check that the distant sounding piano wasn't a mobile phone ringing in the next room - it was eerily lifelike.
To summarise the sound from the S.E.X. I'd have to say things like clean, transparent, accurate and detailed. It's definitely a smooth listen, but not at all warm like you might expect from a tube amp. It's not sterile, analytical or dry, but it also doesn't gloss over everything with a rose-coloured hue. It just finds a really nice balance that has instantly placed it as my favourite amplifier of all time (so far).
Comparison to the Crack
I'm basing this comparison on the stock Crack + Speedball with stock tubes. I will also briefly compare the Crack with the GEC 6AS7G brown base, but want to start with the 2 kits in essentially their baseline states.
Moving between amps, both using the same DAC, RCA cables and headphones (Beyerdynamic T1), the difference is stark, but not in the way you might expect. The S.E.X. doesn't wipe the floor with the Crack, they just kind of shake hands and walk comfortably in different directions.
Where the S.E.X. is clean, transparent and open, the Crack is warm, smooth and intimate. Both are enviably good so my aim here is more to help you choose which you might prefer.
The Crack's signature is undoubtedly warm. The bass is more present, the mids are lush and creamy, and the treble is ever-so-slightly rolled off to a smooth, but detailed finish.
Returning to the S.E.X. I find a cooler presentation, but not cold. Both amps are probably on the warm side of neutral, but the S.E.X. is almost right on the line whereas the Crack is 2 steps into warm territory. Bass is reduced on the S.E.X., but still present. The nearest analogy I can think of for the bass is the HiFiMan "RE" range of earphones. I've owned the RE-0 and RE-272 earphones, both of which are beautifully transparent, but often left me wanting a little more in the bottom registers. Anyone who's heard these earphones probably knows what I mean and might be getting worried about where I'm going with this, but don't worry!! My point in raising the RE earphones is to clarify that the S.E.X. does not go as far away from the bass as something like the REs. Is it leaner than the Crack? Yes, without a doubt. Would I describe it as lean or analytical? No, not at all. Accurate, clean and quick, but not lean or analytical.
To use a really inaccurate, but illustrative method of description, I would describe the Crack's signature as sounding like a diagonal frequency response starting above neutral in the bass, staying much the same through the mids and trending downwards in the treble. The S.E.X. on the other hand starts basically neutral and continues flat across the board - end-to-end flatness. For some that will be desirable. For others, it may be a detractor.
Staging & Imaging
Once again, the two amps are different here, not better or worse.
The S.E.X. presents that beautiful, open and spacious stage I've described above while the Crack is much more intimate. Despite the Crack's intimacy, it doesn't feel crowded or congested, just intimate. I know many people who like one or the other so this is once again a question of taste.
Jumping back and forth, there is no way to choose a winner based on staging because it's a preferential choice. Imaging though is a little different. There is absolutely no doubt that the imaging from the S.E.X. is a step ahead of the Crack. It's not miles ahead, but definitely a good step ahead. Where the Crack has accurate imaging, the S.E.X. has crystal clear and almost holographic imaging. This might be in part due to the extra space available in the S.E.X.'s soundstage.
Resolution and Detail
I'm jumping back and forth between the two amplifiers as I write this and although I hadn't originally planned to include this heading it became abundantly obvious that it is necessary.
The reason this is so important is the difference in resolution and detail retrieved by each amp. The Crack is very good with detail and clarity, but the S.E.X. is on a whole other level. There are sounds I hear from the S.E.X. that I can't hear from the Crack even once I know they're there. I think this is in part due to the extra treble extension from the S.E.X., but it may also be a difference in the coupling of the headphones with the output tube versus an output transformer - I'll leave it to more qualified minds to answer that question though.
I'm calling this a reality check for 2 reasons. Firstly because I wanted to confirm if I can match the S.E.X.'s level of performance just by rolling tubes in the Crack and, secondly, because the tubes involved bring the total cost of the Crack to the same level as the S.E.X.
I began by installing just the Cleartop 12AU7 in the Crack to see what the affordable little marvel could do...
The sound was clearly better defined once the Cleartop was in the circuit, but was it as good? Nearly... very nearly. The Crack still didn't quite have the top-end extension of the S.E.X., but it was near enough that you might not miss it if you weren't directly A/B-ing the two amps. The Cleartop didn't bridge the gap in terms of imaging and the detail level was still a fraction behind the S.E.X., but it was definitely closer.
Next step was to pull out the big guns with the GEC 6AS7G and the results were actually very interesting. The GEC refined the Crack's sound a bit, but I don't feel like it pulled it any closer to the S.E.X. in the areas that it falls behind. What it did do though was take the Crack's mid-range to a new level and perhaps a level not achieved by the S.E.X. in terms of creamy, liquid goodness. I guess what I'm describing here is that it made the Crack better at everything it's already good at without really changing the overall presentation.
We all have different tastes and preferences so here's a summary of where each amp excels (remembering that this comparison was completed with the Speedball installed on the Crack. I'm only including factors where there is a clear difference. If something's not there it probably means they're about the same, but feel free to post any specific comparison questions in the rest of this thread.
- Bass quantity / body - Crack
- Bass speed / refinement - S.E.X.
- Lush mids - Crack (esp. with GEC tube)
- Treble extension - S.E.X.
- Detail retrieval - S.E.X.
- Intimacy - Crack
- Stage size - S.E.X.
- Imaging clarity - S.E.X.
It feels like there's a lot to summarise here so hopefully this crystalises it effectively. In my mind the S.E.X. clearly deserves to cost more than the Crack. Not taking into account the fact that the cost of materials is undoubtedly higher, the sound from the S.E.X. is more refined, more detailed and just plain impressive.
I still love the sound from the Crack and if I was told tomorrow that it was the only amp I could use for the rest of my life, I'd be completely OK with that. Since building the S.E.X., though, the Crack has had close to zero airtime because the S.E.X. is just too good.
I love the subtleties in music. I love to hear the little textures that the musicians and producers chose to include, but that we often don't hear during day-to-day listening. These subtleties help me to continue rediscovering my music collection and the S.E.X. shares new subtleties with me daily.
The Crack is an incredibly enjoyable amplifier and flat-out unbeatable for the price (when driving high impedance cans), but the S.E.X. is on another level overall.
If I had to recommend just one amp, I'd ask if you want warm, musical sound (Crack) or smooth, detailed sound (S.E.X.). Ideally though I'd suggest that you try both - start with the Crack as a practice run for the S.E.X.
Even if you don't spend a further $200+ on tubes, the Crack is an exceptional buy and one that still holds it's weight against its twice-the-price big brother.
Of course, if you want to drive speakers and headphones or if your headphone collection consists of <300ohm cans like HE-500s, AKG Q / K series headphones, or Audeze LCDs then go straight for the S.E.X. and love every second of it!
DAC Upgrade Update - 27th October 2013
A recent upgrade to my DAC has brought some very interesting changes.
The new DAC is a Matrix X-Sabre based on the very detailed ES9018 Sabre DAC chip. The extra separation and clarity offered by this DAC (compared to the previous Audio-gd NFB-5.2) has brought the Crack (with Speedball) very close to the S.E.X. in terms of overall sound performance. It's so close now that I could actually be completely happy with either amp when driving the Beyerdynamic T1s. For lower impedance cans, the S.E.X. is still the only choice due to the Crack's high output impedance, but with high impedance Beyerdynamic or Sennheiser cans I would probably choose the Crack simply because it is cheaper and still excellent.
I think the key to this change is the signature of the DACs. The NFB-5.2 was slightly warmer than the X-Sabre. The X-Sabre is still musical, but a little closer to neutral than the NFB-5.2. The result is a cleaner sound from the Crack - still warm and rich, but not smoothed over at all. The S.E.X. can sound a little dry at times in comparison which makes the Crack a bit more seductive - it soothes the ears with detailed, mellow tunes while the S.E.X. presents oodles of details and clarity, but isn't always soothing.
Edited by Loquah - 11/15/13 at 8:52pm