Nelson Pass B1 with Korg Triode Preamp Kit

Introduction

The B1 with Korg Triode was introduced by Nelson Pass in 2017 at the Burning Amp Festival. The B1 is an established design which is as about as easy as it gets - a buffered passive preamp. 

The Nutube from Korg is a vacuum fluorescent display that operates similarly to a triode vacuum tube. The green glow reminds me of the old computer monitor that came with my cousin's Apple II computer ages ago. This also gives this kit a cool factor that only audiophiles are able to appreciate. The rest of the world probably just thinks that we are dorks! 

Why not just use a vacuum tube? Vacuum tubes use considerably more power and have short operating lives. The typical vacuum triode would have a lifespan between 2000 to 5000 hours. In comparison, the Nutube has a continuous life expectancy of 30000 hours (about 3.4 years) and 2% of the power consumption of a vacuum tube.   

Korg's Nutube website would be a great place to read up more on this device - https://korgnutube.com/en/

This is an ideal kit for a beginner that has some experience in building a kit or two, and comfortable with a soldering iron. The kit as supplied from diyAudio is powered by a 24V wall-wart which makes this a safe project too - no messing around with mains voltage. 

Put simply, there is an input buffer, followed by the Nutube, and an output buffer. The input buffer is required to lower the output impedance of the potentiometer used, while the output buffer lowers the output impedance of the Nutube, which is necessary to drive a typical power amplifier load.

You can read the following links for more information about the technical design. 

https://cdn.shopify.com/s/files/1/1006/5046/files/DIY_NUTUBE_PREAMP_Revised_2020-07-25.pdf

https://www.diyaudio.com/community/threads/b1-with-korg-triode.313612/

The kit from diyAudio Store is priced at USD 299 for the full kit with all parts you need. The enclosure is well made, with a thick solid aluminum face plate. There are only two inputs, although this should be enough for most users.  

The complete kit

The chassis

Sorting out the resistors

Assembly

This is pretty straightforward and you should be able to get everything done in an evening or two, depending on how fast you are. The build instructions are very clear and the PCB is easy to work with. In fact, the most challenging part of this kit is getting your hands on one. They are made in limited quantities, and disappear in a flash when available. Otherwise, the hardest part for most people would be soldering the transistors and Nutube. The latter in particular requires very precise soldering as the pins are very close together. 

Stuffing the resistors

Setting the plate voltage

The comforting green glow from the Nutube

All wired up

The completed product

Back panel

Adjustment of the two voltage pots at T7 and T8 adjust the plate voltage, which affect the level and phase of 2nd order distortion to suit your taste.

Audiophiles have experimented with boutique parts with varying degrees of success. The coupling capacitor pads are spaced for electrolytic capacitors, so you will need to be creative if you want to use film capacitors instead. 

The Nutube is microphonic and some builders I know have encountered problems with ringing. I damped the gap between the Nutube and PCB, and also used silicon spacers to damp the PCB standoffs. My unit is well-behaved, even when flipping switches or tapping on the chassis.

Unlike most of my DIY projects, this worked fine from the start. I imagine that most builders with an intermediate level of experience would have similar success.

I kept this build as stock as possible, although I did use some solid silver wiring and KLEI RCA jacks just to satisfy the audiophile in me.      

Sonics

Tonally, the B1 Korg is neutral, with a slightly soft edge. Music flows with a fluid and noticeable warmth. The effect is not overdone, and detail, speed and dynamics are still delivered intact. Where the B1 Korg stands above its competition, is the dimensionality imparted to the soundstage. Instruments and vocals are able to glow and occupy acoustic space. Many preamps are able to provide sharp and precise imaging and staging, but in a flat and 2-D manner.  The subtle flavour of romance offered will not suit the cold, hard and clinical listeners out there though.  

From a quality point of view, I would be comfortable recommending the B1 Korg for use even  in entry-level high end systems.    

Conclusion

This is an excellent kit to start off your DIY journey. The build is easy, and you end up with a simple preamp that sounds really good too - Best Buy 

B1 with Korg Triode - USD 299

https://diyaudiostore.com/products/korg-nutube-b1?variant=39438124482633

 

Markaudio-SOTA Tozzi One Speaker Kit

Introduction

The Tozzi One speaker kit is likely the easiest speaker kit on the market. I assembled it in an hour, half of which was spent looking for my tools, and cleaning up. This is the perfect kit for beginners as there is no soldering involved - all you need is a screwdriver. 

The kit costs USD 395 per pair if purchased direct from the manufacturer, but it can sometimes be found cheaper from other merchants. 

Description

Based on their in-house CHN 50 full-range driver, the Tozzi One is built around an ABS and fiber-reinforced cabinet. 

The driver is mounted in a shallow wave-guide, while the cabinet is rear-ported. Sensitivity is rated at 85 dB, and impedance at 6 ohms. The anechoic frequency response is specified at 80 Hz - 22 kHz (+/- 6 db). The cabinet measures 200 x 126 x 200 mm, and weighs 1.42 kg. The cabinet is angled up slightly, so you should be fine listening to it in the near-field while placed on your desk. 

The waveguide has a textured finish, while the sides of the cabinet are finished in a faux leather wrap. 

Assembly is straightforward enough. The instructions were in Japanese, but the diagram is clear enough to figure out. 

A thin gasket is placed between the front baffle and the speaker driver. The driver is held in place with five hex nuts. The supplied wiring is terminated in push-on terminals and o-rings, so you just need to connect them to the speaker driver and supplied five-way binding posts. The rear panel foam needs to be affixed using the supplied double-sided tape. Install the gasket into the rear panel groove, and attach it to the speaker cabinet with screws. That's it! Building and programming a custom keyboard is far more challenging than this. 

The beauty of full-range driver designs is that there is no crossover to mess around with. From a technical viewpoint, you get the best possible coherence from using a single driver and higher efficiency and purity from skipping the passive crossover. There is no free lunch though. Asking a driver to cover the whole frequency range results in uneven response. Most designs have to rely on complex cabinet designs with some form of a back-loaded horn to get usable bass output. 

Sound Quality

Straight out of the box, the Tozzi One has a clear and engaging sound, but with some rough edges. A few hours of run-in sorts that out nicely.

As expected from a full-range driver speaker, you get a lovely transparent and coherent sound. The Tozzi One sounds bigger than it looks although the very limited low-frequency output and extension makes it more suited for background listening in a large room, or listening in the near-field. In a large room, you definitely need to pair this with a subwoofer.  

Fast forward a month later, and the Tozzi One has had everything thrown at it while it sat on my computer and work desk - gaming sessions, background music, serious listening sessions, etc. As desktop speakers and with proper amplification, the Tozzi One will eat your computer speakers for lunch. I paired them with a spare Kingrex T20U amplifier that I happened to have lying around. The Kingrex delivers 10W per channel into a 4 ohm load and is enough to drive the Tozzi One to fairly loud levels for near-field listening purposes. I found it to have enough grunt to make explosions, gunshots, and orchestral crescendos equally satisfying. The rest of the frequency range was handled quite well without the midrange honk or peaky top-end that I sometimes hear from full-range drivers. In fact, the midrange is laidback and on the warm side of neutral. 

Where the Tozzi One really nails it is staging and imaging that is both spacious and pin-point. There is plenty of soundstage width, depth, and a good sense of dimensional layering.  

 

Conclusion

The Tozzi One is an excellent addition to my work desk. With the present world situation, this may be just the thing you need to preserve your sanity during long work-from-home stints. It may need more effort to set up than the usual powered speaker suspects, but it is well worth it.

MarkAudio-SOTA

http://markaudio-sota.us/

Price : USD 395 per pair

Elekit TU-8600R Integrated Amplifier

Introduction

Problem Statement - You want a quality integrated tube amplifier, but no means to afford one. No problem, just build your own ! Assuming you have decent soldering skills, and are not instruction-intolerant (sadly, that rules out my teenage daughter), the Elekit TU-8600R lets you enjoy quality on the cheap. You will need about four full days to build one, but the effort is well worth it.

Description

The Elekit TU-8600R is a 300B single-ended integrated tube amplifier kit from the nice folks at Elekit of Japan. The TU-8600R is neither a basic kit nor design, and has parts quality and design features found in high-end models.

The power transformer is a high-quality R-core type, with low magnetic flux leakage. The solid state rectification uses Schottky fast recovery diodes. The power supply circuit includes ripple filters and plenty of regulation stages. An active automatic bias adjustment system means no fiddling with bias pots, and optimal sound quality at all times.

Parts quality is generous with plenty of Japanese branded resistors and capacitors. The PCB thoughtfully provides sufficient space for you to install large boutique coupling capacitors too. After all, isn't that the whole point of DIY, the freedom to express yourself ?

The TU-8600R's circuit is based on a single 12AX7 input tube, which then feeds dual 12AU7 tubes. The latter's two triode sections are wired in parallel to drive the 300B power tube. The output transformer has speaker taps for both low and high impedance speaker loads (selectable by a switch on the rear). A headphone socket allows you to enjoy your Elekit with your favourite pair of cans. Jumpers on the PCB allow you to adjust the headphone output level, and the colour of the power LED.

Although the TU-8600R is an integrated amplifier, there is only one set of RCA inputs. This could be a deal-breaker for some, although you could purchase or build an input switching box to get around this. 

Build Experience

Elekit gets first prize for having the best instructions I've ever received with an audio-oriented kit. The instructions rely on very clear diagrams and steps to guide you every step of the way. The PCB is marked clearly and even reminds you when components are required to be installed on to the reverse side of the board. Plenty of due care and consideration went into ensuring that the assembly is as painless as possible. 

The sheer parts count and complexity of the PCB makes this project highly unsuitable for a first-time build. The soldering of the transistors was the most delicate part of the build, as the solder pads are dangerously close. I would also highly recommend that a temperate controllable iron be used. 

In my case, I chose to upgrade the stock resistors to Takman Carbon film ones, and the coupling capacitors to Amtrans AMCY Golden Black. I also bypassed the volume pot and wired the input jacks directly to the main PCB. The input sensitivity will be high, but if you are able to adjust the output level on your source (e.g. a DAC with volume control), you should be fine. 

Starting off at the professional assembly area a.k.a. dining table.

The Takmans are too large to fit and the legs have to be bent in a curved fashion to fit the board.

Soldering of the resistors is complete.

Plenty of space for upgrading the coupling capacitors.

This is the top side of the board. The main circuit is on the underside.

Testing phase. I made a boo-boo here. 

Running-in phase. 

The only mishap suffered was when I wired the input wiring to the wrong solder pads. I happily soldered them to the input pads. They should have been wired to the output pads instead (Elekit refers to them as output pads in the sense that they receive the output from the potentiometer). 

The power and output transformer connect to the PCB via push-on Molex connectors. Since the stars were aligned, I decided to run in both the stock output transformers and the Lundahl ones which are optional. 

One criticism I have is with respect to the sheet metal covers. They have a fair amount of ring, and degrade the sound quality. This was very noticeable when I installed both after my run-in process was completed.

Sound Quality

Paired with Genalex 300B tubes and a variety of 12AX7 and 12AU7 tubes from my stockpile, I gave each set of output transformers about 10 hours of run-time before I did any critical listening. I used my Totaldac DAC (using digital volume control) and icOn4 Pro as preamplifier, and my Vivid Giya G4 speakers. 

The Elekit is highly detailed, fast and open. The tone is light and clear, so if you are seeking the vintage 300B tone (warm, full and midrange-centric) you should look elsewhere. Despite the low power on tap, vocals and smaller works were an absolute treat with the Vivid. While the midrange was not overly liquid, the presentation was clearly in the tube amp camp. 

Soundstaging and imaging was holographic with pinpoint placement and excellent depth and width. The bass control and dynamics were satisfactory, but this is not the reason why you choose a single-ended tube amp. I believe that given the right set of loudspeakers (i.e. high efficiency), the Elekit would have no problem bringing the house down.

Swapping in the Lundahl transformer is the point where the Elekit is transformed from competent to world-class. The gains in detail retrieval, control over both ends of the frequency spectrum and refinement make the Lundahl a solid investment proposition. Elekit supplies the stock transformer even if you opt for the Lundahl, so you could always upgrade in the future, only losing out on having additional shipping costs.

The Elekit is good enough to be your end-game amplifier unless you suffer from equipment polygamy (which Audiophile doesn't ?). I was heartened to find such high quality at an affordable price, knowing that many would be able to enjoy its fine musicality.  

Conclusion    

There is a sense of rightness to the Elekit, and there is the invaluable ability to dial it in precisely to your taste through judicious choice of parts. 

It comes in at an attractive price tag, so the only real downside is that you need to spend the time and effort to build it yourself. However, most Elekit dealers would offer a build service for a fee, or be able to refer you to someone who could. Best Buy and Highly Recommended.

Elekit TU-8600R Integrated Amplifier

Price - POA

Elekit kits are available from :-

Horizon Acoustics

1 Pemimpin Drive

#08-11, One Pemipin

Singapore 576151

http://www.horizonacoustics.com

Pass Labs ACA Power Amplifier

Introduction

The Amp Camp Amplifier ("ACA") is a simple amplifier that was designed to be built in a single afternoon. It was created by Nelson Pass for an event called "Amp Camp" in which a small group of people turn up and by the end of the day, they would have built a small amplifier.

This means that the build has to be straightforward, even for the first-timer. Indeed, the build is quite easy, and the very detailed build guides on the internet will certainly ensure that you get this up and running in no time at all.

A complete kit with everything you need is available at the Diyaudio Store - just be quick, because they sell out really fast !

Description

The ACA is a low power Class A power amplifier which is able to deliver 8W per channel into an 8 ohm load (at 3 % distortion), or 15W if operated as a monoblock. It is built in a very compact chassis, with a separate power brick supplying 24V DC to the ACA. This is a great idea for a first-time project as you don't have to mess around with potentially lethal voltages.  

The current version of the kit at the time of this post is V 1.6, which was the version I built. Other important specifications :-

Input impedance - 10 Kohm
Gain                    - 14 db
Damping factor  - 10
Output noise       - 100 uV

For a detailed description of the circuit, you can read what Papa Pass (as he is affectionately called in the DIY audio scene) has to say here.

Build Experience

I highly recommend this for the beginner. Like any kit, it would be helpful if you practice your soldering on a practice or waste board first. Everything you need is in the kit, except for soldering iron, solder and a multi-meter. I assume of course that you have basic tools around the house, like screwdriver set, pliers and a cutters to snip of the component leads.

This is a PCB kit, and the very low parts count means that you really can finish this in half a day if you are minded to do so. 

The kit includes both blue and red LEDs - choose your favourite colour. I friction fit those LEDs for fun, and settled for red LEDs.

Like any Class A circuit, this runs quite hot. It settles down at about 18-20 degrees C above ambient temperature.

Like anything in life, things can go wrong if you do not take due care. This kit is straightforward enough that your possibility of messing things up are quite low. The most difficult part of assembly is likely to be affixing the transistors to the heatsinks (installing the insulation pads wrongly could either short out your transistors, or cause them to overheat. The second most difficult part (for a beginner) is biasing the transistors. Well, for me the most difficult part was aligning up the chassis as one of the rails arrived bent out of shape.

In operation, the ACA runs hot - it needs every square inch of those heatsinks ! After about two hours of operation, the faceplate is quite hot to the touch too. There is no anti-thump circuit, and the ACA will make rude sounds when powering off, and a loud thump when switched off. If you are using sensitive speakers, this is loud enough to scare both pets and probably their owner too.   

Sonic Quality

The limited power requires careful partnering. If you have typical speakers (e.g. 86-89 db sensitivity), you certainly can’t go very loud with the ACA. However, the few watts on tap will suffice for background music, and even reasonable listening levels if you are sit close to your speakers and listen to less complex music. To extract the most out of this amplifier, high-efficiency speakers are highly recommended.

The ACA has a very pleasant smooth and warm quality that makes listening very pleasurable. I spent more than a week during this lock-down, paired with my Vivid Giya G4 speakers (hardly the easiest load). Used within its power limitations, the ACA actually sounds very good for the money invested (Let's face it - pickings are slim for Class A amplifiers below USD 500).

Soundstaging is reasonably good, with good dimensionality. The ACA has a very nice grain-free and refined sound that eludes most solid state designs. The only obvious weakness was a lack of bass control with a flabby and loose low-end. Given the low damping factor of the ACA and the unsympathetic load, this was hardly surprising. Time to try out the ACA with more suitable speakers !

A pair of Tannoy Kensington GR speakers proved to be a better match although it was evident that more power was needed. Although they are rated at 93 db sensitivity, the Tannoys are not known to be an easy load either. They sound quite good at background music levels, with a usable limit at a volume in between my usual listening levels and that. Pushed harder, and the amp begins to harden in sound, as well as lose its limited grip on the woofers. Perhaps my very easy to drive Zu Dirty Weekend II speakers would be a perfect match ? I'll update this post once I've tried that.

Conclusion

The ACA is a pleasant amp that is easy to build and an excellent introduction to the wonderful world of DIY. If you have reasonable expectations and a suitable partnering pair of speakers, you could end up with sonic bliss at a very modest budget. If you are expecting something really special with a sound that rivals First Watt or Pass Lab's offerings, you are going to walk away disappointed. 

Pass Labs ACA Power Amplifier
Available direct from diyaudiostore.com
USD 327

Bottlehead Crack and Bottlehead S.E.X. Headphone Amplifiers

Introduction

COVID-19 and the lockdown making you sing the blues? Maybe it's time to get out your soldering iron, and start building a kit that you had your eyes on? That's exactly what I did - my poor Bottlehead S.E.X. kit has been collecting dust since I ordered it sometime last year. 

Bottlehead is an established company that has been offering vacuum tube kits to audiophiles since 1995. Their product range covers a wide variety of tube equipment, as well as a speaker kit. 

While kits are not for everyone, I encourage every audiophile to at least try assembling a kit at least once. A lot can be learnt from the experience, including soldering, basic circuit design, patience, and the ability to use swear words in ways that you never thought possible. 

On a more serious note, immense satisfaction can be obtained from building something that you can truly call your own masterpiece. Photos of builds around the world show that audiophiles are a pretty talented lot, with some builds exhibiting build techniques and wood / metalworking quality that can put even professional companies to shame.

As an educational process, I probably learnt more from DIY work than anything else. Mistakes in assembly or poor construction technique will teach you many things, including the importance of good grounding practice, and the importance of proper wire routing.

Bottlehead kits are far from being the cheapest on the market, but their builds are guided by very clear instructions with lots of pictures. They also have a very supportive online forum where you can find a lot of tips and suggestions for modifications. If you encounter problems, the folks there are helpful and willing to go the extra mile to ensure your build is successful.

Introduction to Crack 

This type of Crack is legal around the world and no need to risk your liberty or health to enjoy this. 

The Bottlehead Crack 1.1. OTL Headphone Amplifier kit is described as a Level 1 kit, perfect for first time builders, involving an evening or two of build time. The cheeky name is a common trait across Bottlehead products - they believe that their products involve feelings of euphoria!

The circuit of the Crack is simple, with a low parts count. The power supply is a C-R-C-R-C design, so no chokes to complicate your life (and more importantly, bump up the cost of a starter kit). A lone 12AU7 tube is directly coupled to a similarly lonely 6080 tube used as a cathode follower. As both tubes are dual triodes, each triode section handles one channel. 

There is no output transformer (OTL means Output Transformer Less). Tube designs typically need an output transformer to match the high resistance of the tube output stage, to the low impedance load being driven, e.g. a loudspeaker or headphone. The choice of the 6080 tube (which has a relatively low plate resistance), allows the omission of an output transformer provided that the matching headphone has a high impedance. The Crack has an output impedance of 150 ohms, and is recommended to be paired with headphones of 200 ohms or higher. Parts quality is decent with nothing fancy save for the ultrafast rectifiers. The two most obvious cost-saving measures are the electrolytic output coupling capacitors and the cheap carbon potentiometer.

The Crack can also be upgraded with the Speedball upgrade kit, which is a constant current source supply for the plate of the 12AU7 tube, and the cathode load of the 6080 tube. A similar upgrade kit is also available for the S.E.X.   

Introduction to S.E.X.

This is a family-friendly blog, and this is one three-letter word that can be legally enjoyed with the whole family. Like Crack, S.E.X. is a two-stage circuit. Version 3.0 of the S.E.X. uses a 6FJ7 tube. If you have never heard of the 6FJ7, that makes two of us. The 6FJ7 is a dual triode with dissimilar sections fitted in a Compactron envelope. Described as a TV oscillator tube, this is not a tube that you will be fighting over with other audiophiles.     

The S.E.X. is a substantially more complicated build compared to the Crack. I took more than four evenings to complete the kit, taking my time to carefully check the instructions, and building the kit at a leisurely pace. The S.E.X. has five transformers, consisting of one power transformer, two output transformers, and two plate chokes. Unlike the Crack, the S.E.X. is able to power sensitive speakers, with 2W on tap. 

After completing the kit, I admired my extremely skillful soldering, powered up everything, and music flowed forth like voices from Heaven. The truth of the matter is that I could not pass the resistance tests as set out in the instruction manual and had to go to the Bottlehead Forum for help. Bottlehead's Paul Birkeland noticed almost immediately that one of my ground wires was not connected and all resistance tests passed after I fixed that. Interestingly, I had no plate voltage on one channel. Checking all connections carefully with a magnifier and torchlight showed that one of my connections had not yet been soldered. Some of my sloppier solder joints were re-flowed and everything was good after that, or so I thought.

I switched on the S.E.X. only to be greeted by loud popping and static from one channel. This was puzzling since I was pretty sure that all issues had by now been addressed. After swapping interconnects, I realised that the sound would stop when I gently tapped the chassis near the left tube. I removed the left tube and after a few sharp taps to the envelope (please do not do this to a hot tube), it was quiet - time to look for a replacement tube.      

Build Experience

I bought the Crack pre-owned, and it came with the Speedball upgrade already installed. So, my experience relates to my build of the S.E.X. kit.

Thanks to the excellent instructions and well-thought-out kit, assembly of either kit should be achievable, even for the novice who cannot read a circuit diagram. However, understanding the circuit makes things a lot easier, as well as good soldering techniques. Neither of these kits is in my opinion suitable for a person with no soldering experience, nor a basic understanding of electronics. My suggestion is for the inexperienced to do some basic reading, and practice stripping wires, trimming parts and soldering some waste or spare components on a practice board.

The instructions are also catered for the world of Imperial measurements. I had absolutely no idea what a number #4, #6 or #8 screw size is, although to give Bottlehead credit, some of these parts are listed in the instructions with metric dimensions.

It also pays to be very attentive when reading the instructions. As multiple connections may be made to a single terminal hole, you have to make sure that you only solder the point when asked to do so. Despite taking my time, I made this mistake a few times. Thankfully the terminal strips have plenty of space for fixing these mistakes.

Due to a mistake made in stripping the supplied ethernet cable (used for signal hook-up), I had to use some spare Canare star-quad microphone cable to run from the RCA sockets to the potentiometer. Otherwise, I used all the parts as supplied. The carbon potentiometers could have better tracking, and show noticeable channel mismatch at very low volume levels. At practical listening volumes, the channel tracking was acceptable.  

Sound Quality

In today's episode of Spy vs. Spy, will White Spy (S.E.X.) or Black Spy (Crack) emerge triumphant? 

To give both spies a level playing field, only two high impedance headphones were used - a Sennheiser HD6xx (300 ohms) and a Beyer DT-880 (250 ohms). Both spies were sent on physical training camps and a few simple missions to ensure that they were in tip-top condition. 

Black Spy by virtue of its creamy and wet midbass will win over a lot of fans. I thought it would make the Sennheiser sound too dark, but it actually worked quite well. For the brighter sounding Beyer, it added fullness and heft to the sound. Black Spy was not the most meticulous or detailed of spies and glossed over some details. However, if you have an aversion to thin, bright and etched recordings, Black Spy will be your best friend.

The Crack is not tonally neutral. It adds a pleasing warmth to your recordings and takes an edge off all the nasties. Bass control is a bit loose and if you favour fast-paced rock or EDM tracks, this is probably not the best choice for you. 

White Spy, on the other hand, is leaner, faster, and a lot more detailed. The immediate thought that strikes you is, "Where did the bass go?". The bass is taut, tuneful, and very controlled with no flab. I actually appreciated the detailed and articulate bass lines of the S.E.X. 

In similar fashion, vocals are more open and textured, with a deeper insight into the recording. The neutral approach also means that your enjoyment will be dependent on the quality of your recording. My only criticism of the S.E.X. is that I did find myself missing the bass impact of the Crack. A half-way house between the two would have been perfect. I will revisit how the S.E.X. performs after installation of the CCS upgrade kit. 

Conclusion

Which kit is best for you ? My thoughts on this :-

Crack 

• First-time builder
• Preference for a warm and forgiving sound
• To be paired suitable headphones (>200 ohm impedance)

S.E.X.

• Second-time or advanced builder
• Preference for a faster and more neutral sound
• To be paired with a variety of headphones, including low impedance models
• To be paired with sensitive speakers 

A select few listeners would prefer the Crack over the S.E.X. I personally think the S.E.X. is worth the extra cost for a more sophisticated sound, better transparency, and more flexibility with partnering equipment. 

Bottlehead Crack
USD 315 or 430 with Speedball Upgrade

Bottlehead S.E.X.
USD 539 or 574 with C4S Upgrade

Products are sold directly from bottlehead.com

SB Acoustics Ara Beryllium Speaker Kit

Introduction

Welcome to Part II of the SB Acoustics Ara Speaker Kit review. This article covers the assembly process of the speaker kit, an upgrade to the Beryllium tweeter, and our very first episode of "Pimp my Speaker" !

Description

A short walk back to the initial article of the SB Acoustics Ara Speaker Kit review would be useful to understand the speaker in depth. For now, let's have a look at the assembly and tweaking process.

Assembly of the speaker kit is quite easy for anyone with some DIY experience. I would not however recommend it for first timers as decent soldering experience is required, and the speaker driver units are quite expensive - one slip of your screwdriver is all it takes to destroy them.

Assembly

My kit came with fully assembled cabinets and crossover boards. The crossover board is wired with their leads terminated in push-on clips for the drivers, and tinned leads for the binding posts. 

The most tedious part of the assembly would be the cutting of the fiberfill pads to size, and pushing / gluing everything into place. The crossover board can be a bit tricky to install though, as you need a short stubby cross head screwdriver to attach the board to the base of the cabinet. In my case, one of the cabinets did not have any pre-drilled guide holes and I had to hammer the screws into the cabinet to make my own guide holes.

The rest of the hook-up process is quite idiot-proof. The push on clips are sized to match the terminals of the speaker drive units, so you can't install them in reversed polarity. I also liked the fact that the holes for the binding post plate and both drivers had metal thread inserts - no more stripped MDF, and you can torque the bolts with confidence (but not gorilla strength please !). The length of the supplied cables were generous and you do not need to be a contortionist or Octopus to attach the wires to either the binding post or the speaker drivers. The binding post leads do need to be soldered though - the only time your soldering iron will get any action. A glue gun is also required to seal the guide holes where the crossover board wires connect to the binding posts, or you could use your imagination to seal them in any other way you deem fit.

Pimp My Speaker

Good Audiophiles like to milk every ounce of performance out of their gear and DIY equipment are a great way to express and showcase your creativity and talent. I installed the crossover board on top of the speaker, and extended the leads using Belden wire and terminals blocks. The speakers were given about 10 hours of run-in time in between each stage of modification unless otherwise indicated.  

Part 1 - Replace the sandcast resistors with Ohmite and Mills resistors

Nothing fancy used here - just wirewound Ohmite and Mills MRA-12 resistors. The latter have non-inductive windings. Despite their specified tolerances, all of the resistors measured very closely, within +/- 0.1 ohms of their stated values.  

The stock resistors are "thoughtfully" glued into place. Brute force is required here to detach the resistors from the board. 

There is a slight but noticeable improvement here, with an uplift in clarity and reduction in grain. 

Part 2 - Replace the plastic capacitors with Auricap XO film capacitors

The stock Jantzen Cross Caps supplied are quite decent, but the Auricaps are well worth the expense. The Auricaps improve clarity and lend an extra level of dimensionality and detail to the speakers. In comparison, the Jantzen sound flatter and drier. 

Stock crossover board in the middle of surgery

All complete except for the wires

Part 3 - Replace the speaker drive unit leads with Neotech OCC cables, and the binding posts with Furutech.

I used 20 AWG Neotech Pure Silver solid core OCC wire for the tweeters, and 16 AWG multi strand copper OCC cable for the woofers. I am not really fond of push-on terminals, and soldered the cables directly to the drive unit terminals.

The initial impressions were quite negative, with the speaker losing both drive and vitality. These cables use Teflon insulation, which have a reputation for long run-in time -  I put in 48 hours of run-in here. Post run-in, the cabling provided a higher level of refinement and micro-detail. The stock wiring has a more forward and incisive sound, but in terms of layering and staging, the Neotech is noticeably better. The Furutech FP-803B(G) binding posts just happened to be lying around - the stock posts would do just fine.  

I would rate the capacitor upgrade as the most effective, followed by the internal wiring upgrade. The resistors and binding posts could be left alone, unless you are the sort that leaves no stone unturned. Actually even with the stock crossover board, the performance level is already very high. 

Comparisons

The Beryllium tweeter is well worth the upgrade in my opinion. In my earlier article, I pointed at a slight discontinuity between the two drive units, and a prominence to the tweeter that called a bit of attention to itself. There were no such issues with my personal build (the version I heard used the silk dome crossover board with some modifications). I would only recommend the fabric dome version if budget is tight, or you have a dislike for extended high-frequencies.

If you felt that the base level kit was great value, this premium version will have the competition running scared - it's that good !