April 2015

Bottlehead Quicksand Battery Powered Amplifier Kit
A great starter amp kit with plenty of room to build upon.
Review By Jeff Poth

  I recently reviewed the Bottlehead Quickie linestage, which is a great value and a lot of fun. Along with the Quickie, I also built the Bottlehead Quicksand amplifier. This amp is similarly inexpensive at $119 versus the Quickie at $99. Wooden bases are $40, putting a "full" Quicksand at $159 if ordered separately ($169 for the Quickie 1.1 with base and PJCCS upgrade). The Quickie and Quicksand are currently also sold as a combo deal with a $20 discount, giving a battery powered hi-fi system, with bases and CCS, for just over $300. Pretty good deal for interesting, portable separates. The amp is built upon the same acrylic top plate/wooden base construction as the Quickie, with one of the quirks being that the top plate comes in any color you want- so long as the color they ship is what you wanted (IOW, it's random). Mine happened to come in red, matching the Quickie, and I quite like the look of it. The massive bank of 12 C-cell batteries gives the chassis plenty of heft, and the controls are minimal giving the amp a very unique look. The front of the chassis has a power switch, gold plated input RCAs and headphone jack, with the good quality but generic binding posts occupying the back side of the chassis, with the middle of the amp dominated by the bank of batteries.

Not surprisingly, the Quicksand is a low powered amplifier, and uses Class D integrated amplifier technology from Texas Instruments. The IC is the TPA 3122 chip which generates 4/8 Watts per channel into 8 and 4 Ohms respectively (a normal doubling of power into the lower impedance due to the doubled current required). Battery life will vary widely with power output requirement, ranging from 5 to 300 hours, per Bottlehead. The circuit board is very compact and packed tightly with good quality components, and there is a boatload of room under the chassis for any modifications one might desire.

Construction
Construction is a simple afternoon affair, mine went together headache free in only a few hours. This excludes glue setting time for the base, and finishing time likewise (another 25 hours to cure more or less depending on finish technique). My daughters at 8 and 12 were able to contribute to some of the soldering (not to worry, as there was plenty of oversight and safety!), but the assembly of the amplifier board itself is a little more advanced, with fairly tight spacing on some of the solder pads. You'll want a narrow tip for your iron, if you have interchangeable tips, though I got away with a fairly broad one because I was too lazy to pull out the narrow tip- don't try that at home, I'm a professional! In true Bottlehead fashion the instructions were superb with clear explanation and lots of pictures. This, like the Quickie, is something that should go together painlessly for anyone who can follow directions and knows how to solder and assemble things at a very basic level.

The wiring supplied is largely network cables, stripped and repurposed to be used as audio cable. Small size solid core copper of reasonable purity in Teflon is a pretty decent budget conductor and a good match for the budget-oriented nature of this kit. The component quality as previously mentioned is very good, though modders might choose to go with fancier input capacitors, or add power supply bypass caps.  There's plenty of room though the board connections are small and won't support heavier-duty leadout wires, so some care and planning is required if one wants to do any modification. As with the Quickie, I did not perform any mods to the amplifier prior to review. Two options are provided for the wiring of the headphone jack -- it can either be resistively loaded for low impedance phones like the Etymotic ER6i or used directly for higher-impedance phones. The resistive loading is via a 113 Ohm resistor in series with the earphone output.

Listening Details
The Quicksand got its first test when I was testing it along with the Quickie driving my older Zigmahornet cabs (now utilized in my younger daughter's room). The Bottlehead gear was compared in this system to the inexpensive Audiosource Amp100. The Quickie alone did help flesh out this spartan rig with only modest compromise, which is a positive since it meant that adding the extra preamp in-line with the integrated amp was not a huge loss, speaking to the relatively high level of quality of the Quickie in sonic terms. The little bit of added tube color was welcome, despite a little compromise on some of the audiophile words. I didn't analyze too deeply, focused more at that point on the microphonic nature of the 3s4 tubes, but the overall system was improved.

When the Quickie with the PJCCS was brought into this system along with the Quicksand, the story changed quite a bit. The Quicksand was a much better sounding amplifier; the soundstage was wider and deeper, voices had better tonal accuracy, and voices and instruments were more "holographic". Single drivers excel at illusion, and the Quickie/Quicksand combo made sure that the Zigmas were given every opportunity to shine. One note is that the Quicksand has a turn-on pop, and this aspect can be managed with a muting switch. In stock form, there is a meaningful noise on startup. The level is not problematic for typical speakers but if you were to run a high output compression driver in an active system (and no protection cap), this could be an issue. More "normal" systems where an amp like the Bottlehead Quicksand would be used, the noise is a mere annoyance and doesn't represent a risk to the loudspeakers. Some high efficiency low impedance phones might have issue with it, yet it is hard to say for sure. I'd definitely take care if using an esoteric playback device, but with my efficient speakers and the Etymotic canalphones, it was not a problem (with the output series resistors on the headphone jack).

Given the high performance against the modest Audiosource, it was time to put a battery powered system into play in the big rig, with my 16 Ohm, 99 to 100 dB/W/m sensitive floorstanders. Apart from the microphonics of the 3s4, background noise was minimal, meaning that only the highest efficiency setups (105dB+) would be likely to have any meaningful concerns with hum, buzz, or hiss. The unshielded preamp is sensitive to placement though, so care had to be taken with that aspect of the Bottlehead gear. Compared to the big Tripath, the Quicksand gave up the edge on dynamics and transparency, with a smaller soundstage and lower key, but still enjoyable sound. I gave it quite some time to compare, but the advantages of the big tripath amp remained. That said, I listened to a lot of music through this amp, and even watched some movies, and the Bottlehead performed admirably with good intelligibility, musicality, a smooth and well-balanced presentation. Despite the very modest power delivery capability of the Quicksand into my 16 Ohm speakers (2 Watt), it didn't seem to be dynamically compressed by the output power to any great extent, helped, no doubt, by the high efficiency and relatively small listening room. The dynamics were not to the level of the tripath, which at 100 Wpc (and capable of passive bi-amplifying for 200 Wpc) does very well in this regard.

To put things on a more level playing field regarding power, I brought back an old friend- Bottlehead's Enhanced SEX kit (with Magnequest Iron). This much more expensive kit unsurprisingly outperformed the Quicksand, bringing a more open-sounding top end, a more full-bodied image, broader and deeper soundstage, better clarity and improved musicality.  This had darned-well better be the case- the Magnequest iron alone is nearly twice the cost of the Quicksand (with base).

Headphones
Higher sensitivity low impedance phones can be difficult to control noise on and so the resistive loading helps with that quite a bit and keeps the amp operating in a lower distortion output range. Most audiophiles know that distortion increases as amplifiers approach their maximum output, but don't realize that the same is often true at extremely low power- noise and other issues tend to creep out when you're in the milliWatt range. The series resistor performs the function of limiting noise and letting the amp work in a more linear range. It brings with it somewhat of a challenge, however, in that the Class D circuit includes a second order filter on the output -- this filter creates a load-dependence on the frequency response, and the 133 Ohm resistor means variation at the top end of the frequency response. Bottlehead recommend using the series resistor only for low impedance high-efficiency phones, and provides a jumper (0 Ohm resistor) for those who have more conventional headphones. In any case, the headphone output will tend to have more frequency response variation at high frequency than the speaker output, which may or may not be a positive for a given set of phones and listener.

My listening with the Etymotics found the headphone output bright, yet dynamic, clear, and without problematic noise issues. It was somewhat less sensitive than my loudspeaker setup to the startup pop and noise from the Quickie. I spent less time with the phones than through loudspeakers, which are more my area of expertise, but I will say that one would do well to take time to play with how the resistive loading is utilized, if the stock configuration isn't optimal with a given set of phones.

Overall
This has been a tough review to write and I've taken my time doing so. Bottlehead’s Quicksand is a unique product, superior to the low-end pre-manufactured Class D amplifiers I've worked with, but not competitive with (much more expensive) amplifiers that it was compared to. For a beginning DIYer, it's a great amp, with good clarity, dynamics, and smooth sound, and an easy build. This amp is perfect for a higher-end portable setup, or for use with desktop speakers, or any time when low power requirements are needed and portability is important. There is plenty of room for modification, and I could see some users bringing up the quality level with tweaks to the headphone output configuration, power supply, and possible swapping out the input caps (though the compact size of the stock caps is helpful to keep noise down, on a Class D board). At the price point, the Quicksand is a good value, and is a very stylish way to run a portable or other system. The ratings below are on an absolute scale, so please remember that they are in the context of a very inexpensive amplifier as compared to cost-no-object designs.

Specifications
Type: Battery powered vacuum tube amplifier kit
Power Output: 4 Watts per channel into 8 Ohms, 8 Watts per channel into 4 Ohms,
THD: 5% with both channels driven
Input Impedance: 60 KOhms
Gain: 20dB
Battery life: 5 to 300 Hours depending upon usage
Power Supply: 12 C-cell batteries
Price: $119

Options:
wood base kit $40
Bottlehead Badge $6.75

Manufacturer
Bottlehead
9415 Coppertop Loop NE
Suite 101
Bainbridge Island, WA 98110

Voice: (206) 451-4275
E-mail: docb@bottlehead.com 
Website: www.Bottlehead.com