We snuck another new kit in without telling anyone! Quicksand is a 4 watt per channel Class D speaker and headphone amplifier designed to match up with the Quickie battery powered tube amp. Quicksand also uses batteries. I could continue to divulge the design rationale, but instead I will let the designer, Paul Birkeland, do that. Here's what he says about the design -
"Introducing Quicksand
Having established a benchmark of performance and affordability with the Quickie directly heated preamp, demand quickly arose for a matching power amplifier. Consequently, we set out to determine how to create an inexpensive power amplifier that would deliver the goods with a very low noise floor, adequate output power, upgrade potential, and compatibility with both speakers and headphones. With a $99 price point in our sights, we forced ourselves to look beyond vacuum state amplification, and determined that only a Class D amplifier could satisfy our needs.
The challenge was not coming up with a class D power amplifier in our price point, but rather the need to create a power amplifier requiring no apologies down the road. Sonically, we have always found class D amplifiers to be a little bit on the harsh side, especially at high frequencies and through loud passages. To clean up the dynamic crunch associated with this topology, we took a cue from the Quickie and used a battery power supply. When a class D amplifier is operating at high power levels and at low frequencies, it can actually pump some energy back into the power supply. A typical wall transformer used with such an amplifier will exhibit poor performance under these conditions, and designers must intentionally filter out low frequency content to prevent an unstable power supply from generating distortion in the amplifier. A bank of batteries, however, is easily able to sink that energy without the instabilities of a switching supply. Compared to the evaluation circuit most commonly seen with this device, Quicksand is able to deliver bass two octaves lower without excessive distortion. To open up the high frequency response as much as possible, careful attention was paid to board layout and parts selection, with premium components being supplied and a generous ground plane covering the underside of the PC board. The result is a very clean and dynamic 4 Watt per channel digital amplifier using the TPA3122.
Quiet, efficient battery operation
As a consequence of selecting the battery power supply, Quicksand's low noise floor means that it is well suited to driving headphones, and will even do quite well with demanding loads like AKG K-1000's, as well as headphones from Audeze and Hifiman. Being a class D amplifier, nailing down the actual battery life of the Quicksand will depend greatly on the music listened to, load presented to the amplifier, and output level demanded. We have calculated that the amplifier could drain a full set of batteries in 5 hours under the worst of circumstances, and would otherwise operate for just over 300 hours if the power switch was inadvertently left on.
What's the catch?
Well, we really can't afford to sell the kit at $99, so it has to be priced at $109. But if you buy it with a Quickie at the same time we will bite the bullet and send you both for $199 plus shipping. And, as with the Quickie, batteries are not included. Why should we charge you for batteries that have been sitting on the shelf going stale when you can buy fresh batteries for discount prices online or at your local retailer? Also the kit comes without a base, just like the Quickie. You can build your own, buy a Hammond 1444-15 aluminum chassis for a few bucks from an electronics supplier like Mouser or Digi-Key, or we can sell you the same alder wood base kit we supply with our Crack headphone amp kit, for $40, as shown below. And the last catch is that the chassis plate is made from acrylic plastic and the colors we get are random. Actually that makes it kind of fun – you might get purple like the Quicksand shown above, red, bright yellow, green, white or who knows?
Specifications:
Gain: 20dB
Power: 4 Watts per channel into 8 Ohms, 8 Watts per channel into 4 Ohms, 5% THD, both channels driven
Battery life: 5-307 Hours depending upon how hard the amp is driven. Louder = more power output = shorter battery life.
Power Supply: 12 C-cell batteries
Input Impedance: 60K Ohms"
There you have it - PB has now popped his cherry writing copy for Bottlehead products!
So the question begs - is it better than the $30 class D amps you can buy on the web? I am a pragmatist. Thus the first thing I did was buy a $30 class D amp and tell PB that if his didn't sound 3.33 times better I would fire him. I have been running a Quicksand in my home system for a while, replacing a Stereomour that drives a pair of Blumenstein Orcas and Dungeness Subs. Not only does it sound better than a $30 class D amp, it is a lot closer to the Stereomour than I really want to admit, with the Stereomour edging out the Quicksand on treble balance and midrange realism, and the Quicksand showing off a very clean and neutral, black background sound with most ample and punchy bass. It also works great with headphones, very quiet and with power to spare for pretty much any dynamic headphone you can throw at it. And it's a design that will allow for experimentation. One could build higher voltage power supplies and get more power, parallel a couple of Quicksands and drive 2 ohm speakers, convert to rechargeable batteries, use three for 5.1 surround, etc. Lots of cool ideas will come up I'm sure.
