Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Quicksand => Topic started by: Doc B. on June 19, 2014, 02:15:28 PM
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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.
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Cool! An office headphone amp! Can't wait to see the insides.
How would the crackphones sound with this?
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The Crackheadphones are designed specifically to work with the Crack headphone amp. That's why we call them the Crackheadphones. Just buy the stock Monoprice 8323 cans to go with the Quicksand and Quickie.
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One more question: will it sound good without a Quickie in front of it, too?
Never mind: I see that it's a power amp and needs a pre.
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I have been running it with a Submissive passive control as well and it sounds great. It is a power amp, no attenuator.
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This is an interesting one, i had been toying with the idea of building another Quickie headphone amp with a SS output stage. If it can drive Hifiman headphones as you say i'm very tempted to give it a try. Can we see some pics of the internals?
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Sweet. When can I buy it.
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We will have pictures of the underside once we get the production prototype built, which we are just waiting for PC boards for. And I will begin work on getting an order page up tomorrow.
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Great idea!
Perfect for a somewhat "portable" system!
Just wondering, how many volts is the 12 battery array producing for the Quicksand?
My Quickie uses several S.L.A. 12 volt cells, and a similar setup comes to mind...
Keep on exploring new directions for kits, you are definitely on the right track to my ears!
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12 C Cells are 18V DC.
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I guess my question to the designer, is if all of the batteries are in series or is there something else going on?
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They are in series.
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Using 3 6-volts in series or a 12-volt in series with a 6-volt would work, right?
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Precisely!
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I'm sure that PB will jump in here and correct me if I'm wrong. The TPA3122 will run on 10 to 30 volts. Operating the chip at lower voltages will produce a little less power. I'm running a TPA3122 on a single 12 volt SLA behind a quickie. It sounds great in my shop where I don't require a ton of power.
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@Natural Sound:
Do you know how many watts you can get with the 12 volt supply?
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Suggest you check the specs here: http://bottlehead.com/quicksand-battery-powered-solid-state-amplifier-specs/ (http://bottlehead.com/quicksand-battery-powered-solid-state-amplifier-specs/)
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@Natural Sound:
Do you know how many watts you can get with the 12 volt supply?
No, I have no way of measuring that. The Bottlehead circuit is different from what I'm using so it's a moot point anyway.
.
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I'm sure that PB will jump in here and correct me if I'm wrong. The TPA3122 will run on 10 to 30 volts. Operating the chip at lower voltages will produce a little less power. I'm running a TPA3122 on a single 12 volt SLA behind a quickie. It sounds great in my shop where I don't require a ton of power.
Yes, this is true. (The chip actually seems to run OK on 9V as well)
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Will it be possible to use a (good) 18vdc switching psu?
Will this deteriorate sound quality too much?
Thank you
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I suspect that the 18V switching supply will work, but that the sound quality will deteriorate greatly.
There are some good papers available online that go into what happens in a switching supply when you operate outside of the rated supply current. Essentially, things are really bad at either end, and a Class D amp is going to run you into the low end and high end of current demand frequently.
-PB
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I suspect that the 18V switching supply will work, but that the sound quality will deteriorate greatly.
There are some good papers available online that go into what happens in a switching supply when you operate outside of the rated supply current. Essentially, things are really bad at either end, and a Class D amp is going to run you into the low end and high end of current demand frequently.
-PB
Got it!
What about input sensitivity? It would be lovely to mate it with a quickie, but I noticed chip amps needs attenuation rather than amplification of the input signal
PS:Any underside pics? ;-)
Ciao!
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What about input sensitivity?
IIRC, gain is right around 20dB. Since the Quickie isn't a particularly high gain preamp, they are a well suited match.
-PB
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IIRC, gain is right around 20dB. Since the Quickie isn't a particularly high gain preamp, they are a well suited match.
-PB
Thank you very much Paul!
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Nice one! I look forward to hearing it!
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How well would this amp do with 24V instead of 18? 2 12 volt SLAs would be a nice battery choice for this :) I like my current SS power amp but this is kinda intriguing!
Dave
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The amp will run on anything from 10 to 30 volts, just like it says a few posts up.
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Sennheiser HD800 compatible?
I'm still using crack OTL + speedball
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Sennheiser HD800 compatible?
Yes.
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Thanks for all of the Quicksand orders the past 24 hours! The guys will be photographing the assembly today for the manual. We should have the oft requested underside photo very soon.
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Just ordered mine yesterday, it will be demonstrated at the Northern California DIY show in October.
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I have been OK with the low power, unmodded tripath chip amps with the quickie in my bedroom stereo, I anxiously await the bottlehead quicksand.
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First post edited to add a picture of the underside of the completed amp.
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I think that there is room for bypass caps and upgraded output caps there.
It is tiny. Not at all like my ChipAmp Gain Clone.
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Looking at how clean the underside is, my first thought is: Can this be built into the same chasis/enclosure as the quickie...
Only one way to find out!
;D
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Looking at how clean the underside is, my first thought is: Can this be built into the same chasis/enclosure as the quickie...
Only one way to find out!
;D
I don't see how, unless you planned on making the plates at 90-degree angles to one another or on opposite sides of the chassis. But you could probably just saw your Quickie chassis in half (horizontally, of course) and use the two pieces for the two amps.
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I was thinking more along the lines of mounting the PCB to a standoff on the underside of the quickie chassis, hardwiring the quickie output into the quicksand input, then installing the various audio outs and power switch into the base itself. The only problem will be figuring where to mount all those batteries. Maybe on the inside of the base itself...
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I think it is a natural progression. But the problem I see is all those batteries! The Quicksand has 95% of the top of the chassis covered with batteries.
Maybe put the Quickie batteries under the top and the Quicksand batteries on the top?
If you lead others will follow.
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The only problem will be figuring where to mount all those batteries.
Yeah, there are a lot of batteries!
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Since battery power is what makes this amp special and there are so many to replace, maybe Bottlehead will offer an upgrade kit to run it from SLA batteries. Something like the upcoming DAC if that would work. Not that those are small, but they could charge when you weren't listening. Anyway just a thought.
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I just saw the picture of the underside and circuitry, and it looks to have a shared/common ground. I thought Class D/T amps didn't have a shared ground? When I was messing with the HE-500 with speaker amps, one of the limitations on using a speaker tap to TRS adapter was the requirement of a common ground, and all of the sub $100 class D/T speaker amps on the market had separate grounding and would go up in smoke if connected with a TRS adapter. And to get a balanced cable generally defeated the goal of a cheap speaker amp solution (to keep it economical). The king of affordable speaker amps for headphones ended being the Emotiva MiniX which is an AB amp and has a common ground, but is also $220. It's nice to see a potential new solution to the affordable speaker amp for headphones quandary.
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Since battery power is what makes this amp special and there are so many to replace, maybe Bottlehead will offer an upgrade kit to run it from SLA batteries. Something like the upcoming DAC if that would work. Not that those are small, but they could charge when you weren't listening. Anyway just a thought.
Note to PB - I have attached a link to the full bill of materials for the Quicksand SLA battery adapter kit.
http://www.mouser.com/ProductDetail/3M/FDI18-250Q/?qs=SfU69DRKVGBj%252bw1YFkqIaw%3D%3D&gclid=CjkKEQjwodmdBRDm_ZLhorWm68UBEiQAKhO3_TzDJjUcXQ6SeXN3xDP2uRsp9BVJ2xyUV4oStf2a5Wjw_wcB (http://www.mouser.com/ProductDetail/3M/FDI18-250Q/?qs=SfU69DRKVGBj%252bw1YFkqIaw%3D%3D&gclid=CjkKEQjwodmdBRDm_ZLhorWm68UBEiQAKhO3_TzDJjUcXQ6SeXN3xDP2uRsp9BVJ2xyUV4oStf2a5Wjw_wcB)
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That's FUNNY ! !
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Yes it is and that's why my degree is in computer science not electrical engineering! Looks like Doc gets to keep the corner office for another week! Heck, I'll give him the next two weeks! 8)
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Another question: it seems headphone output isn't lowered at all (the resistors across the jack seems 0 ohm), isn't it a bit dangerous?
Ciao!
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Another question: it seems headphone output isn't lowered at all (the resistors across the jack seems 0 ohm), isn't it a bit dangerous?
Ciao!
There are provisions for padding resistors in the manual (and we include them). A 4 Watt amplifier isn't dangerous to power hungry planars or orthos. If you'd like to run Grados with this amp, you will need to install the supplied padding resistors. (But really, running hyper efficient, low impedance headphones on a 4 Watt per channel amplifier isn't the most sensible plan to begin with)
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Thank you and sorry for the dumb question, but I fried my beloved koss for not having buying from you ;)
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Note to PB - I have attached a link to the full bill of materials for the Quicksand SLA battery adapter kit.
http://www.mouser.com/ProductDetail/3M/FDI18-250Q/?qs=SfU69DRKVGBj%252bw1YFkqIaw%3D%3D&gclid=CjkKEQjwodmdBRDm_ZLhorWm68UBEiQAKhO3_TzDJjUcXQ6SeXN3xDP2uRsp9BVJ2xyUV4oStf2a5Wjw_wcB (http://www.mouser.com/ProductDetail/3M/FDI18-250Q/?qs=SfU69DRKVGBj%252bw1YFkqIaw%3D%3D&gclid=CjkKEQjwodmdBRDm_ZLhorWm68UBEiQAKhO3_TzDJjUcXQ6SeXN3xDP2uRsp9BVJ2xyUV4oStf2a5Wjw_wcB)
Can we get those cryoed? :)
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Any updates?
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A pound and a half package coming from Redmond tells me these may be shipping!!
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The first handful are either shipped or are in a pre-shipping limbo. The limbo ones will be out the door tomorrow. Still have some parts to get in for the rest, not really sure about timing quite yet.
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I like the idea of having a portable battery powered amp to use with a sensitive low maintenance speaker, like the Blumenstein Thrasher. Is there any particular reason why I wouldn't be able to integrate a volume pot with this?
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The volume pot is doable, but most portable sources tend to already have a level control built in.
-PB
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This is so close to what I have been longing to build: a hybrid loudspeaker power amp that can run off batteries (even better if it could be remotely triggered)--the holy grail, I'd say.
I don't have the know-how or the bravery to mod the Quickie and Quicksand into my true desire (bypassing: headphones, source switching and volume controls).
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I don't have the know-how or the bravery to mod the Quickie and Quicksand into my true desire (bypassing: headphones, source switching and volume controls).
The source selector on the Quickie is also the power switch. To mod it to just be a power switch, you can reduce its switching positions from 3 positions to 2 before installing the switch. To bypass the level control, you can move the wiring on the pot slightly once it's working to turn the pot into a pair of 100K resistors.
The headphone jack doesn't interrupt the speaker feed from the Quicksand, so there isn't a huge need to bypass it.
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Can the quicksand handle a 6 ohm speaker? I'd like to try my hand at diy and the quickstand seems like a good place to start. Right now I currently only have a pair of the pioneer sb22 speakers but plan on getting something from Blumenstein. I'm in a townhouse so volume isn't that important. Maybe 75db max.
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Sure, 6 ohms is no problem.
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Thanks Doc. Is the quicksand a skill level 1?
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It's a nice clean, easy and compact layout. It does require soldering up a PC board. The TPA3122 chip is socketed, which makes the process of stuffing and soldering the components pretty easy.
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Would the quickie work with an IEM using balanced armatures? I enjoy the quickie with and a matching set would be nice. In my case they are about 40ohm with 114db sensitivity. Main concern would be about the noise floor.
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This is a thread about the Quicksand, not the Quickie, so I'm little unsure of the question. No, the Quickie is not suitable for 40 ohm headphones, it's a preamp. Yes, the Quicksand would work quite well.
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Yes I meant the Quicksand. Now for the big questions, what is the output impedance of the headphone output? And if I would like to limit the power of the headphone jack so it will not be too loud using headphones with high sensitivity could this be done by changing the resistor on the headphone jack?
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Yes I meant the Quicksand. Now for the big questions, what is the output impedance of the headphone output?
There are two options while building presented in the manual, you'd want to use the high impedance resistors.
And if I would like to limit the power of the headphone jack so it will not be too loud using headphones with high sensitivity could this be done by changing the resistor on the headphone jack?
Yes, this can be done. If you want to strongly limit the power, you may end up wanting a set of 4 resistors to both lower the output and keep the output impedance more reasonable.
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Since we're talking about resistors and phones- has anyone measured the frequency response with the output resistors in place (instead of the jumpers)? Class D amps, like this one, have a 2nd order filter on the output and the transfer function depends upon the load impedance, so I'm wondering if resistive loading on the output might be a challenge in shifting the filter down into the audioband.
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Class D amps, like this one, have a 2nd order filter on the output and the transfer function depends upon the load impedance
Indeed it does. If one wanted to use the Quicksand for headphone-use only, loading the output with an 8 Ohm L-pad loaded by an 8 Ohm resistor might make for an interesting modification.