Fire 7" Tablet (2015) and Android OTG Audio

It's been a while since my last post. The past few months have seen a big change in my audio setup. I now use a Fire 7" (2015) tablet, an external HiFiMe DAC and an APPJ mini 2013 amplifier. I'm still using and enjoying my Axiom M3 speakers. The seismic shift has been from using an iOS device to Android. A few years ago, Android audio was abysmal. I wasn't aware of it, but Android had audiophile potential. As the Geeknizer points out in his excellent post on the Complete Guide to Android Smartphone Audiophile, Android is Linux at heart and "Linux uses ALSA, the most advanced sound engine every made by humans. Its not just advanced in terms of features, but also the best sounding. We cannot tell you how much better it is than the Windows Direct sound architecture found in Windows 7, 8, etc. Even with windows audio mods like ASIO4all, JACK, you simply cannot match the bit-perfect quality from ALSA system found on Linux."

It's only recently that production Android devices have taken advantage of Android's audio capabilities. The most significant improvement has been USB OTG or "On The Go." Bear with me as I geek out a bit, but it's significant topic. Anyone who uses a computer is familiar with the USB connector. What I didn't realize is that the USB standard is based on a "Master Slave" relationship. In practical terms, Android devices were slaves like printers or scanners and were unable to "host" and power a USB device like a digital audio converter. The OTG connector is wired differently than a standard USB cable, and it tells your Android device that it is the master or host. Recent improvements to the Android OS allows more and more (but not all) Android devices to use OTG to host an external digital audio converter.

Here I've laid out my Android USB paraphernalia. The three on the left are all OTG connectors that would allow your Android to host and power an external digital audio converter or DAC. The two on the right are digital audio converters I got from HiFiMe. The conventional audiophile wisdom that I grew up with said that the turntable stylus cartridge and speakers were the two most critical pieces of equipment in an audio system. The DAC is the modern equivalent of the cartridge on a turntable as it has a equally dramatic effect on the sound of an audio system. The two DACs I've used from HiFiMe are the best I've ever heard. A simple A/B comparison with the headphone jack of my Fire tablet is night and day.

The Fire 7" (2015) Android tablet is a complete surprise. I bought it on a whim when Amazon had it on sale for $35. I never expected to use it for audio. Not only does it work with OTG and an external DAC, it will also take a 128Gb micro SD card. Mine had a sporadic problem recognizing the micro SD card until I bought the SD card Amazon recommends for the Fire tablet, but I can't complain at the price. With one of the HiFiMe DACs it sounds fantastic. It's coherent, vibrant and punchy. The sound is definitely better than any combination of iOS devices and DACs I've used previously. 

The two HiFiMe DACs I have are the $30 Sabre Android DAC based on the Sabre ES9023 dac chip and the $70 Sabre 9018 USB DAC based on the Sabre ES9018k2m DAC chip. Both are outstanding, but I can't tell them apart. The specs suggested the 9018 would be a bit louder, a good thing when your amp has 3 watts per channel like my APPJ, and at first I thought it was. Honestly though, my ears can't tell the difference between the two on my system. The cheaper Android DAC has the convenience of a micro USB connector that will connect directly to your Android device without an OTG connector.

You might want to get a OTG connector anyway. I got a fancy one that has one micro USB for power in and three standard female USB ports that can host a DAC. The nice thing about the fancy connector is the Charge/OTG switch. Because of the USB spec, a host device cannot be charged. In the Charge position, the switch allows you to charge your Android device when it is not playing music. In the OTG position, power is provided to the DAC reducing drain on the tablet's battery.

Carot One Ernestolo TA2024 T amp with tube preamplifier

I've had the Ernestolo amp for over 3 months now, and I can say it's now my current favorite T-amp. It's a beautiful looking jewel of an amp, and non hifi people compliment me on it's looks. It sounds even better than it looks with the focused, coherent, and punchy sound the TA2024 chip provides. It sounds even better than the typical TA2024 amp though, because the Ernestolo feeds the TA2024 from a tube preamplifier that is built into the same chassis.

The case design makes the separate nature of the the amp and preamp apparent. There is a clear "hole" in the chassis between the amp and the preamp. The amp and preamp are completely separate devices and each have their own power and audio connections. There are pluses and minuses of this design, so let's start with the pluses. This is one hot 15 watt amp! One of the biggest disadvantages of the Tripath TA2024 is its low power. The preamp of the Ernestolo feeds the amplifier a very loud signal, so this amplifier plays louder than you would expect. Louder even than my TA2021 25 watt T-amp. You would probably be happy with this amp connected to speakers with only average sensitivity, though I haven't tried it with any speakers other than my Axiom M3 speakers which are fairly sensitive at 93 db. The resulting sound is fantastic, and I'm very happy with the setup. It has a very small footprint, smaller even than my other T-amps.

The small footprint of the unit coupled with the fact that this is actually two devices mean the backpanel is cramped and cluttered. The preamplifier isn't connected to the T-amp internally, there is a small black 1/8" to 1/8" jumper that makes the connection. The power supply uses a splitter to connect to the barrel power sockets on both devices. With banana speaker plugs and an RCA audio patch cord connected to the back, you really can't reach the rear mounted amplifier power switch with out picking the amp up.

You might be tempted to just leave the amp on all the time, but you'll be rewarded with a very loud pop when you use the front mounted volume control to turn on the preamplifier. The instructions that come with the Ernestolo are very specific. Turn the preamplifier on first, then turn on the power amplifier. Neither has a "soft start," so even if you are following the directions you'll hear a clear pop as you turn on the device. The front mounted volume control has a great feel, and has a clear indent to turn the power to the preamp off. Also on the front is an 1/8" headphone jack and an 1/8" input which overrides the reat RCA inputs.

The preamp is a low voltage design (probably what is referred to as "starved plate") that barely makes the tube glow. For visual appeal, there is a very pleasant blue led to light the tube. I got my Ernestolo for $300 on amazon.com. That's significantly more than I've paided for my previous T-amps. Still, it's cheap by audiophile standards, and competitive for a (presumably) Chinese manufactured tube amp. The Ernestolo sounds an order of magnitude better than the Qinpu A-3 for example, and it's only $100 more expensive. If you can live with the cramped and cluttered back panel connections, the fussy powering sequence and in the inevitable pop when you turn it on, you'll be pleased with the sound of the Ernestolo.

Sure AA-AS32171 TDA7492 Amp

I just got this in the mail today. At $38 with a power supply and free shipping it was hard to ignore. This new Sure amp has the same form factor as my much loved TA2024 Sure amp, but it comes with the higher power Texas Instruments TDA7492 chip which claims 50 watts per channel. It's got a few improvements compared to my other Sure amp: a headphone jack, as well as both RCA and 1/8" stereo miniplug inputs. My first impressions are positive. It's well built and sounds great. It has the best digital volume control I've used with excellent feel. While the volume control has discrete indexed settings, there are many and it takes a few rotations to go from silence to full on so it shouldn't be a problem to find the right volume level. The volume control also doubles as the on/off switch; pressing it turns it on and off. If you are looking for a more powerful amp than the TA2024 tripath amps you should definitely check out this one.

So, the million dollar question: Does it sound better than the TA2024 amp? (The TA2024 version is the one on top with the silver volume knob) Well, my initial impression is that I still favor the TA2024. The increased power of the TDA7492 is noticeable and the bass is much stronger with the new Sure amp. I'm using it currently with the supplied 19 volt power supply, but it's claimed to work with a variety from 9 volts to 24. I'll have to give it some time and experiment with other power supplies before I have a definitive opinion.

Indeed Hifi TA2021 25WX2 Amp

I was curious to try a TA2021 based amp, so when Indeed Hifi introduced one I quickly bought it. Indeed is run by a guy named Peter, and is well respected in the audio forums, especially for it's tube based buffers, preamplifiers and headphone amps. I've bought a couple things from Indeed before and been impressed. The first is Indeed's shielded 12V 5A power supply which I highly recommend. While most of these tripath based amps will run off 3 or 4 amps, the 5 amp power supply really seems to flatter them. The extra juice seems to give the amps just a little more oomph. Since Indeed's power supply is shielded, it should also reduce noise and distortion. I'm very pleased with mine and use it with all my T amps. I also bought the cigarette lighter power cord from Indeed which lets me run my T amps off a portable 12V battery jump starter. Many audiophiles rave that running t amps off 12V batteries greatly improves the performance of the amp, but I'll admit that I can't tell the difference, maybe due to shielding on the Indeed power supply. The cool thing about battery power in my opinion is I can quickly and easily setup a stereo outdoors "off the grid." I ran my Hlly TA2020 amp of the 12V battery jump starter at a recent block party, and it happily put out party volume music for over 4 hours.

Back to the TA2021 amp, it sounds great. It's got that smooth, focused tripath sound. The extra wattage is very noticeable. While the TA2024 amps are adequate for my 92 db Axiom M3 speakers, the TA2021 has much more headroom, and turning the analog volume knob just a quarter turn gets it's louder than I'd ever want. If your speakers are rated 90 db or less, I'd recommend this amp. You can get even more powerful T amps, but then you'll need a more specialized and possibly bulkier power supply, and you'll lose the easy 12V battery power option.

How does this TA2021 amp sound compared to the TA2020 and TA2024? That's tough for me to put into words. I'd say it's very similar, maybe even indistinguishable from the Topping TA2020, with solid punchy bass and a wonderfully focused, coherent sound. To my ear, I think there is something special about the TA2024 that gives it the most musical quality, but it is very, very subtle. Ask me on a different day, or with some different music and I might give the nod to the TA2021 or TA2020 amps. Peter recommends a 100 - 200 hour break in period for the amp because of the large BC capacitors, so it might well improve.



Indeed's TA2021 exudes quality. Externally it's very similar to the Topping TP20. It has exactly the same footprint, but it's a little shorter. In terms of volume, it's probably the smallest T amp I own. Mine has the brushed silver faceplate which is a little shinier than the Topping. Like the Topping and Sure amps, the volume knob is back lit, in the Indeed's case by a soft blue light that is just the right intensity. There is an additional red led under the front power switch which shows the status of the speaker protection circuit. The amp has a soft start to guard against against pops. After a 2 or 3 second delay the red led is lit and your ready to go. The red led is a little bright for my taste, but no where near as obnoxious as the bright leds on the Trends and Hlly amps. As for the build and appearance of the TA2021, I can say it's my favorite of all the T amps I've used.

I think Peter at Indeed Hifi has designed a real winner here. If you are interested in trying a TA2021, using a T amp with less efficient speakers, or looking to put out party volume music off a 12V battery, this amp is a no brainer at roughly $55 shipped without power supply. An easy and enthusiastic thumbs up.

Hlly Tamp-20

The Hlly Tamp-20 has the most annoying power LED ever, a blinding green light. If you can get past that though, it's a great amp. Actually, dimming the light is straight forward. The front panel removes easily with four hex screws. Pulling the led back so it sits behind the front panel reduces the light to a tolerable level.

Surprisingly, it sounds different than my other TA2020 amp, the Topping TA-20. It's not as loud or powerful, but it's very clear. I have trouble with audiophile vocabulary, but the sound is crisp and clear, maybe a little less boomy than the Topping TA-20. Construction is top notch, and it's a very attractive piece of equipment. Mine has a different appearance than most of the Tamp-20s I've seen on the internet. The logo is shiny silver, and looks good against the matte silver of the faceplate. Most of the ones I've seen have a black logo. The only other gripe I've got is the rear mounted power switch, a small annoyance. I have no trouble recommending the Hlly, especially as they are sometimes sold without a power supply for around $50, significantly cheaper than the Topping.

Topping TP20

I had the Topping TP20 hooked up when the Sure amp arrived, and at the time I was convinced the Sure sounded better. I pulled the Topping out of retirement today, and now I'm not so sure. The first thing that is noticeable with the Topping compared to the Sure is the increased power. While I routinely crank the Sure past the 50% mark when I want to get some real volume, the TP20 has plenty of output and puts out more volume than I'd ever want with my system well before the half way mark. It's also much stronger in the bass, maybe a bit too much for my taste.

The Topping TP20 looks more expensive, and it is. It's got a front mounted volume control and a pleasing blue ring around the volume control to indicate it's on. The Topping is hard to fault. My recollection is that the Topping has more output and sounds better than my Hlly Tamp-20, which is another TA2020 model. I'll have to pull out the Hlly and do some A/B comparisons. At this point though, I'd have to say the Topping TP20 is an easy thumbs up, and it is my current favorite TA2020 based amp, and it's giving the Sure a run for the money as my all time favorite T-amp.

Sure TA2024

The Sure TA2024 is my current favorite T-amp. It's cheap and commonly available on ebay for around $50. It sounds fantastic. It's well built, attractive and it has a couple improvements over my previous favorite, the Trends TA-10.1. Unlike the Trends, it has a front mounted power switch, a small, but to me important, detail. I hated the Trends' obnoxious blue power led and the Sure has a softer glowing ring around the volume knob. That's not to say everything is as I'd like it. Sure added an odd feature. When the amp is off, the orange ring around the volume knob slowly pulses. The Sure manual calls this "breathing" and comments that it will help you find the amp in the dark. Whatever.

There are several variations of the Sure TA2024. I have the AA-AB32157 model which has the Tripath TA2024C chip and uses a digital volume knob. It is definitely different than the volume controls I'm use to. It takes a little over 3 turns, 1080 degrees, to go from completely off to full on. It is an indexed volume control with roughly 25 detents, or clicks in 360 degrees. Based on this, I'm guessing the volume control is Sure model AA-AB11117 which has 83 total positions. When the amp is off, spinning the volume knob has no effect, the amp always starts with the same volume level it was set at when it was turned off. I would probably prefer a normal analog volume control, but honestly the digital one is fine. It has a good feel and even though it's indexed, there are plenty of settings and I can always find the volume I want.

There are at least 5 different variations on this model. The earlier ones have the normal analog volume knobs, and there is one variant with a headphone jack. Here's my understanding of the different models:

AA-AB32151: Front headphone jack, Digital volume knob with 12v 3a Sure power supply
AA-AB32152: Analog volume knob and 12V 3A Sure power supply, no headphone jack
AA-AB32156: Analog volume knob and no power supply, no headphone jack
AA-AB340: Seems to be identical to AA-AB32156
AA-AB32157: Digital volume knob with 12V 3A Sure power supply, no headphone jack
AA-AB32159: Digital volume knob with no power supply, no headphone jack

I'd sold the Trends TA-10.1 long before I got my Sure, but the Sure sounds like what I remembered of the Trends with an exceptionally musical presentation. I'm not good with audiophile terminology so I don't know quite how to express it. It's obvious that at least some parts like the speaker binding posts are made with cheaper materials than the Trends, but somehow the Sure seems more finished and less of a DIY project than the Trends. Still, if I look closely at the Sure from the right angle, I can see that the case isn't perfectly straight. That's quibbling though. This is a world class amp and an easy thumbs up.