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New Portable USB DAC/Amp to preview at Maryland Meet


justin
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I'm going to be previewing a new portable USB DAC/Amp -- no official name yet -- at the Maryland meet next weekend, in the form of a working prototype circuit board. I'll have it hooked up to a MacBook with lossless FLAC.

There are several portable USB DAC/Amps available but all of them use the same DAC design -- one of the all-in-one chips from TI which has a USB receiver, 16-bit DAC, and analog/headphone output stage. This chip is really intended for use in things like cheap USB speakers, LCD monitors w/ built-in speakers, and the performance is not very good (my prototype has 10% the THD of this chip, and that's including my headphone amp stage set at a gain of 6 capable of driving all headphones).

Some features of this new USB DAC/Amp, most of which have never been done before in a portable DAC/amp or even just a portable DAC:

- Upsampling design!

- Uses a flagship level 24-bit/192KHz digital-to-analog converter chip!

- Extremely low distortion analog filter

- Protects USB ports from over-current

- Extreme care in keeping noise to a minimum, separate power supplies for each stage

- 4-layer circuit board for optimum digital layout

- Separate analog input to use as headphone amp only

- Gain switch (toggle) on front panel

- Alps volume control w/ built-in power switch

- Lithium-polymer battery (estimated 35 hours, or 70 hours w/ extended battery option)

- Built-in battery charger w/ charge status LED on front panel (2-4 hour charge time depending on battery option)

- Back panel has the USB jack (Mini-B) and DC adapter jack

Also, it is very, very small -- within 5% of the size of some amps designed for IEMs only.

I'm very excited about this new design and have been spending a lot of time revisiting my FLAC library with my MacBook I got a few weeks ago. Nothing like this has ever been done before, except in home wall-powered DACs 10 to 100 times the size of this portable.

I'm going to be having a beta test of 5 to 10 units after I complete the 2nd prototype, and there are probably about 2 spots still open for that.

I may post some early distortion/noise/frequency response measurements this week before the meet.

There will be 2 versions available (the DAC/Amp, or just the Amp), an option of the regular battery or extended battery, and several color choices.

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Good work HeadAmp. Hopefully the choices of DAC and OPAMP are okay. I'm guessing the DAC is a delta/sigma? I think R-2R DACs are better, but I guess those are a little more complex (not too much) to implement than desired here since you will need to deal with a separate upsampler. I'm still waiting for someone to make a portable upsampling R-2R DAC. That would kick arse.

Oh, I'm making assumptions again. Damn it.

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Here are some of the testing results....

A note on the frequency response....currently waiting for a part, so the bass roll-off is about -2dB at 20Hz until I get it. The final version will not have this roll-off.

fr.png

Frequency Response

noise.png

Noise Level

dynamics.png

Dynamic Range

thd.png

THD+Noise (0.0007%!)

imd.png

Intermodulation Distortion (0.0058%!)

cross.png

Stereo Crosstalk

imdswept.png

IMD (Swept Tones)

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Hey Justin, are you going to be showing the upgraded modules for the Gilmore amps at the VA meet this weekend?

Toshiba recently discontinued the 2SK389 and 2SJ109, the matched dual-FETs that I use on the Gilmore modules and will use on new discrete modules since there really aren't (or weren't) anything else like them. Linear Systems has come out with a 2SK389 replacement, and is expected to have a 2SJ109 replacement this year. The modules are going to be on hold until I can get these.

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Wow! Justin, that sounds like it's going to be really nice. I'm assuming the DAC is USB only? Is there any chance of it having a coax or optical input as well? To me that would make it much more versatile which would be more in keeping with your other offerings. The versatility of the AE-2 and GS-1 are part of what I love about them. I absolutely love the fact that my AE-2 has both a mini input on the front and RCA's on the back, in fact, what I'd personally really love to see would be something along a similar line as the AE-2 with all it's features but adding a USB/Coax or Optical DAC of reasonable quality.

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No, there will be a headphone output, and an analog input that becomes the input instead of the DAC when a cable is plugged in. There's no room anywhere to add an additional switch that would be required to have a DAC-only output. However, the headphone output can be used as a variable output of the DAC. Really just a marketing difference in calling it a headphone output vs. variable output which is seen on many DACs.

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Wow! Justin, that sounds like it's going to be really nice. I'm assuming the DAC is USB only? Is there any chance of it having a coax or optical input as well? To me that would make it much more versatile which would be more in keeping with your other offerings. The versatility of the AE-2 and GS-1 are part of what I love about them. I absolutely love the fact that my AE-2 has both a mini input on the front and RCA's on the back, in fact, what I'd personally really love to see would be something along a similar line as the AE-2 with all it's features but adding a USB/Coax or Optical DAC of reasonable quality.

It would have to be significantly larger to have a coax and/or optical input. This DAC/Amp is only 40% the size of the AE-2. Also, with a coax or optical input the DAC would have to run on battery power, and it consumes a lot of current compared to a headphone amp. This would drop the battery life to 4 hours or 8 hours with the extended battery. I don't think that is enough. A larger portable DAC/amp with a coax and optical input may come later, and would have a much larger battery. It would be about the size of the AE-2.

My goals for this portable USB DAC/Amp were:

- to make the best portable USB DAC/Amp available regardless of size

- have features that aren't on anything else (lithium-ion battery, upsampling, 24-bit/192khz DAC chip, etc)

- keep the size as small as the smallest Amp-Only portables

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