justin

They have low distortion but this is usually with loads of 600, 1k, 2k ohms, or higher. Very few op-amps are able to properly drive low or medium impedance headphones directly, and many of the ones that do have high output current capability have poor performance in all other areas.

This is really the problem, because the best use of the switch on the amp-only version would be a gain switch. To have a gain switch on the amp-only, but none on the DAC+Amp, would definitely bother a lot of people (and also make it more difficult by having 2 different front panel layouts).

There isnt any room for an internal jumper

The DAC runs on USB power, and is filtered and regulated extensively. The headphone amp always runs on battery power. The power draw from the USB is 100mA (0.5W)

Poll time... The toggle switch on the front of the amp could do 1 of 3 things. I'd like to find out what is the most desirable 1) Gain switch (this is the current use) 2) Change the analog input into a DAC line output 3) This one is unlikely to win, but could be done....a voltage switch, giving a shorter or longer battery life depending on position.

Computer/Meridian 500 CD Transport -> Benchmark DAC-1/my new USB DAC+Amp -> Any amp I build -> Stax Omega II/Stax 404/HD650/K701/Grado RS-1/Ety ER-4S

I prefer same as in the Arcam CD33 (one of the first and best high-end CDPs I owned, which led me to consider the WM8740), Rega Apollo/Saturn, and many other players. There were only about 3 or 4 DAC chips that were serious options, and of course there are various DIY projects that use all of them

PCM2707 performs USB to I2S conversion AD1896 is the upsampling WM8740 is the DAC OPA365 are for the analog filter TPS79333 and TPS73150 are the voltage regulators MAX1896 steps up the DC voltage on the analog side the headphone amp section isn't final yet

WM8740

Probably October/November, some of the parts have a 3 month lead time. The closest competition to it would probably be HeadRoom's upcoming Max Micro DAC (as far as quality of the DAC, with upsampling and a flagship DAC chip) but for USB input mine is probably the only one that avoids the extra conversion to SPDIF

I would have to assume he's cutting off all but 1 or 2 of the strands from the wire and soldering that, probably adding epoxy or glue so it doesnt fall apart

http://www.redwineaudio.com/iMod.html Reading over the iMod page, it sounds like they're just removing the opamp and its supporting components, which likely are a filter, from the output of the iPod's DAC. This is just going to result in a lot of high frequency noise being present and then being further amplified by your headphone amp. Not a good thing...these are exactly the kind of mods done by people who don't know what they're doing or just looking to make a lot of $$$

Yes, I'll bring it to the Boston meet if it happens Here are a couple of better pics, I've had a few questions about the size. Subway cards are the same size as credit cards Back has USB and DC jack, inbetween the boards are the li-ion battery and a capacitor

i liked denon d5000

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

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.

M-Audio Audiophile Firewire

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.

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. Frequency Response Noise Level Dynamic Range THD+Noise (0.0007%!) Intermodulation Distortion (0.0058%!) Stereo Crosstalk IMD (Swept Tones)

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- 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.

What is it, a 2.5mm jack? I think that's standard on phones

Did you put the ZD on top of the FirstWatt?

Unless he bought it from grawk/tkam it sounds like sloppy fourths

If you're that concerned, spend $100 (just an estimate) on an SPL meter. Only 1% the cost of the rig you just bought. I think anything over 80dB for an extended period of time can cause permanent damage.

Peter, Are you going to have them at the July maryland meet?