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Old 4th December 2009, 07:11 PM   #1
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Join Date: Dec 2009
Default Confused about USB/DAC choice.

New here, but have read hundreds of threads on the probelm and lots of serious reccomendations from members on the issue of how to handle USB audio.
I have a hybrid amp right now (HiFiMan EF2) which has a USB/DAC/Tube/OpAmp configuration for headphone output.
I recently acquired Denon D5000's and can detect many flaws in the USB/DAC section (sizzle, jitter, gapping) and I am geeting fed up with it.
I would like to diy a solution but want a quick fix for now, and I can build in my leisure (who says leisure anymore?).
I saw a USB-DAC on a site and was wondering if you could tell me if you thought the chips and tech used was a good start.
iBasso D4 Mamba
USB-DAC/Headphone AMP
- Dual Wolfson WM8740 DAC Chip + TI PCM2706
- USB signal input, provides I2S interface for decoding
- Works as a DAC+AMP Combo, a standalone AMP, or a standalone DAC (Line out function)
- 2-Setting Gain Switch for impedance matching
- OPAMP rollable
- AMP section can be powered by either USB or 9V battery
- 9hours play time with 9V 300mAh battery (when powered by battery)

Cost is $220 USD which is in my budget. I am going to purchase a HiFiMan EF5 which takes RCA analog in as my headphone amp.
Opamp: OPA275
Tube: RCA Clear top 12AU7
Frequency Response: 20-30K Hz
THD+N: less than 0.2%
S/N: more than 95dB
Input impedance: 50K Ohm
Output impedance: 22K Ohm headphones
Output signal strength: up to 15 Volts at 32 Ohm
Input: RCA*1
Output: 1/4 headphone jack*1
Acessory: 12AU7 tube, DY-1 power supply, compatible from 110v to 240v

Thank-you all for your time.
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Old 5th December 2009, 01:57 AM   #2
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The WM8740 DACs are well regarded.
The PCM2706 is the go-to chip for usb DAC interfacing. The PCM2706 has a DAC aboard but if they are using the Wolfson chips then they are using the PCM2706 as a usb gto I2S decoder, as they mentioned.

If you follow the manufacturers' guidelines about building DAC circuits around their chips it is hard to screw up a DAC. The devil is in the analogue section of the DAC. It's what a builder does in the analogue section that defines the quality of the DAC.

That said, it may be difficult to drive a good set of headphones with either a 9V supply or USB bus power.

It might be better suited to preamp duty rather than as a headphone amp. However for the price...there are cheaper USB DAC / headphone amps out there, but you get what you pay for. The HiFi Man EF5 seems like a good choice to use as a headphone amp.
What's the output circuit on the EF5? The opamp or the 12AU7? Neither are overly good to drive low impedance cans.
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Old 5th December 2009, 01:58 AM   #3
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Location: Santa Cruz, California
My personal opinion (and I'm not a windows programmed) is that the problem with USB audio is the host computer. Windows wasn't designed as a music serving device and as such gives audio a pretty low priority. Consequently, the buffers can underflow causing drop outs. The USB is a burst mode bus and so generates lots of HF noise and then I've noticed a particularly annoying habit of sending a full scale sample here and there producing a random intermittent "snap".

I think the "network media tanks" over LAN or possibly wifi (depending on RF interference in your neighbourhood) are a better approach.
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