Pro-Ject USB Box, A USB DAC

Well, i bought it.
It's just a little thing like a pack of cigarettes size like, based on the (famous..) Burr-Brown PCM2702 USB interface with built-in DAC.

http://www.project-audio.com/inhalt/en/pdf/usbbox.pdf

This same chip is used also in :

FubarII/III, GoVibe Petite USB, Ti Kan's Alien DAC, Hotaudio40 HotUSB1,Keces USB DAC, TooleAudio BantamDAC, Silverstone Ensemble EB01 USB Dac, KingRex T20USB and even the $1600 Sutherland Engineering 12dAX7 USB DAC/preamp. This just show how good and versatile it is.

For now - i just listen to it a couple of hours - it certainly seems an improvement regarding my resident sound card - the SoundBlaster X-Fi.

Some Pro-Ject USB DAC specs:

Line-level output : 1 pair RCA/Phono sockets
Output voltage : 0,775V
Op-amp : JFET AD823A
A/D converter : 16-Bit Delta Sigma
Sampling rate : 44,1kHz
USB-input : digital serial data protocol USB 1.1

If you compared the X-Fi specs with Pro-Ject USB DAC the differences are huge.... all in favor of the X-Fi, but we in fact we don't listen to specs, but to music.... and in reality the Pro-ject USB DAC sound much better than the X-Fi...but, that's one of the factors we must get an external DAC if we really want to use a computer as a source.

Attached Image (Click thumbnail to expand)

Moving On Up ( An introduction and first impressions)

Before I tell you about my options, it’s important to look at the weakest links in almost all sound cards: the DACs and the OP-AMPs. While the DAC better than most PC sound cards, this is the one component where there is sufficient room to grow.
The DAC plays the crucial role of translating the 1’s and 0’s of the audio signal into the analog domain. It’s responsible for reconstructing the audio waveform. The OP-AMP is the low-power amplifier that takes the output of the DAC and amplifies the signal so that it’s usable with you headphone. Since these components are on the sound card and the inside of the PC is an “electrically noisy” environment due to all the fans and EMI, noise and distortion get introduced into the audio signal. The noise and distortion are minimal, but it can be a problem if your speakers or headphones are good enough to resolve the details. Therefore, the trick is to move the DACs and OP-AMPs outside of the computer. IMO, there is only one approache to take.

USB External Sound Cards
The idea is that we can move the entire sound card outside of the PC environment. Remember M-Audio Audiophile USB?! Unfortunately, consumer-grade external USB sound cards never seemed to work as well. Turns out that the problem was jitter...
For some people, jitter is a voodoo science of digital audio. Bits are bits right? Perfect sound forever, remember…? It turns out it’s not that simple.

How would you pronounce “cho pho use?" Think about it for a while. Sound it out.

What if I wrote it as “chop house?”

All I’ve done is change the timing in which the data has come to us. When it comes to audio, a DAC expects data to come every 1/44100 seconds. If the data comes in a fraction of a second too early, the sound card buffer can overfill. If the data comes in a fraction of a second too late, the DAC has to “guess” at what kind of data it needs to send out. This corrupts the audio resulting in worse fidelity.

USB is a high-jitter interface

Although a USB sound card helps you move the circuitry away from the noisy environment inside a PC, the USB interface itself has a substantial amount of jitter. USB has four different transmission modes. Two of those are designed for transferring a large amount of data.
1) Isochronous mode. A fixed number of packets are sent and received.
2) Bulk mode. A fixed quantity of data is sent each time. If data is lost, it’s resent.

Bulk mode works well for hard drives and printers because errors can be corrected through retransmission. For audio data, retransmission wouldn’t work because the delay would cause the music to stutter. So for audio, you have to use the isochronous mode where there’s no re-sending of packets.


In the end, USB sound cards end up being a wash. The benefits from moving the sound card out of the machine are cancelled out by distortion that gets added from the USB circuitry.

Burr Brown solution

The engineers at Burr-Brown Japan came up with a better way: a very high-speed tracking system in which the transmitting frequency is determined by calculating the differences between those two packets. The chip was the PCM2702.

http://www.audiodesignline.com/showArticle...119&queryText=3

What makes it special is that Pro-Ject took a purist’s approach to audio. Rather than just trying to focus on specs and selling a “24-bit / 96 kHz” sound card which may offer compromised performance, Pro-Ject chose to go with the Burr Brown PCM2702 chip given its ultra-low jitter performance.

The simple design of the Pro-Ject USB Box is what gives it its performance. It is more transparent and more natural sounding. With a pair of great speakers the improvement over the SoundBlaster X-Fi is immediately noticeable.

The gains in using this “low-end Pro-Ject USB dac” are through all the freq's. soundstage spectrum:
More accuracy, detail and depth.

The sheer pace, attack and energy of the music are much more noticeable than before. Seems to me that i was listening to the first time to some of the songs that i thought i knew well for a long time.
Okay, it doesn't have the kind of delicacy and the huge soundstage of other expensive dac's... or even like the Audio Alchemy V.1(my other dac), but what you expect from a 90,00 € usb dac?!

The combination with the heavily modded Musical Fidelity X-10D buffer (with Siemens ECC85 NOS valves) gained a little extra weight and definition in the lower registers which improves sound warmth being replaced by a noticeably punchier and dynamic sound. Not only because of the valve “magic effect” but also because its load matching ability.

I'm always amazed at how much bass you can get from a small set of speakers....

Conclusion:

I LIKE IT.


Equipment:

OS : Windows Vista.
Music Formats: MP3 192/256Kb and FLAC
Player: Foobar 2000 and J.River MediaCenter12 (both with Pro-Ject ASIO output driver) at 16/44100Hz
Buffer: Musical Fidelity X-10D (heavily modded)
Amp: Nad C325BEE ( slightly modded)
Speakers: B&W CDM1 SE
Speaker Cables: Supra Rondo

An interesting link:

Benchmark's Guide for Computer Audio
http://extra.benchmarkmedia.com/wiki/index...k_-_Setup_Guide

Some pix.







If there is something that explains the KISS theory in audio design this is it, more simple and purist it's hard to find.

A solid box, few good SMT resistors, a dac chip, a good JFET dual op-amp, great caps from WIMA, et voilá......a great "plug 'n play" USB DAC.

A couple more pix of the Pro-Ject USB box in my comp system:





Today i trade the B&W for Paradigm Studio Reference 20. Not so much detail but a little more low end. I love the Paradigm speakers.

you got all those cool do-dads, and gadgets, kinda like 007, cool picts.

elroy

i missed this detail the first time around. interesting that you prefer the Paradigms ... how does the other guy like the B&W's?

i missed this detail the first time around. interesting that you prefer the Paradigms ... how does the other guy like the B&W's?

Sorry, but i think i can't understand your question. Can you please be a little more precise?

you said you traded the B&W for the Paradigm's, i was wondering if the other guy is as happy as you are with the arrangement.

Sorry about my English...but what i'm trying to say is that i traded the Paradigm from my main setup to my comp system.
The B&W love detail but i don't need that kind of detail in my comp. This doesn't mean that the Paradigms doesn't have detail - of course they have - but they are more "musical" than the flat and transparent B&W, now in my main setup.

i see. i didnt think you would part with the B&W's.

nothing wrong with your English mate, its much better than my Spanish.

With two wives (one ex-wife) and three kids, one in University and the others in high school there's not much money left to spend in our hobby. Sometimes i feel not like James Bond but almost like Ethan Hunt in Mission Impossible ...so i'll tend to explore to the limits all the little things i have or i can afford...and i feel great.

I came across this interesting link and i've decided to take it shot in my usb dac before moving in another directions.
I'd tried it with what i have at hand, in this case a poly from wima. The idea is to reduce noise bypassing hf noise to ground as well as stabilise whatever ripple that may still be at OP Amp supply side.






I tell you, this tweak really works and it sounds exactly like this guy describes it.
Improvement in depth, stereo separation and a wider music image. Also i find the sound more "in control", more tight.
It's incredible what caps in the right place can do to sonics... Of course i don't have any silver mica caps but only with this average wima i have a glimps of what this tweak can do. Maybe later, if i found another caps, i.e electrolytics, i would like to tried those aswell...

Soon i'll tried this too in my nad cdp op-amps'.

Well, i'd tried this time with a non polar Rubycon lytic 1uF and it's simply far out!!!
I must try with another capacitance values, let's say around 2,2-4,7uF and see (listen) to what happens...i'm drowened in the Yeah Yeah Yeahs' sound. Music's my religion and sound is my flag.

I had some poly caps apart and i decide to take a shot and change the Wima MKS4 - which i found a little harsh in the high freqs after i'd made a decoupling cap on the opamp - with a metalized polyester cheap ones. These are made in Germany by Vishay Roederstein to be exact, model number MKT 1822. They were previously know as the ERO capacitors.

Most guys will disagree because it goes against all audiophile grade logic. I mean, they don't have teflon, copper foil, silver foil, polypropylene/foil design, silver leads, etc. But what they have is what counts, absolutely stunning sound. They have great resolution and a bit of sparkle in the high frequency. The best part is that they are very cheap. Just great.

Edited:

After a couple of hours i get the feeling that something's missing...i'll found out that was the lack of bottom end. They have incredible mids and highs but little low end, so i'd put a pair Wima's MKP10 120nF ( plyprops) in parallel with the MKT polyesters and everythings turn the way i like.
Always learning, always moving forward...

Just a pic of what i have described in my last post:



These are not valves but i'm certain that i will make some caps rolling, with this baby.