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Old 21st May 2009, 11:17 PM   #1
jkeny is offline jkeny  Ireland
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Default Cheap Asynchronous USB

How about a new group project - something like what the Shigaclone did for transports, I believe this could do for PC audio - an inexpensive way to realise high quality audio from a PC.

First off Asynchonous USB is a big deal - it avoids the clock jitter problems that plague USB audio by using the clock in the USB device to synch the PC USB. This avoids the usual scenario where the PC clock is used as the timer for the USB signal.

So, there are only a few products that operate in this mode from Wavelength & Ayre &?. Why because the development of the drivers for Windows is a big task!. This development has also been done by Tascman for their inexpensive Pro audio portable recording products Tascman US-122L & US-144. ($120 & $150).

Steve Nugent of Empirical Audio already uses this Tascam unit (modded) along with his Pace Car reclocker(which provides the low jitter clock) as a solution for I'm guessing > $1,000
Quote:
I have a number of customers using async USB with my Tascam US-144/Pace-Car combination. It is a more expensive solution than the Off-Ramp 3, and sounds a little better
So with a Tascam 144 platform as a base we need to do some mods
- first change the internal clock to a low jitter type with a low noise PS (not one of those Chinese clocks)
- run the unit from a clean external PS supply rather than the USB PS
- maybe tap into I2S signal to feed an external DAC

So for possibly < $200 (depending on clock costs, etc) we get
- a very low jitter USB audio DAC

The standard unit can be found here: http://www.tascam.com/products/us-144;9,15,70,16.html

The internal chip IDs & pics can be found here and mods look very do-able: http://www.everholt.org/abel/tascam/...144_chips.html

Does anybody have one of these Tascam units and/or a service manual?

Edit: Oh forgot to say the Tascam will do 24/192 also!
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Old 21st May 2009, 11:58 PM   #2
jkeny is offline jkeny  Ireland
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Read more about Empirical Audio's use & mods of the Tascam here: http://www.audiocircle.com/index.php?topic=64017.0
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Old 22nd May 2009, 08:17 AM   #3
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The Tascam looks like a terrifying box of junk. I would rather desolder the only two chips needed and rebuild using proper power supplys and clock. Still, it may be a solution if you are really dedicated. Thanks for posting it.
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Old 22nd May 2009, 10:05 AM   #4
jkeny is offline jkeny  Ireland
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What are the only two chips needed - the uC & the USB chips? Don't need the AKs Digital Interface Receiver chip?
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Old 22nd May 2009, 10:43 AM   #5
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That's the way it looks. If one could bust the read protection of the Atmel you can use a micro of your own choice too

The DIR/DIT chip appears to convert to and from spdif and that is probably where you can tap the I2S from. I don't see any need to keep it if you don't need an spdif output.
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Old 26th September 2009, 11:24 AM   #6
Korrah is offline Korrah  Malaysia
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Pardon my ignorance, but lets say that I needed to keep the Tascam (because the recording features are quite useful for me), and wanted to swap out the clocks for better crystals, is it just X1, X2 and X4 that I need to swap out? Thanks
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