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Old 4th January 2006, 08:16 PM   #1
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Default transit clock

Hi all,
I wonder if could be possible to fit a better clock in the transit usb external soundcard. It uses a 6 Mghertz clock, I didn't found any of this frecuency, anybody knows?
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Old 4th January 2006, 08:25 PM   #2
pburke is offline pburke  Germany
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I'm sure it'll worh with a 12mHz clock as well.

Nugent at Empirical Audio slaps a superclock on that thing. Wonder what he's using. I have a half-modded Transit laying around and may just try swapping that clock. Actually - why don't you just try a cheap 12mHz clock that fits the board before you spend the big bucks on a better unit?

Have you spent some time thinkgin about galvanic isolation of the board from the PC? I have built a custom power supply to feed 3.3V from a battery source, but cutting off the power/ground pins that come from the computer may not be such a good idea (since it's part of the shielding of the cable). Would it make sense to put a resistor on those two pins, rather than just cutting the leads? Just wondering if you worked on that as well, since you're modding the little thing as well.

Peter
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Old 4th January 2006, 08:45 PM   #3
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Hi Peter,
At this moment, I've already cut the power line from computer, but only the live cable is possible, if I cut the ground cable the transit will not connect with computer, so I can provide 5V. regulated from 12v battery instead of usb power and tie grounds together, no time yet to be sure about sound results.
Don't know about to put a resistor, perhaps somebody ?
It is good idea to try a 12 Mgh clock, hope I will not fry anything
Also have connect Dac chip to aes/ebu digital out, it works,
David
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Old 4th January 2006, 09:35 PM   #4
pburke is offline pburke  Germany
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interesting that the ground must stay connected. Wonder how then the Transit mod at Empirical Audio can be "galvanically isolated" from the PC?

I get pretty nasty noise in my system when my laptop is running on the power supply/charger, while when I use the M-Audio Audiophile with it's won power supply, I get none of that. I will have to open that thing up and take a look as to what's done differently in there regarding the power and ground lines.

Will have to cut up a USB cable to experiment a little.

Peter
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Old 4th January 2006, 11:20 PM   #5
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Well, perhaps it is computer fault, mine is the cheapest dell laptop, and no noise, I've not noticed any difference between laptop powered from AC or from its battery.

My plan is to improve the transit analog out, first the clock and then connect a Zap filter to the Dac chip, I hope this will make a great Dac.

David
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Old 8th February 2006, 07:55 AM   #6
GrayZee is offline GrayZee  United Kingdom
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Hi All,

Has anyone made any progress with modding the M-Audio Transit?

I'm particularly interested in "galvanically isolation" and upgrading the audio output.

Thanks,
Gray.
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Old 8th February 2006, 08:56 AM   #7
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Lightbulb KWAK-CLOCK

hi my clock will work with a 6 or 12 MHz crystal.
You can download it here:
http://www.diyaudio.com/forums/showt...928#post199928
Best regards,
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Old 8th February 2006, 01:41 PM   #8
gmarsh is online now gmarsh  Canada
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That 6/12MHz clock is likely only used for the USB data clock itself. There's probably a PLL hidden in one of the chips somewhere that creates a 44.1/48/96KHz related frequency derived from the PC, similar to what happens inside a TI PCM290x type of chip.

Don't disconnect the ground from the PC, it's required for USB to operate.
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Old 8th February 2006, 05:40 PM   #9
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Thanks to all,
I'm now about to connect the Zapfilter to AK4584, I'll report the results, I have no background in electronics, but I was reading the datasheet and I think this is an output voltage chip, not sure yet if I should connect Zap grounds to Vref or to analog ground in the chip, anyone?
I will try the clock later, if this works

Best regards
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