Adding a word clock output to the PCM4222EVM

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living sounds

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This evalution module has become my main AD converter, beating many higher priced professional units. But it lacks a dedicated word clock output. There's a LRCK output though (schematic attached), that puts out the clock signal. Looks exactly like word clock on a scope, but lower amplitude.  It needs amplification and probably termination (?). A buffer and a driver for the low impedance, and a fast one, too. Voltmeter shows ca. 1.3 V AC, no idea how reliable that is. Needed would be at least 2V single ended I guess. My Lynx Aurora16 won't sync to it.

So my question is: Can I get away with using a generic video amplifier like this one:

http://www.ebay.de/itm/Video-Verstaerker-BNC-Koaxial-CCTV-Video-Balun-Verstaerker-Videoverteiler-J5-/182228272539?hash=item2a6da6c59b:g:iR8AAOSwbsBXoEn2

I would rather not DIY digital circuits... ;-)

Thanks!
 

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living sounds said:
This evalution module has become my main AD converter, beating many higher priced professional units. But it lacks a dedicated word clock output. There's a LRCK output though (schematic attached), that puts out the clock signal. Looks exactly like word clock on a scope, but lower amplitude.  It needs amplification and probably termination (?). A buffer and a driver for the low impedance, and a fast one, too. Voltmeter shows ca. 1.3 V AC, no idea how reliable that is.
What is the peak-to-peak voltage on the scope? Don't rely on a voltmeter of unknown bandwidth to measure a 6MHz+ square-wave!
Needed would be at least 2V single ended I guess.
Are you sure? The AES standard requires the receiver to operate from as low as 0.2V p-to-p. So you may want to try...
So my question is: Can I get away with using a generic video amplifier like this one:

http://www.ebay.de/itm/Video-Verstaerker-BNC-Koaxial-CCTV-Video-Balun-Verstaerker-Videoverteiler-J5-/182228272539?hash=item2a6da6c59b:g:iR8AAOSwbsBXoEn2

I would rather not DIY digital circuits... ;-)
I can't access the link you provided, so I can't tell, but I can assure you that builing a suitable buffer is not very difficult, even built on the kitchen table. I can't access my database, but there are suitable digital circuits and alternatively you can use a video opamp.
 
abbey road d enfer said:
What is the peak-to-peak voltage on the scope? Don't rely on a voltmeter of unknown bandwidth to measure a 6MHz+ square-wave!

Word clock runs at the sample rate.

The AES standard requires the receiver to operate from as low as 0.2V p-to-p. So you may want to try...

There's an AES standard for word clock?
 
Andy Peters said:
abbey road d enfer said:
What is the peak-to-peak voltage on the scope? Don't rely on a voltmeter of unknown bandwidth to measure a 6MHz+ square-wave!

Word clock runs at the sample rate.

The AES standard requires the receiver to operate from as low as 0.2V p-to-p. So you may want to try...

There's an AES standard for word clock?
Sorry, I turned on the keyboard before the brains...Indeed, WC runs at sample rate, but being squarewave, the meter must have proper response at several times base frequency.
And AES standardised only WC over AES3.
 
This tiny logic (in SOT23-5 case from NXP) will do the level shifting for LRCK signal to a 5V TTL, which is the widely used logic level for a word clock sync signal, and most likely what the Aurora expects to work with.

Output connector is a 75 ohm BNC female socket (i.e: Tyco 1-1478032-0)

 

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metalb00b00 said:
This tiny logic (in SOT23-5 case from NXP) will do the level shifting for LRCK signal to a 5V TTL, which is the widely used logic level for a word clock sync signal, and most likely what the Aurora expects to work with.

Output connector is a 75 ohm BNC female socket (i.e: Tyco 1-1478032-0)

Thanks! Could I use a sn74lvc1g125dbv, too (got one here)?
 
It has to be 74HCT, because the T stands for TTL.

Alternatively, you can also use the easier to get 74HCT125/74HCT244/74HCT245, and connect the unused inputs to ground.
 
metalb00b00 said:
It has to be 74HCT, because the T stands for TTL.

Alternatively, you can also use the easier to get 74HCT125/74HCT244/74HCT245, and connect the unused inputs to ground.

Thanks, I'll see if I can get one at the local electronics shop.
 
A bit off topic, but do you really need wordclock? The Aurora has lots of clock/sync options, you could feed the Aurora off a digital signal and lock to that. Plus then you have a wordclock out on the Aurora.

I think the LRCLK is more of a bit clock, so if you truly need wordclock you would need to divide it down as well.
 
john12ax7 said:
A bit off topic, but do you really need wordclock? The Aurora has lots of clock/sync options, you could feed the Aurora off a digital signal and lock to that. Plus then you have a wordclock out on the Aurora.

I think the LRCLK is more of a bit clock, so if you truly need wordclock you would need to divide it down as well.

I use two RME cards in my computer, so I could in theory connect them internally and clock the Aurora off the AES signal. But a direct connection without the reclocking involved within the computer makes more sense, doesn't it?

LRCLK appears to be the same thing as word clock,  both run at sample rate.


 
That is for external master clock source.

"An external clock source (EXT CLOCK), may be input at BNC connector J11 and is buffered by U19. The
buffer includes a tri-state output, so that it may be disabled when one of the crystal oscillators is used as
the master clock source. Buffer U19 is always operated from the +3.3V supply generated by voltage
regulator U22, and is tolerant to +5V input logic levels. The maximum external master clock frequency is
27.648MHz."

from page 9.
 
living sounds said:
john12ax7 said:
A bit off topic, but do you really need wordclock? The Aurora has lots of clock/sync options, you could feed the Aurora off a digital signal and lock to that. Plus then you have a wordclock out on the Aurora.

I think the LRCLK is more of a bit clock, so if you truly need wordclock you would need to divide it down as well.

I use two RME cards in my computer, so I could in theory connect them internally and clock the Aurora off the AES signal. But a direct connection without the reclocking involved within the computer makes more sense, doesn't it?

LRCLK appears to be the same thing as word clock,  both run at sample rate.

I confused it with BCLK, strange that it doesn't work then. Maybe give Lynx a call and see what it expects to see,  they are usually pretty helpful.

If you use an LT-HD card you get access to both analog and digital i/o, but yes in your case would need to daisy chain. Might still be worth a shot though. There is no clear cut answer, but sometimes AES clocking can be better, so even with the extra steps it may still be as good as word clock.
 
Can also replace U9 with 74LVT245PW (same footprint TSSOP-20), so BCLK and LRCLK signals going out via the AUDIO PORT header become TTL compatible. Though not really recommended because you might break a trace when doing the mod.

BTW,  this probably doesn't matter, but... might wanna set the digital audio serial format to LEFT JUSTIFIED if you use 74HCT1G125. If you use 74HCT1G04, then just leave it at I2S.
 

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Okay, got a PC74HTC125P.  What's best practice regarding grounding? I can use the PSU ground or the PCM4222EVM PCB's ground where the PSU connects or the ground for the RLCK output.

I guess the three unnecessary inputs should go to the PSU ground directly. But what about the rest? Also, should I add decoupling caps to the 5V rail?

Thanks!
 

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