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Old 21st March 2012, 04:43 PM   #121
TheGimp is offline TheGimp  United States
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On switching the clocks...

Use two separate power supplies with shutdown function to power the two oscillators.

Take the outputs of the two oscillators and feed them through two 74VHC125 tri-state buffers.

Use a control pin from (pick your source) to drive the ps and tri state enable of one oscillator, use an inverted control signal to enable ps of the second oscillator and tri state buffer enable.

Proper bypass, ferrite beads, etc are standard.

Does this sound sufficient?
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Old 22nd March 2012, 07:41 AM   #122
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indeed, many thanks!
though a bit complicated for me

btw, by two oscillators did you mean quartz near the coax input?
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Old 22nd March 2012, 01:21 PM   #123
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24.576MHz and 22.5794MHz for the WM8740.

Both are necessary to be able to operate at data rates 44.1K, 48K, 96K, and 192K according to table 1 on sh12 of the data sheet.
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Old 22nd March 2012, 11:16 PM   #124
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hi,
I have always found it best to turn off the amps first,and then back up the line saves speakers and pops,I do it just backwards turning on ,give your system a little time before you flip the amp switch on though, just to let it all equalize power wise,like you know how you turn off and watch the LED glow for a several seconds ,well that time can create those pops and cracks because power is still in the caps in the power supply,Try it ! ^5 soft start and relays will do it to but more stuff in the signal line,snubber circuits too!
Happy listening,


I wonder how many people ordered and built this DAC?
Ps I think it was 10 people on first buy.

It has one feature that needs to be improved for sure. I guess everybody experienced it. When you turn the power switch off, cracking noise comes from the analog output to the amp and it's quite annoying and even terrible on high volume. As I've understood it happens due to direct opamp output and some filter or muting circuit should be added, am I right?[/QUOTE]
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Old 23rd March 2012, 07:46 AM   #125
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Quote:
Originally Posted by TheGimp View Post
24.576MHz and 22.5794MHz for the WM8740.

Both are necessary to be able to operate at data rates 44.1K, 48K, 96K, and 192K according to table 1 on sh12 of the data sheet.
where did you get these frequencies from the board? Sorry for my complete misunderstanding, but I've got nothing in regard to tri-state buffers that need separate supply and two oscillators of frequencies that I do not see on the board at all (mine has only 12Mhz quartz) even after searching in the net Perhaps you could post some scheme pls?
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Old 23rd March 2012, 07:57 AM   #126
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Quote:
Originally Posted by noSmoking View Post
hi,
... ^5 soft start and relays will do it to but more stuff in the signal line,snubber circuits too!
well, to my mind soft start affects only when you turn it on. Probbaly relays could be implemented somehow, though I have no idea how to make that.

The thing is that I've added headphone preamp to the box based on LME49710HAs and it behaves in the same way - you turn down the whole box (same button for dac & pre), some cracking/ slapping signal appears.

I've modified the design again and now it's done more professionlly I hope
added:
-shunt reg for preamp
-preamp section
-AC filter
-swapped to DALE resistors

-will add preamp RCA input and output soon
-something needs to be done with 7808 regs, they are simply burning, t >80-85c


The whole box heating like hell now, about 55-60c on the transformators inside, 45-50 on top of the case, 60-70 bottom part where IRFs from the shunt are placed.
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Last edited by dtses; 23rd March 2012 at 07:59 AM.
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Old 23rd March 2012, 02:05 PM   #127
TheGimp is offline TheGimp  United States
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Quote:
Originally Posted by dtses View Post
where did you get these frequencies from the board? Sorry for my complete misunderstanding, but I've got nothing in regard to tri-state buffers that need separate supply and two oscillators of frequencies that I do not see on the board at all (mine has only 12Mhz quartz) even after searching in the net Perhaps you could post some scheme pls?
What I am proposing would be a mod to the board.

The frequencies are from the data sheet.

http://www.wolfsonmicro.com/document.../en/WM8740.pdf

One can not get all bit rates with a single oscillator, and not interject occasional resync of the bit clock which impose a half clock jitter in the audio stream.

It seems to me that the WM8740 is designed specifically to use a switched clock to achieve all bit rates.

See page 12 "System Clock" in the data sheet. Particularly the second paragraph.
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Old 26th March 2012, 02:00 PM   #128
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Quote:
Originally Posted by TheGimp View Post
On switching the clocks...
Use two separate power supplies with shutdown function to power the two oscillators.
sounds nice, though what did you mean by shutdown function and does that mean that initially I'd need to switch off these supplies and then by pushing DAC's power button no nasty cracking sound would be heard?

Quote:
Originally Posted by TheGimp View Post
What I am proposing would be a mod to the board.

The frequencies are from the data sheet.
sorry for beeing inattentive, now I've got the point

Neither WM8740, nor 74VH125 buffer's manual doesn't come with any similar schemes. I've tried to find anything here and in google, but was unlucky.

have you made this mod to your dac?
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Old 26th March 2012, 06:12 PM   #129
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No, I actually have a different DAC board using the same components. I'm considering doing this mod once I have completely debugged my board.

The shutdown function would disable the oscillator not being used by shutting off it's power. This helps prevent inter-modulation from occurring and helps keep noise out of the system.

The downside of switching off the unused oscillator is that when you switch, it takes a few milliseconds for the oscillator to start up.
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Old 26th March 2012, 06:33 PM   #130
Turbon is offline Turbon  Sweden
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Quote:
Originally Posted by noSmoking View Post
hi,
I have always found it best to turn off the amps first,and then back up the line saves speakers and pops,I do it just backwards turning on ,give your system a little time before you flip the amp switch on though, just to let it all equalize power wise,like you know how you turn off and watch the LED glow for a several seconds ,well that time can create those pops and cracks because power is still in the caps in the power supply,Try it ! ^5 soft start and relays will do it to but more stuff in the signal line,snubber circuits too!
Happy listening,


I wonder how many people ordered and built this DAC?
Ps I think it was 10 people on first buy.

It has one feature that needs to be improved for sure. I guess everybody experienced it. When you turn the power switch off, cracking noise comes from the analog output to the amp and it's quite annoying and even terrible on high volume. As I've understood it happens due to direct opamp output and some filter or muting circuit should be added, am I right?
[/QUOTE]

I believe I have the same incarnation as TheGimp. I have no atifacts at power on but power off gives a ~2s PEEEEW...

Some of the 5 regs get hottish - not that I can't keep my finger on them but hottish. The same goes for the WM8741. The rest of the IC's are quite cool ( below 50C ).

Brgds
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Last edited by Turbon; 26th March 2012 at 06:35 PM.
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