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Old 22nd December 2003, 04:06 PM   #1
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Default Asynchronous reclocking problem

Hello, I'm experimenting a little with my DAC (TDA 1543 x 4), and while trying the ASR out (the schematic of the ASR is like the one of the NONOZ dac and is fed by a canned oscillator) I noticed a crackling noise at the output superimposed to the music.
The funny thing is that if I put my finger on the oscillator this noise stops.... does anybody have a idea of what's going on?

BTW the ASR/oscillator have a separate 5V supply made with a 2.2 mH choke followed by a 7805, the CS8412 has 2 separate supplies with TL431 for analog and digital, while the PS of the TDA1543 is made with a LT1085.

I replaced the previous supply of the DAC (taken from TNT Convertus) because, using a battery, the supply of the DAC did follow the discharge of the battery and the pass mosfet had too much dropout, which prevented me from using Vsupply>7V.

Fro now the DAC is bolted on a piece of plywood and placed on the top of the CD player.

Any hint will be appreciated...

Cheers

Andrea
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Old 22nd December 2003, 04:12 PM   #2
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I believe in a ground loop. Try lower the voltage of the sinchronizer and see if something happens( say 3.5 volts ).

If the noise goes than it is a ground loop.
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Old 22nd December 2003, 04:24 PM   #3
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Default Beware of RFI!

Lifting the DAC from the CD player seems to have solved the crackling noise problem (that now seems a RFI problem), however now and then the dac outputs pops and clicks... is that a normal behaviour for a DAC with ASR?

Cheers

Andrea
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Old 22nd December 2003, 04:32 PM   #4
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Cool Crackling Noise

Hi Andrea, The cannned oscillator must have a direct and short ground connection to the ground of the ASR PCB. It occurred me too with Tone's oscillator (80MHz).
Thanks again Tone for trying it!
Or better build the complete circuit with the discrete oscillator, which does not have this problem.
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Old 22nd December 2003, 05:33 PM   #5
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Default Re: Crackling Noise

Quote:
Originally posted by Elso Kwak
Hi Andrea, The cannned oscillator must have a direct and short ground connection to the ground of the ASR PCB. It occurred me too with Tone's oscillator (80MHz).
Thanks again Tone for trying it!
Or better build the complete circuit with the discrete oscillator, which does not have this problem.
The canned oscillator and the ASR are very close and fed by the same supply, so their ground connections are direct.
Moving the DAC from the CD player solved the crackling noise problem, however the clicks are still present...

Cheers

Andrea
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Old 22nd December 2003, 06:51 PM   #6
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The clicks are likely to be the result of the ASR dropping bits fom the data stream as the setup and hold times of the flip flop are frequently violated.
I think you could get a rough idea of what percentage of cycles this happens by dividing the setup time plus the hold time by the clock period.

I think that the ASR is a very flawed idea. There are far more intelligent ways of doing this, like a small FIFO right before the DAC to decouple any timing requirements from the rest of the digital section enabling you to clock data output of the FIFO and into the DAC directly from the master clock.
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Old 22nd December 2003, 07:16 PM   #7
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Cool Metastables?

Quote:
Originally posted by Dave
The clicks are likely to be the result of the ASR dropping bits fom the data stream as the setup and hold times of the flip flop are frequently violated.
I think you could get a rough idea of what percentage of cycles this happens by dividing the setup time plus the hold time by the clock period.

I think that the ASR is a very flawed idea. There are far more intelligent ways of doing this, like a small FIFO right before the DAC to decouple any timing requirements from the rest of the digital section enabling you to clock data output of the FIFO and into the DAC directly from the master clock.
Hi Dave,
I did not get any metastable in a 10 minute measering time.
The two flips-flops in series prevent that. With a single flip-flop you get dropouts now and then though I did not hear these.
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Old 22nd December 2003, 08:07 PM   #8
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Cool Asynchronous reclocking problem

Hi Andrea,
What I meant is that you must solder the groundpin of the cantype oscillator directly to the groundplane of the ASR. Don't use a piece of wire. You are using a groundplane, do you? Do you have a powersupply bypass cap directly at the oscillator?
What is the frequency of the oscillator?
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Old 23rd December 2003, 09:14 AM   #9
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Hello Elso,
I found out that the main problem was the noisy environment I tested the DAC into ... close to the PC, with ballasts and so on... I wrongfully thought it was a problem of the ASR while it was innocent!

Yesterday I tested it vs the converter of a Arcam AVR200 (which has the converters of the "old" Alpha 7 if I'm not wrong.. initially the Arcam was slightly better, then I raised the voltage to 8.5V (before it was 7.5V) and inserted the reclocker (with a 80 MHz oscillator)... the little DAC became MUCH better than the Arcam, when it started playing all we (4 persons !) didn't believe to our ears.. sweeeeet!!!

Now I'm doomed to build 2 other DACs

Cheers

Andrea
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Old 23rd December 2003, 09:21 AM   #10
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Smile "Noisy" Environment

Quote:
Originally posted by Andypairo
Hello Elso,
I found out that the main problem was the noisy environment I tested the DAC into ... close to the PC, with ballasts and so on... I wrongfully thought it was a problem of the ASR while it was innocent!

Yesterday I tested it vs the converter of a Arcam AVR200 (which has the converters of the "old" Alpha 7 if I'm not wrong.. initially the Arcam was slightly better, then I raised the voltage to 8.5V (before it was 7.5V) and inserted the reclocker (with a 80 MHz oscillator)... the little DAC became MUCH better than the Arcam, when it started playing all we (4 persons !) didn't believe to our ears.. sweeeeet!!!

Now I'm doomed to build 2 other DACs

Cheers

Andrea
Hi Andrea,
Glad it works now. Seems you have Tones oscillator.
I can confirm my DAC works better is a separate box than in the player.....
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