How about using a 24.5535 MHZ clock in a dac?

acaudio · 17th February 2008, 06:58 PM

Hi folks,

I found following oscillator at digikey:

Citizen CSX532T24.5535M3-UT-10 (Digikey number: 300-8277-1-ND )

Specifi cations: • Frequency Tolerance: ±1.5ppm @ 25°C, ±2°C • Frequency/Temperature:
±2.5ppm, -30°C ~ 75°C • Frequency/Voltage Coeffi cient: ±0.3ppm/Vdd±5% • Frequency/
Load Coeffi cient: ±0.2ppm/(10kΩ/10pf) ±10% • Power Consumption: 1.0mA Max./13MHz
• Output Level: 0.8Vp-p minimum; 10kΩ/10pF • Frequency Adjustment: ±8ppm minimum/
Vdd/2±1.0V • Start-up Time: 3.5ms Max. • Aging (First Year): ±1ppm

I´m just wondering to use it as a clock in a dac. It is not available with 24,576MHz, only with 24.5535 MHZ. Would it go? Is the difference to 24.576Mhz audibly?

I´m plant to use CS8416 / AD1896 / DF1704 / PCM1704. With this technical specifictions it should be very low jitter clock, or not?

Thanks in advance for your opinion.
Adam

oshifis · 18th February 2008, 09:34 AM

Adam,

I can see three problems here:

1. The frequency is not an integer multiple of 44.1 kHz, the sampling frequency of the CD
2. They do not specify phase noise (jitter), so it may not be a special low jitter oscillator
3. The output voltage is most likely sinewave (0.8 Vpp). You will need an oscillator with TTL output level.

Aging and stability is not important in digital audio, unlike in radio communication.

Laszlo

gmarsh · 22nd February 2008, 03:28 PM

Since you're using an ASRC, the selection of clock frequency isn't critical at all.

In my headphone DAC, I'm using the same architecture (but PCM1792 instead of DF+PCM) and a 29.4912MHz crystal, giving a 115.2KHz sample rate coming out of the ASRC and into the DAC. Since the clock frequency doesn't matter, you also don't need stability in your clock so there's no need to use a TCXO.

Your main criteria in picking that part is phase noise performance. Go through the Digikey catalog, compare Citizen, Epson, CTS, etc datahseets, and pick the part with the lowest phase noise number in the 100Hz to 10KHz range. When I did this last time, it ended up being a CTS "CB3LV" part.

I'd add a few pads next to the oscillator footprint so you can solder in a Tent/Kwak/etc. clock if you ever feel the need to.

17th February 2008, 06:58 PM	#1
acaudio diyAudio Member Join Date: Sep 2004 Location: Germany	How about using a 24.5535 MHZ clock in a dac? Hi folks, I found following oscillator at digikey: Citizen CSX532T24.5535M3-UT-10 (Digikey number: 300-8277-1-ND ) Specifi cations: • Frequency Tolerance: ±1.5ppm @ 25°C, ±2°C • Frequency/Temperature: ±2.5ppm, -30°C ~ 75°C • Frequency/Voltage Coeffi cient: ±0.3ppm/Vdd±5% • Frequency/ Load Coeffi cient: ±0.2ppm/(10kΩ/10pf) ±10% • Power Consumption: 1.0mA Max./13MHz • Output Level: 0.8Vp-p minimum; 10kΩ/10pF • Frequency Adjustment: ±8ppm minimum/ Vdd/2±1.0V • Start-up Time: 3.5ms Max. • Aging (First Year): ±1ppm I´m just wondering to use it as a clock in a dac. It is not available with 24,576MHz, only with 24.5535 MHZ. Would it go? Is the difference to 24.576Mhz audibly? I´m plant to use CS8416 / AD1896 / DF1704 / PCM1704. With this technical specifictions it should be very low jitter clock, or not? Thanks in advance for your opinion. Adam __________________ http://www.acaudio.de

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18th February 2008, 09:34 AM	#2
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	Adam, I can see three problems here: 1. The frequency is not an integer multiple of 44.1 kHz, the sampling frequency of the CD 2. They do not specify phase noise (jitter), so it may not be a special low jitter oscillator 3. The output voltage is most likely sinewave (0.8 Vpp). You will need an oscillator with TTL output level. Aging and stability is not important in digital audio, unlike in radio communication. Laszlo

22nd February 2008, 03:28 PM	#3
gmarsh diyAudio Member Join Date: Apr 2004 Location: Halifax, NS, Canada	Since you're using an ASRC, the selection of clock frequency isn't critical at all. In my headphone DAC, I'm using the same architecture (but PCM1792 instead of DF+PCM) and a 29.4912MHz crystal, giving a 115.2KHz sample rate coming out of the ASRC and into the DAC. Since the clock frequency doesn't matter, you also don't need stability in your clock so there's no need to use a TCXO. Your main criteria in picking that part is phase noise performance. Go through the Digikey catalog, compare Citizen, Epson, CTS, etc datahseets, and pick the part with the lowest phase noise number in the 100Hz to 10KHz range. When I did this last time, it ended up being a CTS "CB3LV" part. I'd add a few pads next to the oscillator footprint so you can solder in a Tent/Kwak/etc. clock if you ever feel the need to.

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