Audio Line Level output?

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pepillo

Joined: 23 Jan 2006
Posts: 94
Helped: 3
Location: Spain

11 May 2007 2:10 ad1854 3.3v

I am using the AD1854 as a DAC for an MP3 player, I see the output is line level voltage, but each channel is double-ended (+ and -). How do I drive these outputs from the chip to the headphones?
Any schematic, circuit?
Thanks

ynhe

Joined: 28 May 2001
Posts: 326
Helped: 4
Location: China

11 May 2007 3:00 Re: Audio Line Level output?

You need a OUTPUT BUFFERS AND LP FILTERS,see datasheet of ad1854 for details

http://www.analog.com/UploadedFiles/Data_Sheets/AD1854.pdf

pepillo

Joined: 23 Jan 2006
Posts: 94
Helped: 3
Location: Spain

11 May 2007 18:53 Re: Audio Line Level output?

Thank you I have already read the datasheet and I see the circuit the suggest. However, I wonder if I can make it with less external components.
I was about to use the AD1857 which has single-ended outputs, what's the advantage on having differential line level outputs? it's nonsense, it just adds complexity to the output circuit, need of op-amps, more passives (I see you need 1% resistances for the filter)...

Any idea to simplify the design?

xxargs

Joined: 28 Jul 2002
Posts: 231
Helped: 44

11 May 2007 21:43 Re: Audio Line Level output?

pepillo wrote:

Differental output make higher voltage swing than 5 Volt single end power supply can make. and also make lower noise and intefrence from enviroment and power supply. Make IM, noise and spurr free dynamic range above 100 dB is not easy in single end enviroment.

AD1854 output impedance is a still high (~200 Ohm) and cannot drive earphone load as 32 Ohm in loud level and high quality. But possible to make 'line level' as maximum 245 mV RMS ( -10 dBu) for consumer HIFI-equipment. For single ended output you must AC-couple output from AD1854 and after this using (resistive) voltage divide take down single end output from around 2.5 Volt swing to ~ 600-700 mV p-p for line level and make still low impedance (~300 - 600 Ohm).

You not exactly need but want low pass filtering for frequency above 96 kHz to make high quality sound and not load amplifier/stereo with high freqency noise/alising effect from AD1850 and can possible make intermodulation and mixing products in voice range frequency in your stereo. Embedded SC-filter cannot take away every thing and have periodic/cyclic suppression shape depend of frequency and describes by time discret theory.

all digital D/A-stuff need some type of sharp analog LP-filter (time continous-type) in last step on output to avoid high frequency noise/alising effect and mixing/IM-product in later step, not so good audio amplifiers.

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pepillo

Joined: 23 Jan 2006
Posts: 94
Helped: 3
Location: Spain

13 May 2007 21:54 Re: Audio Line Level output?

xxargs wrote:

AD1854 output impedance is a still high (~200 Ohm) and cannot drive earphone load as 32 Ohm in loud level and high quality. But possible to make 'line level' as maximum 245 mV RMS ( -10 dBu) for consumer HIFI-equipment. For single ended output you must AC-couple output from AD1854 and after this using (resistive) voltage divide take down single end output from around 2.5 Volt swing to ~ 600-700 mV p-p for line level and make still low impedance (~300 - 600 Ohm).

Thanks xxargs for your reply.

I didn't exactly understand what you mean whith this paragraph. I want to drive an earphone load, I don't understand why 200 ohms is too big source impedance. What does 'line level' mean? I have seen I can easily drive earphones with single-ended line level outputs from, say, CS4340 with an easy passive filter. Do I really need the op-amp? Is the schematic in the AD1854 the only possibility? Can I simplify the design in any way?

By the way, do you know any 3.3V supply DAC (with I2S input interface)? Because I'm working on a 3.3V system and I realised that the AD1854 has 4.5 V minimum supply.