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Category: DAC Page 1 of 2

PCM2706 + TDA1543 x 4 DAC SCHEMATIC

Here is an interesting schematic diagram for USB DAC based on the famous PCM2706 chip by Texas Instruments.

The design incorporates opto isolators to reduce the high-frequency garbage and prevent it from entering the analog part of the DAC. Like most of the DIY minimalistic designs, this one uses passive low-pass analog stage at the output of the DAC chips. The current to voltage conversion is done passively (duh) thanks to R19 and R17. Those are subject to experimentation to obtain the optimum value. Too high the resistor value and you get increased THD. Too low means you get lower output level.

PCM2706 + 4 x TDA1543 – LINK

Universal I2S interface. Line + cable

Here is a way to make an I2S output from your CD player. This one includes a reclock option inside the CD player.

This idea uses a standard cat5 network cable. I personally don’t like the idea of reclocking the I2S bus and then sending it over the cable. A way better solution would be to include a low clock source inside your DAC. This source could have two outputs. One used to make the reclocking and feed the DAC chips with clean clock. The other output could be sent out over the same cat5 cable (using the 4th pair inside the cable) to the transport. This would make the transport a slave to the DAC and will practically eliminate it as a source of any troubles.

Discrete I/V For Current Output DAC’s. AES Publication.

Here is an article by AES, describing a very interesting solution for the I/V stage. This one is fully discrete and includes LPF and emphasis equalization. For current output DAC’s like TDA1541A and PCM63 etc.

Abstract- A family of current-steering transimpedance amplifier circuits is presented for use in high-resolution, digital-to-analogue converters.  The problems of achieving accurate current to-voltage conversion are discussed with a specific emphasis on digital audio applications.  Comparisons are made with conventional virtual-earth feedback amplifiers and the inherent distortion mechanisms relating to dynamic open-loop gain are discussed. Motivation for this work follows the introduction of DVD-audio carrying linear PCM with a resolution of 24 bit at a sampling rate of 192 kHz.

1 Introduction
This paper investigates the design and performance requirements of the transimpedance amplifier used in association with a current-output, digital-to-analogue converter (DAC) [1].  The principal motivation for this work stems from the extreme resolution requirements determined by the advanced audio specification available in digital versatile disc (DVD) applications [2]. Following a theoretical discussion, two principal circuit topologies are presented, the first based upon wide-band, current steering circuit techniques enhanced by input-stage error correction [3], while the second incorporates dual operational amplifiers with nested differential feedback and an embedded low-pass filter.

Current-steering transimpedance amplifiers for high-resolution digital-to-analogue converters – >>>[LINK]<<<

I/V conversion & differential analog stages, filters

A quick reference guide for the analog stage and I/V conversion of a high-quality DAC or CD player.

1-bit Sigma-Delta DAC’s and High-Quality Applications


Single-stage, 1-bit sigma-delta converters are in principle imperfectible. We prove this fact. The reason, simply stated, is that, when properly dithered, they are in constant overload. Prevention of overload allows only partial dithering to be performed.
The consequence is that distortion, limit cycles, instability, and noise modulation can never be totally avoided. We demonstrate these effects, and using coherent averaging techniques, are able to display the consequent profusion of nonlinear artefacts which are usually hidden in the noise floor. Recording, editing, storage, or conversion systems using single-stage, 1-bit sigma-delta modulators, are thus inimical to audio of the highest quality. In contrast, multi-bit sigma-delta converters, which output linear PCM code, are in principle infinitely perfectible. (Here, multi-bit refers to at least two bits in the converter.) They can be properly dithered so as to guarantee the absence of all distortion, limit cycles, and noise modulation. The audio industry is misguided if it adopts 1-bit sigma-delta conversion as the basis for any high-quality processing, archiving, or distribution format to replace multi-bit, linear PCM.

Why 1-Bit Sigma-Delta Conversion is Unsuitable for High-Quality Applications  – >>>[LINK]<<<

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