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Category: DAC

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]<<<

PCM1704, AD1862 DAC, NOS, DIY schematic

Non oversampling DACs are by many people (includung me) regarded as better sounding than
conventional oversampling systems. The easiest way to enjoy that kind of sound is to build a DAC with the “outdated” TDA1543/TDA1541 DAC ICs or modify an old Philips/Marantz CD player.

But why not building a nonos DAC with higher quality converters like PCM1704, PCM1702 or AD1862? Well, you need to convert serial DATA to parallel DATA which requires some glue logic. Further glue logic is needed to align 16bit DATA with the 20bit or 24bit inputs of these DAC ICs.
While there are many well documented TDA based nonos projects available on the www, almost nothing can be found about building a nonos DAC with more recent Burr Brown / Analog Device ICs. That’s why I’ll try to give some advice and share some of my experience in building such a DAC. If there wouldn’t be this glue logic issue, I guess more DIYer would build nonos DACs with Burr Brown chips.

Creating a DIY non oversampling DAC with PCM1704 >>>[ LINK ]<<<

DIR9001+TDA1541A Classic NOS DAC

The whole thing started as a simple idea – to design a simple S/PDIF input DAC for my PC. So I turned to the classical chipset – DIR9001 + TDA1541A in NOS mode. I just wanted to keep thing simple and at low cost(compact PCB). So eventually the thing grew up to a group project with many people sharing opinions on the mater.
The whole discussion thread is here(Bulgarian language):

Since some people suggested to make it possible to use TDA1541(non A) DAC chip the project was altered this way. The interesting thing about TDA1541(non A) is that it allows a master clock to be fed directly to pin 4. This one accepts 11.2896MHz clock frequency. In TDA1541A non such thing is available.

From TDA1541 datasheet:
“A separate system clock input (SCK) is provided for accurate, jitter-free timing of the analogue outputs AOL and AOR.

So the PCB was designed to allow this mode, should a TDA1541(non A) was used. For some reason Philips had decided to turn that feature off in their later TDA1541A DAC chip. Here is how it should be implemented according to a Philips application note from 1985 :

The application is a bit misleading. The SAA7220 chip actually outputs 11.2896MHz at pin 9.

As for the analog section. It’s of course a pure classic. Opamp based I/V converter, followed by an active low-pass filter. Nothing fancy here. The project uses one double opamp (NE5532) per channel. Of course a DC null correction is used at the DAC chip outputs. Despite that a output coupling capacitor is paced on the PCB.

Here are some pictures of the PCB:

Almost completed project forum mate Stanislav
Higher end implementation from forum mate Nikolay Kolev
Here is a set of measurements taken by user pid_58 (thnaks mate 😉 ) using EUM 0404 sound card.

The final version of the schematic is available for download HERE.

I am adding the gerber files for this project. To download click here – >>>[ LINK ]<<<

Update 19.08.2012
The project was further tweaked by a fellow Plamen Todorov by adding a ECC88 tube stage. More info on this HERE

WARNING – this project is provided to the DIY community for free and is intended for personal usage ONLY. Therefore a commercial usage is NOT allowed without author’s exclusive permission!!!

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