4-Channel DSP-DAC-Preamp-PowerAmp System

Published 23.11.2014

High-quality four-part DIY audio system consisting of the following parts:

  • SharcDSP: 8-Channel Digital Signal Processor for crossover filtering and digital room correction, also acting as digital input selector with 6 stereo inputs.
  • Quad DAC: 4-Channel 192 kHz / 24-bit DA-Converter with balanced and unbalanced outputs.
  • Quad Preamp: 4-Channel analog preamplifier with balanced and unbalanced inputs and outputs, also controls SharcDSP and Quad DAC via wired remote control interface.
  • Hypex Power Amplifier: 2-Channel power amplifier based on Hypex UcD180HG modules.

Philosophy of this system inherits from DD Preamp. It offers similar functionality in three separate devices and also a power amplifier. So why use many times more money, time and space to create the same all over again? Well, mostly for a hobby. But also for better design and quality, and also for the possibility to change some components in the signal chain and to make comparisons between them. For example, I have ideas for more complicated and possibly higher quality DA-converter which I will start designing somewhere in the future. One could also say that this will be a “living room system”, while DD Preamp will be a “desktop system”.

I was designing and building these more or less concurrently although Quad DAC is based on HWDAC board of HP DAC I had designed earlier. Needless to say, all these four devices together was quite remarkable project and required most of my free time (and money) for quite long time. You shouldn’t have deadlines with hobby projects but I did because of plans in life which will stop such activity for some time. Due to lack of time, and also equipment, I have to admit, the system is not as well tested as it should be. However, everything works and it will end up being in everyday use. When I have time again, and also proper measurement equipment at hand, I will do some more technical measurements and fix the possible flaws to further improve overall performance. Therefore, the project is still not finished. If something like this never is.

Overall wiring diagram of the system. Dark gray arrows illustrate active signal path, while light gray are unused connections. SharcDSP has 6 digital stereo SPDIF-inputs and 4 SPDIF-outputs for all 8 channels, from which 4 are used in this system – main channels and one or two for subwoofers (2.1 or 2.2 system). DSP carries out crossover filtering and digital room corrections. 4 channels from DSP are connected to Quad DAC, 4-channel Digital-to-Analog Converter, which is connected to Quad Preamp, 4-channel analog preamplifier. Quad DAC and Quad Preamp also provide additional 4-channel inputs. At the moment the system contains stereo power amplifier which can be used for main speakers or subwoofers, depending if active speakers or active subwoofers are used. Here it is drawn for speakers. Active subwoofers with all the filters are not needed since DSP performs all filtering, therefore plain power amplifiers are preferred for subwoofers as well. Quad Preamp controls SharcDSP and Quad DAC via 2-way wired remote control interface.

Final touch for enclosures from eBay is provided by custom rear panels from Schaeffer AG.

Every device is presented on its own page in more detail. This is just an overview of the components.

SharcDSP

8-channel digital signal processor. DSP-board and related PC-software are not mine but I am using Analog Devices ADSP21369-based miniSHARC board, meant for OEM-applications and custom products, from Hong Kong -based company miniDSP. The board does not work on its own so I have designed a motherboard for the DSP providing 6 digital inputs and input selector, and SPDIF-outputs for all 8 output channels. It is used for digital room correction and subwoofer crossover filter but it could be also used as crossover filter for multi-way DIY-speakers. In this system 4 channels are used for 2.2 (or 2.1) system. There is a wired remote control possibility for 2-way control between SharcDSP and Quad Preamp.

Quad DAC

4-channel DA-converter to be used after SharcDSP. It is made of two HWDAC boards of HP DAC and power supplies. It has two 4-channel inputs and balanced and unbalanced outputs. There is a wired remote control possibility for 2-way control between Quad DAC and Quad Preamp.

Quad Preamp

4-channel analog preamplifier to be used after Quad DAC. It is made of two 2-channel analog boards along with proper power supplies and control logic. These two analog boards are combined to get two balanced 4-channel inputs, one unbalanced 4-channel input and 4-channel output with both balanced and unbalanced connections. There is a microcontroller board to control the preamp but also SharcDSP and Quad DAC via wired remote control interfaces.

Hypex Power Amplifier

This is not my own design but I have used two Hypex UcD180 class D amplifier modules along with their switched-mode power supply to get quite powerful stereo power amplifier. The modules used are the smallest ones but still provide 180 W per channel to 4 ohms. At the moment it has two channels but I can expand it with two additional channels in the same enclosure if necessary. I will first need to see if I end up having active speakers, active subwoofers or separate subwoofer amplifiers.

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