Posted on Feb 5, 2014

A dual channel audio preamplifier as an appropriate preamplifier for the high quality Audio Analog to Digital Converter AD24QS. It is, of course, easy to build a much smaller and much cheaper preamplifier with comparable functionality, but making it cheap and small was not my goal. A slightly modified version of the AD24QS is piggyba

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ck mounted on the preamplifier`s board and together they fit into a 200 x 100 x 50mm ³ enclosure ( Fischerelektronik SG210 ). The design goal was definitively not a cheaper preamplifier than commercially available ones - it is designed to be a better one. As a consequence, even as a kit, it is expensive! The fully balanced design is more expensive than a single ended one, of course, but it has advantages: No (or 40dB less) hassle with ground loops, crosstalk by common grounds, hum or switching noise caught by ground etc. Also the maximum internal signal level can be increased by 6dB which may help to increase the dynamic range under certain circumstances. Note that for a single ended design by far not half of the circuitry can be saved: In order to de-balance input signals and re-balance them for the outputs again, actually 2 op-amps (one dual op-amp) per channel could be omitted only(!). The 2ChPre is a high quality dual channel preamplifier designed to operate in conjunction with the Audio Analog to Digital Converter AD24QS. It is available as kit for DIY (Do It Yourself). It features: The microphone input is an XLR receptacle, the line input a 1/4" TRS jack, both combined in one XLR / TRS hybrid chassis connector. When the TRS connector is plugged, the microphone preamplifier is disconnected automatically. The nominal output level of the analog, unbalanced Cinch- (or RCA. ) on-board monitor output is -2dBu (615mVRMS). As...

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