Gainclone in the inverted mode with the pot at its input is great amplifier, so it will work fine without any preamp or input buffer. However, here is a suggestion for the further improvement of some parameters of the sound of the inverted gainclone. During experiments, I paid special attention not to loose the good sides of the original, unbuffered inverted gainclone.
Posted on Saturday, May 3, 2008 • Category: Volume Control
The DS1802 is the dual audio 45kOhm (typically) pot with 65 steps (64x1dB and mute), known around for its possibility to be controlled by its own pushbuttons instead of, usually needed, certain logic circuitry. It is available in DIP package and hence seems very appealing for DIY.
Most of the digital potentiometers (there are exceptions like WM8816 and X9312) can not accept signals much beyond their supply voltages. For DS1802, 0.5V below the potential at its Gnd pin is the bottom, and 0.5V above the Vcc (whose safe maximum is 5.5V above the Gnd pin) is the upper limit. There are a few ways to center the signal inside these boundaries and Dallas recommends Wheatstone Bridge circuit (see App Note 161). I decided to shift the supply rather than signal, thus with one more regulator I could keep the signal path clean. So, DS1802’s Gnd pin went down to -2.5V and all the other pins of DS that normally should go to ground went to this pin: Agnd, Zero-Crossing (enabled) and Mode (stereo), as well as the Up/Down buttons. Resistive networks themselves are connected straightforward. The DS1802’s pin layout appeared almost ideal for such application.
Posted on Sunday, April 27, 2008 • Category: Audio DAC
High quality USB Audio DAC with PCM2702. The PCM2702 is a single chip digital-to-analog converter offering two D/A output channels and an integrated USB 1.0 compliant interface controller. The newly developed SpAct™ (Sampling Period Adaptive Controlled Tracking) system recovers a stable, low-jitter clock for internal PLL and DAC operation from the USB interface audio data.
The PCM2702 is based upon Texas Instruments Enhanced Multi-level Delta-Sigma Modulator, an 8x oversampling digital interpolation filter, and an analog output low-pass filter.
The PCM2702 can accept a 48kHz, 44.1kHz and 32kHz sampling rates, using either 16-bit stereo or monaural audio data. Digital attenuation and soft-mute features are included, and are controlled via USB audio class request.
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