With this topology the amplifier is wired as a unity gain buffer (0 dB), and has much lower noise and distortion than an amplifier required to provide a gain of 20-26 dB). The other resistor string is used to adjust the gain of the amplifier. One is placed in the traditional position before the amplifier. In a modern electronic volume control, two resistor ladders are integrated on the chip. This part has been discontinued, favoring a more modern design discussed below. This old IC contained only one resistor ladder and was a direct replacement for the potentiometer. In some older SSI (Small Scale Intgration)-based multi-channel products and stereo preamps using an electronic volume control, an obsolete IC was used. Under these conditions, the gain following the volume control is unnecessary. For most of the range of the volume control, the attenuation exceeds the gain.
The fixed-gain stage introduces significant noise and distortion. In a traditional volume control, a fixed gain stage follows a voltage attenuator (potentiometer). The difference between the THD of the best IC-based volume control ICs (Integrated Circuits) and typical AVR LSIs (Large Scale Integrated Circuits) is 2.5 bits using measurements sourced from data sheets with the control set to unity gain. While AVR and pre-pro marketing focuses on the highest-resolution component – usually the DAC chip – an audio signal chain is ultimately limited by its lowest-resolution circuitry. The section on circuitry interfacing to a DAC, digital reconstruction filtering, and jitter attenuation are integral to stereo devices with digital inputs.Įlectronic Volume Controls that Enhance Performance The sections on electronic volume controls, op-amps, and CMOS-based signal switching are also relevant to the stereo preamplifier design. I carryover the term, AVR LSI, from the first part of this article and refer to AVR when I comment on products with power amplifiers. Pre/Pros tend to use analog SSI chips, while most AVRs use the LSI solution (see the chart in Part I of this article for the make and model numbers of the AVRs and Pre/Pros using the LSI chip). Herein, I refer only to Pre/Pros, but everything discussed applies equally to AVRs. Specht v.Up Next AVR – Audio Video Receiver – Build Quality: Part III – Component Choices for a High Performance Designĭesign of High-Performance AVRs and Pre/Pros: A More Technical Perspective with Material Relevant to Stereo Preamplifiers and Outboard DACsįollowing on Part I of this series, “ AVR – Audio Video Receiver – Build Quality: Part I“, here, in Part II, I dig a bit deeper into the performance of a single-chip Large Scale Integrated (LSI) analog AVR chip and introduce better solutions employing Small Scale Integrated (SSI) analog chips.
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