Technical Articles and Editorials

AVR - Audio Video Receiver - Build Quality: Part I


Enhanced Performance with SSI Parts

Previously, a single chip analog AVR LSI was associated with lower priced AVRs. In contrast, higher-priced units would use Small Scale Integrated circuits (SSI) to provided performance advantages.

An opamp is an SSI chip. Opamp packages separately contain as many as four units.

To form the electronic volume control, an SSI part containing only resistor strings and switches is used. External opamps are added to form the complete circuit.

The switches are grouped in SSI packages with 4 – 50 switches pairs per package. Multiple switch packages are dispersed throughout the AVR to perform functions such as stereo analog input selection and signal routing to the electronic volume controls.

One downside of some AVRs built with SSI chips is the latitude afforded to the designer to incorporate extra functions to the analog path. This is most common in top-of-the-line Japanese designs using SSI chips. Additions, such as analog bass management high-pass filters, analog tone controls, and analog down mix add solid state switches and extra opamps to the main signal path even when the functions are bypassed. The additional components reduce channel separation and can increase distortion.