Scratch is the scratching noise that occurs mainly with old records. This high frequency noise is eliminated by the filter found in the February 1990 issue of Radio Electronics magazine.
The basis of this circuit is the HA2400 released at the time. The circuit is from a Radio...
This circuit with TTL output was found in a 1968 EEE. The transistor can be of general use. The...
This circuit can be found in a 1970 Motorola documentation. The circuit can be implemented with general...