NE5532 OP-AMP HIFI Preamp Preamplifier Volume Tone EQ Control Board Module | eBay
5 Tone control (bass mid treble) circuits using NE5532, 4558, LF353
BooiParts DDS Function Signal Generator DIY Kit Module Sine Square Sawtooth Triangle Wave Function Generator 1602 Digital LCD Display: Amazon.com: Industrial & Scientific