Behringer HA400 4-Channel Stereo Headphone Amp with Audio-Technica ATH-M30x Professional Headphones + 5-Pack, Gold Plated 6.3mm 1/4 inch to 3.5 mm Male to Female Stereo Adapter - Walmart.com
EQ-7 Car Audio Headset Amplifier 7-Band EQ Equalizer 2 Channel Digital Sound Equalizer - Walmart.com
EZ-MXA20 ‐ 20 W Stereo Audio Mixer-Amplifier with EQ - 8 Ω, with Power Supply
Amazon.com: 7 Band Car Audio Equalizer with 3.5mm Input, 2 Channel Sound Power Amplifier Stereo System, Input Output, 12dB High Bass Adjustment for Smartphone, Speaker : Electronics
Amazon.com: Moukey Headphone Amplifier DAC -Coaxial/RCA/ 6.35mm,1/4'' Headphone Output( with 1/8" to 1/4" Adapter) for Phone/PC/Compuer,OLED Display Screen to Show 5-Segment EQ Adjustment- MPHA1 : Electronics