JDS Labs c421 v1.00 Operating Instructions

General Use
Battery must be fully charged prior to first use. See reverse side.
1. Connect an audio player to the Source jack using a Line Output Adapter or 3.5mm interconnect cable.
2. Connect headphones to the Output jack.
3. Upon first use, set bass to Flat, gain to Low, and turn the Volume knob to its minimum position.
4. Turn the rear Power switch on (see reverse side).
5. Slowly raise the Volume knob to an appropriate level. See Listening Tips below.
 Bass boost can be turned on or off by moving the toggle up or down, respectively. Reduce volume
before switching bass boost on. This feature boosts low frequencies by +8dB, which can overdrive
the headphones and/or opamp at especially high listening levels.
 You should hear no noise or whining with your audio player connected and paused/muted. Every
amplifier is hand tested to ensure proper operation. If noise is present or audio is significantly
distorted at all volumes, try a different input cable.
Listening Tips
 Use Low gain unless volume cannot be further increased with your source and headphones.
 For maximum sound quality, use a line‐output adapter (LOD). If using a 3.5mm interconnect cable, set
a high source volume (60‐80%) and only use the amplifier's volume control.

c421 can produce dangerously loud music. Be sensible and listen safely: www.hearingloss.org
Thank you for purchasing c421. If you have additional questions or comments, please contact us at:
contact@jdslabs.com
c421™ v1.00 Headphone Amplifier
Operating Instructions
JDSLabs
.com