676 Tube Channel Strip Valve Microphone Pre-Amp 2UDbx Professional 676 Tube Mic Pre Channel Strip. The 676 represents all of the best of dbxs more than 40 years of dynamics processing. The 676 offers a pristine high voltage, Class A tube preamp section that runs on 250 volts, so your signal can be as crystal clean or dirty as you need it to be. The 676 also incorporates the compressor limiter design from the highly sought after dbx162SL, as well as a 3 band parametric EQ with sweepable mids. The 676