darTZeel NHB-10 model one Technical Manual
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darTZeel NHB-108 model one Audiophile's technical manual Page 27 of 2812. Special adjustments12.1. Output DC voltage driftCaution! The procedure described belowcan present some risk, since the darTZeelNHB-108 model one must remain poweredON.WE DECLINE ANY RESPONSIBILITY INTHE EVENT OF ELECTRIC SHOCK DUE TOINCORRECT MANIPULATION.WARNING! ONLY A QUALIFIED PER-SON OR A TECHNICIAN CAN SAFELYPERFORM THIS ADJUSTMENT.When darTZeel NHB-108 model one's eyesare blinking, it means that an output DCvoltage greater than ±0.6 volt is presentat the terminal speaker outputs. An ad-justment is then necessary.Before doing any task, it is important toensure that:- Ambient room temperature is be-tween +15°C and +35°C.- The darTZeel NHB-108 model one isproperly vented, as described in theOwner's manual.- The loudspeakers are connected tothe speaker terminals!- The darTZeel NHB-108 model one hasbeen in idle state for a minimum of 2hours, allowing an optimum distrib-uted heat across the entire housing.To make this adjustment, you need thefollowing tools:- A No. 4 flat blade screwdriver for re-moving the glass cover; this tool issupplied as standard with the darT-Zeel NHB-108 model one.- The 2 suction cups supplied with thedarTZeel NHB-108 model one. Please donot forget to slightly wet them, to getfirm vacuum on the glass.- A No. 0 flat blade screwdriver for ad-justing the 12-turn trimmer; this toolis supplied as standard with thedarTZeel NHB-108 model one.- A universal DMM (Digital Multi Me-ter), not supplied.Procedure:1) Using the DMM, check that the DCoutput voltage is more than ±0.6volt. In practice the value is generallynegative.2) Before opening the glass cover, lo-cate the trimmers, using a pockettorch if need be; the trimmers areclose to the RCA input connectors.On left channel, the trimmer is lo-cated on PCB solder side, betweenPCB and heat sink. A clockwise rota-tion induces a negative voltage shift.On right channel, the trimmer is lo-cated on PCB component side, ori-ented toward the inside of the ma-chine. A clockwise rotation induces apositive voltage shift.When adjusting, it is important toturn the trimmer's screw slowly.Please allow 5 seconds at least aftereach tuning step, to wait for thevalue to stabilize.3) Connect the DMM to the left output,and open the glass cover.DO NOT FORGET THAT THE AMPLI-FIER IS POWERED ON!NEVER TOUCH THE COPPER BUSBARS, WHICH ARE AT A POTENTIALDIFFERENCE OF 115 VOLTS DC.A SHORT CIRCUIT INDUCED BY THESCREWDRIVER WILL PARTIALLYEVAPORATE THE BLADE BY IN-STANTANEOUS MELTING OF THEMETAL OF THE LATTER!4) Within the next 2 minutes, set theDC voltage drift at -300mv (-0.3V).5) Connect the DMM to the right output,and perform, within the next twominutes, the same tuning as for leftchannel.6) Put back the glass cover, withoutscrewing it yet. Wait for one hour.7) Then measure again the output volt-ages. They should be be-tween -300mV and -400mV.8) Power the amplifier OFF, and wait forone or two hours for total coolingdown.9) Power the darTZeel NHB-108 model oneON again, and recheck the outputs.DC drift should not be greater than+500mV when ambient room tem-perature is +22°C.10) If everything is okay, you can screwon the cover glass. |
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