THEORY OFOPERATION
The US Audio Mix 6 has four mic or line input channels and two stereo aux line inputs. All of the
XLRand1/4”inputandoutputjacks,exceptaux1,areactive electronically balanced circuits. The
Theoutputsection of the Mix 6 was designed to accommodate any configuration, line or miclevel
inputsectionsofchannels1-4on the Mix 6 use the relatively new Analog Devices 2017 integrated
balanced or unbalanced XLR and balanced or unbalanced 1/4” connectors. Each channel's output
circuit, which was designed to yield high amounts of gain with the lowest possible noise. This IC,
jacksareindividuallybufferedsoanycombination ofthe outputs,at anyimpedance, willnot affect
alongwith carefulcomponentselection, atoroidalpower transformer,andtrue stargroundingon a
theotheroutputs. WiththeMic/Lineoutputswitch intheMicposition,theXLR'soutput isreduced
2 ounce copper double sided circuit board, enable the Mix 6 to achieve a working signal to noise
by 20db (this switch does not affect the 1/4” jacks). The Mix 6 uses an H-Pad resistor network at
ratio (S/N) of 92db with 22dB of headroom at unity gain. The Mix 6 holds a working S/N ratio of
the XLR to maintain the S/N ratio, regardless of the position of the Mic/l.ine switch. For the XLR
85dbat 40db ofgainandcan provide upto76dBof gain, stillmaintaining10to 15db ofheadroom.
outputs,ifgroundliftingofpin 1isdesired,jumpersJMP6andJMP7insidetheunitcan beclipped
Withthe mic/line switch is in the micposition,the2017is factory set at 36db of gainbyaninternal
off. Then, in Line mode pin 1 of the XLR is completely lifted and in Mic mode the XLR's pin 1 is
resistor. This 36db plus the two sections of 20 dB available from each of the channel volumes and
ground isolated and referenced to pins 2 and 3. If unbalanced operation is desired from the XLR
mastervolumeofferatotalgainof76db.Forapplicationswhichneedevenmore,theMix6canbe
outputs,pin2ishot,pin1isground, andpin3 shouldbeleftUNCONNECTED.
orderedormodifiedtoobtainupto50dBof gainfromthe 2017viaasimpleresistorchange.
LEDdBmeters provided on the Mix 6 are precisely calibrated at 3dB incrementsandspanarange
Allthe gain controls on the Mix6 (Channel gain, Aux and Master)have a range of -60 to+20dbm.
of -15 to +l2dBm measured unbalanced at the 1/4” output. The output of the XLR, with the switch
With the input and output switches in the Line position and with both the channel and master
inLinemode,is6dbgreater,measuredbalanced.
volume controls at the same position, unity gain is at the 9 O'clock knob position, 10dB gain at 12
O'clock,and 15dBgainat 3O'clock.The 60dbof attenuation inthe off positionallows the Mix6 to
adequately turn off line level signals. Maximum signal level through the Mix 6 at clipping is
The limiter section of the Mix 6 is pre master fader, allowing versatility in selection of output
+28dBm balanced and +22dBm unbalanced. The sonic figures apply to both the input and the
levels while the peak limiter is active. The limiter is true stereo, with separate detectors for each
outputandindividualclipLEDsareprovidedwhichilluminateat-3dBbelowactualclipping.The
side, which engage at 0dB and limit up to 15dB. The left and right LEDs on the front panel
OL(Over Load) circuit sensesthesignal level in 2places(input diff amp andafterchannelgain) to
illuminate when the limiter is working and get brighter as limiting increases. With a quick attack
ensurefoolproofvisualindicationofdistortion.
timeandmoderateratiothelimiterisidealforopenmicsituationswhereunexpected levelchanges
canoccur.
Channels 1-4 have a pan control. The center detented, dual element, audio taper pot provides a
wide range of stereo positioning for the input signal. The center detent allows quick centering of
The Mix 6 has a headphone monitoring section consisting of a source select switch, a volume
the signal. Also included on channels 1-4 is a low frequency rolloff switch for elimination of sub
control, and a 1/4” TRS headphone jack. The headphone circuit is stereo and drives any
frequencies such as mic handling or wind noise. The cutoff frequency is 120Hz with a 24dB per
headphones with 20 Ohms or greater impedance. The volume control has a gain range of -60 to
octaveslope.
+20db to accommodate a wide range of audio levels. The select switch allows listening to either
theprefaderstereomasteroutputsorthepostfadersignal comingfromthe aux2inputs.
Aux inputs one and two are true stereo line level inputs. Aux input 1 is via unbalanced RCA jacks.
Aux input 2 is accessed through left and right balanced 1/4” TRS jacks, which can be used
The Mix 6 utilizes a dual primary toroidal power transformer which is configured with internal
balanced or unbalanced. Aux 2 has a unique main/off switch which routes the input signal to the
jumpersfor 120 VAC60Hz or 230VAC 50Hz operation.Thereis aninternalfuse on thehotside of
left and right stereo busses when activated. This feature allows aux 2 to be disconnected from the
theACcord,andthepowerswitchmakesandbreaksboththehotandneutrallegsoftheACcord.A
mainoutputandin combinationwith theheadphone main/monswitch,routesthesignal toonly the
ground lift switch is provided which can disconnect the audio circuit ground from the AC chassis
headphones for cueing or monitoring. The Mix 6 aux inputs will interface easily with most all
ground.
typesofconsumerorprofessionalequipment.
