MOTM-830 User Manual
Contents
1. 4 U2A OP285GP R13 100K 1 5 6 7 8 4 U2B OP285GP R15 51K RED OUT 2 R14 1K J4 114B R4 1K J8 OUT 1 3 2 1 8 4 U1A OP285GP R3 49K9 1 R18 100K 1 R1 49K9 1 BLACK SW2 ON PCB IS FOR THESE WIRES C1 22PF 5 6 7 8 4 U1B OP285GP 15V C3 0 1M C8 22PF R24 100K 1 R8 44K2 1 R20 100K 1 15V VR6 100K LIN IN 2 VR5 100K LIN R6 100K 1 15V 3 2 1 8 4 U3A TL072 J5 J6 IN 1 R19 100K 1 15V 15V VR4 100K LIN 15V C2 0 1M R7 10K BIAS S1 SW SPDT CW CCW R5 10K R2 150K 12. Any solder shorts Too much solder Missing joints Wash the board under warm water Scrub gently Dry SYNTHESIS TECHNOLOGY PAGE 8 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM THIS IS A GOOD STOPPING PLACE TO REST OR PUT THE KIT AWAY UNTIL LATER Don t lose the trim pot it goes on with no clean solder in the next section You are now finished with the Organic flux solder All soldering past this point is using the No Clean solder You do not have to wash the board anymore PART 6 FINISHING THE PCB You will now solder in the remaining parts on the pcb in preparation for wiring to the front panel USE THE NO CLEAN SOLDER BE CAREFUL Locate the Spectrol pots They mount into VR1 VR4 Be sure they are flat and sticking out perpendicular to the pc board VR4 is different It has 149 marked on the top VR1 VR3 are marked 148 Locate the 8 pieces of RG 174 black coax cable Again note that one end has longer wires stripped than the other The short ends will go in the pc board in locations J5 J8 Look at the pc board Notice that in the coax positions there is a large hole pad lower pad and a smaller pad top hole The braided wire is soldered into the larger hole The smaller inner conductor goes in the top hole BE SURE THE SHORTER BRAIDED END GOES INTO THE PC BOARD The 2 LONG coax cables solder into J1 and J5 The 6 SHORT coax cables go into the other locations Solder each coax cable into the holes Attach a tie wrap to se
3. Note that there is a stripe on the NEGATIVE terminal The pc board has a on the POSITIVE terminal Carefully stick the capacitors into C9 and C10 with the stripe away from the pad on the board PART 4 MISC and IC STUFF Almost done with the parts on the pc board This will finish up the soldering with the organic flux Locate the MISC 1 bag and the IC bag Locate the ferrite beads 2 They are axial parts gray colored with no markings These are non polar and are soldered into L1 and L2 by JP1 Locate the MTA 156 power connector Solder into JP1 Note that the connector has a locking tab on one side This side is the inside facing relative to the pc board Note the silkscreen symbol for JP1 has a line on one side indicating this is the side where the locking tab goes Locate the OP285GP op amps 2 Solder into U1 and U2 Note that all ICs are pointing down towards the bottom edge of the pc board The IC will have a notch or indentation in the top by Pin 1 Locate the TL072 op amp Solder into U3 Apply a small bit of solder to the via holes These are the small pads that allow traces to change sides of the pc board DO NOT SOLDER PADS FOR THE REMAINING COMPONENTS As an example if you look at R8 you will see 4 via holes around it PART 5 FINAL BOARD WASH amp INSPECTION Verify all the parts are in the correct locations Make sure all of the ICs are pointing the same direction Inspect the solder joints
4. R18 or 0 5 SW2 is built into J4 which is a stereo jack But being the clever designers that we are will use a trick The trick is that when a mono patch cord is inserted the ring connection of the jack is shorted to ground by the plug We depend on this to short R18 to ground when the plug is inserted Why is this a big deal Because if R18 is floating it acts like an antenna It picks up all sorts of buzz noise and even radio stations So we purposely use a stereo jack and a mono plug So if NO PATCHCORD is plugged into OUT2 all 6 inputs are summed as above and are present on OUT1 If you insert a plug into OUT2 the switch SW2 OPENS and the Mixer splits into 2 parts IN1 IN3 appear on OUT1 and IN4 IN6 appear on OUT2 This is explained further in the USE OF THE MOTM 830 section TROUBLESHOOTING If your MOTM 830 does not work please verify ALL of the following before contacting us The following reference directions assume that you are looking at the pc board with the panel to the right and the power connector to the left All of the ICs are pointing the same way and all notches are down SYNTHESIS TECHNOLOGY PAGE 13 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM The braided wire on the coax goes to the beveled side of the jacks Check all of the pots and switch wiring Check the wiring color codes on the pcb versus the instructions The parts are in the right places and the panel pots switch are wired correctl
5. audio or precise control voltage application some design compromises were used to accommodate the inputs On the left side of the mixer IN1 IN2 and IN3 are all controlled by linear pots If you need to add up to 3 control voltages use this side of the mixer You can also add a constant DC bias voltage by turning BIAS to ON and adjusting the BIAS pot The definition of a linear pot is that at 50 angular rotation ie straight up on the pointer the pot wiper is 50 of the resistance to either side This means at 50 rotation 50 of the input voltage is on the wiper Linear pots are useful for adjusting voltages SYNTHESIS TECHNOLOGY PAGE 14 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM On the other hand the audio side of the mixer IN4 IN5 and IN6 uses log called audio taper pots These pots when at 50 rotation are about 15 85 of resistance from wiper to lug So if you put in 1V dc into a log pot and set it at 50 rotation you DO NOT get out 0 5V as expected for a linear pot if you are really bored you can figure out what the answer is So what good are these log pots The answer is they are for attenuating audio signals The reason is that your ear is non linear The log pot s strange taper is to make you think the volume is decreasing increasing linearly The linear versus log pot tapers are just to make the human interface easier to deal with In terms of the electrical characteristics of the mixer the
6. chemical called flux is embedded in the solder The flux leaves a residue on the pc board that should be cleaned with warm water DO NOT USE SOAP OR OTHER CLEANSERS Most of the parts in the kits are waterproof and can be washed in the sink The flux is OSHA approved for flushing down the drain so don t worry about that A soft brush is used to gently scrub the board We recommend a fingernail brush which is about 1 x 2 and can be found for about 1 The other type of solder is called No Clean Flux because as the name implies it does not require washing This solder is used for wiring the pots switches jacks etc This solder is harder to use on the pc board because even when melted it is not very fluid about the consistency of toothpaste We will use it VERY SPARINGLY on the pc board OK let s get started on the board PART 1 SOLDERING THE RESISTORS Since there are more resistors than anything else we will start here If you do not know the resistor color code refer to the parts list Resistors are not polarity sensitive but the board will be easier to debug and look nicer if you point the first color band in the same direction for all the parts The color code is also in the README FIRST document that every customer receives with his or her first order You will start by soldering in ALL of the resistors Find the RESISTOR bag Find the MOTM 830 blank pc board There is a copy larger than actual size o
7. goes to the BEVELED lug The inner conductor goes to the LEFT lug This is true of ALL coax wires Solder red black wire in SW2 to the OUT2 jack The Red wire goes to the RIGHT lug below the Beveled lug The Black wire goes to the BOTTOM lug The TOP lug is NOT connected SYNTHESIS TECHNOLOGY PAGE 11 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM Solder the coax in J4 to the OUT2 jack Braid to beveled inner wire to LEFT Solder the coax in J7 to IN3 Solder the coax in J3 to IN6 Solder the coax in J6 to IN2 Solder the coax in J2 to IN5 Solder the coax in J5 long to IN1 Solder the coax in J1 long to IN4 Use a tie wrap to bundle the coax together you don t have to bundle ALL of them just enough to get them out of the way Now we will solder to the 3 blue Bourns pots In all cases the Orange wire goes to the LEFT lug the Gray wire to the MIDDLE lug and the White wire to the RIGHT lug The wire sets and pots are in order VR5 is the IN1 pot VR6 is the IN2 pot and VR7 is the IN3 pot The 1 2 3 silkscreen indicators match the teeny tiny 1 2 3 numbers stamped above the pot lugs Rotate all of the front panel pots fully counter clockwise Locate the KNOBS Notice each knob has a white line on it Place the knob on the pot shaft align the white line to the 0 or 5 tick mark and tighten the hex screw The silver part of the knob has a protective clear plastic overlay that can be removed if desired Gently rub wit
8. resistors 13pcs Solder the resistors into R6 left of U1 R9 R10 R11 by VR3 R12 and R13 left of U2 R18 below C1 R19 R20 R21 R22 by U3 and R23 amp R24 below C2 Locate the 10K resistors 3 and solder into R5 by VR2 R7 by R6 and R16 below R18 Locate the 1K resistors 2 and solder into R4 by J8 and R14 below C6 Locate the 44K2 1 resistors 2 and solder into R8 below C8 and R17 by VR3 Locate the 49K9 1 resistors 2 and solder into R1 and R3 left of VR2 Locate the 150K 1 resistor and solder into R2 by VR2 Locate the 51K resistor and solder into R15 by C5 This completes the resistors PART 2 BOARD WASH 1 Verify all the resistors are in the correct position Verify all the resistors are flat on the board Correct if needed Check solder joints Wash the board in warm water gently scrubbing both sides DO NOT USE ANY SOAP Just water Blot dry with old towel and let it sit for at least 15 minutes Take a little break You are about 1 3rd of the way finished PART 3 CAPACITORS Locate the CAPACITOR bag SYNTHESIS TECHNOLOGY PAGE 7 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM Locate the 22pf ceramic axial caps 4 and solder into C1 by VR2 C6 above R14 C7 by VR3 and C8 above R8 DO NOT GET THESE MIXED UP WITH THE OTHER CERAMIC CAPS OR THE MIXER WILL NOT OPERATE PROPERLY Locate the 0 1mfd axial ceramic caps 4 and solder into C2 C3 C4 and C5 Locate the 10 fd electrolytics 2
9. 4 and IN5 turning both to 10 the output would be 8 84V pk pk The panel pots used on IN4 IN6 are called log or audio taper pots These pots have a non linear resistance versus rotation because the human ear is non linear in terms of perceived loudness versus signal amplitude In other words making a signal twice as big say 1V pk pk to 2V pk pk does not make the signal twice as loud The log pots try to attenuate the signal in such a manner that as you turn the knob the loudness volume changes smoothly from soft to loud The DC path of the Mixer is more fancy than the audio portion IN2 and IN3 have a circuit called a reversing attenuator on them This allows the panel pot to select gains of 1 to 1 before the summing amp Signals and DC voltages can be inverted change of polarity Note that due to the fact it s nearly impossible to set the panel pot perfectly in the middle of rotation you cannot expect 100 muting of inputs on IN2 and IN 3 Like the 3 audio channels the channel gain is set by R8 R6 for IN1 etc which is 0 442 U1A is the inverter but is has other functions First a DC bias offset can be added to the output by SW1 and VR4 The amount of bias is set by R1 R2 or 1 3 of 15 15 which is 5 to 5V of bias Second the audio channels can be added in by SW2 and R18 If SW2 is closed the 3 audio channels are added in as a group with a gain of R1
10. ECH COM Pots 7ea containing the following 3ea 100K linear conductive plastic Bourns VR5 VR6 VR7 1ea 100K linear cermet Spectrol 149 VR4 3ea 100K log conductive plastic Spectrol 148 VR1 VR2 VR3 Front panel Mounting bracket Wire bag containing the following 14 wires 6ea RG 174 coax 4 inches 2ea RG 174 coax 7 inches 4ea 3 wire set 22ga 6 inches orange white gray 1ea 2 wire set 22ga 3 inches red black 1ea Power Cable 20 Hardware bag containing 4ea 8 32 x 3 8 black screws for mounting module to rack 4ea 6 32 x 1 2 zinc screws for attaching pc board to bracket 4ea 1 4 inch aluminum spacers 6ea 6 KEPS nuts 2 for attaching bracket to front panel 4 for pc board 3ea small heat shrink tubing 9ea small tie wraps Organic Solder No clean Solder PC Board MOTM 830 SYNTHESIS TECHNOLOGY PAGE 4 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM GENERAL INFORMATION Thank you for purchasing the MOTM 830 Dual Mode Mixer If you have any issues concerning the building or use of the kit please contact us at 817 498 3782 or by email synth1 airmail net This kit should take the average builder between 2 and 3 hours The kit contains many different resistors and special parts However please remember this is NOT a speed contest it is an accuracy contest There is no rule that you have to complete the entire kit in one day as long as you wash the flux off Successful kit building relies on having the proper tools
11. Here is a list of what you will need to build your MOTM 830 Soldering iron 50W max power Needle nose or chain nose pliers Diagonal cutters Allen key set for securing the knobs 1 16 or 1 6mm Magnifying glass to read the capacitor codes and to inspect solder joints Lead bending tool optional but makes the job go much faster DVM Digital Volt Meter or oscilloscope to check the output 1 Philips screwdriver Fingernail brush for washing off the organic flux Old towel for blotting dry pc board Heat shrink gun is highly recommended For more information of tools used and suggestions see the MOTM FAQ and Tutorial pages at http www synthtech com HOW TO FOLLOW THE DIRECTIONS Please read the entire instruction before proceeding There may be valuable information at the end of the instruction Each instruction has a check box next to it After you complete the instruction check the box This way you can keep track of where you are in the process VERIFY THE PARTS LIST Verify that all of the parts are in the kit as shown on the parts list SYNTHESIS TECHNOLOGY PAGE 5 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM A WORD ON SOLDERING There are 2 very different types of solder used in the kit Most of the soldering uses Organic Flux solder This is strictly for use on the pc board and is NOT to be used on the front panel wiring In order for solder to stick to the copper a
12. If you want to INCREASE the individual channel gain you DECREASE this resistor by the you want You should use 1 resistors for their low noise and temperature drift The GROUP gain is set by R8 for IN1 IN2 IN3 group and R17 IN4 IN5 IN6 group This is set at the factory for 0 442 the keen reader will see this is the feedback resistor divided by the input summing resistor SYNTHESIS TECHNOLOGY PAGE 15 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM The value of this resistor is somewhat arbitrary but within a range of possible values This resistor sets the MAXIMUM VOLTAGE OUT when all 3 inputs are at maximum ie the pots are cranked up to the right Assuming the worst case of 3 VCO outputs in phase That s 10 10 10V possible out if the group gain is 1 Rather than have the poor op amp clip and heat up we decide that the maximum output voltage is 30 0 442 or 13 26V pk pk Now you will raise your hand and point out that this exceeds the 10V pk pk standard and you are correct This extra voltage is called headroom in MixerSpeak This means in real life you don t crank all 3 pots to 10 to get 10V out Rather you will find they are set on roughly the 8 tick mark So when the mixer is split into 2 3 1 sections the channel gains are all equal and the group gains are 0 442 which gives a maximum out not counting BIAS of 13 26V pk pk for 3 10V pk pk input signals WHEW The clever re
13. MOTM 830 Dual Mode Mixer Assembly Instructions amp Owner s Manual Synthesis Technology 6625 Quail Ridge Dr Fort Worth TX 76180 817 498 3782 www synthtech com May 30 2001 SYNTHESIS TECHNOLOGY PAGE 2 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM MOTM 830 PARTS LIST Please carefully check that all parts are in your kit If you have a suspected shortage please call or email If you get free extra stuff keep it for next time Capacitor bag containing the following 10 parts 2ea 10mfd 50V Electrolytic C9 C10 4ea 22pf marked 220 ceramic axial C1 C6 C7 C8 4ea 0 1mfd marked 104 ceramic axial C2 C3 C4 C5 Resistor bag containing the following 24 parts 13ea 100K 1 brown black black orange R6 R9 13 R18 24 3ea 10K brown black orange R5 R7 R16 2ea 1K brown black red R4 R14 2ea 44K2 1 yellow yellow red red R8 R17 2ea 49K9 1 yellow white white red R1 R3 1ea 150K 1 brown green black orange R2 1ea 51K green brown orange R15 IC bag containing the following 3 parts 2ea OP285GP precision dual opamp U1 U2 1ea TL072 dual op amp U3 Misc 1 bag containing the following 4 parts 2ea Axial ferrite beads plain gray things L1 L2 1ea MTA 156 power connector JP1 1ea SPDT ON ON toggle switch M2012 SW1 Knobs 7ea ALCO PKES90B1 4 Jacks containing 7ea Switchcraft 112A 1ea Switchcraft 114B contains switch SW2 SYNTHESIS TECHNOLOGY PAGE 3 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHT
14. Y TO THE LEFT of the oblong holes Loosely tighten the 4 KEPS nuts on the bottom THIS IS A VERY IMPORTANT STEP SO PAY ATTENTION AND READ ALL OF IT BEFORE PROCEEDING Note that each of the 4 pots on the pc board have 2 hex nuts and a flat washer Remove the first hex nut and the washer Set aside What you will do now is adjust the remaining hex nuts so that when the bracket is all the way down on the panel s threaded studs all the pot hex nuts touch the rear of the panel SYNTHESIS TECHNOLOGY PAGE 10 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM Screw by hand each hex nut on the pots so that it is all the way on touching the face of the pot Now pick up the pc board bracket assembly and carefully slide it over the 2 threaded studs making sure the pots are aligned in the holes Use 2 6 KEPS nuts and tighten the bracket to the panel Loosen the 4 KEPS nuts on the bottom of the bracket Slide the pcb ALL THE WAY TO THE RIGHT AS FAR AS IT WILL GO so that the 4 pot nuts are all pressing against the panel By hand put hex nuts on the outside threads of VR1 and VR4 to keep the pc board in place Now tighten the 4 KEPS nuts on the bracket The pcb and bracket should be secure with no gaps visible between the panel and the pot nuts You may need to loosen the nuts on the pots so that they are touching the back of the panel Again make sure each pot s nut is touching the back of the panel no gaps There will be a gap from the edge of th
15. ader will now catapult out of his her chair to shout What happens in 6 1 mode Do you get 13 26 13 26V pk pk out or a whopping 26 52V pk pk signal Answer NO Give us some credit Looking at the schematic the value of R18 is setting the group gain of IN4 IN5 IN6 when in 6 1 mode In other words the log taper group is added to the linear taper group by R18 through normally closed switch jack SW2 This gain is set by the ratio of R1 divided by R18 or This means we FIRST sum IN4 IN5 IN6 together with a group gain of 0 442 THEN add HALF of that result to the other 3 channels So in 6 1 mode the IN4 IN5 IN6 levels are cut in half This prevents massive output levels with everything cranked to 10 What is the maximum Assuming 10V on every input and every pot set to maximum level the answer is 19 89V This level is WAY TOO BIG to be used for anything BUT is below the op amp s clipping level So even if you set the mixer up to do this NO CLIPPING WILL OCCUR You will find that in 6 1 mode you will get reasonable output levels with all the pots set to mid gain which is again a design decision you can alter by resistor swapping Certainly it would have been nice to reduce both groups by an equal amount rather than have the mixer with this imbalance of gains But the goal was a minimal path for best performance an the switching jack was the compromise if you think there are lots of engineering decisions in a simple mixe
16. cure the coax cable flush to the board The tie wrap goes down into the left hole and up through the right hole Secure and trim off any excess Find the 4 white orange gray twisted wires They go into VR5 VR6 VR7 and SW1 Solder the White wire into pad 1 the Grey wire to pad 2 and the Orange wire into pad 3 Solder the short stripped end into the pcb Find the red black twisted wires It solders into SW2 The Red wire goes in pad 1 and the Black wire into pad 2 YOU ARE NOW FINISHED WITH THE PC BOARD WORK BREAK TIME PART 7 FRONT PANEL PREPARATION You will now attach components to the front panel It is HIGHLY recommended that you use a set of hollow shaft nut drivers NOT PLIERS to tighten the nuts This prevents scratching NOTE all references to part orientation is from the REAR of the panel Locate the 8 Switchcraft jacks Notice that from the rear there is a beveled corner This corner is ALWAYS CONNECTED TO GROUND USUALLY WITH A SYNTHESIS TECHNOLOGY PAGE 9 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM BRAIDED CONDUCTOR Each jack has a flat washer a lockwasher and a hex nut Remove the nuts and washers from each jack Place aside Keep the lockwasher on the jacks One of the jacks is different It has 5 lugs out the back instead of 3 This jack contains a switch SW2 and you MUST insert it into the OUT2 hole Insert the 8 jacks lockwashers with the beveled corner in the upper right corner into the 8 holes Place
17. e pc board to the panel Remove the hex nuts on VR1 amp VR4 For all of the pots first put on the flat washer then the hex nut Tighten with a nut driver PART 9 FINISH WIRING TO THE PANEL Please read the following instructions carefully In order to neatly attach the many wires to the front panel components the wires are soldered in a specific order Find the SPDT toggle switch Insert the switch into the panel hole labeled BIAS Tighten the outside hex nut but DO NOT OVERTIGHTEN Be sure the switch is oriented so the lever operates up and down and not side to side The lockwasher goes on the inside of the panel Now you will solder to the BIAS switch The 3 pieces of heat shrink tubing are for the switch lug First untwist the wires once or twice to leave about 1 inches free for each wire Slide a piece of tubing on each wire The Orange wire goes to the TOP lug the Gray wire goes to the MIDDLE lug and the White wire goes to the BOTTOM lug Wait 1 MINUTE before sliding the tubing over the switch lugs which retain heat because they are silver plated Use a heat shrink gun to shrink the tubing over the wire lugs Now you will solder to the 8 jacks Each jack has 3 lugs except OUT2 which has 5 from the rear we will refer to them as LEFT TOP and BEVELED The TOP lug is for the switched contact this is a NC normally closed contact that is opened when a plug is inserted Solder the coax in J8 to the OUT1 jack The braid
18. f the silkscreen which shows where the parts go at the end of this document It will be useful if you locate the part on the print first put the part in the board then check off the silkscreen All parts are inserted from the side of the board with the white silkscreen the top side NOTE some reference designators are under the resistor Be careful We will stuff the resistors by value to make things easier The resistors and other long leaded parts are inserted on a 0 4 inch spacing The important thing is to be sure that the part is sitting all the way down on the board Push the leads in the holes push the part on the board and then bend the leads on the bottom outwards to a 45 degree angle roughly This is called cinching the leads and keeps the part from falling out From the bottom of the board solder using the organic flux applying heat to the pad for about a half second first then applying just enough solder to make a small puddle that SYNTHESIS TECHNOLOGY PAGE 6 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM looks like a tiny pyramid Enough solder should flow in the hole such that on the top component side a small amount is on the top pad as well The rule of soldering don t use too much you can always add more Cut the leads flush with the top of the solder joint with your diagonal cutters NOTE later in the assembly you will need 6 scraps of resistor lead Be sure to save some Locate the 100K 1
19. h your fingernail across it and it will peel off CONGRATULATIONS YOU HAVE FINISHED BUILDING THE MOTM 830 All that s left to do is test it But before we do please read the following Theory of Operation THEORY OF OPERATION Compared to most other MOTM modules the MOTM 830 is fairly simple well that s easy for us to say The audio portion of the Mixer IN4 IN6 consists of an inverting summer U2A followed by an inverter U2B The 22pf caps C6 and C7 are used to keep high frequency overshoots out of the outputs The OP285 is a special type of opamp not only is it fast and has low THD for audio it also has superior DC drift and offset specifications The gain of each channel is set by the ratio of the feedback resistor R17 to the input resistance seen at the negative terminal pin 2 which are R9 R11 The gain equation is R17 R11 for SYNTHESIS TECHNOLOGY PAGE 12 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM IN4 R17 R10 for IN5 and R17 R9 for IN6 This corresponds to a gain of 0 442 per channel The following inverter has gain of 1 so the total path gain per channel in the audio path is 0 442 So if you put in 10V pk pk into IN4 and set the panel pot to 10 the output on OUT A jack is 4 42V pk pk If you put 10V pk pk into IN
20. r wait until you try to design a VCO BIAS should ONLY be used for control voltages DO NOT APPLY DC BIAS TO AUDIO POWER AMPS OR DAMAGE TO THE AMPS AND SPEAKERS MAY RESULT SYNTHESIS TECHNOLOGY PAGE 16 MOTM 830 ASSEMBLY 5 30 01 WWW SYNTHTECH COM SPECIFICATIONS MOTM 830 Dual Mode Mixer Input signal level any input 7V to 7V Output level 20V peak peak before clipping Output distortion lt 0 01 at 1Khz Output SNR 86dB min CONTROLS IN1 Linear input IN2 IN3 Reversing attenuator input 1 to 1 gain IN4 IN6 Audio taper input BIAS Sets DC bias level between 5V and 5V BIAS switch Adds DC bias to OUT 1 jack GENERAL Power Supply 15VDC 15 ma nominal 15VDC 15 ma nominal Size 2U x 5U 3 47 x 8 72 88 1mm x 221 5mm Depth behind panel 4 375 inches 111mm Date June 5 2001 Sheet 1 of 1 Size Document Number REV B M830 SCH A Title MOTM 830 DUAL MODE MIXER 888 818 MOTM FORT WORTH TX 76180 6625 QUAIL RIDGE DR SYNTHESIS TECHNOLOGY 1 2 3 4 JP1 MTA 156 L1 FERRITE L2 FERRITE 15V 15V C9 10M C10 10M 15V C5 0 1M R12 100K 1 C6 22PF C7 22PF R17 44K2 1 R10 100K 1 R11 100K 1 VR1 100K LOG VR2 100K LOG J2 J1 IN 4 IN 5 R22 100K 1 5 6 7 8 4 U3B TL072 J7 VR7 100K LIN IN 6 IN 3 R21 100K 1 R9 100K 1 VR3 100K LOG R23 100K 1 J3 R16 10K 15V C4 0 1M 3 2 1 8
21. summing op amps don t know or care what the taper is They happily add up whatever is presented to it This means you can put audio or CV into ANY INPUT CHANNEL YOU WANT Just realize that the loudness of the audio based on the summed output voltage For example IN1 is a straight input on a linear pot IN4 is a straight input on a log pot If you put the same audio signal into both and set both for equal loudness the tick marks will not be the same Conversely if you are scaling a keyboard voltage to 1 5th range the IN1 tick would be very different from the IN4 tick mark CHANNEL GAINS There were several design compromises made from selecting the channel and group gains of the Mixer IF YOU DON T LIKE THE CHOICES THAT WERE MADE YOU CAN CHANGE THEM BY SWAPPING RESISTORS Read the following discussion closely to understand how amp why the gains are set the way they are from the factory The intent of the 830 is to mix signals within a MOTM system This means the audio signals are very hot compared to standard audio signals The MOTM system uses 10V peak peak audio signals which is 10 times hotter than normal The first design decision was to set the channel gains equal This means IN1 IN6 all sum the same when the pots are fully clockwise The individual channel gain is set by the input summing node resistor for that channel From the factory this is a 100K 1 resistor R11 is for IN4 R10 is for IN5 etc
22. the flat washer on the jack then the hex nut Hold the jack with one hand on the backside keeping it square Tighten the hex nut with a nut driver NOTE when tight not much of the exposed threads of the jack are exposed Remember those resistor lead scraps you have been saving They solder on the IN1 IN6 jacks Solder the scrap in between the TOP and the BEVELED lugs Be sure to leave enough space on the beveled lug to attach the coax braid You are now ready to attach the pc board to the bracket and then wire up to the panel PART 8 ATTACH PC BOARD TO BRACKET PANEL In the HARDWARE bag locate 4 6 32 x 1 2 screws 6 6 KEPS nuts and 4 spacers Locate the mounting bracket The pc board attaches to the bracket with the 4 screws threading from the top of the board through the spacers through the bracket and then out the bottom of the bracket The 6 KEPS nut attaches on the bottom of the bracket Note the bracket has 2 long mounting flanges with a hole in each These attach to the 2 threaded studs sticking out of the rear of the panel The 4 pots each stick in its panel hole when the bracket is screwed down on the 2 threaded posts Attach the pc board to the bracket The flanges will point upwards when the pc board is sitting on the bracket Note that the bracket holes for the pc board are actually oblong This is to allow adjustment for the pc board to firmly press up against the back of the panel As a start set the 4 screws ALL THE WA
23. y No solder shorts or missing joints USING THE MOTM 830 The main use of the 830 is to add audio signals control voltages or both to form a single output The most common use is to add the outputs from multiple VCOs together before feeding a filter or other processor The MOTM 830 is NOT INTENDED to replace a standard audio mixer in your studio Rather it is a simple module without coloration or EQ that adds stuff up The unique feature of the 830 is that it can be split into 2 separate mixers by inserting a mono plug into the OUT 2 jack This engages a switch which splits the mixer into the OUT1 group IN1 IN2 IN 3 all added together and the OUT2 group IN4 IN5 IN6 all added together This is like a headphone jack on a stereo that switches the speakers off when you plug in the headphones The 1 difference between the 830 and a studio audio mixer is that there are 2 reversing attenuators on IN2 and IN3 These are usually used to invert as well as attenuate signals plugged into these 2 inputs Due to the circuitry used you CANNOT mute these channels to zero as you can on the other 4 inputs Therefore avoid using IN2 and IN3 if you need to fade out during a mix You just can t set those pots to 50 rotation perfectly The MOTM 830 is set up to attenuate only You cannot get gain out of this module See the CHANNEL GAIN section for more information AUDIO VERSUS LINEAR POTS Since the MOTM 830 can be used for both
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