MOTM-485 User Manual
Contents
1. opposed to dual PNP or Dual NPN This was done because the converter is really a PNP NPN NPN Q1B and Q1D are both driven off QLA Why two exponential current outputs Well remember the diode bridge likes to be balanced specifically it likes having the same amount of current injected at the top as pulled out of the bottom So Q1D provides the current sink at the bottom whereas Q1B operates a current mirror made from Q5 which provides a current source at the top These identical source and sink currents are of course the control current for the filter frequency The left over transistor Q1C is used for the Q control circuit as described previously Highpass Mode The operation of the filter in highpass mode is essentially the same as for lowpass save that the input signal is introduced into the now series capacitor SW2 switches C12 from being grounded to being used for series input and the impedance element Q10 has the left side fixed at a DC constant again by SW2 of half the power supply voltage in order to most efficiently use the bridge as a parallel to AC ground resistor Series R with parallel to ground C being the simplest lowpass model it is reasonable to assume Series C with parallel R is the simple highpass model And such is the case the filter now behaves as a second order highpass filter save for that region where the input signal is close to the cutoff frequency at which point it assumes a bandpass within the2. VRS 3 sus Sooz TT 3snbny aeG S8 HIN 3 z quwunN Jzu wun doqj zTS JOA HAAL T XD S8v WLOW STATL 9LLL TS8T LTB ost9L XL HLYOM LOA MOT AST MOT AST ud HOUIYU TIVNO SZ99 i evu Sza KDOIONHOAL SISHHLNAS T T 980ENT 980ENT TT t SNIG TO HOTO ZT ALO ZT v t t t 2 OPELVHL x MOLT TEA AOS AOS MOOT LA aN WEE WOT Lt WOT sea eeu 950 Lt rao TD LNO Fe aN WOT ie l 7 mvad O rn PEA RD ZEA aN ENE MT Dossa 3 v AST AST Lea xz TAL e 209508 90 CMT EZA MST 9 4 Mada aa Vv AST n v AST 8M9 980 ENT ST lt Vv Q 9 0 WLO LA ZAZ WOT T LA eva TZA ED Zra MOOT aN WOT T MOTT ZAZ ETA sn 6eu DOSSDE cca T 80 60 MOOT e TMOOT lt ZAA PTA AST Saints AST hee ae d I dH SHA Tru MOLD ZTA AST MLD V sta AST TAZZ TL osu ato DTO 4 NZZ AST 980ENT OL MT ooz y er l ETO WIO T TTA OTA T NI SHAHN AOZT LaS440 AD f OvVELVHL s LA adOTO WOTO PS ALMOT ora T 6u zar x WA x L o AST T 5 9 DOTO CIOTO 6 T WTO IF TMTS MOT gt X vo Nee 6MHS 4 4 9TA AST 8a T ETOTLT 8 g amp DossDad TITO arn ETOTLTI 2 s ST MOOT WTO TIMOOT L IMTS TAZZ TAZZ 9 T ae PZA 6TA p Su z GOW NA La NT O0 209504 ZO L SD AS
3. R27 Locate the 2K2 resistors 3 and solder into R21 and R22 by C3 and R18 by Q9 Locate the 120K resistors 2 and solder into R9 by TP2 and R13 by Q8 Locate the 51K1 1 resistors 2 and solder into R7 and R8 by U1 Locate the 6K8 resistors 2 and solder into R26 by Q1 and R30 close to SW1 Locate the 1K 5 resistors 2 and solder into R34 and R37 by C7 C6 Locate the 47K resistor 2 and solder into R15 by SW2B and R32 behind VR2 Locate the 8K3 resistors 2 and solder into R38 by Q9 and R44 by C11 C12 Locate the 150K resistors 2 and solder into R39 and R40 by C10 Locate the 200K resistor and solder into R10 by TP2 Locate the 1K2 resistor and solder into R23 by J4 Locate the 470K resistor and solder into R12 by C12 Locate the 54K9 1 resistor and solder into R16 by Q1 Locate the 470 ohm resistor look closely and solder into R31 by VR2 Locate the 15K resistor and solder into R36 by SW1 Locate the 47 ohm and solder into R48 by Q8 Leave the Tempco resistor for a later step After soldering all the resistors wash and dry the pc board PART 2 Soldering the ICs amp Misc parts SYNTHESIS TECHNOLOGY PAGE 6 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM 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 7 Locate the ferrite beads 2 They are axial parts gray colored with no marki
4. The waveforms were limited the amplitudes under tight control and many hours were spent in trimming remember this thing cost like 50 000 when it came out as much as a large house In updated modular format as open ended as it gets the how shall we say quirks of the design can be seen So what I m saying is don t be surprised if the MOTM 485 doesn t sound like my other filters or puts out all sorts of strange distorted sounds because that s part of its charm Quirk 1 HP mode has all sorts of IM intermodulation distortion at high resonance This is will be based on the input level see Quirk 2 and the setting of the Q PEAK trimmer But in general once the RES pot is past 4 or so in HP mode all hell can break loose It s not broken OK It can almost sound like an overdriven ring mod at times If you look with a scope you will think something is terribly wrong with the output sine wave turns into odd ramps etc Quirk 2 the filter is sensitive to input levels You will be tempted to jam 2 full level VCO waveforms into the 2 IN jacks Prepare for all sorts of messed up tones If you want tamer outputs run a mixer before the inputs like a MOTM 890 Again HP mode will be more wacky than LP mode with large inputs Quirk 3 limited sweep range The filter cannot sweep 20Hz 24Khz like say a MOTM 440 The MOTM 485 is more on the order of 80Hz to 6Khz Again this is a function of the diode c
5. above TP2 running along the edge of the board by the R9 white silkscreen PART 3 BOARD WASH 2 7 Wash the board in warm water gently scrubbing both sides 7 Shake the board a couple of times blot dry with an old towel the leads will frazzle a good towel Let dry at least 15 minutes SYNTHESIS TECHNOLOGY PAGE 7 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM r Take another break or set the kit aside for later You are about 75 finished at this point this is a good stopping point 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 4 CAPACITORS TEMPCO RESISTOR Locate the CAPACITOR bag Locate the 1K Tempco resistor and your heat sink compound 7 Locate the 22N caps 2 They will have 223 stamped on the side They solder into C10 and C11 Locate the 47N cap with 473 stamped on the side Solder into C12 Locate the 0 1uf axial ceramic caps They solder into C4 and C5 by U1 Locate the 3M3 non polar cap and solder into C9 by J2 Locate the 33uf non polar cap Solder into C6 Locate the 10uf non polar caps 2 Solder into C7 and C8 UO 1 GO oD Oo n Locate the 10ufd electrolytics 8 Note that there is a stripe on the NEGATIVE terminal The pc board has a on the POSITIVE terminal Carefully stick the capacitors into C1 C2 and C3 with the stripe away from the pad on the board d Locate the
6. black Tempcvo resistor This will solder on top of Q1 A small amount of heatsink compound is first applied to the top of Q1 and the Tempco is placed so that the DIP package is in contact with the bottom of the Tempco Be sure the Tempco is level and flat before soldering SYNTHESIS TECHNOLOGY PAGE 8 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM PART 5 FINISHING THE PCB Trimmers pots and wire 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 r Locate the 2K blue trim pot It will have P 202 marked on one side Solder into TP1 labeled Q TRIM 7 Locate the 20K trim pot It will have P 203 marked on one side Solder into TP2 labeled CV OFFSET 7 Locate the Spectrol pots 3 IMPORTANT in order for the pc board to properly align with the front panel each pot must be absolutely flat on the pc board with the shafts pointing away from the pc board These are marked on the top side as 71104 Solder these pots into VR1 VR2 and VR3 Remove the outer pot nut and the flat washer The rear pot nut should be tightened all the way back then rotated 1 4 turn looser This allows the stress of mounting to be on the threads of the bushing not pressing against the pot body itself 7 Locate the WIRE bag The MOTM 485 has lots of wires be very careful when soldering to the pc board in order that the wire colors are correctly into the proper ho
7. bounds of Q PRELIMINARY CHECKOUT amp TROUBLESHOOTING The first thing to remember this filter will not self oscillate Blame Yamaha The most common mistakes when building this filter are a Make sure the 3 film caps are in the correct place C10 and C11 have caps marked 223 and C12 has one marked 473 b Verify the 2 trim pots are correct TP2 must have a mark of P 203 and TP1 must have the P 202 mark c Make sure C9 is the 3M3 non polar cap To verify operation of the filter an oscilloscope is most helpful But Ill assume you don t have one for now start saving there are many good ones on eBay for 100 But you will need a signal source such as a MOTM VCO you cannot plug a mic or guitar into the 485 directly you first must amplify the signal a Set both trim pots to the center positions use a small flat screwdriver b Set the top switch to LP the bottom switch to F RES to 0 and FREQ to 0 c Apply power and apply an audio signal to IN 1 A VCO Saw at A440 is a good starting place d Monitor the OUT jack with an audio amp turn the volume down and do NOT use headphones e Slowly rotate the FREQ knob towards 10 At first the volume should be very low because the VCF if it is working will be attenuating most of the signal As you rotate the FREQ knob more and more of the signal should pass through SYNTHESIS TECHNOLOGY PAGE 15 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM f I
8. one module For the purposes of adapting the filter core to patchable modular use the original circuit has been updated to a MOTM voltage control front end for 1V Octave frequency as well as reversing FM input Aside from that and the passive audio mixer circuit to provide three signal inputs the core filter circuit remains the same as that used in the original submodules Diode rings as Voltage Controlled Elements Referring to the schematic note there are two diode rings or bridges that are made from the base emitter junctions of four transistors of Q7 as well as Q10 In each ring the transistors connected as diodes form an equivalent impedance circuit a control current enters the top of the ring pins 6 and 9 of the Q7 or Q10 array while the same amount of control current leaves through the bottom pin 3 These control currents are supplied from the CV front end for resonance Q7 and filter frequency Q10 As current flows through either side of the diode ring a corresponding forward voltage is developed across each diode The voltage current aka V I characteristic of diodes being nonlinear on paper it typically appears as an exponential curve upward The math starts to get a little complex here is things head toward AC systems analysis and we discover we re talking about impedance and not simple resistance but for simplicity just consider that for each value of control current I there is a resul
9. order for solder to stick to the copper a 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 x2 andcan 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 7 Find the MOTM 485 blank pc board There is a copy larger than actual size of 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 We will stuff the resistors by value to make things easier The resistors are inserted on a 0 4 inch spacing this is where the Mouser jig mak
10. rear pot nuts NOW you tighten the 4 nuts on the bottom of the pcb bracket SYNTHESIS TECHNOLOGY PAGE 10 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM PART 8 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 You may find in some cases it is easier to first remove a Jack from the panel and solder the wires then reattach it to the panel g J J Mount the 2 switches in the panel The larger DPDT switch goes in the top hole marked HP LP and the SPDT switch 3 lugs goes in the lower hole marked F H In both cases the rear nut needs to be tightened all the way then backed out 1 4 turn Put on the toothed lockwasher insert the switch so the handle toggles up down in a straight line then place a nut on the front and tighten The lockwasher always goes on the back side of the panel There is no top bottom orientation for the switches just be sure they are straight Solder the white gray orange wire SW1 to the SPDT switch The Orange wire goes on the Top lug the Gray wire to the middle lug and the White wire to the bottom lug hopefully the same order they are in the 3 holes on the pcb Solder the white gray orange wire in SW2B to the lower set of 3 lugs of the DPDT switch the set nearest the pcb Orange on the top Gray on the center and White on the bottom lug Now repeat with
11. 2ga orange white long J1 3ea 3 wire set 22ga orange white gray short SW1 SW2 lea 2 wire set 22ga 3 red black J2 lea Power Cable 20 7 Hardware bag containing 4ea 48 32 x 3 8 black screws for mounting module to rack 4ea 46 32 x 1 2 zinc screws for attaching pc board to bracket 4ea aluminum spacers 4ea 6 KEPS nuts for pc board 5ea small tie wraps rJ Organic Solder AND No Clean solder 1 bag each type SYNTHESIS TECHNOLOGY PAGE 3 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM GENERALINFORMATION Thank you for purchasing the MOTM 485 VCF 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 to 3 hours 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 Here is a list of what you will need to build your MOTM 485 Soldering iron 50W max power Use 700 F tip temperature setting Small amount of heatsink compound not supplied Needle nose or chain nose pliers Mouser lead bending jig for the resistors Diagonal cutters Allen key set for securing the knobs 1 4e or 1 58mm Magnifying glass to read the markings and to inspect solder joints DVM Digital Volt Meter to verify
12. 3 and R37 The signal is tapped here so that with increasing Q the overall amplitude decreases to avoid clipping of the resonant peak by the final amplifier made from the gain of 10 Q4 Q6 circuit The filter output is then AC coupled to remove any DC offset imposed by the variable Q and provided on output jack J4 Voltage Control Front End The 1V OCT and reversing input FM jacks are MOTM standards employed here They are not of course part of an original NE 10400 or NE10500 The original filters used discrete transistors instead of the matched array Q1 which is one reason why they potted them for temperature stability and no active summing front end was employed The operation of the reversing circuit built around U1 has been noted elsewhere but in short the 1V OCT input is given a gain of 1 or depending on the setting of the tracking switch This is a Yamaha thing used on their highpass filters Since this is a patchable module the switch is provided so the half tracking mode is available but not mandatory Similarly the FM input is given a knob variable gain from 1 33 to 1 33 The sum of the FM and 1V OCT voltages goes into a traditional exponential V I converter made from Q1 Note that this is slightly different than the servo feedback type of expo converter see the MOTM 300 310 in that 1 it does not use a servo loop and 2 it uses a PNP NPN configuration as SYNTHESIS TECHNOLOGY PAGE 14 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM
13. Remove the nuts and washers from each jack Place aside Keep the lockwasher on the jacks Insert the 6 Jacks lockwashers with the beveled corner in the upper right corner into the 6 holes Place 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 You are now ready to attach the pc board to the bracket and then wire up to the panel PART 7 ATTACH PC BOARD TO BRACKET PANEL J J In the HARDWARE bag locate 4 6 32 x 12 screws 4 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 nuts attach on the bottom of the bracket Note the bracket has 2 notches these are for the 2 switches to mount in between the pots Attach the pc board to the bracket using the 4 screws spacers and nuts the nuts go on the bottom of the pc bracket Do not tighten the nuts all the way so the pcb can slide in the bracket Next place the 3 pot bushings shafts through the 3 holes in the panel With the 4 pcb nuts still partially tightened put the 3 flat washers and 3 nuts on VR1 V3 on the front of the panel and tighten This will pull the pcb up against the panel resting on the 3
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15. TM 485s in series is that now you have independent control of resonance and bandpass frequency just like in the MOTM 480 CS 80 VCF MOTM 485 Hacks e R15 sets how far external voltages sweep the resonance Lower it for a wider range e You can adjust R37 and R28 to alter the feedback for resonance e You can play with the filter caps C10 and C11 must be the same and C12 has to be 2 times C10 C11 If you still cannot get the module to perform correctly please contact us by phone at 817 498 3782 or by email to synth1 airmail net SYNTHESIS TECHNOLOGY PAGE 17 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM SPECIFICATIONS MOTM 485 GX 1 Diode VCF Audio Input Range 10V pk pk nom combined both inputs Control Voltage Range 7V 7V Output impedance 1000 ohms nom Frequency Range 80Hz 6Khz nom CONTROLS FREQ sets filter cutoff frequency RES sets resonance CV MOD reversing attenuator for filter cutoff GENERAL Power Supply 15VDC 8ma 15VDC 15 ma Size 1U x 5U 1 72 x 8 72 44mm x 221 5mm Depth behind panel 4 5 114mm TN Fe GEER 5 F wR iil 4 Le LE Jar Ah LEE de See ee k de a nai es SYNTHESIS TECHNOLOGY PAGE 18 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM e 080 I CUE TL E QB ERT mi 88 i rf w AE III P or EE da ga WWW SYNTHTECH COM x B Bye 3 JULY 2004 REV A Ele IN 2 F Q PEAK 34 P TEMPCO RIS N U O Z O U 4 N x7
16. as R47 and Rq as the R23 R37 TP1 C9 Q7 chain Yes there is a capacitor in there never mind a transimpedance diode cell made from Q7 but we re dealing with AC impedance so think of it as a resistor It is much easier that way The op amp Well get to that SYNTHESIS TECHNOLOGY PAGE 13 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM An incoming audio signal applied to inputs J5 J6 is AC coupled by C8 into the emitter follower buffer circuit around transistor Q9 The buffer output is well suited to driving signals into variable impedances such as the impedance cell diode ring built from array Q10 In the LP mode this is precisely what happens Remembering that the control current flowing top to bottom in the ring changes the impedance for the signal flowing across the ring we effectively have a variable series resistor connected to a tuning capacitor C12 This R C circuit forms the first order of our filter As the control current increases the apparent resistance decreases and the corner frequency of the filter goes up Now the output of this R C circuit is buffered by the high impedance gate of the FET Q8 into the amplifier made from the circuit surrounding Q2 amp Q3 This amplifier is the active element op amp of our active filter The R C circuit alone is a passive filter The output of this amplifier is emitter coupled back to the filter input through C10 and C11 Think of C10 C11 as one capacitor just split up t
17. es things nice and fast 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 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 Locate the 100K 1 resistors 9 and solder into R1 to R6 all near U1 R14 by J3 R28 by Q7 and R35 by VR3 7 Locate the 4K7 resistors 5 and solder into R33 by C6 R41 43 by TP2 and R46 by SW2A SYNTHESIS TECHNOLOGY PAGE 5 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM d DQ l G G G dj 3 3 nunan Locate the 22K1 1 resistors 4 and solder into R19 by Q5 R20 by L2 R24 next to Q5 and R50 by C11 Locate the 10K resistors 4 and solder into R25 by Q7 R45 by Q2 Q3 R47 by Q8 and R49 by Q10 Locate the 18K resistors 3 and solder into R17 next to R49 that you just did R27 by J1 and R29 2 over from
18. ff k 2 3k 2k 2k RR RR CONGRATULATIONS YOU HAVE FINISHED BUILDING THE MOTM 485 k 2 3k 2k 2k zk gt gt F ee 3 2k 2k k 2k gt F 9 3 3 9k 2k 2k E E 9 OK K 2k 2k F 9 9 OKE 2 R E 9 9 K KR R R E 9 OK OKR RR E 9 9 OK RR R R 9 OKE RR ee R R R RO OS de de a All that s left to do is test it But before we do please read the following Theory of Operation THEORY OF OPERATION by Scott Rider Chief MOTM 485 Designer The MOTM 485 is a 2nd order Sallen Key switchable highpass lowpass filter that is based on the same circuit configuration as that discovered to be used in the Yamaha NE submodule set that Yamaha developed in the early 1970s for their GX 1 stage synthesizer The filters represented by the MOTM 485 are the NE10400 lowpass and NE10500 highpass filter potted submodules that is the NE modules were small circuit boards composed of standard parts and placed in shallow plastic potting boxes with connection pins facing up then an epoxy resin catalyst was poured into the boxes and allowed to harden This is similar to the way ARP modules for machines like the 2600 and Odyssey was made The Yamaha NE submodule set was used in their SY 1 and SY 2 preset solo synthesizers and their Electone CSY 1 amp CSY 2 organs in addition to the GX 1 Since the NE10400 and NE10500 are nearly identical circuits with the use of a DPDT switch it is possible to route the signal path such that both filter modes can be provided in
19. fthis is properly operating switch to HP mode and rotate FREQ back and forth Now you should hear the opposite effect only the higher harmonics are passing through the filter g Put the filer back into LP mode and play with both RES and FREQ You should be able to hear the effects of increasing resonance the volume will drop some but the filter will squeal more Limitations Hacks and General Weirdness of the MOTM 485 The MOTM 485 is unlike any other MOTM VCF because it uses a pair of diode rings to act as the variable element The diode ring topology has several issues they have smaller dynamic ranges for the control current the VCF cannot sweep as broadly the diodes introduce lots of IM distortion especially in HP mode and in this particular implementation the resonance characteristics are based in part on the harmonic content of the audio output this will be evident when using narrow pulses in HP mode So why use diodes at all Because Yamaha needed to build a very inexpensive filter for the GX 1 which is an organ and so has 1 pair a HP LP set for every note Of course the MOTM version uses matched pair transistor arrays and has temperature compensation for the control voltage Also the OTA in chip form was very expensive in the mid 1980s compared to the diode version Even though the MOTM 485 is faithful to the original Yamaha overall design and topology the GX 1 was a controlled environment
20. i s 2 W w w ste fee m 4004 wall PUYO estrein LI i P Li Fe N Er wa Py An MOTM 485 GX 1 Diode VCF Assembly Instructions amp Owner s Manual Synthesis Technology 6625 Quail Ridge Dr Fort Worth TX 76180 817 498 3782 www synthtech com Aug 11 2005 MOTM 485 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 7 Capacitor bag containing the following 12 parts 3ea 10ufd 50V Electrolytic 2ea 22N reddish brown film cap marked 223 lea 47N reddish brown film cap marked 473 lea 3M3 50V non polar electrolytic lea 33ufd 16V non polar electrolytic 2ea 10ufd 50V non polar electrolytic 2ea 0 1ufd axial ceramic cap marked 104 7 Resistor bag containing the following 50 parts 9ea 100K 1 brown black black red Bea 4K7 yellow violet red 4ea 22K1 1 red red brown red 4ea 10K brown black orange 3ea 2K2 red red red 3ea 18K brown gray orange 2ea 120K brown red yellow 2ea 51K1 1 green brown brown red 2ea 47K yellow violet orange 2ea 6K8 blue gray red 2ea 1K 5 brown black red 2ea 3K3 orange orange red 2ea 150K brown green yellow lea 200K red black yellow lea 470K yellow violet yellow lea 54K9 1 green yellow white red lea 1K2 brown red red lea 470 ohms yellow
21. les g The long coax wire solders into J4 A tie wrap is used on each wire to secure the coax flat onto the pc board Note that the coax wires have one end stripped back shorter than the other the short end solders to the pc board See the photo below for details this is a generic photo Ja P w L l a L 2 need E E r Solder the 2 short coax cables into locations J5 and J6 Secure with tie wrap r Solder the long white black twisted wire into J3 White into 1 Black into 2 r Solder the orange white twisted wire into J1 White into 1 and Orange into 2 SYNTHESIS TECHNOLOGY PAGE 9 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM g g Solder the 3 white gray orange wires into SW1 and SW2A SW2B In all cases the White goes to 1 the Gray into 2 and the Orange into 3 Solder the red black twisted wires into J2 The Red is in 1 and the Black solders into 2 YOU ARE NOW FINISHED WITH THE PC BOARD WORK BREAK TIME PART 6 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 g Locate the 6 Switchcraft jacks Notice that from the rear there is a beveled corner This corner is ALWAYS CONNECTED TO GROUND Each jack has a flat washer a lockwasher and a 1 2 hex nut
22. ngs These are non polar and are soldered into L1 and L2 7 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 7 Locate the LT1013 IC Solder into U1 with the dimple on the top of the package on Pin 1 Pin 1 has a square pad all the others are round 7 Locate the THAT 340P transistor array and solder in Q1 There is a dimple by Pin 1 7 Locate the SSM2220P and solder into Q5 The notch depression on the top of the package matches the notch on the white silkscreen symbol Locate the CA3086s 2 and solder into Q7 and Q10 match the notches Locate the BC550C transistors 3 and solder into Q3 Q4 and Q9 The flat side of the transistor matches the flat side of the white silkscreen symbol 7 Locate the BF245 FET transistor and solder into Q8 Note the center lead is angled backwards slightly rJ Locate the BC560C transistors 2 and solder into Q2 and Q6 g Apply a small bit of solder to the via holes These are the small pads no components go in them that allow traces to change sides of the pc board DO NOT SOLDER PADS FOR THE REMAINING COMPONENTS The via holes need a VERY SMALL AMOUNT of solder For example there is a via hole on the top side trace that is
23. o cover both sides of the diode bridge The effect of this feedback is the diode bridge now acts as the impedance element for a second order filter convolving both the original R C12 and the feedback R C10 C11 The math sucks trust me If an audio signal enters the filter with a frequency much higher than the cutoff frequency the filter operates as a second order lowpass filter If however an audio signal enters which is close to the cutoff frequency the circuit behaves as an active bandpass filter with emphasis Q What is interesting is how the Q of this circuit is manipulated The filter output is taken from the source side of the amplifier buffer FET and a variable impedance diode bridge Q7 in combination with C9 TP1 R23 R37 and R47 form a negative feedback circuit Strictly speaking R47 alone provides negative feedback it is the rest of the parts that attenuate the signal that R47 couples back into the filter from the source negative side If negative feedback decreases the emphasis Q increases This Q is voltage controlled given that there is the variable impedance element Q7 which is controlled by the simple voltage to current circuit made from Q1C and R26 to R30 Resistors R12 to R15 set the range of control seen by Q1C from the panel knob and input jack which sweeps Q7 The final output of the filter is a buffered amplified signal taken from the Q negative feedback attenuator at the junction of R2
24. ontrol currents SYNTHESIS TECHNOLOGY PAGE 16 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM Quirk 4 setting Q PEAK will alter the tone There is no correct setting for this It s like adding Tabasco sauce to your soup Some people will crank this all the way up others all the way down Start in the middle and tweak to taste Use several waveforms amplitudes to hear what difference it makes If you can t decide leave it in the middle The Full Half switch is for the 1V Oct input jack Full means Full tracking or standard 1V Oct The Half position is for emulating a GX 1 MOTM 485 pair of filters The GX 1 has 2 filters in series HP at Half tracking followed by a LP at Full tracking So if you really want a GX 1 sound you need 2 MOTM 485s The OUT of the first goes to the IN 1 of the second the first VCF is a HP response with Half track The second VCF is LP mode with Full tracking The keyboard CV feeds both 1V OCT jacks via MOTM 910 mult at once The trimmer TP1 CV OFFSET is like the FREQ panel knob in parallel It allows you to set the default center frequency of the module for a given FREQ pot setting For example you may prefer bass sounds so you can set the FREQ pot tick to 5 to be 220Hz by adjusting TP1 Or set the 5 tick to be as high as 3Khz with the trimmer at the other extreme If you can t decide leave it in the middle and this makes the 5 tick around 800Hz The advantage of using 2 MO
25. resistor values 1 Philips screwdriver Fingernail brush for washing off the organic flux Old towel for blotting dry pc board For more information of tools used and suggestions see the MOTM FAQ and Tutorial pages at http www synthtech com The 2 trimmers on the board are set by ear no special test equipment needed An oscilloscope is handy and fun to look at the output waveform seeing the effects the VCF has using various settings 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 CJ next to it After you complete the instruction check the box This way you can keep track of where you are in the process Note that this kit uses 5 different decades of 47 ohm resistors be careful and don t get them swapped Also don t swap the 2 trim pots they are clearly stamped on the sides in black ink The 1 resistor color bands can be confusing so always measure them with the DVM before soldering VERIFY THE PARTS LIST g Verify that all of the parts are in the kit as shown on the parts list SYNTHESIS TECHNOLOGY PAGE 4 MOTM 485 ASSEMBLY 8 11 05 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
26. tant voltage V on the curve Taking the basic electrical formula V I x R voltage current times resistance rewriting it as V I R the apparent SYNTHESIS TECHNOLOGY PAGE 12 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM resistance of the diode ring changes with the control current Q7 is the resonance amount control element and Q10 is the filter frequency voltage control element If it is difficult understanding how a transistor can be a diode look at it the following image The canonical diode ring is illustrated on the on the left where Ain is the signal input O is the signal output and Ic are the control current source input top and output sink bottom Since a diode is a P N junction device with the P material called an anode and the N material called the cathode for their natures of harboring positive an ions or negative cat ions it should then be apparent that a bipolar transistor in this case N P N junction devices can act as diodes if one junction is left unused traditionally the collector Thus the bases of our NPNs become anodes and the emitters become cathodes and we get the diode ring made from transistors as shown on the right The Sallen Key Filter Model Using Diode Rings The classic 12dB octave or decade Sallen Key lowpass model can be drawn as Rf Aout AIn CTO7ZC1T1 For the MOTM 485 circuit think of Rd as the diode bridge Q10 Rb as R48 Rf
27. the 3 wires in SW2A soldering to the upper set of 3 lugs Use a tie wrap to bundle the 6 wires together in the middle of the wires Solder the short coax in J5 to the IN 1 jack The braid goes to the beveled ground lug and the inner conductor goes to the right lug the top lug is not connected Use just enough solder so that the hole in the lug is filled with solder All 3 coax wires attach in this manner Solder the short coax in J6 to the IN 2 jack Solder the red black wire in J2 to the FM IN jack The black wire goes to the beveled lug the red wire to the left lug Solder the orange white wire in J1 to the 1V OCT jack The orange wire goes to the beveled lug and the white wire goes to the left lug Solder the white black wire in J3 to the RES CV jack The black wire goes to the beveled lug and the white wire goes to the left jack Solder the long coax in J4 to the OUT jack braid to beveled inner wire to left lug Use the remaining tie wrap to bundle the wires to the jacks 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 SYNTHESIS TECHNOLOGY PAGE 11 MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM align the white line to the 0 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 with your fingernail across it and it will peel o
28. violet brown lea 15K brown green orange lea 47 ohms yellow violet black lea 1K 1 3300ppm Tempco resistor black 7 IC bag containing the following 11 parts 3ea BC550C NPN transistor 2ea BC560C PNP transistor 2ea CA3086 transistor array IC lea BF245 FET transistor lea LT1013 op amp lea THAT 340P transistor array lea SSM2220P PNP array SYNTHESIS TECHNOLOGY MOTM 485 ASSEMBLY 8 11 05 WWW SYNTHTECH COM C1 C2 C3 C10 C11 C12 C9 C6 C7 C8 C4 C5 R1 R6 R14 R28 R35 R33 R41 R42 R43 R46 R19 R20 R24 R50 R25 R45 R47 R49 R18 R21 R22 R17 R27 R29 R9 R13 R7 R8 R15 R32 R26 R30 R34 R37 R38 R44 R39 R40 R10 R12 R16 R23 R31 R36 R48 R11 mounts on Q1 see text Q3 Q4 Q9 Q2 Q6 Q7 Q10 Q8 U1 Q1 Q5 PAGE 2 7 Misc 1 bag containing the following 7 parts 2ea Axial ferrite beads plain gray things L1 L2 lea MTA 156 power connector JP1 lea SPDT toggle switch SW1 lea DPDT toggle switch SW2 lea 2K Bourns 3386P 202 trim pot TP1 lea 20K Bourns 3386P 203 trim pot TP2 J Knobs 3ea ALCO PKES90B 1 4 Jacks 6ea Switchcraft 112A 7 Pots 3ea containing the following either part will work 3ea 100K lin Spectrol 149 71104 148 71104 VR1 3 7 Front panel 7 Printed Circuit Board 7 Mounting bracket 7 Wire bag containing the following 10 wires lea long RG 174 coax JA 2ea short RG 174 coax J5 J6 lea 2 wire set 22ga white black long J3 lea 2 wire set 2
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