MOTM-490 User Manual
Contents
1. T 3eeus zooz v asnbnv v O6tW a soz ATA ST IDAN 06 WLOW eTatL zza LOO AT WLOW 8Ts 888 OST9L XL HLYOM LAOA nee 9299 ex AST JL SI ADOIONHOAL SISSHLNAS E z PED 2 EX MOOT sa D09924 WOT WOT THA vo AST 82 L5 E X 9ST XLW T MOOT SVIVNTI ZX T AST 4 ES Wa T ota t MOOT ASTE AST EAA ALIJAAA AZT AT La 3T vo LZA 9 MOOT STO LAZ E AST 6TH saa 4 S AST MOOT 209sod ec ZAA I m 9 09 MOOT Dru sa AST OTZZWSS 9 azz 089 089 otzewss A sca ou 7 L veo e 7 6 ao B T va o Nt AST j ag eta vo zT ASI A zr fuv HF 20sso8 20ssos KJ LISSSN so A s MOOT ale zea Tea 92u AO2. RC I m now just going to breeze through the math here so if you never had dealings with complex algebra you are truly blessed or in Marketing We can write the transfer function T in what s called rectangular coordinates as T jo T jo 7 Im To SYNTHESIS TECHNOLOGY PAGE 13 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM Where Re means the real part and Im means the imaginary part In filter design what we really want is the actual measurable magnitude of the output what you can see on an oscilloscope and what the phase shift is from input to output The magnitude of the output is given by the square root of the squares of the real plus imaginary parts r The phase in radians is given by 0 jo tan du ie ReT jo If you really want to know where the arctangent came from you have my pity Let s now figure out for the RC lowpass what the actual magnitude and phase equations are To make things simpler HA let s introduce a term a that is 1 RC Rewriting the transfer function we get PUES RC If we multiply both numerator and denominator by the conjugate of the denominator we then get l jola Im From this we get the real and imaginary parts as follows Jo 1 Im7 joy 1 a And hence Vout _ 1 Vin 1 SYNTHESIS TECHNOLOGY PAGE 14 MOTM 490 ASSEMBLY 7 25 02 WWW SY
3. 0258 Iforward 2 50 000 which is 258 nanoamps That is not much current at all As you can see the audio signals and the control currents flow up the ladder in the schematic There are 4 capacitors and 8 resistors that make up the 4 pole filter stage no I m not going to discuss what a pole is either What happens when we get to the very top of the ladder The input to the ladder was a differential current and the output is a differential voltage We need some sort of differential to single converter This is exactly what U1A is doing It is V6 of a dual OTA used as a differential voltage to current converter The resistor R2 to ground sets the voltage gain as the output of an is a current The OTA has an internal buffer called BI and BO for Buffer In Out and this is used as remarkably a buffer Since the buffer has DC offset capacitor C12 AC couples this to the resonance section Since the output is 180 degrees out of phase with the input we can make an oscillator by feeding a portion of the output back into the input This is the function of the other half of the OTA U1B It acts as a simple feeding the output back into the base of Q2B SYNTHESIS TECHNOLOGY PAGE 17 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM Now there is subtle thing going on here that you need to be aware of if you send me email or call about this you will be publicly humiliated See capacitor
4. 10 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 Solder coax in J6 to the OUT jack The inner wire goes to the LEFT lug and the braid goes to the BEVELED lug The TOP lug is not connected Solder the Red Black wire in J4 to the FM IN jack Red wire to Left Black wire to Beveled Solder the Red Black wire in J5 to the 1V Oct jack this will cross over the previous red black wire Red wire to Left Black wire to Beveled Solder the long coax in J3 to the IN 3 jack The inner wire goes to Left the braid goes into the Beveled hole along with the resistor wire scrap Solder both filling up the lug hole completely with solder Trim off any protruding resistor wire Solder the long coax in J2 to the IN 2 jack The inner wire goes to Left the braid goes into the Beveled hole along with the resistor wire scrap Solder both filling up the lug hole completely with solder Trim off any protruding resistor wire Solder the coax in J1 to the IN 1 jack The inner wire goes to Left the braid goes into the Beveled hole along with the resistor wire scrap Solder both filling up the lug hole completely with solder Trim off any protruding resistor wire SYNTHESIS TECHNOLOGY PAGE 11 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM Use the remaining ty wrap to gather up the wires and bundle to
5. g IC bag containing the following 13 parts 2ea SSM2210 NPN matched pair 7ea BC550C NPN transistor 2ea BC560C PNP transistor lea 1N4148 diode lea NE5517 dual OTA SYNTHESIS TECHNOLOGY MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM R6 R15 R18 R27 R33 R5 R23 R32 R11 R12 R13 R3 R28 R31 R4 R26 R14 R19 R20 R21 R24 R25 R1 R2 R7 R8 R9 R10 R22 R29 see text for possible mod R30 Q1 Q2 Q3 Q5 Q10 Q4 Q11 D1 U1 PAGE 2 g Misc 1 bag containing the following 5 parts 2ea Axial ferrite beads plain gray things L1 L2 lea MTA 156 power connector JP1 lea trimmer 100K Bourns 3386P TP1 lea trimmer 20K Bourns 3386P TP2 Knobs 3ea ALCO PKES90B1 4 Jacks Switchcraft 112A g Pots 3ea containing the following 3ea 100K cermet Spectrol 149 VR1 g Front panel Mounting bracket g Wire bag containing the following 7 wires RG 174 coax 4 12 inches RG 174 coax 7 inches 2ea 2 wire set 22ga 3 inches red black lea Power Cable 20 g 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 4ea 6 KEPS nuts 5ea small tie wraps Organic Solder No clean Solder PC Board MOTM 490 SYNTHESIS TECHNOLOGY PAGE 3 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM GENERAL INFORMATION Thank you for
6. left of R27 Locate the 100K 146 resistors 3 and solder into R5 by C13 R23 by TP2 and R32 by C21 Locate the 10K resistors 3 and solder into R11 R13 in a row beside Q2 Locate the 15K resistors 3 and solder into R3 by J6 R28 above Q11 and R31 also by J6 Locate the 22K resistors 2 and solder into R4 by C13 and R26 below C12 PART 2 BOARD WASH 1 o 0 o 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 Shake the board a couple of times blot dry with an old towel the leads will frazzle a good towel Let dry about 15 minutes SYNTHESIS TECHNOLOGY PAGE 6 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM PART 3 Complete the Resistors Locate the 2K7 resistors 2 and solder into R14 above Q1 and R19 by C14 Locate the 360 ohm resistors 2 and solder into R20 above Q2 and R21 by C15 Locate the 680 ohm resistors 2 and solder into R24 and R25 right of U1 Locate the 470K resistor and solder into R1 by J5 Locate the 270K resistor and solder into R2 below R1 Locate the 12K resistor and solder into R7 by Q3 Locate the 200K resistor and solder into R8 by Q10 Locate the 3K resistor and solder into R9 below R8 Locate the 680K resistor and solder into R10 above R9 L
7. with the shafts pointing away from the pc board Solder the pots into VR1 VR2 and VR3 Locate the trimpots The value is stamped on the side in black ink The 100K trimpot is marked 104 and goes into TP1 The 20K trimpot is marked 203 and goes into TP2 g Locate the 4 pieces of RG 174 black coax cable Again note that one end has longer wires stripped than the other Look at the 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 longer piece of coax solders into J3 The shorted coax solder into J1 J2 and J6 SYNTHESIS TECHNOLOGY PAGE 9 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM Solder each coax cable into the holes Attach a tie wrap to secure 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 2 red black twisted pairs They go into J4 and J5 Solder the red wire into the TOP 1 hole and the black wire into the BOTTOM 2 hole YOU ARE NOW FINISHED WITH THE PC BOARD WORK BREAK TIME PART 8 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
8. C20 a 1mfd non polar That is forming a high pass filter with R20 and R21 So This prevents the filter from oscillating at low cutoff frequencies Why is it done this way Because that s the way Dr Bob designed the Moog 904A which is the model we are using The filter s self oscillation will die off at around 140Hz It s a critical part of that Moog sound PRELIMINARY CHECK OUT amp CALIBRATION The first thing to check is to see if the filter self resonates Center both trimpots to mid scale Set RES to 8 and slowly turn the FREQ knob from 0 to 10 There should be a sine wave at the OUT jack slowly building in amplitude past 140Hz and extending up to over 18KHz If you do not get a sine wave output refer to the Troubleshooting Section SETTING THE RANGE TRIMMER For the widest useable frequency span set RES to 9 set FREQ to 5 at the 12 o clock position and adjust the RANGE trimmer up by the power connector for approximately 440Hz at the output This is not critical at all just get it close You can use a scope a frequency counter or compare it to A440 the A above middle C on another synth The output should then be around 16KHz at 10 tick mark on FREQ SETTING THE 1V OCT TRIMMER Apply a known good 1V Oct source into the 1V OCT jack Start with the trimmer in the middle of rotation With RES at 9 play low A 220Hz and set FREQ to be close as you can Play A440 and slowly turn the trimmer to matc
9. NOTE all references to part orientation is from the REAR of the panel Locate the 6 Switchcraft jacks Notice that from the rear there is a beveled corner This corner is ALWAYS CONNECTED TO GROUND USUALLY WITH THE BRAIDED CONDUCTOR Each jack has a flat washer a lockwasher and a 12 hex nut 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 Remember those 2 resistor leads you saved They solder on the 2 CV jacks 1V OCT and FM IN The wire goes from the TOP lug to the BEVELED lug However since the BEVELED lug is also the ground connection for the coax DO NOT solder that end just yet Solder the TOP lug adding enough solder so that the lug hole is completely filled Leave the other wire end inserted into the BEVELLED hole You are now ready to attach the pc board to the bracket and then wire up to the panel PART 9 ATTACH PC BOARD TO BRACKET In the HARDWARE bag locate 4 6 32 x 3 8 screws 4ea 6 KEPS nuts and 4ea spacers Locate the mounting bracket The pc board attaches to the bracket with the 4 screws threading from the top of
10. changes From Ohm s law I V R This means if V is some constant voltage and we vary I we get a variable This virtual R is split between Q9 and Q10 making really 2R in parallel with C16 So Mr Smarty Pants what generates the T in the equation The control current is coming from Q3 Transistor Q4 is a buffer that sums up the FREQ pot voltage and the external CVs 1V Oct and FM The input voltages are greatly attenuated by R9 by about 45 1 C14 overdampens Q3 so it won t oscillate due to something called the Miller effect You may be wondering where the TEMPCO resistor is for Q3 there isn t one Why Because there isn t one on the original 904A either Yes the cutoff frequency will drift with temperature Isn t analog grand SYNTHESIS TECHNOLOGY PAGE 16 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM Now we can write an equation for one stage of a Moog ladder filter oc 2z 2Re C Where Fc is called the cutoff frequency where the amplitude is 0 707 of the input C is 1000pf in this design and Re is called the effective emitter resistance and is given by _ 25 8mv Iforward Where Iforward is 12 of the forward current flowing in the collector of Q3 it s V because of the differential split To duplicate a cutoff frequency of 1592Hz as in the previous example that requires Re to be 1 1 2z 2Fc C 2 2 1592 1000 or about 50K To simulate 50K resistance we need a current of
11. frequency increases more and more the impedance gets less and less The smaller the capacitance the higher the frequency needs to be to create a short where it s not a capacitor anymore Since this relation is inversely proportional we write the impedance of the capacitor as 1 jaC Now what in the world is this jo pronounced Jay Omega business First the easy part o This is called the radian representation of frequency For some unexplained reason maybe I was sleeping that day in trig class mathematicians like to SYNTHESIS TECHNOLOGY PAGE 12 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM measure angles in radians instead of degrees If you were sleeping circle has 360 degrees or 2x radians So imagine a second hand on a clock it sweeps 360 degrees or 2x radians per minute for a frequency 1 60Hz If it did it in say 1 second that s 1Hz So in 1 second we swept 2x radians So the astute can see then that 2 where f is the frequency in Hz Remember this is the simple part What about that j term The 5 is the symbol for the square root of 1 WHAT You can t take the square root of a negative number and if you did what does that have to do with a capacitor It has been my experience that at this point in EE 101 a full 1 4 of the class drops out and become Web designers It has to do with correctly calculating the phase response of the circuit By correctly calculating I mean h
12. 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 There are 2 types of resistors in the MOTM 490 kit standard 5 1 4W parts and 1 1 4W resistors with an extra color band The precision parts use a slightly different color coding scheme If you are unsure of a resistor s value use your trusty DVM to measure it Inserting the wrong resistor in the VCF kit will cause interesting behavior And it s very hard to find the error You will start by soldering in ALL of the resistors 7 Find the RESISTOR bag g Find the MOTM 490 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
13. the board with the white silkscreen the top side g 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 SYNTHESIS TECHNOLOGY PAGE 5 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM 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 A SMALL AMOUNT not a blob 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 This pc board has parts very close together It may not be clear where a certain resistor or capacitor is We will try to give you a hint for the hard to find parts NOTE you will need to save 2 of the resistor leads after you cut them Don t forget Locate the 1K resistors 7 and solder into R6 by C15 R15 R18 in a row left of Q7 R27 left of VR2 and R33
14. 10 6 g All of the transistors are correctly oriented and Q4 Q11 are BC560C parts not BC550C parts g The braided wire on the coax goes to the beveled side of the jacks g All electrolytic caps have the black stripes all facing the same direction up g No solder shorts or missing joints Do NOT blob solder onto the top side of the pc board If you still can not get the module to perform correctly please contact us by phone fax at 817 498 3782 or by email to synth1Gairmail net USE OF THE MOTM 490 VCF The MOTM 490 is easy to use There are 3 Audio inputs that are internally summed together Note that the circuit is set up such that you can plug 2 VCO outputs directly into any 2 of the IN jacks without clipping the filter However you cannot have 3 10V pk pk inputs or the filter will clip which may be just what you want Since there are no input attenuators you may want to use a MOTM 830 or MOTM 890 Mixer in between your VCOs and the 490 The 1V OCT and FM IN jacks can be DC control voltages or audio signals The panel pot FM attenuates the signal into FM IN jack The resonance on a Moog ladder is quite unique and distinctive First increasing RES will greatly reduce the overall signal level at the output Second you will detect that resonance setting will depend on the input audio level This is another quirk of this filter topology The resonance on the 490 is set up like a Moog 904A You will notic
15. HTECH COM g Locate the BC550C transistors They solder into Q3 and Q5 Q10 Note that Q3 is flat up against Q4 This is for a so so temperature compensation see the Theory of Operation for more details g Being careful NOT to solder the remaining component holes solder 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 pe board DO NOT SOLDER PADS FOR THE REMAINING COMPONENTS The via holes need a VERY SMALL AMOUNT of solder An example of a via hole is in between Q10 and C16 PART 6 FINAL BOARD WASH amp INSPECTION g Verify all the parts are in the correct locations Make sure all of the ICs are pointing the same direction as well as all of the transistors g Inspect the solder joints Any solder shorts Too much solder Missing joints g Wash the board under warm water Scrub gently Dry THIS IS A GOOD STOPPING PLACE TO REST OR PUT THE KIT AWAY UNTIL LATER 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 7 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 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
16. NTHTECH COM What does this mean Let s do an example and then move on to how the MOTM 490 mimics this simple RC filter CH Let s pick R 10K and C 0 01mfd The a term 1 RC becomes number 10 000 and since our brains think in Hz as opposed to radians per second w 2rf Plugging these numbers into the equation Let s make Vin 1 0 to make things simple Now we can use Excel or some other program to give us a table of values as we change frequencies Vout _ 1 Vin 1 2af 110 000 FREQ Hz Vout Phase 50 1 00 1 80 100 1 00 3 60 200 0 99 7 16 500 0 95 17 44 1000 0 85 32 15 1592 0 71 45 02 2500 0 54 57 53 5000 0 30 72 36 10000 0 16 80 97 20000 0 08 85 47 100000 0 02 89 10 Amazing after all of that math we actually get useful data that can be measured This chart shows several key points a we have indeed made a lowpass filter As the frequency goes up the output goes down b the phase goes from essentially 0 shift at DC to 90 degrees What does the mean It means if you look at the input waveform and the output waveform at the same time on a scope the output waveform is lagging behind the input You may have heard the term lead or lag filter this refers to the phase of the output with respect to the input the frequency 1592Hz is special Why Two reasons first the phase shift is 45 degrees Second the amplitude is 0 7071 which happens to be 1 divided by the squar
17. T NOOT LTA 3T WOT eta EEA Dossoa KJ 20ssogu KJ NI A Lo TL AOT MST AST ea TIO 3T M 9TA jl Ji T TONI ASI 2 o 9 Dossoa KJ Dossoa KJ MOT 56 or azz 8 908 m NOOT tty TB LNO Jl NI s v M z 1a 7 aTa vo MOLE OIZZWSS 9 zu r T8Y ND se orzzwss KJ L T 8 LISSHN t MOLD 5 It an LAZ z AST AST PTA E 62 AST e Zz SYNTHESIS TECHNOLOGY 557 MOTM 490 uVCF REV A WWW SYNTHTECH COM 0 JS E durer
18. aving a mathematical representation that matches up with real world observed results The proper term for this is that the impedance of the capacitor sometimes called the reactance by purists has both real AND imaginary parts also referred to as a complex impedance It has been my experience that at this point in EE 101 of the remaining class drops out and become Network Administrators The word imaginary is probably the single most STUPID term in all mathematics because normal people ie non math majors immediately relate imaginary to you just made that up or it doesn t exist What it means in our electronics world is that the value of the impedance depends on an AC part and a DC part For example a resistor has the same measured value if it has DC voltage or AC voltage flowing through it This is all real and no imaginary The imaginary part is the part that changes with frequency So and this is the freaky stuff a capacitor has no real part it only has an imaginary part Remember at DC a capacitor is an open circuit meaning infinite impedance By now you may see that the term impedance means a resistance that changes with frequency and you would know more than middle management at electronics companies If you are still reading this let s rewrite the simple RC filter transfer equation in terms of the actual capacitor behavior Vout _ 1 1 Vin RC jo
19. e root of 2 SO WHAT This gentle reader is the infamous filter cutoff frequency You probably are used to seeing the cutoff frequency expressed in dB or 20log 7071 3dB What is 6dB figure That is the point that the output is 12 of the input or in decibels 20log 0 5 6dB SYNTHESIS TECHNOLOGY PAGE 15 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM d the 1592Hz number is 1 2xRC Now that we have beat that to death and then some let s see how Dr Bob came up with his design We will analyze the first filter section The filter has 4 cascaded filters of 6dB Oct each for a total of 24dB Oct Since the phase shift is 45 degrees stage the 4 stages give 180 degrees of total phase shift from input to output inverting but this is turn allows the filter to self resonate more on this later The ladder filter is a differential signal path The input audio is split into positive and negative halves fed through the filter then combined at the end back into a single ended signal Why The reason is noise reduction The VCF operates at quite low signal levels around 50mv and since transistors are cheap this is a clever way to cut the noise in half The audio is summed through passive mixer R5 and R11 R12 R13 then AC coupled through C13 into the splitter network A passive mixer is used to mimic the loading effects of the 904A filter explained later The full level input is divided by R4 and R20 to about 1 62th of the
20. e that the panel knob is very touchy and that the filter will break into self oscillation when the RES pot is past 6 or so If you want to make resonance start later in the pot s rotation say at the 9 tick increase R29 set now at 39K Try a value of 51K to 68K The output of the MOTM 490 is about 6V pk pk with a single 10V pk pk input The original Moog 904A only has a 1V pk pk output This is to reduce the output noise SYNTHESIS TECHNOLOGY PAGE 19 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM Please note that the MOTM 490 is NOT a MiniMoog filter and will NOT sound like MiniMoog The Mini s sound is a combination of VCF and interaction along with certain VCO waveshaping However the MOTM 490 is very close to the sound of the original Moog modular filter SYNTHESIS TECHNOLOGY PAGE 20 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM SPECIFICATIONS MOTM 490 Voltage Controlled FIlter Audio input levels Waveform output level Input impedance Frequency Range CONTROLS FREQ RES FM GENERAL Power Supply Size Depth behind panel SYNTHESIS TECHNOLOGY MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM 5V to 5V 6V pk pk nom 10K ohms nom 150Hz to 22Khz in self resonance mode sets initial cutoff frequency sets resonance amount attenuates the CV applied to FM jack 15VDC 10 ma 15VDC 10 ma 1U x 5U 1 72 x 8 72 44mm x 221 5mm 4 3 inches 109mm PAGE 21
21. gether 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 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 off ket so ree eee CONGRATULATIONS YOU HAVE FINISHED BUILDING THE MOTM 490 roe reete eee that s left to do is test it But before we do please read the following Theory of Operation THEORY OF OPERATION The MOTM 490 is based on the Moog 904A lowpass filter This filter uses a unique arrangement of transistors and capacitors to form a 24dB Oct lowpass You may have heard this referred to as a ladder filter this is because the schematic drawing looks kind of like the rungs of a ladder Let s first examine a simple RC lowpass filter as shown Vin This filter section is analyzed as you would a resistor divider If capacitor C was a resistor the transfer function Vout Vin is just CR C However the impedance of a capacitor is a function of the frequency of the signal going through it A capacitor is open at DC and as the
22. h You will have to go back and forth several times to get it accurate but this circuit is in no way as precise as a VCO or the other VCFs Remember the filter stops oscillating close to low C around 125Hz and will not track very well above 1Khz Concentrate on 220Hz 440Hz 880Hz range INCREASING RESONANCE RANGE If you want a wider resonance range than the original Moog 904A filter change R29 from 39K to either 56K or 62K TROUBLESHOOTING If your MOTM 490 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 C The 3 DIP packages Q1 Q2 U1 all point to the left with a DVM check the following DC voltages This assumes the power supply is SYNTHESIS TECHNOLOGY PAGE 18 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM 15 0 and there are no external CV inputs plugged in a The circular pad on R6 1K changes from close to 3 85V to 1 85V as FREQ moves from 0 to 10 These voltages will vary slightly depending the RANGE trimmer but should be close to these b The circular pad of R28 15K changes from 13 7 to about 0 6 RES is moved from 0 to 10 c Pins 3 and 4 of U1 are close to 10 3V d One side of R19 2K7 is ground and the other side is near 4 3V e One side of R14 2K7 is 15V and the other is near
23. ocate the 127K 146 resistor and solder into R22 by TP2 Locate the 39K resistor and solder into R29 below C12 Locate the 16K resistor and solder into R30 by C20 This completes the resistors Check your solder joints and wash the board again Let dry 15 minutes Take a little break PART 4 CAPACITORS Locate the CAPACITOR bag Note that the capacitors are numbered starting with C7 C1 C6 are not there it s a long story Locate the 22pf ceramic axial cap marked 22P or 220 Solder into C10 by U1 Locate the 0 1mf axial ceramic caps attached to the 2 pieces of removable tape and solder into C9 and C11 top bottom of U1 Locate the 100nf stacked metal film caps 4 marked 104 Solder into C16 C19 above SYNTHESIS TECHNOLOGY PAGE 7 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM Locate the 220nf stacked metal film marked 224 Solder into C12 below TP2 Locate the 1nf 0 001mf yellow box cap and solder into C14 by Q9 Locate the 1md 50V non polar electrolytic caps 2 The lead orientation is not important it s a non polar cap after all Solder into C13 by C8 and C20 above Q1 Locate the 10 electrolytics 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 C7 C8 and C21 with the stripe away from the pad on the board Solder the 220mfd electrolytic cap into C15 again ob
24. original amplitude and sent to matched transistors Q2A and Q2B Resistors R20 and R21 are equal so that equal currents flow in Q2A and Q2B this is why they need to be matched so that over temperature the currents are equal Since the emitters are tied together and the bases receive the same input we have formed a differential pair I could beat this to death as well but you re on your own for that Now turn your attention to the string of resistors R14 R19 These resistors form a voltage divider chain as the top resistor R14 is tied to 15V and the bottom resistor R19 is tied to ground Closely examine that each pair of transistor bases is tied to points along the divider chain Why is this needed The reason is that each stage above the other has to be at least 1 diode drop above in potential at the base emitter junction to be biased on The actual voltage is not a factor at all it just has to be some positive voltage For analysis these resistors can be ignored completely The first stage of the filter is actually C16 and the 2 transistors Q9 and Q10 Capacitor C16 is obviously the in our equations but where is R That s a good question and what makes the Moog ladder unique it was patented in 1967 and prevented mostly all other companies from duplicating it for 17 years afterwards The R is the change in emitter current in 99 910 as the voltage difference from base to emitter
25. purchasing the MOTM 490 Micro Voltage Controlled Filter 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 The VCF kit contains many different resistors and special parts that require very accurate soldering skills 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 490 Soldering iron 50W max power Needle nose or chain nose pliers Diagonal cutters Allen key set for securing the knobs 1 16 or 1 58mm 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 Small flat screwdriver for adjusting the trimmers Fingernail brush for washing off the organic flux Old towel for blotting dry pc board HE 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
26. serving proper polarity Check to be sure all 4 electrolytic caps have their stripes facing the SAME WAY Wash the board again gently scrubbing both sides Use ONLY warm water PART 5 MISC and IC STUFF Almost done with the parts on the pc board This will finish up the soldering with the organic flux o 0 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 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 2ea SSM2210s they look like ICs Solder into Q1 and Q2 Carefully orient the part such that the notch in the top of the package matches the silkscreen Locate the NE5517 OTA Solder into U1 noticing that it points in the same direction as Q1 and Q2 If you are not sure please CALL OR EMAIL FIRST Locate diode 1N4148 Solder into D1 next to VR2 making sure the stripe on the diode matches the stripe on the silkscreen stripe to the left Locate the 2ea BC560C transistors Solder into Q4 and Q11 Match the flat side of the transistors to the flat indication on the silkscreen SYNTHESIS TECHNOLOGY PAGE 8 MOTM 490 ASSEMBLY 7 25 02 WWW SYNT
27. synthesis technology MOTM 490 Micro Voltage Controlled Filter Assembly Instructions amp Owner s Manual Synthesis Technology 6625 Quail Ridge Dr Fort Worth TX 76180 817 498 3782 www synthtech com Aug 22 2005 MOTM 490 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 g Capacitor bag containing the following 15 parts C1 C6 not used 3ea 10mf 50V Electrolytic lea 220mf 10V Electrolytic 2 1mfd 50V non polar Electrolytic lea 22pf marked 220 ceramic axial lea 220nf film reddish brown marked 224 cap lea 1nf yellow box cap 4ea 100nf film reddish brown marked 104 cap 2ea 0 1mfd marked 104 ceramic axial C7 C8 C21 C15 C13 C20 C10 C12 C14 C16 C19 C9 C11 g Resistor bag containing the following 33 parts 5 unless noted 7ea 1K brown black red 3ea 100K 1 brown black black orange 3ea 10K brown black orange 3ea 15K brown green orange 2ea 22K red red orange 2ea 2K7 red violet red 2ea 3600 orange blue brown 2ea 6800 blue gray brown lea 470K yellow violet yellow lea 270K red violet yellow lea 12K brown red orange lea 200K red black yellow lea 3K orange black red lea 680K blue gray yellow lea 127K 1 brown red violet orange lea 39K orange white orange lea 16K brown blue orange
28. the board through the spacers through the bracket and then out the bottom of the bracket NOTE the bracket may have a protective plastic covering If so remove the covering by carefully peeling it away from the metal The 6 KEPS nut attaches on the bottom of the bracket Note the bracket has 3 large holes on the flange where the 3 pots stick out The first step SYNTHESIS TECHNOLOGY PAGE 10 MOTM 490 ASSEMBLY 7 25 02 WWW SYNTHTECH COM is to attach a hex nut without the washer and outer hex nut to each pot Tighten each nut by hand all the way until it touches the face of the pot Then loosen the nut one fourth of a turn Attach the pc board to the bracket You will have to angle the pc board slightly as you insert the 3 pots through the 3 large holes on the flange Place the 4 spacers over the 4 holes and thread the screws in from the TOP side 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 Slide the pcb ALL THE WAY TO THE RIGHT AS FAR AS IT WILL GO so that the 9 pot nuts are all pressing against the flange By hand put hex nuts on the outside threads of VR1 and to keep the pc board in place Now tighten the 4 nuts on the bracket The pcb and bracket should be secure with the pc board snugly against the flange Slide the 3 pots through the 3 holes in the panel add the 3 washers and tighten the 3 outer hex nuts PART
29. the instruction Each instruction has a check box J next to it After you complete the instruction check the box This way you can keep track of where you are in the process VERY IMPORTANT PLEASE READ It is critical that you follow the steps exactly in order for proper operation This kit contains expensive hard to find parts Please read ALL of an instruction before proceeding 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 490 ASSEMBLY 7 25 02 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 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
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