Jupiter 6 Waveshaper
- At March 28, 2022
- By amsynths
- In Oscilliator
0
Introduction The Roland Jupiter 6 (and MKS-80) use a custom hybrid chip (EHM-S226W83S ) for transforming the CEM3340 oscillator waveforms to a consistent level of 5v centered around 0V (-2,5V to +2.5V). The CEM3340 creates waveforms that are at different levels (Pulse 0 to +12V, Triangle 0 to +5V, Sawtooth 0 to +10V) which need level shifting for mixing into the VCF. This is implemented by a mixture of SMD resistors and transistors.
The chip also contains a transistor based sync circuit, as Roland chose not to use the inbuilt CEM3340 sync (weak and strong), possibly because they wanted to control the sync on/off with a +5V programmable signal from the micro-controller and didn’t want use an analog switch.
Roland took this approach to reduce the footprint of the waveform translation to a minimum using a 12-pin SIP package. This enabled the Jupiter 6 PCB’s to be more compact than the Jupiter 8. An alternative approach is to use resistors and Op Amps but this is 5x the PCB size in the days before SMD components could be used.
Pin Out The EHM-S226W83S pin out can be easily determined from the schematic in the Jupiter 6 Service Manual:
- +15V
- -15V
- Pulse Output
- Pulse Input
- Sync Input from second VCO sawtooth
- Sync ON/OFF from microcontroller
- Sync Output to CEM3340
- Triangle Input
- Sawtooth Input
- Triangle Output
- Sawtooth Output
- GND
How it works There are four separate circuits; one for each waveform and one for the sync. The triangle wave generated by the CEM3340 is the 0V to +5V and is level shifted to -2.5V and +2.5V by a PNP transistor (Q1) and a resistor network (R2, R5, R6).
The 0 to +10V sawtooth wave is reduced and shifted to -2.5V to +2.5V using three resistors (R1, R3, R4).
The 0 to +12V pulse wave is reduced and shifted to -2.5V to +2.5V using a more complex circuit of six resistors, an external capacitor and a NPN transistor (R13 – R17 and Q4.). The SH-101 service manual uses a similar circuit without the final level shifting. So it is easy to determine what most of the values are without measurement.
The sync circuit is also more complex. The sawtooth wave from the source VCO is switched off by grounding the input to a NPN transistors (Q2), or going high to enable the Sync. The sawtooth is then pulse shaped by a NPN transistor, 2 diodes, a capacitor and 3 resistors, The narrow pulse resets the VCO integrator via its capacitor (Q2, Q3, C1, R7-R12), creating hard sync.
Tear Down For my Jupiter 6 VCO clone I wanted to replicate the EHM-S226W83S circuit, along with the RA3A resistor array connected to the CEM3340. The array resistor values are easy to determine from the schematics and values in the MKS-80 service manual. The Jupiter 6 makes use of all 6 resistors in the array, whilst the MKS-80 only uses five of them.
The EHM-S226W83S was harder to replicate, as although the schematics are in the manual, the values are not printed and are a mystery. I bought one in April 2018 and removed the plastic encapsulation with acetone (took 2 days of soaking), so that I could then measure the various printed on resistors using a multi meter, some components had to be desoldered to be measured.
Prototyping Once the values had been obtained the full VCO schematics were laid out using Eagle CAD. Roland has implemented the VCO with some changes to the original CEM3340 datasheet which have also been captured.
A prototype PCB with THD components was ordered in April 2022. The AMSynths Jupiter 6 VCO will operate with 12V power rails, so the resistor values will need changing anyway, as the original uses 15V power rails. I plan to keep with THD components rather than building SMD replicas.
Moog Modular Routing
- At December 20, 2021
- By amsynths
- In Filter, Mixer, Oscilliator
3
Introduction The Moog Modular system has internal signal busses, which from 1968 onwards were controlled by utility modules, both full height like the 992 and 993, and half height like the CP3. These modules are very useful as they replaced external patch cables, provide switches for routing and potentiometers for mixing. The original control panel range of modules was reworked in the System 15, 35 and 55 as CPxA modules.
The Behringer System 55 includes some of these utility modules (992, CP3A-M and CPA-O) but there is no internal bus structure, and some Moog modules have not been replicated. The objective with my “Big Moog” is to get as close to the Moog Modular workflow as possible, so I have designed a set of four AMSynths Eurorack modules, and an optional Bus Board, to fill these gaps and provide the much needed internal bus structure.
CV & Gate Control The original Moog modular has a set of internal busses and external “trunks” that are pre-wired between the back of all the modules using edge connectors, to reduce the amount of patch cables needed. In a System 55 there are three sets of CV signal (CV1, CV2, CV3) and three sets of S-Triggers (ST1, ST2, ST3), They are typically connected to external keyboards, ribbon controller or a 960 sequencer.
I have replicated the Moog bus structure with a 6-pin cable that runs behind the modules, with IDC sockets on the new AMSynths utility modules. There are three sets of CV signal (CV1, CV2, CV3) and three sets of V-Triggers (VT1, VT2, VT3) which can externally patched into from Eurorack keyboards and sequencers (including the 960). The conversion of V to S-trigger for the Behringer 911 modules is done within the AMSynths AM-CP1 or AM-CP4 modules which are used to drive the bus from external signal sources. The receiving modules are the AMSynths AM-CP3 and AM992, which are used to connect VCO’s and VCF’s to the CV signals (CV1, CV2,CV3).
Trunk Lines A Moog Modular system has up to eight “trunk lines” which are simply wires from a front panel module (e.g. CP2, CP3, CP3A, CP35) to rear mounted 6.35mm mono jack sockets. They are not universally popular with owners but they enable connections to and from out board equipment (FX, Tape Recorders). They are usually marked as TRUNK LINES on the panels and are sometimes connected to multiples.
This feature was obviously left out of the Behringer CP3A-M (which is actually a replica of the earlier CP3 with transistors), as Eurorack has no rear jack sockets and customers are used to patching everything into the front of modular synths. The AMSynths AM-CP3 module does have “trunk line” capability, with two pairs of front panel jack sockets available via internal connectors to be wired to rear mounted 6.35mm jack sockets.
AM-990 This 4HP module is based on the Moog CP1 console panel, which provides front panel jack sockets connected into the Moog bus for three CV signals and three S-Triggers. The AM990 does the same job, with six jack sockets with LED indicators for V-trigger On. A 6-pin IDC socket on the back of the PCB enables connection with AMSynths utility modules, using a 6 way ribbon cable or via the AM900 BUS BOARD PCB.
Only one AM990 is needed in a Moog Modular Eurorack system, to bring the signals onto the 6-way IDC bus. If interconnection is needed with additional cabinets I recommend using a rear mounted 6-pin DIN socket and cable set, wired via a ribbon cable to the IDC bus on the AM900 BUS BOARD. The AMSynths utility modules take the three sets of CV and V-Trigger signals and apply them to VCO banks (AM996), VCF banks (AM992, AM-CP4) and VCA/Envelope Generator banks (AM993, AM-CP4).
AM-CP3 This 20HP module is a recreation of the mixer section of the Moog CP3 console panel, which is intended as a four channel mixer for VCO outputs. The oscillator CV input routing is provided by the AM992 module. The original CP3 was used in the Moog Modular I,II,III and then upgraded to the op amp based CP3A in the 15, 35 and 55 models.
The left hand side of the panel provides accurate CV selection and mixing for a bank of AM901A/B’s or Behringer 921A/B’s. The first three jack socket inputs are normalised to the internal IDC 6-pin bus whilst the fourth CV input goes via an attenuator potentiometer and is mixed into the other threes signals using a precision Op Amp. All four inputs have slide switches for selecting on/off with LED indication. The output of the mix is available as an internal connection for AM901A VCO Controllers and as a jack socket for Behringer 921A VCO Controllers.
The AM-CP3 has a faithful reproduction of the Moog transistor based four channel mixer, with input jack sockets at the top of the panel. The mixer has a master gain potentiometer and dual normal and inverted outputs. The click filter from the original has been retained, with an on/off slide switch and amber LED indication.
The front panel also has provision for Moog style “trunk lines” with two pairs of jack sockets, which can be connected from the back of the module to two rear facing 6.35mm jack sockets in the cabinet which the AM-CP3 is mounted in. The levels of the outgoing and incoming signals can be adjusted with potentiometers, which use the CP3A Op Amp circuit. There are also four jack sockets arranged as Multiples.
AM-CP4 This 16HP module is recreation of the Moog CP4 console panel with filter CV routing, and trigger & envelope control for two sets of adapted Behringer 911 and 902 modules. The CP4 was used in Moog 1C and IIP, and the nearly identical CP4A was used in the Moog 35. This handy module reduces external patching by providing CV and trigger routing via switches. with LED indicators. The AMSynths version contains dual V to S-Trigger converters, which are Eurorack compatible.
The left hand side of the panel provides filter CV routing with four independent inputs that can be switched on or off (red LED indication). The fourth input has an attenuator potentiometer and a green LED indicator. All inputs are mixed together at unity gain using a precision Op Amp and can be used to drive VCO’s as well as filters. The output CV can be manually patched into the CV input of a 904A or 904B filter module, to control frequency cutoff. The output is also available internally for patching to an AMSynths 904 or 904B filter module, which have internal inputs.
The right hand side of the panel provides trigger selection from two V-trigger inputs, which are converted to S-Triggers and internally patched to two 911 modules. At the top of the panel there are two toggle switches (red LED indication), to select the trigger signal inputs. The LED’s indicates the presence of a gate signal when in the switch is in the on position.
The left hand column of switches (orange LED indication) route the selected S-trigger signals to two modified Behringer 911 modules (LEFT and RIGHT). The right hand switches (with green LED’s) connect the DC control voltages from the 911’s to their respective 902 Voltage Controlled Amplifiers (LEFT and RIGHT).
AM992 This 8HP module replicates the Moog original with four front panel CV inputs, selected by slide switches with LED indicators. The first three inputs are connected to an internal IDC 6-pin bus and normalised to the front panel jack sockets. The fourth CV input goes via an attenuator potentiometer and is mixed into the other three signals using a precision Op Amp. The original Moog used a passive mix approach. The AM992 has replaced the Behringer 992 modules in my “Big Moog”.
AM993 This 8HP module replicates the Moog original with eight slide switches and indicator LED’s. It is designed to work with a set of modified Behringer 911, 911A and 902 modules to provide signal selection and routing. An AMSynths AM997 provides the V-trigger to S-trigger conversion and is easily internally patched into the AM993. Daughter boards are provided to enable the supplied internal cable harness to be connected into the Behringer 911, 911A and 902 modules.
The Moog 993 was used in both the IIIP and System 55 to provide routing for a set of 3 VCA’s and Envelope Generators. In smaller system the Moog CP4 provides routing for two set of VCA’s and Envelope Generators and is replicated by the AM-CP4.
AM996 This 8HP module replicates the CV mixing section of the Moog CP3/CP3A with four front panel CV inputs, selected by slide switches with LED indicators. The first three inputs connected to an internal IDC 6-pin bus and normalised to the front panel jack sockets. The fourth CV input goes via an attenuator potentiometer and is mixed into the other threes signals using a precision Op Amp. The original Moog used a passive mix approach.
The AM996 has replaced the Behringer CP3A-O modules in my “Big Moog” and complements the Behringer CP3A-M modules.
Typical System Setups A smaller replica Moog modular will be based around one or two oscillator banks, a single filter and a pair of 902/911’s. The AM-CP4 is an ideal companion for this setup along with a AM-CP3. A larger system with 3 or more oscillator banks, more filters and three 902/911’s deserves multiple AM-CP3’s with both AM992 and AM993 modules. The AM-CP1 enables the bus to be expanded across multiple cabinets.
Availability This range of four new AMSynths utility modules (and internal AM900 BUS BOARD PCB, are available from our webstore, and the AMSynths 904A, 904B and 904C will be launched in 2022.
Moog 901A/B VCO – Part I
- At December 07, 2021
- By amsynths
- In Oscilliator
1
Overview In December 2021 one of my customers asked me if I could build the 901A/B VCO’s as an AMSynths product. In the past I had rejected the idea as they are relatively unstable and I cant get anywhere close to a Behringer 921A/B price point. However I have a small stock of CA3019 diode array chips (and they are still available new), and there is space in my “Big Moog” to fit a set of 901A/B/B/B, so let’s have a go! I will also add the rare 901C module which creates a LFO from a 901B.
The early 901’s used diodes whilst the later versions used enclosed diode array chips. The stability issue is caused by the uncompensated exponential converter, which was never corrected (MOS-LAB have produced 901 VCO’s with a modern expo). The limited pitch range is caused by using a unijunction transistor as the sawtooth core of the module, 3 octaves of reasonable scaling appears the limit. I will be measuring this once my design is completed.
Research and Design The 901A/B went through many schematic changes in its life to make it more reliable/stable, so I will base my replica on the later 1970 version, to hopefully capture the best ideas from Bob Moog. This later version is the one in Klaus Schulze’s 1969 IIIP “Big Moog”. The modules have been successfully cloned by various 5U/MU manufacturers, and of course Moog have re-issued them as exact replicas. I haven’t seen one squeezed into EuroRack but the clones do seem relatively easy to get working.
My design criteria is to follow the original Moog schematics and use the same components, except where I cant find them or I can chose a better part. I will improve the power supply design as that is clearly what Bob was trying to achieve but without access to modern components in 1965! I have squeezed the designs into 8HP EuroRack modules with 3 PCB layers. No SMD components will be used (except possibly in the power supply), all THD, so I can solder them up myself.
Stable Power The power supplies of the original are -6V, -10V, +12V and +11.5V, with the 901A powering the tracking circuit of the 901B from its +12V supply. Precision power rails are very important to the front end of a VCO and I have used modern LDO regulators across the modules.
The -6V is generated by LM2991 LDO regulators from the EuroRack -12V supply and a LM2941 LDO is used to generate the +11.5V in the 901B. The +12V power supply is interconnected across the modules using the BUS connector – see discussion below. The -10V is delivered from a LM337 adjustable linear regulator.
Voltage Divider The 901A uses a resistor ladder to generate the initial frequency control voltages, with a set of 12 voltages from -5V to +6V. I have used a precision voltage source (REF02) to provide +5.00V, which is then buffered and inverted by a LT1013 Op Amp. VCO transposition is therefore limited to 5 rather than 6 octaves, but I doubt I would ever transpose up 6 octaves!
Semiconductors The transistors used in the later versions are 2N3392 and 2N4058, which I will use as they are easy to obtain. Switching to modern transistors with higher HFE needs changes in resistor values which I wish to avoid. The transistors need to be hand matched in some of the circuits, for example the exponential generator.
There are two selected transistors; the 2N2646 UJT at Q10 and the 2N4058 at Q7. These will be hand selected using the Moog calibration process of the correct voltage at Test Point A and the sine waveform symmetry. The 2N2646 is surprisingly easy to obtain new, 50 years after it was used in the Moog 901B’s!
The later 901A modules use two CA3019 diode array chips as temperature compensation (heated like the CA3046 in the Prodigy) and are an improvement over the early versions which had no temperature compensation at all. I have located a source of NOS CA3019 chips and ordered a batch. There are five 1N34A germanium diodes, which are fortunately still available. The unobtainable CL-1 regulator diode is replaced with a contemporary 1N458A, which is what Moog used in the Minimoog re-issue.
Resistors Whilst the original made use of carbon composite and carbon resistors, with precision resistors in the voltage ladder. I have used 1% metal resistors throughout, with 0.1% in the voltage ladder of the 901A and the tracking circuit in the 901B’s (to match the tracking across the three 901B’s).
Trimmers All trimmers have been upgraded from single turn in the Moog to multiturn Bourns. The later versions of the 901A have Scale, High and Low compensation trimmers, with the Mid compensation trimmer removed (as Moog did). I have added a Pulse Width trimmer to the 901A to get accurate pulse widths. The 901B has a Tracking trimmer, as well as Sawtooth offset, Triangle symmetry and Sine offset and symmetry.
Capacitors The timing capacitor values are critical to the octave matching of the 901B and have the following values;
- 10uF – low mode, not critical
- 200nF – use x2 100nF in parallel
- 100nF – use 100nF
- 50nF – use 2x 100nF in series
- 25nF – use 22nF and 3n3F in parallel
- 12nF – use 10nF and 2n2F in parallel
The first three octaves will be accurate and use hand matched Wima MKP2 polypropylene capacitors, although the upper two octaves will be out a bit, This can be corrected manually by the frequency pot and its unlikely I will be switching octaves live. These capacitors have 5mm lead spacing to get them to fit on my 901A panel PCB.
There is a second set of capacitors on the 2P6W rotary switch that go into the Triangle output (to help symmetry?). These were independent of the timing capacitors in early 901A’s but later versions only added a capacitor at low and a high range points, and reused the timing capacitors for the first 4 octaves.
The rest of the capacitors are either ceramic (pF) or polyester (nF).
Mechanical Design The 901A and 901B are each built from three PCB’s, with the circuit spread across all available board areas.
- POT PCB holds the Alps rotary switch
- JACKS PCB holds the jacks sockets and pots.
- MAIN PCB holds the power supplies and 10-pin connector.
Traditional 1P12W and 2P6W rotary switches are used for the frequency ranges, they require more space between the PCB and panel than my usual designs. This created the 3 layer PCB approach which also provides more room for the circuits. The 901A and three 901B’s are inter-connected using a 6-pin IDC cable, this replicates the Moog design but with a more direct dedicated wiring system.
901C Output Stage This is a rare Moog module with only 15 made on perf board in 1967. It provides complementary outputs (one normal, one inverted), for each of the four waveforms and further 2 inversion modes for the pulse waveform. The circuit is transistor based and provides waveform amplification as well, with a dual gang gain potentiometer.
The circuit requires a 3P6W rotary switch which is expensive and simply too big to fit in an 8HP module. I have used CMOS 4051 switches to replicate the functionality, with a modern Alps rotary switch controlling the six signal paths on three layers (input, output+, output-). 2N3392 and 2N4058 transistors are used, along with metal film resistors. There is one ceramic capacitor and single turn trimmer to adjust the initial gain.
Behringer 1004 VCO
- At October 17, 2021
- By amsynths
- In Oscilliator
0
Introduction One of the projects I worked with Behringer on during 2019/20 was the range of ARP 2500 clone modules, and the toughest modules to get right were the 1004 VCO and 1050 Mix Sequencer. I bought a Behringer 1004 module in September 2021 to see how well the VCO had turned out and to consider using it in a 5U replica of the ARP 1045 Voltage Controlled Voice.
The Behringer 1004 The Behringer VCO is a close replica of the original ARP schematics and the early prototypes proved impressive and worked first time! SMD components are a big advantage when it comes to VCO accuracy and stability, the B2600 VCO’s also proved precise (possibly too precise). High quality SMD Tempco resistors are used in the VCO cores.
The Behringer Manchester team completed the production version and added LDO regulators to the VCO to provide well regulated +/-11.34V voltage rails, which helps VCO stability. This is the same approach I use at AMSynths to create precision voltage rails for VCO circuits. There are five 4580 dual Op Amps, which are low noise and use BJT’s not JFETS at the input. They are a good replacement for the original 1339 and 301’s.
Timing Capacitors The original ARP 1004 used a set of seven timing capacitors in the VCO cores which are way too big to fit in a Eurorack module, and required manual selection. Behringer have chosen 4x polyester capacitors for the larger values (yellow and grey boxes in the photo) and SMD ceramics for the lower values. The low range capacitors are larger than the original; 1,150nF, compared with 710nF.
What is surprising is that the 3.45:1 ratio of capacitor value between the triangle and sawtooth cores in the original has not been retained, it is more like 10:1. This probably explains the extra frequency scale trimmer for the Triangle core (VR5).
Trimmers The B1004 has a total of six trimmers, five of which are blue multiturn versions and not accessible, and one single turn which is accessible by the customer from the rear of the PCB (VR9). The Quick Start manual provides no details about the trimmers, so here is what they do:
- VR10 OFFEST – adjust the overall frequency of the VCO
- VR11 SCALE – adjusts the overall volts per octave scale of the VCO
- VR12 SAW ADJUST – adjusts the shape of the sawtooth waveform
- VR5 TRI SCALE – adjust the volts per octave of the Triangle core
- VR6 TRI OFFSET – adjust the frequency of the Triangle core
- VR9 HI END ADJUST – adjust the scaling at higher frequencies (4-8KHz)
The additional triangle frequency trimmer is probably used to compensate for using standard capacitor values in the two cores and avoids capacitor selection.
Waveform Accuracy All the waveforms were accurate and calibrated correctly by the factory, except for the sawtooth. The SAW ADJUST trimmer adjusts the shape of this waveform, which is generated by the sawtooth VCO core. The triangle VCO core is separate and is used for generating sine and square/pulse waveforms. The sawtooth waveform that has not been calibrated will show a step in the waveform, but you are unlikely to hear the difference in the audio range. You will notice it when using the B1004 as a LFO.
My B1004 VCO showed exactly this issue and I removed the front panel and adjusted VR12 to create a linear sawtooth with a 10v p-t-p amplitude. I used an expensive oscilloscope to adjust the VCO but a free software plugin can be used, in fact I detected the issue using MScope running in Cubase. The pictures show the before and after, note also the corrected waveform amplitude.
The pulse waveform has a nice wide range from 5% to 95% (in fact 1.2ms of 25ms at 40Hz, which is spot on), and is exactly the same as the original ARP specification. The waveforms are all 10V peak-to-peak, again matching the original specification. The Triangle and Sine are bi-polar +/-5V whilst the Sawtooth , Square and Pulse are unipolar 0 to +10V.
The 1004 uses 100R Tempco resistors which are at R1, R2 and R19. These are also used in the Behringer 1047 filter but in series to give 200R.
Frequency Accuracy Once warmed up for 20-30 minutes the B1004 proved to be calibrated accurately at the factory, with a good set of results from C1 to C4;
- C1 is -4 cents
- C2 is 0 cents
- C3 is +1 cent
- C4 is +3 cents
- C5 is +7 cents
- C6 is +11 cents
The VCO was factory tuned to C1, with the Coarse control at minimum and the Fine control at midway. The VCO goes sharp above 1kHz and the calibration notes of the original ARP 1004 suggest only 1 cent inaccuracy at 1, 2 and 4kHz – this is a pretty demanding specification. There is a High Frequency trimmer (HI END ADJUST) that may help achieve better scaling above 1 kHz, in my own tests this does not do a lot.
Conclusion The Behringer 1004 VCO has worked out very well, good waveform shape accuracy and pitch stability over 5 octaves. I am building one into a 5U 1045 replica, more details in a future post.