Behringer 1050 Mix Sequencer

B1050 module

Introduction During 2019 I worked with Behringer to develop their range of 2500 modules, and one of the most challenging was the 1050 Mix Sequencer. This post describes how it works and how I designed it, ably assisted by the Behringer Manchester team to achieve production status in late 2021.

The original ARP design dates back to 1969 and uses a large number of TTL chips. They draw a lot of current (500mA in total) and only the original 7474 chips from 1970 will work in the circuit (which are impossible to source). I built my own 1050 replica in 2017 and knew of the various issues in trying to recreate it. The CMOS version consumes only 130mA of power, the majority to run the CMOS logic and LED’s.

B1050 rear

The Design Rather than using TTL logic or a micro-processor I decided to use CMOS logic. I have written PIC assembler code to replicate the 1050 but Behringer use ARM chips, so it was quicker to go down a hardware route. The CMOS logic requires an inversion of the negative logic signals used in the ARP design to positive logic. It all requires a lot of IC’s! Over 30.

The original analog clock circuit has been retained, and miniaturized into SMD, with a BJT pair replacing the unijunction transistor. There is a small user accessible trimmer to adjust the base frequency of the clock, this is factory set and should not need adjustment. The clock runs from 0.5Hz to 150Hz and  generates a square wave, which is divided down by a 4024 binary counter and drives the heart of the circuit a 4555 Dual Binary to 1-of-4 Decoder/Demultiplexer. The limitation of not using a UJT is that the lowest clock frequency of the original (1 pulse every 30 seconds) cannot be achieved.

The analog circuit consists of eight inputs which are controlled individually by level pots and mixed into either a 4:2 or 8; 1 configuration with two outputs. 4580 dual op amps are used for the mixing of the analog signals and 4053 analog switches used to select whether the signal is ON or OFF. A toggle switch controls the 4:2 or 8:1 setting and sets the DG403 DPDT analog switch to the correct mixing positions. I originally specified high quality analog switches in both locations, but Behringer have gone with the 4053 for the input channel switching (lower cost).

B1050 Module

The digital circuit is a bit more complex. The clock divides down via a 4024 binary counter (only 3 stages are needed) to create the 8 channel positions as BCD. The 4555 chip is used to create a sequence of 4:2 or 8:1, with the individual channels switched ON/OFF and latched by the dual 4013 flip flops. These eight signals are than combined (OR gates) with the 4555 outputs and the external 12-pin IDC inputs from a B1027.

An eight position switch selects the number of positions before the sequence is repeated. The manual incorrectly states the rotary switch as 9-way. The LED’s in the white button switches are controlled by these 8 channels with transistor drivers, and the red buttons enable a position/channel to be activated, typically used for auditioning.

The EXTERNAL GATE toggle switch digitally enables the 10 gate positions fed in via the 12-pin IDC socket from a B1027 sequencer. A 12 pin cable is used to avoid confusion with the 10-way power cable. The clock has a toggle switch to select ON/OFF, and a single position advance. An external advance jack socket also enable step advance.

B1050 Switch

There is a 3P3T toggle switch (especially sourced by Behringer) for selecting 8:1 or 4:2 for the analog mixing and the digital sequence, so all 3 combinations are possible. The original used an even bigger 4P3T switch but the CMOS logic does some of the switching. The analog path in the B1050 is not AC coupled, so it can be used for mixing bi-polar CV signals up to 20v peak to peak.

There are three tests points on the rear of the PCB:

  • TP1
  • TP2
  • TP3

Conclusion The CMOS version of the ARP 1050 has turned out really well, with a reliable module at a low price with acceptable power consumption. A microprocessor version would be cheaper to manufacture, use less power but require software development and debugging.

Integrated Circuits Used There are over 30 IC’s in the B1050; ranging from Op Amps to analog switches and CMOS logic. The majority of the chips are on the rear of the PCB with only two on the front. Here is a list of the chips used and the functions:

  • U1 HCF4053 – analog switch
  • U2 HEF4013 – dual flip flop
  • U3 DG403 – analog switch
  • U4 HEF4072 – dual 4 input OR
  • U5 HEF4013 – dual flip flop
  • U6 HEF4013 – dual flip flop
  • U7 CD4071 – quad 2 input OR
  • U8 MC14081 – quad 2 input AND
  • U10 CD4071 – quad 2 input OR
  • U11 RC4580 – dual op amp
  • U12 HEF4013 – dual flip flop
  • U13 HC4024 – 7-stage binary counter
  • U14 HEF4069 – hex inverter
  • U15 HEF4069 – hex inverter
  • U16 HEF4011 – quad 2 input NAND
  • U17 HEF4013 – dual flip flop
  • U18 CD4555 – dual binary to 1-of-4 decoder/demultiplexer
  • U19 CD4071 – quad 2 input OR
  • U20 HEF4013 – dual flip flop
  • U21 HEF4011 – quad 2 input NAND
  • U22 RC4580 – dual op amp
  • U23 – not used
  • U24 – not used
  • U25 HEF4071 – quad 2 input OR
  • U26 HEF4071 – quad 2 input OR
  • U27 – Dual NPN transistor (LED driver)
  • U28- Dual NPN transistor (LED driver)
  • U29 – Dual NPN transistor (LED driver)
  • U30 – Dual NPN transistor (LED driver)
  • U31 HCF4053 – analog switch

 

Moog Modular Routing

Inside a Moog CP4

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.

Moog Modular Wiring

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).

Trunking Explained

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 Module

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.

A&H Spectrum Mixer Refurb 2

Overview The A&H Spectrum finally arrived on 20th January 2020, very well packed and at 59 Kg! After some serious unpacking the refurb can now begin, with the PSU being the first to be looked at, so that I can power on the Master/Group section initially then add the Channel sections.

PSU Refurb The power supply is an Allen & Heath RPS3 from 1991 (serial number 7) and is a 3A linear power supply based on tried and trusted LM723 chips. Whilst the metal chassis has some rust patches rusty and the PCB is old, it looks in ok shape, although the 48V rail power cap is either bulging or has a dome! After carefully checking the power supply components I switched it on; +16.3V, -0.8V and +48V. So looks like we need to replace a component!

The original reservoir capacitors are 10,000 uF 35V with 85 degree temperature rating. I want to fit large capacitor values at 105 degree rating, but I am limited to a 30mm diameter as that is the size of the mounting. I located 15,000 uF 35V 105 degree capacitors made by EPCOS and fitted them. This will reduce the ripple voltage into the regulators down to 100 mV.

The LM723 chips have date codes from 1988, so these were replaced and I added IC sockets, then all the smaller power capacitors and the original MJ3001 power transistors and bridge rectifiers were replaced. One of the bridge rectifiers had failed, hence no -15V rail. Remarkably the 723 has become obsolete, so it is was a good time to buy some before they get expensive.

RPS3B and Heat The power supply has been upgraded to the B version, which outputs 4A rather than 3A, but no change was made to the thin 4A 16/0.2 wiring, and as a result all the wiring to the rectifiers has been heat damaged and become brittle and broken, which explains the -15V rail failure. I replaced all the wires into the regulator PCB with thick 32/0.2 which is rated at 10A, this provides a healthy safety margin. I also checked the current limiting resistors and they are not damaged. The refurbished power supply powered on successfully and the voltages were trimmed to 16.00 volts.

The original transformer is a traditional open frame model at 225VA. It provides two secondary circuits at 21.5V for the 16V rails and one at 50V for the 48V phantom power. I am keen to switch in a toridial transformer for the main rails and it has to be 225/250VA which means a diameter over 100 mm. I will have to mount this on the inside of the front panel, as that is the only space big enough. Alternatively I could just buy a cheap secondhand RPS11 which has 5A rails and a toridial transformer – lets see what eBay offers!

Fader Cleaning The high quality Alps K-series 100 mm faders are in generally good condition but they needed a deep clean as the action was not smooth. I started with the Group and Master section and took them apart, cleaned them with IPA, then Dexoit Fader cleaner, and finally put some fader lube on the lower brass rail. Each slider was cleaned so that it would slide from one end to the other on gravity alone, once apart. Sometimes steel wool was needed to remove corrosion on the brass rail.

I may buy two new Alps faders for the Master section but lets see how well the cleaning has worked. At £15-20 each I don’t want to replace all 26. I will clean the Channel faders as part of the Channel refurb once I see what issues there are in each of the channel cards.

Fader Knobs The black slider caps are nice and chunky but well worn with the white line disappearing, however I do have all 26 in place! I will have to keep them as modern caps are too short and stand proud of the panel or it means dropping the fader down by 4mm which is really not possible as there is no room in the chassis.

Panel & Knob Cleaning Whilst I waited for parts to arrive to get the RPS3 working, I cleaned the front panels with surface cleaner and deep cleaned every knob and switch cap (after removing them). This was a very long, but worthwhile task. A small number of knobs were broken or missing, as were some caps. I ordered 8 new knobs which are slightly taller and not faded! I put them in the AUX sends section, thereby releasing some original knobs and minimizing the colour change from new to old.

The brown caps for PAN are not available, so I ordered 30 light green caps and a couple of red and blue caps were also needed but I am hoping these colours match the originals. The caps are slightly smaller and need a little glue to remain in place.

Power On and Testing Once the PSU was working I plugged it into the console and powered up – all ok, no smoke! Testing uncovered a number of issues:

  • Right Master Out no signal (solved)
  • LED bar graph display 1 – 8 non functional
  • Group 2 and 8 input from bus failed
  • Channel 5 intermittent

The rest of the circuits seem to work ok, the switches are noisy but this reduces with use. The noise floor is good but some channels seem to distort easily and there are different levels in the Groups.

Group Channel Refurb The eight Group PCB’s are in good condition but not all working at the same volume. The plan is to upgrade all the electrolytic capacitors and make further changes depending on the outcome of the Channel 1 upgrade. Care is needed with these 30 year old PCB’s, and I use a vacuum desoldering gun to minimize the risk of tracks lifting.

Master Section The master section has a right channel failure, and there are no schematics available for this section, so I am using the Sabre master channel which is not quite the same design. The right channel failure seems to be a simple plug connection that righted itself on re-cabling. The main upgrade in the master section will be to replace the balanced output drivers (NE5532 with trimmers) which live on a separate PCB attached into the Master PCB, with THAT 1646’s on a new PCB.

Input Channel Recap

Input Channel Refurb Channel 1 had a broken shaft on the PAN pot, so I had to pull out the PCB to swap this with a new one, which was easy. At the same time I replaced the electrolytics with high quality Panasonic capacitors (Audio and Power versions), and removed the signal path TL072’s (IC 3-6). I soldered in IC sockets and initially tried a set of TLE2072 Op Amps from a AMEK Rembrandt channel, as these are fast low offset but with only a 14% increase in power current consumption.

I added 100nF decoupling capacitors to every Op Amp, underneath the PCB, as there is only one 15nF for the whole board!

This is an experiment to see if upgrading actually provides any benefits, as the cost per channel is around £15-30 depending on which Op Amp I use to upgrade. The change to the TLE2072 provided a clearer sound and the EQ was improved. The standard EQ uses Mylar capacitors, whilst high end consoles used better capacitor types. The PCB space is tight, so polypropylene capacitors are too large, so I am trying a set of PPS capacitors.

Input PCB

Input Conn There is a small PCB for each input channel that holds the jack sockets and XLR, it has a dual TL072 Op Amp to enable the -10dB and +4dB gain switching on the Tape Input. I have upgraded the Op Amp to a TLE2072. There is also space on the PCB for a SSM2142 Balanced Output chip, and its clearly marked on the silk screen.

This addition provides a balanced output for the Channel Output, which can be switched from Bus Out to Direct Channel Out from the front panel. I soldered in an IC socket and added a SSM2142 for the first 8 channels, as these are used as recording inputs to the Focusrite Octopre. The two 22R resistors need to be removed to ensure the Channel output signal goes into the SSM chip rather than straight to the jack socket.

Tracking Setup The Spectrum is used for tracking up to 32 synths/samplers into Cubase using eight Groups. Cubase is used as a 16 track analog style recorder with analog tape plugin available on every track. A key principle is to be constrained to 16 tracks and not to add more. The channel EQ and the two main FX processors can be used on tracking. I have constrained my use of Cubase plugins to just a TC2290 delay and the Softube Tape, no other EQ or effects are used.

16 synths come in via the Channel line inputs and another 16 via the Group line inputs. The first 8 channel outputs go into Cubase via a Focusrite Octopre which has compression available. I can switch these from Group to Direct Out, if I want to record the first 8 synths directly into Cubase, and the Spectrum outputs are balanced,

Mix Down Setup The Spectrum is also used for the final mix of a song, with 16 outputs from Cubase going into the unbalanced Tape inputs on each channel or they can be brought into the Groups. By leaving them on the channels I can record 16 synths at mix down from the Group line inputs. The stereo master of the desk can be recorded onto DAT and/or into Cubase. All four hardware FX processors can be used in mix down.

 

 

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