Roland MKS80 Power Supply

Introduction This is a feasibility study into a replacement power supply for the Roland MKS80, and it is not a project that AMSynths are aiming to deliver, as Guy Wilkinson owns the rights to the MKS70/JX10 re-engineered power supply which this thinking is based on. Thoughts and ideas are welcomed!

Overview I am fortunate to have a near mint Roland MKS80 (March 1985) and MPG80 (August 1984). This is the second time I have owned one, as I had to sell my first MKS80 in 2001. It is a REV5 with a 110V power supply and therefore requires an external converter, which is all a bit bulky and messy. The transformer in the MKS80 is not tapped for both 240 and 110V operation, so a NOS 240V replacement transformer is needed.

Rather than going down that route I have was inspired by the work done by Guy Wilkinson in replacing the Roland JX10 power supply with a modern switched power supply. Details are here. This approach greatly reduces the heat from the old linear regulators as a bonus, as well as having 240V operation, and is a great long term solution with no capacitors to replace.

Roland are good at designing high quality power supplies with precision rails in the right places for analog circuits. The MKS80 is a completely analog voice circuit, where the MKS70 is using DCO’s and then an analog circuit path. We do not want to fall short of the Roland design specs.

Roland MKS80 PSU

The New JX10 PSU Guy’s design provides +5V and +/-15V rails with low ripple after careful filtering of a set of three Meanwell power converters. Unfortunately this PCB cannot be directly reused in the MKS80 as it requires a +10V precision reference voltage for the VCO/DAC and requires a more power to the 15V rails than a MKS70, even though it has 8 rather than 12 voices and the overall power consumption is similar at 35 W.

The low voltage connections are also in a different location, and the mains filter is on board the power PCB. A new PCB needs to be designed with slightly different Meanwell units to meet the demands of the MKS80. There is an Unregulated +7VDC in the MKS80 to power the MPG80, just like the MKS70 design which also powers the display. Guys design uses a Vigortronix power converter to deliver +9V DC at 0.55A which can be used for the MKS80.

+5V Power
MKS80 Rectifier = 2D4B41 (2A) Main Capacitor = 4700uF 800mA at 8.5VAC
MKS70 Rectifier = 4D4B41 (4A) Main Capacitor = 6800uF
Guys Replacement PSU delivers +5V at 1.5A

+/-15V Power
MKS80 Rectifier = 2B4B41 (2A) Main Capacitor = 3300uF 450mAx2 at 21.5VAC
MKS70 Rectifier = 1B4B1 (1.5A) Main Capacitor = 4700uF
Guys Replacement PSU delivers +/-15V at 600mA x2

Replacement MKS80 Power Supply The MKS80 service manual states that the +5V rail should be within +/-30 mV, which is a tighter tolerance than the IRM Meanwell converter delivers and the actual +4.94 volts measured in Guys design. The +5V does not get used as a reference voltage, but potentially a more accurate converter/solution is needed as AC/DC Converters typically have 2% initial voltage accuracy, and Roland are stating 0.6%.  In the MKS80 the +5V rail is using less power than in the MKS70, so it is possible to retain the Meanwell IRM-10-5 which is rated at 10W (provided we can accept the voltage accuracy).

For the 15V rails the more powerful 20W IRM-20-15, which delivers 33% more current at 800mA per rail, is needed. The 15V rails are at a much lower tolerance of +/-100 and 400 mV, so the Meanwell IRM can easily achieve this accuracy. Other Roland synths require very accurate 15V rails, such as the Juno 60 where the tolerance is +/-10mV which really demands a linear or LDO design.

The +9V supply remains the same as in Guy’s design, using the 5W Vigortronix power converter to deliver +9V DC at 0.55A, more than enough to power the MPG80.

The original Roland +10V power is provided by a 1SZ59 6.5V zener diode, with an Op Amp and trimmer to set this to an accurate +10.00V, the 1SZ59 has a temperature co-efficient of 2ppm/C which is very good! A modern LT1027 precision regulator can deliver the same 2ppm/C. It needs to be buffered with a precision Op Amp on the power supply PCB, although in the voice boards the +10V is further buffered by average performance M5218L Op Amps. The reason to take care here is that this voltage is used in the VCO’s as a reference voltage, as well as the DAC reference voltage.

The rest of the MKS80 replacement power supply can follow Guys design but with a layout and pin out that fits the MKS80 PCB dimensions. The mains power conditioner on the top right of the Roland PCB can be dispensed with and its taking up valuable space at the rear of the MKS80. The power socket needs replacing with a grounded 3 pin IEC socket with power leads going straight to the front panel ON/OFF switch and then running back to the bottom right hand corner of the new PCB.

MKS80 Power Connectors There are 7 low voltage power connectors on the PCB to supply the various MKS80 modules:

  • P1 Analog +15V 10 pin
  • P2 Analog GND 12 pin
  • P3 Analog -15V 8 pin
  • P4 Digital GND 6 pin
  • P5 Digital +5V  6 pin
  • P6 Reference Voltage Analog 2 Pin
  • P7 Unregulated and Digital GND 4 Pin

These need to remain in the same position on the new PCB to ensure the cables and connectors fit.

PCB Design The PCB size can be as large as a rectangular 100 x 200 mm, with the same mounting holes as the original. The removal of the large internal heat sink means there is more space at the rear of the case. I have mocked up a high level design with the 4 converters and the power input at the front corner.

Next step is to do a PCB layout mock up in Eagle CAD to see if the components and the required isolated tracks can fit. A solution to the +5V DC initial voltage accuracy needs to be found as the best AC/DC converter I can find is 1% accurate.

 

Roland IR3R01 Design & Replica

IR3R01 Chip

Introduction The Roland IR3R01 envelope generator chip was used in the early 1980’s in three key synthesizers; the awesome Jupiter 8, the Juno 6/60 and the MKS7. The chip is obsolete and impossible to locate as NOS, which puts these synths at risk of never being repairable in the future.

The chip is a custom design by Roland which although looks similar to a CEM3310 or SSM2055, it is not the same design. This post is about researching how the chip works, building a simulation circuit (especially for the Key Follow Jupiter 8 design) and finally developing an accurate PIC based replica.

Description The IR3R01 generates a positive going 0 to +10V output signal (maybe less on Juno and MKS) with traditional Attach, Decay, Sustain and Release phases. The chip has CV control inputs for the ADSR phases, as well as the usual gate and trigger inputs, and it always runs from +/-15V power with an additional ground pin. The Attack, Decay and Release are driven by 0 to +5V control voltages whilst the sustain control voltage is 0 to +10V. The CEM3310 uses negative control voltages, so is a long way from being a drop in replacement.

The chip also has a Reference Voltage pin as well as a Common pin, and finally a Modulation pin which is used only in the Jupiter 8 to enable the level of the envelope to be controlled by a CV. Here is the pin out:

  1. Modulation Input
  2. Attack Voltage
  3. Decay Voltage
  4. Release Voltage
  5. Sustain Voltage
  6. Common
  7. Reference Voltage
  8. -15V
  9. Ground
  10. Timing Capacitor
  11. Output
  12. Current Input
  13. Gate
  14. Trigger
  15. Retrigger
  16. +15V

Common Pin The input voltage adjusts the timing of the envelope, and a manual trimmer with a Tempco resistor adjusts the attack time maximum, so that all 6 or 8 envelopes have the same timing. On the Jupiter 8 this is set to 6 seconds (although on Page 1 of the service notes its stated as 5 seconds), on the Juno to 3 seconds and MKS 7 to a very short 2.5 seconds. The maximum timing of the Decay and Release is 10 seconds on the Jupiter and 12 seconds on the Juno and MKS. This variation could be due to the increase in Decay and Release CV input resistors from 19k to 22k.

Reference Voltage This is tied to +7.5V (Juno) or +10V (Jupiter) or +5V (MKS). Typically envelope generator chips use this voltage as the highest voltage the attack phase is aiming to, the actual maximum voltage is typically less. Some real world measurements would be useful.

Timing Capacitor This is 68nF (Jupiter and MKS) and 47nF (Juno), this will vary the basic timing of the envelope stages. The manual adjustment of the envelope timing via Common is required because all voices in a polyphonic synth need to have the same envelope times. The adjustment is needed due to variations in the timing capacitor value and variation in chips.

Envelope Oscillator

Modulation Input This is only used in the Jupiter 8 to implement Key Follow, elsewhere the pin is grounded and a different approach is used to implement Key follow in the Juno. In the Jupiter a higher pitch CV shortens envelope time. The IR3R01 circuit is unique with a 28 kHz saw wave being created by a 555 timing chip and sent to all the IR3R01 chips via a buffering Op Amp and a comparator with the Keyboard Follow control voltage.

The IR3R01 receives a 0 to +15V square wave to the modulation pin, which presumably varies in height or frequency to control the envelope speed. It is not yet clear how this works, but it is an important part of the circuit to replicate.

Initial Conclusions The IR3R01 has similarities with the CEM3310 design with a current Input pin and reference voltage, but the control voltages are negative in the CEM3310. The SSM2055 uses positive control voltages and a timing control pin, but no current input. Neither of these chips have the Modulation Pin of the IR3R01. A strong possibility is that the IR3R01 has some basis in the complex Jupiter 4 ADSR which uses oscillators that vary from 10 kHz to 800 kHz, for each of the ADR phases.

The clue is that the ADR front panel sliders on the Jupiter and Juno are non-linear, just like on the Jupiter 4. They have a 4K7 resistor added between pin 1 and 2 to provide a more exponential like CV, rather than getting the microprocessor to do this job. This could be because the ADR voltages in the IR3R01 are controlling the rate of an oscillator, as in the Jupiter 4 design. The modulation pin uses a clocked input to vary the length (not height) of the envelopes, which also suggests a Jupiter 4 ADSR with oscillators. With no IR3R01 datasheet, a more detailed circuit analysis is needed.

Key Follow in JP8

Replicating the IR3R01 There are two uses case of the IR3R01. The simple ADSR in the Juno and MKS where a SMD CEM3310 could be buffered to get a similar “drop-in” response. However a micro controller based design (like Tom Wiltshire’s PIC ADSR here) is going to be less component heavy and potentially could be adapted to the Jupiter 8 use case with the Modulation Pin being used.

By using a digital design the timing will be perfect and the exponential curves can be adjusted if necessary in the data tables, so there is no need for timing adjustment, reference voltage or timing capacitor and these pins can simply be left unconnected. The modulation input needs to be read and the level of the envelope adjusted accordingly. The PIC would need a +5V power supply and most of the input voltages would need reducing (simple resistor dividers?) such as Gate and Trigger, the 10V Sustain CV as well as the 15V Modulation input level.

Whether all this can be done in a 16 pin DIL footprint remains to be seen!

Next Steps I will create a test harness circuit of the Jupiter 8 Key Follow circuit to see what waveform is generated on Pin 1 of the IR3R01 as the Key Follow CV is varied from 0 to +5V.

Replica Design Here are some initial thoughts, I envisage two chips; One for the Jupiter 8 and one for the Juno 6/60, so the envelope timing can be perfectly matched to originals:

  1. Modulation Input – create Jupiter 8 test harness to work out what this does – use a resistor divider to read pulse frequency
  2. Attack Voltage – read directly and map to correct minimum and maximum times
  3. Decay Voltage – read directly and map to correct minimum and maximum times
  4. Release Voltage – read directly and map to correct minimum and maximum times
  5. Sustain Voltage – reduce by 50% using resistor divider
  6. Common – ignore
  7. Reference Voltage – ignore
  8. -15V – use for buffer Op Amp
  9. Ground – use and decouple with +5V
  10. Timing Capacitor – ignore
  11. Output – Op Amp buffer to increase output to 10V
  12. Current Input – ignore or use external resistors with the buffer Op Amp
  13. Gate – reduce to +5V using resistor divider
  14. Trigger – reduce by 50% using resistor divider or ignore and connect internally with Gate
  15. Retrigger – ignore
  16. +15V – use for buffer Op Amp and create +5V power for PIC using regulator

 

Jupiter 4 Voice Card Recap

Overview As part of my Jupiter One project I needed to recap and upgrade the Jupiter 4 Voice Card, ready for fitting to the Controller and Pot PCB’s  that I have designed. Hopefully these notes will help others recapping their own voice cards.

Why Recap? My voice card was made sometime in 1979 and 40 years later the capacitors have deteriorated, losing the original value. This is especially important in the timing capacitors in the envelope generators and the VCO, as well as the power supply bypass. I have used modern capacitors which are higher quality, and specifically upgraded the HPF filter capacitor and the audio capacitor between the VCO and VCF.

Further Changes To fit the Voice Card to my Controller PCB I need to carefully remove the 9 pin connectors as these will be replaced with SIP connectors. I also want to replace all the trimmer pots with cermet types to ensure the tuning of the card is accurate and stable. This includes replacing VR10 which had been swapped out for a potentiometer.

Power Capacitors The 100nF power supply bypass capacitors are C31 and C32 are are replaced with MLCC ceramics. C20 and C29 are 100nF Mylar capacitors (power bypass) and they have been replaced with modern versions that are smaller (this helps fit the Voice Card into 11 mm of clearance). C33 and C34 are 33uF 16V electrolytics mounted on the back of the PCB, and are very important for a stable power supply. I have uprated the voltage to 25V (to provide a safety margin on the 15V power rails) and used 39uF Panasonic FC power capacitors.

Timing Capacitors The envelope generator timing caps C12 and C17 (220pf), C18, C19, C23, C24 (100pf) were all upgraded to MLCC ceramics, along with C2 in the VCO.

VCO Capacitors I have left the two polystyrene timing capacitors alone as they look in good condition. I have replaced C36 and C37 which are kludges by Roland onto the rear of the PCB, they are old ceramic plate capacitors, which I have replaced with modern MLCC type.

Filter Capacitors C10 is the 10uF coupling capacitor between the VCO and HPF which I have upgraded to a nice audio quality capacitor, and at a higher voltage rating. The ceramic disk HPF 470pF capacitor at C11 was upgraded to a precision polypropylene capacitor, which improves the HPF sound. I have chosen to leave the 150pF VCF capacitors as the original disk ceramics until I conduct audio testing. In the AM8104 I use Polypropylene 1% types.

The coupling capacitors going into the VCF and VCA are quite low value 22nF Mylar film, I use much higher 10uF electrolytics in the 8104 JP04 Filter to improve the bass response. I have swapped them out with Vishay MKP 1% types at 68nF. This opens up the bass response of the filter a little, and Roland started using 56nF on the E revision of the PCB.  The capacitor on the CV summing Op Amp at C28 (22pF) has been replaced with MLCC type.

New Trimmer

Trimmers An ideal replacement for the single turn is the Piher PTC10LH10 which has the same pin spacing, however they are difficult to locate at 100k value. I also need a trimmer which can fit within the 11 mm clearance of my Controller PCB, so a smaller trimmer is needed. I have used the Copal CT6 which need Pin 2 bending out to fit the PCB. They are similar to the type used in the Jupiter 8 and are just 7 mm in height. I will also use this trimmer on my Controller PCB.

The VCO multi turn trimmers are easy to replace with Bourns 3006 types which just drop in. I have used real versions rather than cheap copies.

Project Status By early May 2019 the new power supply PCB for the Moog 60HP case has been prototyped and proven. The Controller and Pot PCB’s have been designed, checked and ordered. The panel has also been designed and you can see a mock up picture at the start of this post. More updates to follow!

 

 

 

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