• Mauro

    I have carefully read your exhaustive post about the Roland IR3109 IC, I am an owner of several Roland synths, and I must say that my favorite ones all have the low pass filter containing this IR3109 IC and especially the Juno 60.
    Among the various Roland synths I own an MKS80 rev 5, which in my opinion
    it has the potential to be one of the best classic Roland analog synths, shame about the choice of using a state variable filter instead of a classic low pass like Juno 60 or Jupiter 8.
    Being a bit familiar with analog synth circuits, having built many analog modules, I have recently found the courage to successfully modify some of my analog synths, so I was wondering if it was possible to bypass the 3R05 IR filter. inserting in the circuit a low pass such as Juno 60, or Jupiter 8.
    Basically my idea is to remove the IC IR3R05 from each voice, insert a socket that connects to an additional PCB where to house the circuit based on an AS3901 in low pass mode such as Juno 60 or Jupiter 8 in series with the previously removed IC IR3R05. only as a VCA.
    (passing through the filter of the IR3R05 with the cutoff totally open)
    The voltage controls of the filter (Cutoff and Reso) that were previously wired to IC IR3R05 should be adapted to the operating parameters of the AS3901 and its low pass circuit.
    The same with the low pass audio input and output voltages.
    While the CV and audio out connections of the VCA would remain the same.
    I read on your site that you have a lot of experience with these filters, do you think this modification is achievable?
    Do you have any suggestions to make it happen?
    My purpose is not commercial, only passion for synths, if someone wants to help me develop this modification I would share it for personal non-profit.

    July 07, 2022
    • amsynths

      Many thanks for the post. The IR3R05 can be replaced with an AS3109 either as dual SVF or as 4-pole LPF. But there is a catch. The IR3R05 has its own onboard resonance VCA, which would need to be replicated using an AS662D, and given its a 2x VCA package, I would also add the VCA part of the IR3R05 with linear and expo inputs. I would suggest all SMD parts and a PCB similar to the D80017 design, that slots into the IR3R05 location but with the right values for the MKS-80. Its certainly possible. Use the JP-8 IR3109 implementation as a basis for the new circuit. Hope that helps Rob

      July 07, 2022
  • Mauro

    Thanks Rob,
    very useful suggestion.
    Considering your great experience with these Roland filters, would you be interested in designing and marketing this modification?
    I am convinced that many owners of an MKS80 rev 5 would appreciate this upgrade

    July 08, 2022
    • Pyko

      I would also be interested in such a mod but for a MKS70/JX-10.

      September 12, 2022
    • This would be a popular product. Given the massive difference in selling prices between MKS-80 Rev. 4’s and Rev. 5’s, it’s pretty safe to assume that all Rev. 5 owners or potential owners would buy it. Personally, I own 2 Rev. 5’s and 1 Rev. 4, and the Rev. 5’s sound flat in comparison.

      January 25, 2023
  • ShM

    “1982 also saw the IR3109 used in a mono-synth, the massive selling SH-101 (over 10,000 sold), for the first and only time.”


    August 11, 2023

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