uniPulse FR6M clock

frontpage Forums Product questions and support uniPulse uniPulse FR6M clock

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    I’m installing a uniPulse in a Rhythm Ace FR6M and am only interested in controlling the clock. Using the instructions for the FR3 I think I’ve identified the clock injection points and the clock inhibit point (the start button was obvious). I have two questions:

    [1] The start button on an FR6M is momentary and is latched electronically. The latch circuit is buried inside the machine, so I’d prefer to generate rectangular 0V pulses (from high impedance quiescent) when a MIDI Start or MIDI Stop message is received. This doesn’t appear to be possible in the current version of the configurator because there is no way to specify those individual MIDI events–they are combined into “Sync Gate”. So to do what I want to do, I have to build a circuit to detect a transition on the sync gate and synthesize a pulse, correct? It would be so much easier if I could use a pulse channel and specify a max voltage of 0, assuming that the uniPulse can sink the necessary current. I see that 0.1V is possible, but I’m still blocked by the sync gate problem.

    [2] Your instructions for the FR3 use digital outputs to pulse the clock injection points C+ and C-, and then suggests that there is a way control the phase offset between them. It says “More about this later” but I can’t find the instructions. How is that done (without additional custom glue hardware)? The example configuration just shows how to generate the inverted pulse.



    jlo wrote:
    This is not supported by uniPulse at the moment. The main reason this was not implemented in the first place: When producing a pulse at start and at stop, you will have to manually set the machine to the correct state at the beginning. And once you press start, you will be out of sync.
    So finding the correct point start/stop is a much better solution. Usually there is a way of tapping into the circuit behind the start/stop flip/flop.

    jlo wrote:
    Luckily the UniPulse can create multiple simultaneous clocks with adjustable phase, so we don’t have to build an additional inverter. More about this later.
    I see how this can be misleading. What is meant by this is that the phase of the clock outputs can be shifted by 180° (aka inverted). So you can generate the inverted clock signal as well without needing an additional inverter circuit.

    Here is what I think should work to control the clock on the FR6. I can not test this, because I don’t have one:

    The start button on an FR6M is momentary and is latched electronically.
    Looking at the schematics I have, I get the opposite impression: There is no latch at all, just a (latching) start stop switch.
    When the reset line is pulled to ground the machine is is stop mode, otherwise it runs.

    Here is what I came up with:

    To control start stop, you need to connect a general purpose NPN transistor as shown. The base is connected to uniPulse D3. D3 is configured as start/stop with inverted polarity.

    Clock is injected at the bases of Q102 and Q103. The 1k resistors here are to protect the digital outputs of the uniPulse, but should be low enough to override the signals from the existing clock. The 1k resistors are then connected to D0 and D1 via a 2-way switch. The switch is used to select between internal and midi clock.

    It would fantastic if you could very this and post pictures of these points on the boards themselves, so other can benefit from this info.
    Thanks a lot!


    Thanks for your clarification RE clock phase.

    The schematic you excerpted is not the FR6M I’m working on. Mine implements the clock divider in a DN811 quad flip flop IC, not in discrete transistors. It also very definitely has a momentary start/stop pushbutton.

    RE using start/stop pulses rather than sync gate, I plan to wire the toggle switch to select either the pushbutton or the sync gate edge detector to pulse the start/stop latch. The only state alignment issue one could run into is when switching the FR6M into MIDI sync mode. Requiring the user to do this only while the machine is stopped seems like a small price to pay given that I’m forced to work on this circuit without a schematic and the start/stop latch is not easily accessible. Additionally, I can’t think of a use case where one would want to switch between internal and external clock in the middle of a song. That said, if you could find the right schematic and share it with me I’d be happy to reconsider!

    I’ll post my solution when it’s done.


    Thank you very much for your reply.

    The service manual I have is for the Rhythm Ace FR6 and FR6P. But apparently the FR6M is completely different (does it at least have the same voice board?)


    No, but all the connection points are clearly labelled.


    Here’s how I made a Rhythm Ace FR6M follow MIDI clock using the uniPulse. First of all, this is an FR6M:

    Clock is injected in 2 phases like the FR3 (see these instructions) using opposite polarities and AC coupling. Here are the connection points:

    As discussed previously, I found it easiest to convert the sync gate to a start/stop pulse. I would normally use a CMOS XOR like a CD4070, but I didn’t have any on hand, so I hacked the function together with MPSA06 transistors I had lying around. It’s not a great circuit; the pulse width is dependent on the size of the coupling caps and the hFE of the last transistor, so you’d want to measure what you’re getting to see if it’s in a useful range. Finally, I wired the toggle switch to ground the clock inhibit point and select the open-collector output of the edge detector to drive the switch latch. The switch latch pad isn’t clear in my picture, but when you open up the FR6M the first time, you will see a red wire from the switch to the switch latch pad. Here’s the complete circuit:


    Fantastic! Thank you very much!



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