External clock on MFOS 16 step sequencer

[dummyplugconspiracy]

Sorry… For clarification… Do you want me to remove the resistor completely or put a jumper in place of the resistor?

[eljay]

For the purpose of this test remove it completely and test again with and without an external clock signal.

[dummyplugconspiracy]

I clipped that R12 resistor and tried this again. The sequencer works normally with no external clock when that resistor is removed. When I plug in external clock, the sequencer stops, and I lose my run/stop capabilities, but it does not respond to the new incoming clock either. The generator I am using for this test is capable of 10V maximum output on amplitude. As a test, I turned down the amplitude to see at what point the sequencer would start responding again. It appears the onboard clock switches over to external clock when it reaches around 4 to 5 V of amplitude. At that point The sequencer knows that external clock has been introduced and overrides onboard clock to begin tracking the square wave I’m putting in.

Just to be thorough… I soldered the R12 resistor back in again. When I do that, I get the same results as before. The sequencer will not start/stop with the button or track tempo with the onboard clock. I also noticed I cannot step forward, but I can step backwards, but it skips a step and only hits the odd numbered steps. That’s sort of interesting. The reset button also works. When I introduce external clock at at least 4 V, it works perfectly with whatever frequency I choose on my generator.

I just can’t seem to get everything to work all at once, even though we’ve proven it is recognizing that incoming voltage threshold that defeats the internal clock and defers to external clock. I feel like we’re close here…
What’s next?
Thanks!

[eljay]

From this last test the external clock does require an input with CMOS characteristics so I have modified the Mod board to include the CD40106 that will provide this, in hindsight I should have gone straight to this in the first place, apologies. So here are the new layouts.

Top

Bottom

The BOM is as follows :

D1 Signal diode, 1N914
D2 Signal diode, 1N914
IC2 Hex Inverter, CD40106
C3 Ceramic, 100nF
C2 Ceramic, 100nF
C1 Ceramic, 100nf
SC1 Socket DIL8
SC2 Socket DIL14
IC1 Dual Op Amp, TL072
R12 0.4w Metal Film 1%, 4K7
R11 0.4w Metal Film 1%, 4K7
R9 0.4w Metal Film 1%, 20K
R8 0.4w Metal Film 1%, 130K
R10 0.4w Metal Film 1%, 1K
R7 0.4w Metal Film 1%, 2M
R6 0.4w Metal Film 1%, 100K
R5 0.4w Metal Film 1%, 1K
R4 0.4w Metal Film 1%, 20K
R3 0.4w Metal Film 1%, 130K
R2 0.4w Metal Film 1%, 2M
R1 0.4w Metal Film 1%, 100K

Please note : assuming you are using a +15V/-15V power supply R3 and R8 have been changed to 130K, this lowers the threshold voltage required to generate a clock or start signal to a little over 2 volts. If you are using a 12V supply R3 and R8 can be left at 100k.

You should be able to leave out R5 and R10 (1K resistors) as we are not taking the output straight from the Op amp, I have left them in in case we need to conduct any further tests.

I have added some bypass capacitors to the power rail supplies for the ICs, C1, C2 and C3, they are all 100nF ceramic capacitors. You can leave then out if you wish, they will not affect the functionality of the board, they are there as a belt and braces to remove any potential noise on the power supply.

When you are testing you should use a a signal similar to that being output by your other modular equipment, I would guess this is around 5 volts although it should work at a lower voltage. A 0V-5V square wave would be great.

With the exception of the reset button I don't think the step buttons (Stop/Start, Forward, Back) will work with an external clock being input. They don't on mine, although I do have a Vari Clock version and it is slightly different. I have also noticed on mine that with an external clock driving the sequencer the STOP action at step does not work. I think these differences are to be expected.

[dummyplugconspiracy]

OK thanks! I will give this a shot. I may have to gather some additional components, but this might be possible using strictly leftovers. I'll let you know how it goes. THANKS

[dummyplugconspiracy]

Hi. I built this board finally last night and installed it today. It still isn't working correctly. Without external clock coming in I cannot get the internal clock and start to function when I have the board connected. I can make the reset button work and I can step backwards skipping a step each time I press the button. When I disconnect the external clock input and external start input from the board I can get step forward and backward and individual steps without skipping any. Reset works also. But stop and run still does not work. Only when I disconnect the boards output also do things return to normal. For the record… I have discovered that I can make everything work without the board if I just turn up my pulse input up to 4.8v. That seems to be the threshold that makes it recognize external clock. That just doesn't seem like very much power. I don't understand why my midi clock converter isn't outputting that already. I think I'm going to bring this back in and test it again. If I understood this correctly… The whole purpose of the board was to increase the voltage at the external clock input, right? Seems so simple ....
Thanks!

[dummyplugconspiracy]

I loaded the sequencer into my cabinet and confirmed that it still wasn't reading clock input from my moon modular midi to clock converter. However, I have a Yusytnth CV standards module that lets you increase the voltage across multiple outputs. So as a test, I increased it one volt at a time until the external clock started to work. Thinking about how I will actually be using my synthesizer, it seems like this might be an acceptable workaround. It's likely I will have to distribute clock a couple places anyway, so this isn't really a waste of a voltage control distribution channel. I would still be interested in doing the Modification if we were certain we had a working design, but for the moment I'm going to proceed like this. Let me know if you want my help troubleshooting the design, but right now the board is disconnected and I probably won't put it back in for a while. Thanks! I truly appreciate the help! I'm certainly not dropping this idea completely.

[eljay]

Please post photos of the new board, top and bottom as before. We seem to be going backwards, the design should work so something else is amiss.