HELP! Oberheim Mini Sequencer ... EXT CLOCK IN NIGHTMARE

[tyler477]

Hello, could you PLEASE post photos of this process? I need to wire my 2 voices sequencer trig in also and have been putting it off.

thanks!

[matia]

Ill grab photos in a couple of minutes. It's H of the molex connectors on the mini sequencer board. Pin 1 is ext clock in.

[matia]

This page will show you all the connections for the mini sequencer:

Oberheim MS-1A Mini-Sequencer

Figured it out: The DR 55 and Monotribe were not putting enough trigger voltage to drive the 2 voice sequencer.

Basically the external clock signal I was feeding was not higher than the internal clock, which from the looks of things is I think close to +10 to +15 volts. Since the external clock is switched into the clock path via a NAND gate, the nand gate was not receiving a signal on the second input high enough to switch to outputting the external clock so it kept sending the internal.

The way it should work is, with the correct and powerful external clock signal, you should be able to step the sequencer without flipping the run switch. If you flip the run switch on the mini sequencer, it will return to clocking off of the internal clock ...

Hope that helps somebody out!

-matia

[matia]

And here are the finished mods. The switch routes either the Sample and Hold or Sequence B to the first modules Filter Cutoff modulation when set to EXT ;-)

[LNerell]

And now you know what we all went through in the pre-midi days. Getting things from different companies to talk to each other was a bit of a nightmare at times.

[matia]

Originally Posted by LNerell

And now you know what we all went through in the pre-midi days. Getting things from different companies to talk to each other was a bit of a nightmare at times.

oh yea ... trust me ... i've had my fair share of fun ... like getting sync on an oberheim DMX without midi ... was not fun ...

[bil_g]

Glad you figured that out. After reading the first post, the high voltage was what I thought. 10v is what I remember having to use for reliable stepping.

You're reminding me that I want to get that back to one of the rear jacks. I keep switching the 8 rear jacks around every couple of months. I do love syncing the S/H.

Be sure to try a gate signal to the clock if you haven't yet.

[tyler477]

Originally Posted by bil_g

Glad you figured that out. After reading the first post, the high voltage was what I thought. 10v is what I remember having to use for reliable stepping.

You're reminding me that I want to get that back to one of the rear jacks. I keep switching the 8 rear jacks around every couple of months. I do love syncing the S/H.

Be sure to try a gate signal to the clock if you haven't yet.

are the PCB's labeled to perform the connections easily? if not is there diagram somewhere? I have yet to open mine up.

[bil_g]

Originally Posted by tyler477

are the PCB's labeled to perform the connections easily? if not is there diagram somewhere? I have yet to open mine up.

Check the site matia linked to above. Hit the arrow at the bottom and it will take you to the SEM layout. Great reference. Everything is labelled well on the PCBs. They're pretty simple to mod.

[glome_music]

so did anyone figure this out (how to get the +5V to trigger the clock)? do you simply use some other gear to scale the trigger signal or is there some simpler, self-contained solution, such as swapping the original NAND gate for a modern component accepting +5V? i would hate to tie up other modular resources just to generate +10v triggers for the clock

i recently found a broken 2 voice cheap, am having it restored by a tech, restoration is going well and now have to decide on a few mods... just the minimum for now to get it integrated into my setup... i had definitely hoped to be able to run the sequencer from an 808 or from the raw trigger outs of encore expressionist... but 808 highly preferred... so am very interested in actual solutions to this problem!