Home › Forums › Vintage EHX › DRM 15 – Add clock in?

Viewing 9 posts - 1 through 9 (of 9 total)
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  • October 19, 2016 at 12:29 am #84625
    vigs
    Member

    Hey all,

    I just dug my ol’ DRM 15 out of a box after stumbling upon a note somewhere that it had a Clock In input. I discovered mine is the “Bass Out” version. :/

    So that got me thinking, is it possible to add on the Clock In? I can’t seem to find a schematic anywhere. I dug up the datasheet for the sequencer module (http://www.milton.arachsys.com/nj71/pdf/m252.pdf). Unsurprisingly, the Clock Out comes from the trace that feeds the Clock input of the sequencer. But I can’t for the life of me figure out where that clock signal is coming from. I see a bunch of opamps and OTAs but nothing that seems like a clock generator.

    Anyone tried a mod like this? Or does anyone have schematics? Or just pictures of the innards of the Clock In version?

    Thanks!!

    November 5, 2016 at 4:26 pm #122214
    Stephengiles
    Member

    I have schematic for DRM 16 which uses a CD4040 for the clock and 74s474 for trigger generation (I think), but I can’t remember how similar this was to the DRM15.

    November 5, 2016 at 6:34 pm #122215
    vigs
    Member

    Thanks. Yeah, I have that schematic as well. I’m no expert but I don’t see a CD4040 in this circuit. The only ICs are the one M252B1BW which seems to be the brains, 4 EH104B’s, and 5 RC4558N’s. No counters or other things that might be clocky. But maybe one of these other ICs can be used that way and someone out there with more knowledge than me knows a thing or two.

    I’ve tried tracing back the clock in on the M252 (http://www.milton.arachsys.com/nj71/pdf/m252.pdf) but I’m not knowledgable to enough to figure out where that signal is being generated and therefore, how to interrupt it and send in a different clock source.

    Maybe, I’m just thinking out loud here, I use a scope to try to figure out what kind of signal is present at the clock input and then build a little external circuit that I can use to take DIN sync or the like and convert it to whatever the M252 wants to see.

    But I’m hoping there’s just some unused parts of the circuit that I could wire up as the clock in, where there’s over versions of the DRM 15 that have the clock in. I’m hesitant to randomly circuit bend it but maybe that’s my only hope.

    November 5, 2016 at 6:50 pm #122216
    Stephengiles
    Member

    The EH 1048s are really CA 3094s and not easy to replace these days, although EH may still have a stock.

    November 5, 2016 at 7:12 pm #122217
    vigs
    Member

    Ah, nice, so those EH1048s make up the clock somehow. I was thinking I was looking at a bunch of op amps. I’ll see if I can figure out where I can inject an external clock into the mix.

    November 5, 2016 at 9:22 pm #122218
    Stephengiles
    Member
    Quote:
    Ah, nice, so those EH1048s make up the clock somehow. I was thinking I was looking at a bunch of op amps. I’ll see if I can figure out where I can inject an external clock into the mix.

    No, the EH 1048s will be most likely be used as VCAs or similar.

    June 16, 2018 at 11:36 am #123992
    zykan
    Member

    2 years later … :)
    may i ask if there is any progress in adding the clock in / out to the drm 15 ?
    i also have the 2 outs plus bass out (using this does not cut the bass from the main out btw !?) and really would love to add a clock / sync in and out.
    i have the old super space drum, super replay, sequencer with clock and so on … and planning to connect everything for a ultimate ehx drum array :)

    any info / help much appreciated !
    cheers
    matthias

    July 12, 2018 at 12:49 am #124095
    Fender&EHX4ever
    Moderator

    I’ve always been a bit confused why all of the DRM series didn’t integrate a Clock-In. I suppose in 1980 it made the most sense to most consumers to use it as the master clock source, or forego syncing altogether. I’m surprised there isn’t anyone well known who provides this modification. The DRMs seem to sell pretty well on eBay and Reverb, so there has to be a market for it out there.
    My DRM 15 has both clock in and out, which is great for syncing with the vintage 16 sec delay. I wish the DRM 32 also had clock in, but at least the clock out can be used in Eurorack with something like the Erica Synths MIDI to Clock module to convert the clock to MIDI.
    Now that EHX is reissuing the Dirt Road Special, I wonder if they’ve thought about reissuing all of the DRMs, drum modules, and replays with updated sync options?

    February 11, 2019 at 9:31 pm #124810
    Wapaii
    Member

    Could you take a pic of your DRM15 pcb cardboard to help us ?

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