Emu Drumulator

[djsynchro]

A friend of mine found a Emu Drumulator in the TRASH!!! And gave it to me for my B-Day (And brought his SK-1 Which he's gonna get back bent for his B-Day) 

It's in a bit of a state, only one of the 4 assignable drumbuttons works, microswitches might be replacable.
Software is 2.0 it's doesn't have MIDI (The later 3.0 versions did) 8 bit sound total 64k memory on four ROM chips (one is the cymbal the other 11 sounds are on the remining 3 chips)

It sounds really round and warm - the toms even have 2 analogue SSM chips as filters, might try to mod that for more extreme Freq and Q action. If it should die from bending I will have 2 very rare VCF chips for in my Soundlab mini synth...

Already tried shorting pins on the ROM some very good sounds - a lot fatter than my Cheetah MD-16 which doesn't have much in the bass department.

There's lots of space on the frontpanel but... the PCB is the same size and right behind it - so no patchbay at the front. I recently got two used rotary 10-position switches & was thinking of wiring those up instead - that would rule out combination bends but I never seem to get many good ones of those anyway.

[papaspank]

oddly, just used a multi-way switch in my most current project

Have a rummage around - you can sometimes find that one point on the board connected to many others can make some pretty unusual things occur.

This is the reason I used a mutil-way switch (a cannibalised one that was formerly a voltage selector in an old wall-wart transfromer).

Whilst fuzzying about with the unit in question (a Dane electron pedal) came across around five bends - all with one 'common' point.

This was a chip based bend so - you  could in theory apply it to your project...

It's also an idea to ensure that one switch point is left 'blank' otherwise you'll end up needing another switch to bypass it 

hope that helps in some small way

[djsynchro]

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IF YOU ARE THINKING OF BENDING A DRUMULATOR IT IS A MAINS POWERED DEVICE
YOU NEED TO KNOW EXACTLY WHAT YOU'RE DOING AND WHAT PRECAUTIONS TO TAKE
EVEN WHEN IT'S UNPLUGGED FROM THE MAINS THE CAPACITOR IN THE POWER SUPPLY
CAN GIVE YOU AN ELECTRICAL SHOCK!
************************************************************************

Bent it! 

I got two 12-position switches (one of them only has 11 clicks though... WTF but they were second hand)
I didn't want to do a patchbay for safety also - this is a mains powered machine after all think about it - if a wire came off the chips inside it *could* touch the PSU so then there would be 220V on your patchcable? No thanks 

They rotaries are wired to 12 pins it's a little lame because now I have combinations like 3+5 and 5+3 which is the same bend of course, but the advantage with the way I wired it is that I only needed to solder to 12 pins of the ROM chip.

Those 12 pins were all the cool connections anyway pin 13 was getting a bit too highpitched pin 14 sparks and crashes the machine !!! Don't short this one!!!
(Drum machine upside down looking at PCB drumpads facing towards you, bottom left pin of ROMs - don't short)

I used the 3d ROM chip from the left (out of 4) The leftmost is not a ROM but an EPROM and has the cymbal sample in it. Better not touch that one either, EPROM will be easier to fry, as I said, the bends on all the chips are pretty much identical they're "stacked".

How does it sound? Before bending it well, while it might have been hot sh*t in 1983 it really lacks in high frequencies, but... that makes it PERFECT for bending which generates harmonics.

It sounds great, really fat!!


Todo: The toms have SSM filter chips (one for hi/med one for Lo tom) the trimmers hardly make a difference so I am going to try and mod it so the cutoff frequency is tweakable. Resonance is not connected I think will try & change that too. My drumulator is v2.0 no MIDI, saw a kit on the Net for $50 MIDI and v3.0 OS only 3 wires to connect.
Will probably get that...

[djsynchro]

By the way: The 4 "drumpads" that didn't work: The buttons open really easily, first I soaked them in alcohol, then scraped with a screwdriver where the metal makes contact when the button is pressed. They're working again! That was easy.
But... I soldered them off the PCB to do that, soldering them back on was HARD.

If you have this I recommend leaving them on, pry them open with a screwdriver, clean with a cotton earswab & alcohol , scrape the dirt off where the metal makes contact when the switch closes. (When you look inside the switch you will know what I mean).

[djsynchro]

It's also an idea to ensure that one switch point is left 'blank' otherwise you'll end up needing another switch to bypass it 

Since one of the  rotaries is 12 and the other is 11 positions that's exactly what I did... but in the middle positions there is another setting where it sounds normal (a pin gets connected to itself then, so no short circuit)

[djsynchro]

I found a website from a guy in the UK who has EPROMs for the Drumulator with new sounds. There is an option of using bigger EPROMs, then you can switch betwen 2 banks of sounds!

I'm going to get a set with a 808 and 909 kit, the factory sounds are rubbish, they're not retro they're old NOT the same thing. The bending does interesting things but I think bending more electronic sounding stuff will be much more interesting, I'm particularly interested in the 808.

If anybody has a service manual I really want to look at the schematic of the Drumulator!
Would like to mod the 2 filterchips so the resonance is adjustable.

[Gordonjcp]

If larger capacity chips will physically fit, ie. you're replacing a 28-pin chip like a 2764 with a 27C128 or even 27C256 then all you need to do is ensure that the top address pins are not connected (either check the board tracks or leave the pins bent out of the socket) and ground them to select which "page" of the ROM you want to use.

So, you'd burn two 8K samples into a 27C128, and ground A13 to select the first, or let it float (maybe use a pull-up resistor of about 2k2 to be safe) to select the second.  If you used a 27C256 you'd use two resistors and two switches for a combination of four pages.

[djsynchro]

Hey thanks!

The 2-bank chips are 27256 and the guy actually sells them with a little slider switch attached so I can just re-wire it with bigger switches on the outside. I'm really off 909 sounds but a bit of bending might set that straight, eh bent whatever. 

http://www.strellis.com

[djsynchro]

Ordered the chips! Sound will be interesting anyway 808 & 909 sampled at companded 8bit 24Khz, then hopefully the bending will improve that... Apparently the filtering deal is that: The cymbal and hihats have no filtering. The snare claps etcera have fixed filters. These are candidates for bypassing to set all the aliasing high frequencies free... but I haven't found the Drumulator service manual yet.

The 3 toms share 2 channels and they have proper SSM2044 filter chips in them. SSM was used in the 80's by Roland Sequential Korg etc. I read somehwere the Drumulator filters are dynamic meaning they do a little frequency sweep? There are trimmers near the chips but turning makes the sound go from "somewhat muffled" to "rather muffled". I can't believe I wrote "it sounds warm" in my first post. No high frequecies!

So the SSM filters could do with a modification: A pot to crank the resonance up! I looked at the data sheet and i can see the Q pin but not sure how to connect it. But I know someone who does know so I will ask them.

More later.

[Gordonjcp]

The datasheet for the SSM2044 will have an example circuit with both cutoff and resonance controls.  Be careful with them, because they're quite fragile chips and they're expensive now - although they do crop up on eBay from time to time.

I wonder why some enterprising little Chinese chip fab hasn't started knocking out bootleg SSM and Curtis chips?

[djsynchro]

The datasheet for the SSM2044 will have an example circuit with both cutoff and resonance controls. 

It does have an example circuit and I need to stare at it more like the n00b that I am heh, but it's cool I will ask my bro he built a synth once with those chips. I have also been thinking of bypassing them and pulling them out to use in a project. Drumulator might sound nicer without them.

[djsynchro]

Found this:

After playing around inside the drumulator over the weekend, I've found the ssm
2044s are not used as lpf's for the dac.
They are used to cut off the high frequencies in the tom samples. One chip
does the high and mid toms, the other does the low tom.
When the toms are triggered, a voltage pulse appears on the ssm frequency pin,
with a rapid decay. I have extracted the two chips and replaced them with a wire
link from input to output. The only difference in the sound is a hiss in the
decay phase of the toms. No other sounds are affected, and you can't really hear
it unless you listen to the toms on their own.
The owner is letting me keep the filters.

That's it - they're going OUT!!! And then I can build a nice VCF module with them later.

[Ciderfeks]

Did you ever get around to bending your Drumulator? I am being given one and would like a go at it if its worth doing? The only thing is that its obviously a mains powered machine so I wouldn't want to attempt it without some kind of directions - so I could do it all unplugged. Also, if it was left unplugged for a while, would the caps have discharged by themselves? Any help would be great, otherwise I'll leave it alone!
ps I've just noticed you bought the new chip set with the x0x sounds - are they any good?

[Gordonjcp]

The Drumulator uses - as far as I can tell - a linear power supply, so at most the caps will have about 20v across them with the machine running.  As long as you don't touch bits that are at mains potential, you can't get a shock off it.

I'd recommend using an RCD if you're poking about inside mains-powered equipment, though, just to be on the safe side.  That will cut the power if there's a fault to ground, like a stray finger ;-)

[Ciderfeks]

Thanks for the tips - the Drumulator hasn't materialised yet but when it does I'll let you know what I find.