Ensoniq Mirage Mods

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SynthularModulus
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Ensoniq Mirage Mods

Post by SynthularModulus » Tue Feb 25, 2020 4:18 pm

I just picked up an Ensoniq Mirage for a good deal, and I am interested in what other folks have done in terms of mods. I know there is a mod to replace the disk drive with a USB stick, but I am interested in other mods as well. The analog filter chips in the Mirage should allow for manual control of cuttoff and resonance by adding knobs. Anyone tried this?

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ersatzplanet
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Re: Ensoniq Mirage Mods

Post by ersatzplanet » Wed Feb 26, 2020 2:47 pm

There was a "stereo" mod a while back that split half the voices to one channel and half to the other, but you could not place them in any way, the voices are chosen via a next note manner so the sound would jump around depending on what you played. Some people made it so it was not hard left and hard right but places evenly across the field.

Did a google search and here is one of the pages showing how - http://www.synthzone.com/midi/ensoniq/m ... irage.html
-James

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Re: Ensoniq Mirage Mods

Post by SynthularModulus » Wed Feb 26, 2020 4:04 pm

Thanks for the reply. Looks like an interesting mod, but to me, I'm not sure it's really worth the effort, since I plan to put it through stereo effects anyway, and I can use a modern sampler if I really need multiple outs.

I'm actually surprised there isn't more info out there about modifying the filter(s). It seems like it should be pretty straight forward. Maybe I just need to give it a try, and document what I find out.

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Re: Ensoniq Mirage Mods

Post by ersatzplanet » Thu Feb 27, 2020 2:54 pm

The filter chips in the Mirage are CEM3328 chips so one would think that you could easily just sum a control voltage into the same pins that the Mirage is using to control them. You would have to be concerned about keeping the voltage you are adding lower than the level the CEMs can handle and also isolating your added voltages from going back upstream and frying any of the Mirage circuits. That could be done with switches if you really wanted to be safe (disconnect the mirage control when using yours).

Of course it would help a ton if you got the schematics for the Mirage, but at least almost all the ICs on the Mirage are socketed so you can do it all on proto boards plugged into their sockets and not hack the Mirage itself.
-James

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ersatzplanet
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Re: Ensoniq Mirage Mods

Post by ersatzplanet » Thu Feb 27, 2020 3:00 pm

Just did a Google search on "Mirage Schematic" and there were a few good hits. From one of the downloadable PDFs, this is the section :
Screen Shot 2020-02-27 at 11.57.29 AM.png
Looks like pin #2 is the target.
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Re: Ensoniq Mirage Mods

Post by SynthularModulus » Thu Feb 27, 2020 9:43 pm

Thank you for your replies, great information there.

I am considering several ideas, modding the Mirage, or using the chips in something else, perhaps eurorack. But, assuming I decide to go with modifying the Mirage, I would love it if I could inject CV into the 3328s, but basically sum that with the internal voltage from the machine, so the envelopes still have some effect. But you bring up a good point about protecting the rest of the Mirage circuits from that voltage. I am not sure how to do that, other than your suggestion of using switches.

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Re: Ensoniq Mirage Mods

Post by ersatzplanet » Fri Feb 28, 2020 11:22 am

I had 2 Mirage racks and a Keyboard and tried to sell them a while back with no results. I started trying to sell them as "CEM3328 testing units" and sell them for the cost of the CEMs inside. I finally sold both the racks as Mirage racks recently (Keeping the keyboard) within weeks of each other to people in different parts of the country. I guess there was a sudden resurgence in people's appreciation for these machines.

I would keep yours if it works. You can get the CEM chips for under $20 each nowadays so it would be easier to just buy the chips and not hack the Mirage.
-James

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Re: Ensoniq Mirage Mods

Post by SynthularModulus » Mon Mar 02, 2020 11:46 am

ersatzplanet wrote:
Fri Feb 28, 2020 11:22 am

I would keep yours if it works. You can get the CEM chips for under $20 each nowadays so it would be easier to just buy the chips and not hack the Mirage.
Thanks for the tip. I've decided to keep the Mirage intact, but I am still interested in seeing if I can modify the filter with manual control of cutoff and resonance. Seems like it would just make it much more playable, and I feel like I can probably get a more beefy sound out of the filter than how they have it set up stock.

This might end up being a long-term project on the back burner, but if I end up doing something with it, I will keep folks updated.

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Re: Ensoniq Mirage Mods

Post by SynthularModulus » Fri Mar 06, 2020 10:42 am

Just curious if there is anyone out there who owns a Mirage, who would be interested in collaborating with me on modifying them? We could exchange notes, and each modify our own Mirages, and see what we come up with. Any takers?

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Re: Ensoniq Mirage Mods

Post by ZLAL » Thu Apr 09, 2020 5:01 pm

I’m currently repairing the power supply on my Mirage and will likely be installing one of the HXC floppy drive emulators because the OG discs are so expensive these days. Anyone done one of these mods and have a sense of the difficulty?
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Re: Ensoniq Mirage Mods

Post by jorg » Fri Apr 10, 2020 10:26 am

Not specific to the Mirage, but you'll notice there's a voltage divider at the CV input. This greatly attenuates the CV input; it sort of makes the input look like a "virtual ground" like you see on an op amp. That means it's pretty simple to sum in another CV. The mirage supplies the CV through a 27k resistor. The example in the datasheet uses 43k:
https://pdf1.alldatasheet.com/datasheet ... M3328.html

The Mirage schematic fragment above doesn't show values for the resistors to +8V and GND. If you're trying to achieve 1V/Octave you'd need to know those and do some calculations. But most likely you'll be happy enough if you start with, say, 47k and see if you are happy with the amount of CV range you get on your external input. You can change the value up or down from there. You might choose to wire your input through a pot and a switched jack, so if you unplug the jack, it defaults to a DC value that you can adjust with the pot.

I understand there are 8 VCFs in the Mirage. That would imply you should probably buffer your external input with an op amp, then send it through 8x47k resistors to all the VCF pin2 inputs. Or your could provide 8x input jacks but that seems a bit unwieldy unless you really want to make a filter bank (hmmm...?).

I notice the IN+ (5) and RES (4) pins are unused. If you're doing mods, you'd likely want to provide an external audio input and a resonance control. :party: The datasheet linked above shows the circuit for that. You'll have to cut the ground traces to those pins first. If you are plugging a stripboard into the chip socket, that should be easy (just don't connect 4&5 on the Mirage PCB to 4&5 on the CEM3328 which you will have moved onto your stripboard).

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Re: Ensoniq Mirage Mods

Post by coolshirtdotjpg » Fri Apr 10, 2020 10:40 am

I saw a keyboard mirage sell on craigslist recently for 140 and really wanted to nab it as a spare/potential hack unit. My mirage rack gets used quite a bit now that I sold my ESQ-1 seems like with Reverb (the website) all of these older units are getting a lot more expensive so circuit bending or hacking makes less sense. There is also a eurorack mirage filter, which will cost you as much as a mirage, if you want voltage control over the filter.
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ersatzplanet
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Re: Ensoniq Mirage Mods

Post by ersatzplanet » Fri Apr 10, 2020 3:02 pm

coolshirtdotjpg wrote:
Fri Apr 10, 2020 10:40 am
I saw a keyboard mirage sell on craigslist recently for 140
That is cheaper than the value of the CEMs inside it.
-James

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Re: Ensoniq Mirage Mods

Post by SynthularModulus » Fri Apr 10, 2020 5:56 pm

jorg wrote:
Fri Apr 10, 2020 10:26 am
Not specific to the Mirage, but you'll notice there's a voltage divider at the CV input. This greatly attenuates the CV input; it sort of makes the input look like a "virtual ground" like you see on an op amp. That means it's pretty simple to sum in another CV. The mirage supplies the CV through a 27k resistor. The example in the datasheet uses 43k:
https://pdf1.alldatasheet.com/datasheet ... M3328.html

The Mirage schematic fragment above doesn't show values for the resistors to +8V and GND. If you're trying to achieve 1V/Octave you'd need to know those and do some calculations. But most likely you'll be happy enough if you start with, say, 47k and see if you are happy with the amount of CV range you get on your external input. You can change the value up or down from there. You might choose to wire your input through a pot and a switched jack, so if you unplug the jack, it defaults to a DC value that you can adjust with the pot.

I understand there are 8 VCFs in the Mirage. That would imply you should probably buffer your external input with an op amp, then send it through 8x47k resistors to all the VCF pin2 inputs. Or your could provide 8x input jacks but that seems a bit unwieldy unless you really want to make a filter bank (hmmm...?).

I notice the IN+ (5) and RES (4) pins are unused. If you're doing mods, you'd likely want to provide an external audio input and a resonance control. :party: The datasheet linked above shows the circuit for that. You'll have to cut the ground traces to those pins first. If you are plugging a stripboard into the chip socket, that should be easy (just don't connect 4&5 on the Mirage PCB to 4&5 on the CEM3328 which you will have moved onto your stripboard).
WOW, jorg, this is awesome, thanks so much for the info!! You just greatly boosted my confidence in being able to achieve this. I honestly don't care that much about achieving precise 1V/Oct tracking on the VCF. I mean that would be ideal, but is not a requirement for me. Anyway, I am going to mull this information over a bit, but I may have a question or two. :)

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Re: Ensoniq Mirage Mods

Post by SynthularModulus » Fri Apr 10, 2020 6:02 pm

ZLAL wrote:
Thu Apr 09, 2020 5:01 pm
I’m currently repairing the power supply on my Mirage and will likely be installing one of the HXC floppy drive emulators because the OG discs are so expensive these days. Anyone done one of these mods and have a sense of the difficulty?
I am also thinking of doing the HXC floppy install. Maybe I'll order one next week. If I do, I'll keep you posted, and please let me know if you have any progress with yours.

Now, what I would really love to figure out, but this is wayyy off topic, is how to convert .wavs to a format that can be copied directly to a usb stick and read by the HXC. I believe that is possible using some old DOS software, but that seems more than a little clunky to me.

Anyway, feel free to PM me if you wanna chat more about modding Mirages.

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Re: Ensoniq Mirage Mods

Post by wahee » Mon Jun 15, 2020 4:49 pm

google MIRIMAGE

a program for making HFE files from WAV files
the HFE then should work on your GOTEK floppy emulator

they may need renamed to
DSKA0001.HFE
DSKA0002.HFE
DSK....
etc
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Re: Ensoniq Mirage Mods

Post by rationale_music » Tue Jun 30, 2020 2:32 am

Just wanted to chime in and say that I've been experimenting with some Mirage modifications as well. Adding external filter control would be great, but there's also a custom OS disk someone made years ago that allows you to control the filter cutoffs with the pitch-bend wheel, so at the very least you could use that and just control it with your DAW.

I've been doing hardware mods on the Mirage for years while I've been repairing and selling them. Mostly the stereo/octophonic mods (which is great, btw). I recently was experimenting with adding a rotary encoder to control parameter values but sadly that one didn't end up working.

The next experiment will be adding a switch or variable resistor to control the filter bass cut at high resonance.

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