The Crumar GDS Restoration Blog...

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Re: The Crumar GDS Restoration Blog...

Post by BrianK » Thu Sep 25, 2014 9:21 pm

I have a GDS in good condition with many disks. Also have access to another with as many discs, many dozen. Plus documentation. I suggest buying any VT100-standard terminal off eBay... Not expensive and designed to work with the system.

The cryoflux system is what I will be using to archive these discs and will make things available once we do. It's a pretty robust system, I fund disc drives (and formats) to be the main trouble with old computers...

I have two of the Con Brio systems here, also sturdy and functionally intact. Sharing ideas on drives and backups will be most welcome. Don't worry about the discs, we have lots and are willing to help.

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Re: The Crumar GDS Restoration Blog...

Post by madtheory » Thu Sep 25, 2014 9:36 pm

Woah! Hello Mr. Kehew :)

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Re: The Crumar GDS Restoration Blog...

Post by HideawayStudio » Thu Sep 25, 2014 10:57 pm

BrianK wrote:I have a GDS in good condition with many disks. Also have access to another with as many discs, many dozen. Plus documentation. I suggest buying any VT100-standard terminal off eBay... Not expensive and designed to work with the system.

The cryoflux system is what I will be using to archive these discs and will make things available once we do. It's a pretty robust system, I fund disc drives (and formats) to be the main trouble with old computers...

I have two of the Con Brio systems here, also sturdy and functionally intact. Sharing ideas on drives and backups will be most welcome. Don't worry about the discs, we have lots and are willing to help.
Hi Brian, this is amazing news... are GDS's like buses? - you wait several months thinking none will come along and then three arrive one after another in a day! :D (so that's a significant part of the total population accounted for now!)

I have sent you a private message - we really need to exchange notes (excuse the pun)...

Although I'm well versed with HxC I've yet to experience the Kryoflux disk imager.

I have some amazing news too....

Image

This morning a fresh set of 8" disks turned up - never opened, still in their original film.

I booted up the system on one of the 34 year old disks and managed to format one of the new disks.

To my very great surprise I then managed to copy over 80% of the contents of the really badly scuffed system disk to the new disk file by file using the PIP command.

I managed to 100% copy the demo voice disk to a new disk.

Sadly one of the programs that didn't make it was PERFORM but VOICE, FLOAT and all the test utilities copied fine.

So I turned everything off and refitted all of the custom S100 bus synth cards and the large main oscillator board to the top lid of the IMS8000 computer.

I nervously wound up the variac and reset the system which booted and ran the OSCTEST program for the first time - to my surprise all of the self tests passed. I then ran the KBTEST program and found that all of the switches, LED and sliders were working on the synth console bar the pitch bender.

So I decided to go for the big one and attempted to run one of the main GDS synth applications...

Since I couldn't run PERFORM I had a go running FLOAT instead which is also a performance program.

Up came the menu - I loaded a demo sound patch...

Sound!! Actual Sound!!

I then managed to load the VOICE application which enables you to load and play single voice patches for editing.

The first headache I ran into is that without the infamous overlay you are confronted with a sea of sliders, switches and knobs with no labels whatsoever!!...

Naturally there are problems but at day two of this is really spectacular for a 35 year old beast that has been gathering dust in a non working state for many years.

I managed to run the beast for 4 hours carefully monitoring the heat levels around the computer, Oscillator, PSU and keyboard assemblies whilst recording throughout.

I spent a few minutes putting a quick demo together from the slightly more palatable moments of my testing whilst running through a set of early demo patches to celebrate...

So this is Mr Schulze's old GDS fully awakened for the first time in lord knows how long..........

1979 GDS Awakens:
Last edited by HideawayStudio on Mon Oct 13, 2014 8:17 am, edited 4 times in total.

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Re: The Crumar GDS Restoration Blog...

Post by desmond » Thu Sep 25, 2014 11:28 pm

Sounds pretty good for such an old lady!

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Re: The Crumar GDS Restoration Blog...

Post by SquareWave » Fri Sep 26, 2014 12:07 am

Wow! For some reason this just gives me chills! I was making synth music in the 80's, so this stuff doesn't sound that antique to me, yet I think it's all about the few individuals who still possess the will and knowledge to resurrect some of this old non-standard stuff. It makes you realize how on the cutting edge it was at the time! And how little we value older tech. Makes me wonder what tech we see today will be as rare in 30 years...

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Re: The Crumar GDS Restoration Blog...

Post by StepLogik » Fri Sep 26, 2014 12:50 pm

Amazing! I'll be following this very closely!

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Re: The Crumar GDS Restoration Blog...

Post by HideawayStudio » Fri Sep 26, 2014 10:28 pm

I spent this morning releasing my latest and not totally unrelated new sample library (DK Synergy) and after the usual frenzy I turned my attention back to the GDS this afternoon..

Image

One of the things that was initially preventing the beast boot up was that it turned out that the solid state mains relay (rated at 40 Amps!) used to enable the two huge 220 Volt synchronous AC spindle motors was burnt out. I had temporarily wired this over in an attempt to boot the IMS8000 host computer but the noise of the two huge 8" belt driven floppy drives permanently running and the big cooling fan in the back of the chassis was crazy so I ordered a replacement SSR (which, amazingly, are still in production to this day and eye wateringly expensive!).

Image

I spent a little while removing the large oscillator board in the top lid and set about replacing the relay which is mounted on the very large linear PSU that fills 30% of the chassis.

On partial reassembly it seemed like I hadn't fixed the fault - no spindle motors.. I then came to realise that the system will only boot either if the control card for the oscillators is removed or if it is plugged in and the oscillator board is plugged into it. So on full reassembly the spindle motors came up and the system booted and then after a short pause... the noise levels dropped dramatically :)

Image

This is good news for three reasons... it is much more pleasant to use the instrument this way, it greatly reduces the wear on the disks and it reduces the heat buildup from the motors and motor capacitors.

Image

To celebrate I carried on loading up some sound patches I hadn't tried yet from the demo disk and still really wishing I had a copy of the infamous control surface overlay you see on various historical pictures of the GDS including this one (so where did it go?)

Now I know the GDS is complete and pretty much 100% functional my next task is to start putting together a detailed report of what is needed to make each subsystem a little more robust on a board by board basis. Needless to say with an instrument of this age a good chunk of this involves replacing a plethora of capacitors. As with any recap its about being pragmatic and assessing the risks the old components are to their surrounding circuitry and perhaps less importantly to the signal path as this is a digital instrument. There are some types of capacitor which have great longevity and rarely pose much of a threat to the life of equipment such as metal film polyester/polypropylene, silver mica and PTH ceramics - then there are much higher risks such as old tantalum caps which have a really nasty habit of failing dead short circuit and perhaps those with the worst press - electrolytics - which dry up and can fail either short or open circuit but rather too often fail in a pretty messy/noisy way. There are many tantalums all over the GDS and a handful of very large and scary electrolytics in the PSU (50,000uF each!) The very same type and brand of orange tantalums were what originally killed my DK Synergy and so they must go along with the PSU caps which would be really nasty if they let go (and believe me they do from time to time!). There is also at least one EPROM in a critical position which at 35 years old is really living on borrowed time - it is very important the contents of this chip (the IPL) is read and a fresh chip copied to put in its place. This is now doubly urgent as I'd found another IMS8000 owner in the UK who attempted to make an image of his own IPL chip (a part of the stock computer and not the GDS components) and it didn't survive the task - oops!

The report will also detail all the tasks to improve the cosmetics. Generally the instrument is in nice condition but the there is a metal trim plate missing on the front of the keyboard console that will need to be fabricated. Very fortunately another GDS owner has kindly made a drawing for me. The top panel of the computer chassis is not a pretty thing to look at and doesn't even look pleasantly distressed so that will need repainting. Sadly also the faux wood end caps on the keyboard and system unit haven't taken kindly to being knocked around over the years and, like all restorations of gear with interesting pasts, it's a question of whether these should stay as is or whether they should be overhauled. If this was solid wood like a lovely aged guitar then it would be great but frankly this is more like a chipboard kitchen unit that has had a pan dropped on it - not so nice...

Image

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Re: The Crumar GDS Restoration Blog...

Post by madtheory » Sat Sep 27, 2014 11:27 am

Is it a weighted keyboard like the Synergy?

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Re: The Crumar GDS Restoration Blog...

Post by HideawayStudio » Sat Sep 27, 2014 11:46 am

madtheory wrote:Is it a weighted keyboard like the Synergy?
The key mechanisms are almost identical to the Synergy but the complete keybed is has one less octave (which is curious being the more expensive of the two models) - it's actually quite a nice quality action that somewhat reminds me of that on the Chroma under the fingers (which is weighted the traditional way with slugs of metal screwed to wooden keys) but with plastic keys.

Both the GDS and Synergy are velocity sensitive but not with aftertouch.
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Re: The Crumar GDS Restoration Blog...

Post by madtheory » Sat Sep 27, 2014 1:01 pm

Thanks.

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Re: The Crumar GDS Restoration Blog...

Post by BrianK » Sun Sep 28, 2014 6:07 pm

Agreed, except nothing feels as good as a Chroma! The overlay you seek is one of several - as you might imagine the system IS programmable and customisable, so I will get some photos of various ones we could use to recreate our own. Not too hard, and most-helpful, depending on the mode and version of the software being used.

Happy to be in touch, your discoveries will help mine etc as we restore these to more stable and "sound" condition....

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Re: The Crumar GDS Restoration Blog...

Post by madtheory » Sun Sep 28, 2014 6:50 pm

Wow is the Chroma better than a KX88? The sound it's triggering makes a huge difference to the "feel" :)

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Re: The Crumar GDS Restoration Blog...

Post by HideawayStudio » Sun Sep 28, 2014 7:12 pm

madtheory wrote:Wow is the Chroma better than a CS80 or a KX88? Or a Peavey DPM C8? I've only personally played the KX88, but am reliably told the CS80 is lovely and the Peavey is worth more than they sell for. Have an Akai MX1000 myself, it's fine.
In terms of key action?

I recently restored a Chroma and fell in love with it. It is a very expressive instrument with a wonderfully warm and complex sound, really powerful modulation capabilities and a beautiful key action that just begs to be played.

It is sadly, however, really let down by it's membrane keypad and UI with it's Korg DW style two digit numerical display and single slider which just slaughters the programming experience.

Sadly they don't have the CS80's amazing polyphonic aftertouch but they can be retrofitted with mono aftertouch.

From an engineering point of view the CS80 is a mad mad piece of kit with the wiring loom and calibration procedure from h**l (I cannot imagine the number of hours labour that went into making them!) - it really is the stuff of a crazy man in terms of build and design. The Chroma actually a nice thing to work on with much better access to its internals than say a Polymoog thanks to the sensible modular card cage fashion all the pcbs are layed out internally.

That said, I really missed both the Chroma and Polymoog 203A when they had to go back following restoration.

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Re: The Crumar GDS Restoration Blog...

Post by ppg_wavecomputer » Sun Sep 28, 2014 11:18 pm

Yikes!

Again, you've managed to amaze me quite a bit.

The old Schulze GDS looks so much better than I remembered (with beer and coke spilled over it, and cigarette ashes all over it). I guess the GDS keyboard controller that recently was up for sale on eBay was TD's old one, then (the seller was a bit secretive about it).

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Re: The Crumar GDS Restoration Blog...

Post by MiK » Mon Sep 29, 2014 8:40 am

Hello together,

so finally i also registered because this GDS restoration blog is extremely interesting...

And for one question:
ppg_wavecomputer wrote:The old Schulze GDS looks so much better than I remembered (with beer and coke spilled over it, and cigarette ashes all over it). I guess the GDS keyboard controller that recently was up for sale on eBay was TD's old one, then (the seller was a bit secretive about it).
Did you mean eBay Germany, half a year ago? (And maybe a year ago, it was listed twice). If yes, that's mine now :)

I just have this keyboard controller, the main system is missing - but as a DIY enthusiast, i'm planning to recreate the Synergy/GDS with modern electronics since several years, it would happen already if i had more time. Controlling a modern GDS replica with the original controller just sounds like a nice idea.

...Michael

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