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Anything Analog:  CS question for Old Crow


04-Jan-04 (Richard)
04-Jan-04 (oldcrow)
04-Jan-04 (bulldogge)
04-Jan-04 (oldcrow)
04-Jan-04 (bulldogge)
04-Jan-04 (madmax)
05-Jan-04 (oldcrow)
05-Jan-04 (oldcrow)
05-Jan-04 (oldcrow)
05-Jan-04 (Richard)
05-Jan-04 (bulldogge)
06-Jan-04 (DiyFreaque)
07-Jan-04 (madmax)


Original Message
Richard.... CS question for Old Crow (04-Jan-04  07:25AM )

- Tried emailing you but it got sent back.

I've got a CS-30L and just wonder edif you could help with a few queries I've got about it.

Do you know if it's possible to still get chips for it? Are the chips in a CS-50 compatible? If the VCF chips are the same, how come the filters are set-up different? I presume they're different chips.

Cheers from the Isle of Man

Richard

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oldcrow.... Re:CS question for Old Crow (04-Jan-04  05:14PM )

- The CS-30/30L use the same chipset as the CS-50/60/80. The differences in things like signal routing for the filters happen outside the filter chips. In the 50/60/80, there is only the hardwired HPF->LPF signal path for each VCO. In the 30, this is just one option among several routings.

Anyway, the chip set Yamaha made in the mid-70s has not been manufactured for 20 years. There are only two ways to really replace defective ones: either scavenge them from another instrument--usually CS-50/60 or 80s that have been badly damaged due to shipping mishaps, water damage, etc. and are broken up for parts; or my preferred method of making equivalent circuits out of standard parts.

Now, I realize option#2 isn't what most folks can resort to, but unfortunately, unless Yamaha decides to re-issue the chip set, that is the only way to repair these machines.

What is wrong with your CS-30?

oldcrow

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bulldogge.... Re:CS question for Old Crow (04-Jan-04  05:21PM )

- Thanks, Crow. Are all the main CS-series monosynths based on these chips as well (CS-5/15/40--I figure the CS-01 is different)? I always just assumed that they were discrete, but it does make more sense for them to use the same chips budget-wise.

I think that people don't give enough importance to the hardware around the chips when considering chip-based synths. For instance, there are a lot of synths that use the same CEM chips as the Xpander and sound pretty mediocre, IMO, but the Xpander sounds incredible. Since the chips are the same it would seem that the supporting hardware (and software) must also play a large part in determining the final sound.

One question about option #2: how do these circuits compare in size to the Yamaha chips? I would think that in the long run if you had to replace most of the chips in a CS-80 with these circuits you would be getting into some serious space problems. This isn't a criticism, as I think most people who love these synths should thank you for having any option besides scavenging, but rather something I've been wondering.

bulldogge

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oldcrow.... Re:CS question for Old Crow (04-Jan-04  07:06PM )

- bd,

No idea what is in the CS01 or CS02 as I've never had the opportunity to examine them. Otherwise, the CS-5, 10, 15 and 30 all use the same parts, just in different configurations as to how many VCOs, VCFs, signal routing options, external input options and so on. I would imagine the 'm' instruments (CS-20m, 40m and perhaps 70m) also use some of the chips.

There is an important point that is often overlooked when talking about chip sets like this. That is, how these are chips actually implemented in a circuit. A number of manufacturers that used for example CEM parts typically followed the datasheets when building their circuits. This is fine, but datasheet examples are not the definition of how a part is 'supposed' to be used. Datasheet examples are primarily meant as starting points. Of course, this brings up a whole new issue: the fitness of a datasheet to the part it describes. Thomas Henry, well known for commercial and DIY synthesizer circuits, wrote several handbooks on the use of some parts that by the datasheet seem rather limited, but applied a different way become very muscially useful. Example: Google for "Making Music with the 566".

Anyway, the actual application of a part far more determines the sound of an instrument than the part itself. This where various makes and models get their character. From your example, an Xpander attains a very distinct, musically useful tone whereas something like a rev3 Prophet-5 sounds more "datasheet CEM-y". Understand that I am not relly knocking the rev3 Prophet-5 here, just noting that parts are only a percentage of a circuit and design technique/philosophy and dropping similar parts into different designs cannot help but result in different sounds.

Yamaha is even a bit more different from this, because there aren't any published datasheets for their chip sets. The application of the IG-series chip set, which is derived from the "NE" (I like to think it means 'New Electone') submodules as used in the SY-1, SY-2 and perhaps most famously the GX-1 is based more on engineering notes from NE designers than anything. Just about everything on an IG chip is already normalized so as to need little external hardware to operate it. This is why they can cram 11 chips on a CS-50 M board that is only about 3"x 5" in size.

Which brings me to the equivalent circuit size issue. For something like the CS-50/60/80 M boards the only real option is to build a replacement of the entire board. Otherwise, there is no way to fit them all in the card rack. This is the path I am pursuing, although I am field-testing each sub-circuit (VCA, VCF, EGs, etc) before putting it in the final design.

oldcrow

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bulldogge.... Re:CS question for Old Crow (04-Jan-04  09:19PM )

- "Example: Google for "Making Music with the 566". "

Yup, I've seen this and other Thomas Henry books. It really seems like there's an art to getting different usage out of chips, and obviously not everyone will be nearly as inventive or successful at it--as the Xpander vs. other CEM gear shows (not that I dislike CEM gear--the opposite if anything).

I hadn't really thought of that in terms of the CS-boards--I think I was assuming that by doing them as individual circuits you were intending them to be used that way for repairs. That answers my question quite clearly.

bulldogge

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madmax.... Re:CS question for Old Crow (04-Jan-04  10:48PM )

- I heard that the SK series used some stuff from the CS series.

I have a different size question relating to the chip circuit re-creation. Don't chips have/use much smaller electric values(ohms, volts, farads, etc.) than discrete parts we're used to seeing? Do synths have transformers before after the chips, or do you have to use them in conjunction with the diy circuits?

I don't know about others, but I'd rather have a synth fixed Cuban-style than trash it. :) Thanks for your reply!

madmax

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oldcrow.... Re:CS question for Old Crow (05-Jan-04  12:58AM )

- OK, some general notes on re-creating equivalent circuits for CS machines that explain at least my take on when "drop-in" vs. "LRU" designs should be used.

In some cases, it is not necessary to replace an entire board just for the sake of one or more esoteric parts. A good example would be the Yamaha IG00151 VCA. This is a chip that I can remake using one standard IC and three transistors, plus about eight resistors. An IG00151 is just an OTA with an exponential (2 of the transistors) current converter on its control input and a 3rd transistor to set the converter's linear reference current based on an an input CV. Thus you get an expo CV in, a linear CV in, two OTA (inverting, non-inverting) signal inputs, three supply voltage connections and the OTA output pretty much in an 8-pin 'SIP-pinned' PC board that is perhaps 25mm x 12mm in size. These just fit into the (CS-80 card rack's) boards without touching adjacent boards.

But that is just one VCA out of around 200 that are in a CS-80. There are a few boards in the rack that are nothing but VCAs. Now, IG chips tend to be quite reliable, but like any part it can fail. If it is a single device failure, making only 1 of 24 parts on a board that needs replaced, then the above "drop in" solution is what I would use.

The LRU (least-replacable unit) concept centers more around economy and the ultimate end goals in refurbishing a piece of equipment. "Least-replacable" refers to how far down into the layers of hardware one should go to make repairs and still be able to justify the expense of repairing it. This method largely comes from how service centers cover warranty repairs on active products. For example, if you have a Yamaha Motif-8 (currently an active product) that has developed a fault and the instrument is is turned over to a service center, what Yamaha does is have a service tech locate the general fault area (power supply board, display, processor failire, etc) then *replace that entire piece*. They don't go down to the component level to repair problems simply because it costs the company less to just swap in a new board, power supply, etc. than to pay for the labor of tracking down the ultimate problem. A lot of the old boards get scrapped, but not before they go through a recovery procedure to determine which ones might be repairable and thus be useful as repair parts for the next Motif-8 or whatever comes in.

The LRU concept for out-of-production devices is useful in my case for the CS-80 because it is much easier to do quality control on an entire synthesizer board than just part of it. Take the example URL below. This shows a board I made to repair Korg Polysixes, which suffer from a design oversight that placed an eventually-leaky NiCad battery next to some crucial digital ICs. The resulting corrosion ruins the board. While in many cases this damage is repairable (I have a web site detailing said repair), eventually it became a problem of diminishing returns as some boards could be fixed in 2 hours whereas other boards took more than 40! It takes far less time to just build and calibrate a brand new one that is assured not to have any residual corrosion problems. It takes longer than 2 hours, but certainly less than 40. :)

The same approach I am taking with CS-50/60/80 boards because it is just less of a hassle to adjust an all-new synth voice than try to adjust a board comprised of a mix of old and new circuits, at least for me.

TBC

Link: http://www.oldcrows.net/~oldcrow/synth/korg/polysi ...

oldcrow

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oldcrow.... Re:CS question for Old Crow (05-Jan-04  01:30AM )

- For madmax:

For the kinds of relatively simple circuits we're talking about, the characteristics of the semiconductors either in a chip or built of individual discrete parts are essentially the same. The key differences are chiefly what supply voltages and power dissipation a chip can handle versus the same circuit made from discrete parts. Also, ICs try to avoid the use of internal capacitors as much as possible because they are HUGE chip real-estate hog. For example: an LM301 opamp uses two pins for attaching an external frequency-compensation capacitor which is not a large value, something like 30 picoFarads. An LM741, which is essentially the same opamp but has an internal 30pF capacitor. If you look at the photomicrographs of the chip circuits (old databooks will show these, newer databooks/datasheets seem to have lost this habit) it will be obvious where thre 30pF capacitor in the 741 is, as it takes up 1/3 of the picture.

The main issues in chip vs. discrete linear circuits are related: temperature stability and self-heating. While there are chips made with beefed-up microparts on them (things like dot-matrix printhead driver ICs that have to drive 300mA on each pin), most linear stuff runs on low currents, most of the time 1mA or less for the various transistors or diodes inside the part. In fact, things like OTAs have to run at low current levels or they'll overheat and self-destruct. Also, transistor tolerances can be controlled better when they're all being etched on the same chip die. Now, discrete homogeneity (exact or near-exact behavior between parts of the same device number) has certainly gotten better by leaps and bounds in the past 30 years, but even so, keeping them in an environment where they're all affected by real world changes (carrying your CS-5 from the car to the house, and temperature goes up 10 degrees) still tends to fare better for circuit based on devices settled together on a chip than for the individual parts. This is why Intersil/Harris still sells tons of dual matched transistor ICs.

Unsure what you mean by transformers before and after chips. I'll take it to mean other parts in general. Just about any chip can be expected to connect other various "glue parts" whether they are other chips (like opamps), transistors, or even things like panel controls. An equivalent circuit for a chip would just connect the same way.

oldcrow

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oldcrow.... Re:CS question for Old Crow (05-Jan-04  02:00AM )

- Oh, for for Yamaha chips are where they're used:

Yamaha is a very chip-happy company. There are hundreds of different chips models that have been made by them over the years. Their 'YM' series of largely LSI and VLSI digital parts have been in synthesizers, organs, and combo instruments since the early 1970s. I've found IG-series parts in a number of organs, and YM series parts in every electronic device they make.

oldcrow

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Richard.... Re:CS question for Old Crow (05-Jan-04  03:58AM )

- Thanks for the info.

My CS-30L works fine, just wanted to find out if I could source spares for if anything went wrong. I've also got CS-50 that is working so it could be scavenged for parts. Both synths have their attributes but I prefer the CS-30L, and monosynths in general.

Richard

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bulldogge.... Re:CS question for Old Crow (05-Jan-04  07:40PM )

- Thanks, Crow. That's a great post on different repair needs and the philosophies behind them.

bulldogge

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DiyFreaque.... Re:CS question for Old Crow (06-Jan-04  12:25PM )

- Hmmm...sorry to land on this so late, and it is a bit off-kilter with the jist of this topic, but the Thomas Henry thing with the 566 is amazing. I purchased the book last summer, and only tried it out this past Christmas break (I'm planning to have a couple of simple VCO's in a ring modulator module normalized to carrier and modulator). I intend to have the VCO outputs externally available for 'non-precision' stuff. I was really, really surprised at how well Thomas' exponential design performed - it's a lot less 'non-precision' than I had figured, which was a very nice surprise.....and the sine wave produced by his circuitry is the purest I've ever been able to muster.

Cheers,

Scott

DiyFreaque

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madmax.... Re:CS question for Old Crow (07-Jan-04  11:48PM )

- What I meant by transformer is the thing that change voltages.

I thought that chips have more and smaller components, and thus would need weaker signals as not to fry.

In my second semester of physics, we did a lot of stuff with electricity. That is a few years ago, so I'm a bit rusty in concepts and such. I'll look in a textbook I have to maybe give a good example of what I wanted to ask.

The thing I read about the sk series was something other than digital chips. It was either oscillators or filters.

madmax

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