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jojjelito

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Posts posted by jojjelito

  3. 40x2 Green-on-Black Optrex Displays - ORDERING INSTRUCTIONS

    in Bulk Orders

    Posted

    **

    @olga42 - I guess you're familiar with Austin (I just added that I was from there to my profile last night, LOL)?  Funnily enough I had someone in the office ask me if I wanted to go to Chuy's for lunch earlier today but unfortunately I had already eaten. :-)  As for live music, this weekend is the Austin City Limits Music Festival so I'll be doing that for the next 3 days!

    Haha, this would be way OT, but sometimes you gotta pay respect to the Elvis shrine. Plus, we must all get our obligatory "Keep Austin weird" T-shirts from somewhere...

    Now back to Mountain Dew, Aout and SSM-based good unclean fun. Enjoy the festival!

  5. STM32 based Core Europe

    in Bulk Orders

    Posted

    Weird this. There I was, somewhat puzzled by the lack of any announcement, seeing Smash's Core32-page. Maybe I should

    a) Wait for Smashy

    b) Organize something for folks from my own country (Sweden)

    c) Be patient...

    Anywho, shipping is the proverbial purse of pain (bag o' hurt) and there's nothing Smash can do about it that hasn't been tried or discussed I think. The whole AVI Showtech service is very good so maybe we are not that worse off left to our own devices? Back to holding pattern until the tower says ready.

  10. MIOS Project - Oberheim - M1000 XPANDER {PCB traces uploaded}

    in Design Concepts

    Posted

    Hi again Artesia! I've been looking into this a bit more but my coding skills are rusty to put it nicely. However, I tried to fill in the blanks on the CEM by looking at the schematics of the previous art. Next up is to forge ahead with block diagrams and then pencil in some solutions.

    How to get to an MB3396:

    • Voice card hardware (your very nice board).
    • Rudimentary timing system with rough tuning accuracy, can be done with the Core i/o or PWM.
    • Multiplexed control using data distribution and S/H circuitry. The ghetto method (4051s plus caps) can be employed if we can guarantee fast updates.
    • Improved timing, possibly with range switching of the waveform converter. See below.
    • Improved S&H as in the Xpander service manual (small and large steps, smoothing etc).
    • Waveform trimming. See below.
    • Sync mode logic lifted from the Oberheim schemos.
    • Other autotuning for the DCOs (is this needed?) and the VCF frequency/tracking etc.

    The lite/lab version of the software needs to grow as the above goals are reached.

    3396 timing and range:

    There are quite a few things to realize around the 3396 chips for this to be viable. It was observed in the thread http://www.midibox.org/forum/index.php/topic,7466.0.html that the DCOs are best driven using dedicated timer chips (8253/8254) or with a beefier MCU. Also, the data-sheet gives away that active correction is needed for the waveform converter in order to reach more than 6 octaves of range.

    I was looking at the Cheetah MS6 schematics available at: http://www.butoba.net/homepage/MS6-schem.pdf as well as the Matrix-6/6r schematic at: http://www.flickr.com/photos/matrixsynth/sets/72157607736211309/ in order to see how that may be done. It turns out that I can't really see the range trick implemented since not all ICs can be identified in any event. However, the reasoning behind this is given in the CEM3396 PDF pp.7-8 and a solution lies in the last barely legible page. It seems that the other schematics source at Oberheim Heaven contains corrupt files. Better Matrix-6 scans would be helpful.

    Waveform trimming:

    Also, there is talk about using the processor and successive approximation to trim for the correct waveshape in the CEM PDF. The processor can measure the triangle wave output using an SR flip-flop to detect glitches. I see some circuitry for this in the last page of the data-sheet as well as the circuitry for the [tt]PULSE[/tt] signal visible in the Matrix-6 schematics.

    I am going to try to study these schematics in order to decipher which chips have been used for some reverse engineering. I hope someone else can also gleam something from this. Your board can be tapped for the CEM3396 output and the waveshape circuitry can be placed off-board. Range switching seems trickier to place but can be omitted at first in any case.

    Then there's the software :)

    Suppose that a slave PIC has to update the various CVs at the 4051s if we copy that method. This means that the MIOS node (Core) processes MIDI, takes care of GUI-related tasks, patch mgmt etc and then updates various registers in the slave. Also, someone (the MIOS node?) needs to update the timer if an external timer IC is used. Or we wait for the new Core32 to do all of this. I smell periodic tasks so this won't be a walk in the park.

    Moving on to loftier software goals: It would be really nice to be able to read/convert Matrix-6/6r/1000 as well as MS6r patches whilst observing parameter differences such as lin/log envelopes plus mono/bi/multitimbral settings. This is totally over the top and best done using a proper computer.

    There it is... the road ahead to the old, much talked about MB3396 in some form. This is usually how far it gets it seems. It needs takers and doers. I can at least try to fill in the gaps for the 3396 chip (any help is welcome). Over to our OP Artesia.

  12. MIOS Project - Oberheim - M1000 XPANDER {PCB traces uploaded}

    in Design Concepts

    Posted

    No worries. You're correct of course: it's easy to add an alternative solution to replace the 4051/53 combo. The DG408 ferinstance is of course not pin compatible with the 4051 as that would make life less interesting. When I built my old multimode I used an ADC, pot and jack combo for the mode select :) It was awsomeness in a very small box  8) but might not be for everyone.

    I suspect that RX27 needs to be changed as the signal at cell4/Cd is probably 70 times weaker than that of Ca-Cc. This can be inferred via pouring over and comparing with the 3379 PDF. This is not a problem per se for the Xpander/Matrix 12 since those use the externally available VCF out which is larger in amplitude. Anywho, if need be that's a real quick change which doesn't affect the PCB.

    Now, I need to start looking at the 4 odd CEM 3396s as well as the copy of the Cheetah MS-6 service manual I got with a couple of them courtesy of Ebay. Damnit, this fall/autumn will be busy if it starts depleting my check later stash  :o

    As for nice extras: if you add the frosting on top you could end up with realtime filter mode changes as well as continuously variable waveshapes thanks to PWM and modulating the waveform slope. The M1000 could only do modulation via LFOs as it was never to big on NRPNs or controllers. Almost drool-worthy and very analog sounding.

  13. MIOS Project - Oberheim - M1000 XPANDER {PCB traces uploaded}

    in Design Concepts

    Posted

    Sweet deal!

    The thing is that the old 405x chips produce plopping sounds when switched. They are not ideal if any realtime switching is going on. It's been observed by Marc Bareille that the DG40x chips are more silent. He made this board: http://m.bareille.free.fr/modular1/vcf_multimode/extrapole.htm which is also based on the xpander filter. I would suggest a component change if you want to go "analog Wavestation" with this, but the DGs cost a fair bit.

    Earlier on there was a thread about using CEM filters in Design Concepts where I went through some of the intricate bits involved in the VCF CV in order to help a poster who was looking at making a vcf board. Earlier I was experimenting with the CEM3379 thinking that it too could be xpandified. Turns out it can, but it doesn't have this constant volume/bandwidth trickery that the CEM3372 has, so the VCF output drops a lot with increasing resonance. I might be useful to try out the CEM3396 for this as well before getting high hopes, but the datasheet for the 3396 mentions this and it looks more similar to the 3372 in topology than the 3379 so with some luck it this feasible with a good/useful result.

    Now, it's too bad I don't have a Matrix 1000 in some closet :) There's only some 3396 chips in a drawer and my wish to blow some life into a potential MB-3396 along the lines of the old user project floating around but based on the new core.

  14. gm5x5x5 Bulk Order

    in Bulk Orders

    Posted

    A couple of white PCBs  (maybe it's cupcake frosting?) did arrive in mah mailbox. To think they came all the way from Dresden, beautiful city of the Frauenkirche conveniently located between Berlin and Prague to little old me... Das is echt geil! Thank you!  8)

  18. Swedish Electronic shops

    in Nordisk

    Posted

    I wrote in the http://www.midibox.org/dokuwiki/where_to_order_components where you can go in general. Labb Elektronik mentioned earlier is now gone, Bhiab has some of their old stock, for instance lots of different (even rare) transistors. Trimlog is also gone, BTW.

    Also, JEC has most of the supposedly rare stuff if you are thinking 303-clones (you know which ones I mean :-X) or x0x-stylee drum machines. I can also recommend http://www.electrokit.se/ for various bits and bobs.

  21. CEM 3372 "Xpander" VCF/VCA for MB SID

    in Design Concepts

    Posted

    Hi Gav! You're about to get there but there is some speculation about the OB that doesn't ring true I believe.

    If you take a peek at either the 3378 reduced size data sheet at http://www.synthtech.com/cem/c3378pdf.pdf or at the CEM3389 data at http://www.synthtech.com/cem/c3389pdf.pdf page 4 it says that the upper limit of about 90mV yields an upper frequency limit of 20kHz. Also, it states that the lower limit of 5Hz sits at -150mV and that the frequency control scale is 17.5(min), 19.0(typ), 20.58(max) mV/octave. So, -140mV is still resulting in a lower frequency than the 20Hz you can hear. Low enough to rattle things I have heard  ;D

    But, yes - your numbers are correct. I didn't have my notes near me so I guesstimated the +110mV in my first post - sorry for that. Since you did the math and arrived at the correct numbers (I checked them vs my notes and did the calculations again!) I could add insult to injury by writing down how I manually shortened the equations so that I am really thorough:

    Freq CV = 0v: 0-v/20 - v/1 +(-5-v)/33 = 0

    -v/20 -v +(-5-v)/33=0

    -v/20+(-5-v)/33 = v

    -5-v/33=20v+v

    20(-5-v)=33(21v)

    -100-20v=693v

    -100=713v

    v=-100/713

    Freq CV = 5v gives you v=65/713 (0.091) after some shortening.

    Back to the Obie: I deeply suspect a different CV range. Let me check its' schemos and service manual if you want a checked response plus calculations. However, the above thing plus the data sheet works well. Also, the VCF is very much the same-same in CEM3378/3379/3389 and the CEM3372 - close enough for the data sheets to suggest the same configuration. Also, it may be a good read to see how the recommended caps were chosen (see the 3389 pdf) and compare those with those of the Obie - I wouldn't assume they are identical. The CEM3372 PDF at Synthtech is really short and not very forthcoming. Maybe there is a more full version in the old yellow On-Chip data book I have somewhere?

  23. CEM 3372 "Xpander" VCF/VCA for MB SID

    in Design Concepts

    Posted

    Hello again, sorry for the delayed reply. There was some holiday activities involved. Anyway, back to the theory:

    I remembered Kirchhoff's Current Law: The sum of all currents, into and out of a point, is zero since we cannot store current in an ordinary junction point or a node if you will.

    So, I ran Mathematica using the formula:

    [tt]Solve[(0-v)/20+-v/1+(-5-v)/33==0, v][/tt] in order to find the voltage v at the filter input pin 2 on the CEM chip. This is for the case where the applied filter CV is zero volts.

    This is assuming that we stick with the resistors used in the data sheet (20K, 1K, 33K). Please try this for the OB values and you'll see what they most likely use in terms of voltage range.

    How did I arrive at the formula?  ???

    Assume that the filter CV voltage is v and that the applied CV is 0 volts. Observing the Kirchoff law we get:

    (0V-v)/20kOhm +-v/1kOhm+(-5V-v)/33kOhm = 0  :o

    Also, I used Ohm's law (V = R*I) => I=V/R in order to get an expression for the currents. Sometimes V is called U, E or emf depending on your application.

    Cheers!

  24. CEM 3372 "Xpander" VCF/VCA for MB SID

    in Design Concepts

    Posted

    Hello all,

    I hope I'm not late to the party spoiling something. I just finished a filter using a stereo pair of CEM3379s and couldn't help but noticing the similarities in biasing. The VCF CV is a small signal input so all that is done using the resistor network is some biasing. For instance on the 3379/3389 the VCF input needs to stay in between -155 to +110 mV for a CV input of 0 to 5V before the resistor divider (if we go by the data sheet looking for a control range of 14 octaves). The CEM3372 has exactly the same recommended signal range and its' data sheet shows exactly the same resistor divider of 20K with 33K to Vee and 1K to GND.

    I don't have my lab notes in front of me so please bear with my lack of maths at this time; but circuit analysis of this type of divider can be done using the fact that the sum of all current at any point in the circuit is zero - current into the point equals current out from the point. This means that current in to the VCF CV pin on the chip will give a voltage of around -150mV when the CV signal before the 20K resistor is 0V. Solving this for a +5V CV we get close to +110mV. This is the old manufacturer's data sheets so far. What has been done by Oberheim and others is probably just a re-biasing to fit their chosen CV range.

    Hit me back with questions if this makes no sense so that I can retrieve my lab notes where the formulas exist.

    How about the -5V needed? Couldn't there be a local regulator on your board to generate this?

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