jojjelito

Chipforbrains is Technology Transplant ;D Toodles!

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?

Hehe, the Mathematica thing was just me being too lazy to actually juggle the equation in order to get a tidy expression in the form v= numerator/denominator. I'm no EE by educashun so I usually measure what I calculate before connecting any CEM/SSM or expensive hardware just to be safe :-[

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!

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?

Will there be another run of this? I was reading something that amounted to such a thing? I fear the shipping to Sweden part, but I hafta investigate. Hearsay is that Mouser is expensive, Digikey less so.

The SID chips arrived to Stockholm this promising morning. That was seriously fast! Big thanks to Wilba! ;D

Hello, sorry for the lateness! If I still can I'd like to join by ordering: 50 x 3FTL6 50 x 1E.09.6 Best regards, olga42

Sooner or later I'll get them that chips and then it's building time... Now back to some Dada Life and them pesky CEM chipsorz (3372, 3374, 3350 and 3396). All the cool kids are doing it 8)