OT 40106 oscilator mixing question

[petey twofinger]

i breadboarded a 40106 with 6 oscilators (cds cells) and the problem i am having is with mixing . i have tried diodes which i like the sound of , and also using a few resistors to ground boosts it a lil more , i tried all sorts of combos . the problem is when i add the 6th voice things cut out and battle for amplification . especially a lower pitchs . i would lke to hear all the voices , i tried 10k , 47k and 100 k resistors . taking 3 voices each with a diode to one point , with a resistor to ground then joining that to the output with the identical setup for the other 3 , also a 10 k at the output to ground seemed to help but ...

if i cant hammer out the all 6 channels sounding clear could i do 2 of the channels on the chip for lfo ? would i be able to use the 2 extra cds cells to control that ? then i am guess ing 2 of the oscilators would have lfo and 2 would not . this might sound cool .

any one that could help with an i dea or experience .

i have to look for schematics for doing simple lfo on this chip , any one ever try this ?

just so you understand each channel has a diode , 3 of those channels go to a point with a 10k going to grond , then to the output , the output has a 10k to ground as well . the other 3 oscilators each have a diode going to a point with a 10k to ground , then to the output  .

i tried resistance mixing , didnt care for it as much . but i dont think its using the diodes that is making it cut out . when i pull the cap out of one of the channels , any one , it cleans up nice and you can hear it great .

one more quickie , i am guessing voltage starve for this is just a pot on the hot side ?

thanks so much !

thanks alot !

[R.G.]

i breadboarded a 40106 with 6 oscilators (cds cells) and the problem i am having is with mixing . i have tried diodes which i like the sound of , and also using a few resistors to ground boosts it a lil more , i tried all sorts of combos . the problem is when i add the 6th voice things cut out and battle for amplification . especially a lower pitchs . i would lke to hear all the voices , i tried 10k , 47k and 100 k resistors . taking 3 voices each with a diode to one point , with a resistor to ground then joining that to the output with the identical setup for the other 3 , also a 10 k at the output to ground seemed to help

I can't quite tell what your oscillators look like. Are they the standard resistor/capacitor oscillator, using the Schmitt trigger hysteresis for oscillation?

If so, and you're putting the LDR from output to input for varying the frequency, you probably need to put a large value resistor in parallel with the LDR to keep the LDR from going to really high resistances and slowing the oscillation to sub-sonic frequencies; possibly also a series resistor to keep it from going to ultrasonic frequencies when the LDR is fully lit. These things have a really wide range of resistance in many cases.

For just audio mixing, you can use resistors very well; the outputs are square waves, so at very low frequencies, they will "fight". But this is a natural part of one or more of them being off or on all the time. Restricting the frequency range will help with this.

Also remember that if you take the output from the output of the inverters, it's a square wave. If you "mix" the output with diodes, you're forming what amounts to logic gates with the diodes and any mixing resistors. This kind of MML (Mickey Mouse Logic) is a common dodge among CMOS users, but it can have unintended side effects if you expect it to be a linear mixer. CMOS gate outputs look like a low resistance to either ground or the power supply, depending on whether the gate output is high or low.

Your gating may be a side effect of some part of the circuit I can't guess at. Got a schematic?

if i cant hammer out the all 6 channels sounding clear could i do 2 of the channels on the chip for lfo ? would i be able to use the 2 extra cds cells to control that ? then i am guess ing 2 of the oscilators would have lfo and 2 would not . this might sound cool .

any one that could help with an i dea or experience .

i have to look for schematics for doing simple lfo on this chip , any one ever try this ?

You *can* hammer it out. Beyond that, yes, simple LFOs have been done with CMOS Schmitt trigger inverters. All that's different is that the timing cap and resistor are bigger. Also, if you want a triangle wave output, you have to take it from the capacitor, and that's quite a high impedance source. If you load it, it changes what the oscillator is doing. So you have to buffer the capacitor so as to not change the frequency and duty cycle of the oscillator.  There are some uses of CMOS Schmitt trigger gates for LFOs show at geofex under the article about pseudorandom LFOs and ring counter sine wave LFOs.

just so you understand each channel has a diode , 3 of those channels go to a point with a 10k going to grond , then to the output , the output has a 10k to ground as well . the other 3 oscilators each have a diode going to a point with a 10k to ground , then to the output  .

i tried resistance mixing , didnt care for it as much . but i dont think its using the diodes that is making it cut out . when i pull the cap out of one of the channels , any one , it cleans up nice and you can hear it great .

I think the diodes is what's making it cut out. Got a schematic?

one more quickie , i am guessing voltage starve for this is just a pot on the hot side ?

It depends on what you're trying to do with a voltage starve. In general, an oscillator from CMOS using Schmitt trigger gates does not need a voltage starve because the output is never linear, it's always switched high or low. The average current use is not high like it is with the gate biased to the middle of the supply.

... which you can't do with a Schmitt trigger gate anyway.

[petey twofinger]

no schematic , its pieced together from a few mini schematics from the nic collins book .



that is one of the oscilators .

they each have their own diode .the output of 3 conect after the diodes , with a 10k resistor going to ground . the other side of the chip is the same . both of those "bus's" of 3 connected connect to the output , which has an additional 10k resistor going to ground .

i am really not thinking the issue is so much the diode , because when i remove one of the oscilators the sound cleans up and you can hear all 5 . i would like to figure out how to use the 6th channel as an lfo , but i dont know how to hook that up .

like an idiot i built the enclosure first and it has 6 prominent cds cells , i would like for ach of these to do something or function . 4 voices is ok , i would prefer 5 .

has anyone pulled this off ? a 40106 with 6 oscilators , where you can hear all of them ?

[toneman]

so just build a 6-input mixer   
nothing hard about that....

all signals are zero-to-+5V (?)
U R just mixing a bunch of square waves.

6 10K resistors going to minus input of opamp (TL082)
one 10K resistor from minus input to output of opamp(this is feedback res)
pos input is tied to gnd.
simple inverting mixer with gain of 1.
could use 6 1uf caps in front of the 10K inputs...
don't need no stinkin' diodes....

Oh, i'm assuming opamp is running on bipolar power supply (?)
Say, plus and minus 10V or so...
Probably plus and minus 5V would work as that would give max out close to 10V peak-to-peak.

have fun!

[R.G.]

Here's the thing: it is easy to build the six sections of a hex schmitt trigger chip into six oscillators and have them work That's not an issue.

Diodes prevent current from flowing in one direction and allow it in one direction. Using a diode after each oscillator continuously pumps charge into or out of whatever follows it. While there is no way to say what *is* wrong without seeing a schematic, it is highly likely that the diodes are doing something to you.

There is no reason that six square wave outputs can't be mixed with resistors.

I suggest that you draw out a schematic of what you're trying to do. The problem may become obvious when you do that.

I have personally run oscillators at all kinds of frequencies from CMOS schmitt trigger gates.

[PRR]

The diodes are an OR gate, if any ocsillator is high, the OR-ed output is high.

Assuming 50:50 duty-cycle square waves, random frequencies:

Two sources, random frequencies, the dioded output is high 25% of the time and low 75%.

Four sources, high 12% of the time.

Six sources, 8.3%.

Infinite sources, zero %. Which is no output at all.

I don't know why there would be an abrupt change from 5 to 6 sources (10% to 8.3%). There may be a second-order effect with resistors and any capacitor not mentioned.

I do feel that trying six resistors is cheaper/quicker than thinking too hard.

[petey twofinger]

thanks for the responses . today i went to the bread board and found by running two osc. together , the output of one feeding the input of the other , and by using a 2.2 cap in the first and a 1 cap in the second both of the cds cells for these channels "did something" although it was only one tone .

the problem was i had built the enclosure first with 6 prominent cds cells .

so with just 5 channels it is working pretty well now . i kinda liked they way the diodes made it sound , and i already have a bunch of square wav stuff i have made over the years so this was pretty cool and it does sound  a lil different . its all boxed up , and finished .

i will end up making another one , eventually i would like to build that mixer , and then have it switch able between diode / resistor mixing , then have an option to switch all the cds cells to pots as well. i just need to find a cheap supplier for switches ! the one unit i built a few years back i call the bad idea is 2 apc's with a moded delay with an amp and speaker , it has switchable controls for pots / cds , which i really like . its pretty cool with a strobe light . the only thing is i didnt even use anything to mix them , they just connect to the input of the amp ! so i am going to try a coupla 10k's on that and see if it helps a lil .

i played with the new one today for a while , the chassis is kinda like a cigar box with a sliding lid . i had the unit sitting on its side at an angle from the light source . if you got it at the RIGHT angle all the voices would tune to a nice sounding "chord" . i was sliding the door open and closed for a super cheep wah wah effect , then i would angle it slowly and adjust the wah rate faster til i hit the next sweet sounding consonance chord . it was really fun ! what would be cool is if you could make a dual unit , with 2 chips and 12 voices . stereo with some nice full range speaker , that would be dramatic . it would be great if they made a mixer chip , some thing with 24 channels . i am not sure if that exists i bet it doesn't .

i am thinking i should try to get all my stuff in one room and tune them all to a nice resonant chord , it would be tough cause a lot of em use cds cells , but i am gonna do that and film it some time . i would just be worried about opening a rift , or killing some mice . i would like to pay tribute to the noise in phantasm , that was cool !

when i worked for att as a cable splicer sometimes we would have down time for a few hours to wait for the other guys to finish cutting at the end of the day . i brought a loud karoake amp with echo , a lil homemade lap steel , an ebow , and a 555 theramin , i would use my ryobi drill by the pu of the lap steel , it made this crazy harsh noise . tune the lappie to that and set the ebow up on it then tune the theramin . all this in the back of the van . people would gimme some odd looks , the tv's would be down all day cause we were cutting in new amps / taps . i am guessing they thought i was tuning the system up . it was excellent some of the looks i got ! my boss @#$%ing loved it too , he had a great sense of humor though . it was an excellent noise though .

[Meanderthal]

 Interesting about the diode mixing... I had thought it would form a kind of half wave rectifier, but I guess it's really an OR gate.

Anyway, one thing about these Lunetta style noise thingies is that one oscillator can affect what the others do depending on available current. Check out the Cacophonator schematic for an example of how to use this. I suppose it could be an annoyance if adding another oscillator causes the effect to happen unexpectedly.