TTL 7440 vco and more - help me expand the basic ideas

[jurekprzezdziecki]

Hi - i'm a beginner,

I have started a project based entirely on TTLs. the idea is to make as much as possible with use vintage TTL ics. I have them a lot, especially polish 74xxx series produced by CEMI. those could be trashed buy i hate to waste stuff.

So.. i have made simple square wave oscillator and restricted its range for a reasonable values with pot and two, 100r resistors. It's just NAND gate astable osc.

I have not found a good way to swing a voltage across its range with cv. I think it's because a slow response this IC or a wrong approach. I have used some standard eurorack cv modules like S&H and Maths2. Does not work so good. But i think it's possible.

Please help me with ideas to expand the circuit and develop my first Lunetta- TTL sound device.

So what would be nice to do:

1. How can i make it responsive for CV? How to make a sub - circuit that nicely tracks the oscillator?

2. I need a variable (active) low pass filter. Unfortunatelly i have not found any schematics around. Does this kind of filter exist made with TTL? or maybe you have an idea to make it?

3. It would be nice to build an vca - i have found an interesting circuit in the book (attached) but how to make it voltage controlled?

4. How to convert a square wave into a sinewave with TTL sub circuit? is it possible? i know that a passive filter at the output could make it but it's useless with a variable frequencies.

5. Noise generators. There is a way to generate a pseudorandom binary sequence (PRBS) with a linear feedback shift register (LFSR) and XOR gates. Any other ideas?

6. How to modulate square wave by another TTL circuit? I mean to change a duty cycle like with pulse width modulation?

7. Simple adsr would be nice - would you recommend some TTL circuit?

Thanks a lot in advance.

PS> TTL cookbook is on my table of course:)

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[synaesthesia]

Hi Jurek, it is possible to use TTL, but mind that you will need a capable power supply, because the TTL chips need a lot of current.
Also, most of your resistor and capacitor values will differ significantly from those that are used in CMOS circuits. I also have loads of old TTL chips and would be interested in any good circuits as well.

Regarding the oscillator, it is better to use gates with Schmitt-Trigger inputs. The 7440 or 7400 does not have that. The 7413 should be used here instead.
Regarding modulation, have a look at the first schematic. The left part generates a binary pattern that modulates the 7413 oscillator on the right side.
Regarding sine waves, don't know an easy way to do that. What I did is to approximate a sine wave by using a shift register with a resistor network that generates a stepped output close to a sine wave. The clock frequency needs to be 16 times the desired sine wave frequency. You will find that trick in the TTL/CMOS cookbooks as well. Don't use the '374 if you can, the '574 has a much nicer pin layout.

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[jurekprzezdziecki]

synaesthesia - this is great, thanks a lot for these nice schematics.

i will try them on breadboard soon. the 7413 vco looks interesting.
i assume there is no control voltage input? the way that circuit works is modulation by the second vco, right?
why NAND gate approach is worse then Schmitt trigger?

i will look for the sine wave circuit in TTL cookbook. i'm very curious how this sine wave looks and sounds like.

great start!

[synaesthesia]

Sorry, the NAND gate approach is not bad at all. I only meant to say that it is easier to use inverting gates with Schmitt-Trigger inputs. You only need one gate per oscillator then. You could also use a 555 timer for your oscillators. Not strictly TTL, but a chip from the same era.

To modulate the 7413 oscillator remove the part to the left of C2/R7 and try to insert a CV there. I need to check my old notes for the values of those. I think that 1K and 10uF are a good starting point.

I just checked the TTL cookbook and could not find the sine wave generator there. I guess my memory was wrong here. However, you can find it in the CMOS cookbook on page 379 and following. The sine wave sounds... well, ok..., but with lots of overtones because of the steps. You will hear a bit of the clock frequency coming through.

[jurekprzezdziecki]

[synaesthesia]

The accuracy would be better with a longer shift register, which would result in more steps, which gives more detail. However, that will also need a higher input frequency.
Example: n bits give you n+1 steps (none on, one on,... all on). If you use twice that many bits, you get 2n+1 steps. Better, but not really worth the effort.

[rico C]

I'm all for pushing the boundaries of chips that are acceptable for use in Lunettas, and with that in mind I'd like to recommend the XR2206 sine and triangle wave generator, which I discovered via this article:

http://makezine.com/projects/make-a-wave-shaper-multifunction-sound-synthesizer/

As I mostly run my "breadboard modular" on 12v I found this chip fit in real well and added a whole new sound element.

[jurekprzezdziecki]