Oscillators and Related Circuitry

Inventor · Last edited by Inventor on Sat Aug 31, 2019 11:17 am; edited 1 time in total

Let's play with oscillators! I was daydreaming about oscillators, logic, and assorted networks when it occurred that this topic would make a good electro-music.com project thread. So here we are.

I've purchased some parts and some more that fell through the cracks are on the way. The list includes breadboards, opamps, lamps, jumper wires and assorted "breadboard friendly" parts from Adafruit (pots, jacks, battery holders, etc.). Which, BTW, those breadboard friendly parts are golden because the tiresome task of soldering leads onto parts for breadboard use all but disappear.

So anyway, the plan is to make oscillators and hook them up in interesting ways, then play around interactively to discover something worth building. In other words, the usual interesting stuff.

So here we are at the beginning of yet another project thread and I'd just like to leave you with one thought. When you post to a project thread it motivate me. Probably the single biggest project killer is lack of interaction. So if you have a free moment, I'd love to read whatever strikes your fancy.

Here's to good times!
Les

Grumble · Posted: Sun May 12, 2019 7:11 am Post subject:

I am in the proces of building an Eurorack synthesizer:
http://electro-music.com/forum/topic-69485.html DIY Multichannel Midi to CV converter which I adapted for eurorack and has an USB midi input.
https://ornament-and-cri.me ornament and crime, speaks for itself.
https://www.muffwiggler.com/forum/topic-201663.html a dual adsr generator.
https://electricdruid.net/cem3340-vco-voltage-controlled-oscillator-designs/ I use the memory moog vco, one has a switch to lower the frequency even more in order to use it as a LFO, and two identical vco’s, so I have a total of 3 vco’s.
I made a three input VCA almost straight from the datasheet of the V2164 https://electricdruid.net/wp-content/uploads/2015/07/V2164.pdf
http://electro-music.com/forum/topic-70593.html Transistor ladder filter with input mixer.

If this is not what you are after I’m happy to remove this post.

Inventor · Posted: Sun May 12, 2019 4:33 pm Post subject:

Sure Grumble, it's great to see the gear you have. You could chain those oscillators together to test out some ideas.

What I am doing is circuit level, where it's possible to evolve it into a pedal or enclosed PCB device. Maybe even a modular board.

I am sleepy so I'll write more later.

Les

RingMad · Posted: Mon May 13, 2019 10:41 am Post subject:

Nice to see you again, Les.

Could you elaborate on what you envision? How would nets be connected together?

As for chains or loops, the first circuit I put in a box was based on the one in Nicolas Collins' book "Handmade Electronic Music" (the book that started me on this electronics adventure), wherein he proposed four NAND gate oscillators, each one gating the next one (and the last splitting into the output as well as a feedback pot going back to the first one).

Those of course are simply plugged directly.

Nets would need to involve something more elaborate, right? Resistor or diode mixers? Or maybe the interference or whatever the appropriate technical term is for when signals go backwards, affecting a circuit would actually give interesting results?

.:james:.

blue hell · Posted: Mon May 13, 2019 1:42 pm Post subject:

I think delays in the connection paths would make it Cool

come alive Exclamation

Also this made me think of a performance Howard once did, 2003 I t hink it was, in London, for two oscillators ... so a very simple network which was played by turning knobs ... let me see if I can find a link ... yupsa Smile

RingMad · Posted: Tue May 14, 2019 12:16 pm Post subject:

blue hell · Posted: Tue May 14, 2019 1:10 pm Post subject:

RingMad · Posted: Wed May 15, 2019 4:52 am Post subject:

Inventor · Posted: Fri May 17, 2019 9:22 pm Post subject:

Ty for the comments, also for the link. I used to be in such a hurry that I would not take the time to follow links and actually listen to the music of my friends. That was a mistake.

I enjoyed Howard's music well enough to call it inspiring because with only two oscillators a lot of different sounds were created. I was thinking of a similar idea. Take a look at the schematic of the Wien Bridge Oscillator (attached).

My plan is to lift up the ground terminals on the inverting and non-inverting sides and connect outputs from other oscillators in some creative way. Ideas for how to do so are forming now.

At the moment I have built an LM386 oscillator driving a small breadboard-friendly speaker, tested and working by mimicking a switch's "click" noise from silent to full volume, USB power input, and just beginning on the oscillators by creating a virtual ground.

Lets cross our fingers and hope for good luck!
Les

Wien Bridge Oscillator Reerence Circuit.jpg

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The Wien Bridge Oscillator Schematic (from Google image search)

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Wien Bridge Oscillator Reerence Circuit.jpg

RingMad · Posted: Sat May 18, 2019 5:19 am Post subject:

I'm not sure if I should post this here or in Howard/Mosc's old thread. I built a couple of 555 astable oscillators and cross-modulated them, but I don't get anything like the nice timbres Mosc did.

Specifically, for both oscillators, I took the output at pin3 and split it to its own pin5 as well as the other 555's pin5 (through a capacitor). I also took the output from one and put it into a bandpass filter, and then mixed that with the raw output of the other oscillator. So, I believe this is the essentials of what Mosc did, without the compressor or stereoization stuff. The sounds I was getting never had wild volume fluctuations, so compressing wasn't necessary.

Maybe there's something I'm missing.

.:james:.

Inventor · Posted: Mon May 20, 2019 8:35 am Post subject:

Hi James, maybe it's best to back off a little then move forward in steps.

You could connect one oscillator to the output and vary it's control(s) to observe the range of sounds that it normally makes. Then make a chain but do not close it into a loop, noting the changes in sounds that you can make. Finally add a connection to form a loop and see how you like that.

Les

Inventor · Posted: Mon May 20, 2019 2:36 pm Post subject:

Here is a quick update on my progress.

See "The Electrifried" speaker driver breadboard circuit. It is designed to receive power from the left, generate test signals in yellow wires and drive an 8-Ohm speaker on the right. It works pretty well.

More to follow.
Les

breadboard of speaker driver.jpeg

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"The Electrifried" speakervdriver

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AlanP · Posted: Tue May 21, 2019 9:47 pm Post subject:

Very cool, Les Very Happy

Inventor · Posted: Thu May 23, 2019 1:32 am Post subject:

kkissinger · Posted: Sun May 26, 2019 1:28 pm Post subject:

Hi Les. Look forward to seeing and hearing your results!

Inventor · Posted: Mon May 27, 2019 2:43 am Post subject:

Inventor · Posted: Sun Jun 23, 2019 4:29 pm Post subject:

Friends, checkout this photo of my latest test circuit. It's got my latest test circuit. The idea is to make a "Mr. Microphone" that shifts the burden of the audio output to an AM radio. This is cool because its small and simple which saves space and complexity. An equivalent circuit (single supply and LM386 speaker output with artificial ground) with more typical setup took an entire breadboard and had wires all over the place!

Below and attached to the underside of the breadboard are a pair of 6V battery holders creating Vcc and See. I like this arrangement because it eliminates the virtual ground and does not glue me to a test bench where a bench supply delivers power.

The circuit is simple: just an oscillator that oscillates in the AM band. When it's on and all tuned uo I can hear a frequency from it that drifts or warbles. It h as no antenna yes so I'm surprised that it works that well. I have t here pots: negative feedback, upper RC and lower RC. I chose this arrangement to study how the circuit works.

It's fun to listen to the frequency drift when t he power is switched on. I figure it's due to the lamp warming up (or probably al of the parts). I am currently working on removing harmonics due to the slew rate limit of the opamp of 11 Volts/microsecond. The test for that is to set the oscillator at a low frequency and scan for a harmonic at twice that frequency, then adjust the feedback pot to minimize the upper frequency. I have better pampas on order soon, but this one is what I have for now so I'm working within its limitations.

The transmit distance is about 0 to 4 inches so. At 8 to 12 inches in any direction the signal is completely lost. Of course that is without an antenna. Next up: build an antenna!

I'll post another update soon (I hope).

Les

oscillator testing.jpeg

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oscillator test circuit

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AlanP · Posted: Mon Jun 24, 2019 11:45 am Post subject:

is that a neon lamp? I've got some, but not messed around with them yet

Inventor · Posted: Wed Jun 26, 2019 3:57 am Post subject:

It's a lamp, yes. I'm not sure if it's neon or incandescent or whatever else a lamp can be. I got it from Digi-Key. I'm not sure if it's the right lamp for the job and some kids claim to have damaged half of my stock of 10 lamps including this one. The kids are pranksters. Grrr but not that much!

This lamp reads 100 Ohms when off. I heard it mentioned that sometimes the lamp glowed and other times it did not glow in this application, dependent on the setup. Or it can glow below the visible threshold in daylight and room lighting.

The way it works is the lamp has a positive temperature coefficient meaning that when it heats up it gets higher in resistance. So what happens is the amp starts out with harmonics in it's spectrum then the lamp warms up from all the signal applied to it and this causes the gain of the lamp to lower then the reverse happens, etc. (or the other way around, anyway it stabilizes). This creates a clean sine wave.

When I play with it I see signs of this happening by tuning the lamp so that harmonics exist up and down the AM dial. Then when I tune the feedback resistor (I make it a 10k Ohm pot) I notice the effect. In no case do I not notice the feedback. I think this is because the trimmer pots I am using are 10k Ohms and the resistor is 100 Ohms, so I plan to use a smaller resistor parallel with the pot to get more sensitivity. That or get a 1k Ohm or 100 Ohm pot.

Anyway, it's really fun to play with and the goal is worth the effort. Stay tuned!

Les

Inventor · Posted: Wed Jun 26, 2019 4:51 am Post subject:

"Oh man, he's writing a book!" Well, just skim it - it's not all that much.

I just wanted to make note of the purpose here and good intentions at this point. I made an LM386 circuit with a speaker and it worked pretty well. I could adjust amplitude and hear it well. It required lots of breadboard space and a big rat's nest of wires (I used jumpers instead of the neat freak technique). This worked out OK.

Then we have the simple opamp voltage follower driving a 3.5mm or 1/2 inch jack (or both for widest possible compatibility). That's OK too.

Then I got to thinking and it occurred to me that If I used an AM/FM radio as the output device, then I get hearing quality output from the board into speaker(s), headphone jack output also, and all manner of adjustments if purchased such as filtering, on/off button, volume control, etc. This I called the Mr. Microphone approach after the early 1980's product.

So basically I'm planning to try the Mr. Microphone approach! This is good for the final circuit and also for test and design because it should be easy to tap a signal on the board with a voltage follower driving some simple circuit adjustment and get both test signals and final output signal as required.

So that's the plan.
Les

Inventor · Posted: Thu Jun 27, 2019 1:38 am Post subject:

I just improved the transmit distance from about a decimeter to a full meter (early tests of me playing around show this). First I would an inductive antenna, then I made calculations for a matching resonant capacitor. The website for calculating the inductance value is here:

https://www.eeweb.com/tools/coil-inductance

I invite you to have a try at the calculations so we can discuss the matching technique in-depth.

Les

Inventor · Posted: Sat Jun 29, 2019 5:36 am Post subject:

Results! The attached 17 second file shows the oscillator being switched on (at 4 seconds or so) and then warming up as it moves in frequency space to it's final frequency (or nearly so). This shows that the circuit works.

At this point the device functions as a Mr. Microphone without the microphone, just the output transmitter. How useful is that? Well all joking aside, it is very useful. I'm thinking of steering this project thread to a fun project of a DIY kit including PCB that is breadboard friendly and helps us with audio output and signal monitoring. Such a circuit could be available fairly soon.

What do you think about that?
Les

Proto 1 Test 1.m4a

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Warmup of Oscillator Frequency

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Inventor · Posted: Fri Jul 19, 2019 3:41 am Post subject:

Hey, just a quick update here. I spent a week or two prototyping the new circuits and achieved only very limited response. I was able to transmit very poor but discernible voice from a short distance of about one foot. Also I randomly made a squelcher that worked within the same short distance.

Overall the brief exploration into Wien bridge transmitting was only partially successful. The next time I take a jaunt down this lane I plan to build an audio oscillator first, add vocals next, and radio with some new pampas I've selected. Hopefully things will go better next time.

Les

phobos · Posted: Sun Jul 21, 2019 7:53 am Post subject:

Have you tried connecting the GND to actually earth ?
Not sure if that would make much of a difference and it's not very practical but maybe worth a try.

Also came across this which actually looks more like FM to me.

blue hell · Posted: Sun Jul 21, 2019 8:49 am Post subject:

Maybe not a 'real ground' but things could improve from using a metal plate connected to the circuit ground. A guy at work recently stressed on using ground planes ... sooo ... anyways .. I found http://www.csgnetwork.com/antennagpcalc.html when googling for: minimum ground plane size