Hello everyone, I built the super simple oscillator. I use a different transistor (BC33740), though, cause I could not find the one used in the original layout. All works well, but the 10k potentiometer I use for the tune knob can be turned maximum one fifth of its entire range. If I turn it furhter it just turns the oscillation off. This might be related to the BC33730 starting to oscillate at lower voltages, around 13 V. Is there anaything I can do to increase the range of the potentiometer? I tried a 5k potentiometer, but that started fuming, probably not built for that voltage rangeâŠ
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No need to tag this as a ânewbie questionâ. Weâre all learning here.
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Well. I think it just starts to oscillate too quick or too slowâŠ
Another thing you can change is the capacitor. (bigger=lower, smaller=higher to inaudible) I would say. Play around with it on a breadboard. Change the capacitor, change the pot.
I donât really know what you mean with fuming. Maybe you want your range between 5k and 10k? You could always put a resistor in series. So you limit your range that way. Like a 5k (appr.) resistor in series with a 5k pot? Just brainstorming.
Or is it really like you have an octave and then it shuts down? If you give your values, I could try and replicate it.
edit: Found this here: BJT In Reverse Avalanche Mode â Kerry D. Wong
Using the S9018, I managed to make it work with a single battery as you stated, but it will stop oscillating at one point as i turn my potentiometer all the way to and as it gets higher in pitch.
I understand that itâs supposed to stop at lowest frequency when the pot is all the way to the left, so I thought i needed to reverse something on my circuit, but i canât figure it out.
COuld it be the transistor ??
Youâre not the only one⊠So maybe it does have to do with the transistor.
Nit: The transistor is a BC337; the number after the dash is the gain group which isnât that relevant here. I tested one here.
What capacitor value and supply voltage are you using? Did you cut off the base pin? Which direction are you moving the potentiometer in when it stops oscillating â towards higher or lower frequencies?
The circuit works by charging up a capacitor until it reaches the voltage where the transistor opens. The 1k and the potentiometer controls the charge current, and the higher the combined resistance the longer it takes. It shouldnât stop oscillating if it takes longer, though; the charge cycle looks exactly the same, just covering a shorter or longer period.
(The circuit may indeed fry the potentiometer if the transistor stays on; the 1k isnât big enough to protect it if the wiper is too close to the connected end lug when that has happened. A potentiometer with a lower resistance can handle more current, thoughâŠ)
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On CMOS oscillators I like to add a "stopping " resistor (I think thatâs what it was called); a small resistor in series with the pot that ensures you canât break the circuit or give the caps no way to discharge properly (itâs 5am here I may have got this wrong) , @fredrik 's suggestion of a serial resistor is the way Iâd go first.
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Thanks for all your comments. The values are pretty much the ones from the layout on lookmumnocomputerâs site on the super simple oscillator: 10”F capacitor, 1k resistor in series with the pot and 100k on the way to the speaker. I tried to change the capacitor to 22”F and 50”F which changes the frequency but does not increase the range.
The bit of the potentiometer I can use is the one with the lowest resistance, that is from open to about 1/5th closed. Higher resistance values turn of oscillation.
Hence my idea with a smaller resistance value. As for the fuming: it started to well, melt and smoke. I learned that potentiometers differ in the power they can take an aparently that one was from a series that cannot take much.
Edit: Forgot the supply voltage. I get oscillation at around 10 Volts but turn it up a bit further to ~12 Volts since that produces a clearer sound. A the beginning the frequency is so low its more individuals pulses rather than a sound. (I use a cheap lab supply for this.)
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The bit you found is interesting. My problem though is that it turns off when the frequency becomes too low. As the author argues, this is normal. It just happens too fast. Or stated differently, the frequency range I have should be streched out on the range of the pot.
My intuition would be to reduce the resistor in series with the pot but I am a bit worried of frying more pots. The parts I use are all leftovers from a friend so I donât know much about their specs.
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I think I saw a similar shutoff. I just assumed the avalanche requires some minimum current flow.
You could just put a 2k resistor in parallel with the pot. Then you can use the whole pot range, though the resistance wonât be linear in the wiper position any more.
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This works! Although I do not quite understand why. In my mind (with vague residues of school physics) all the current should go via the resistor that is parallel to the pot as soon as the resistance of the pot exceeds the 2k resistance of the resistor. That cannot be right, because the pot now indeed works on its entire range and not just 2k (which should be a fifth of the linear 10k pot). So what happens here?
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They both have the same voltage over them, so a fixed current will go through the 2k and a variable current through the other one.
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The current goes through both paths, no matter how you set the pot. The resistance of the overall circuit is given by adding the reciprocal (one-divided-by) of each resistance and then dividing the result into one.
R = 1/(1/R1+1/R2)
The effect of having the fixed resistance in parallel with the pot is that the maximum resistance across the terminals is limited. It can never be greater than the fixed resistance. When the pot is equal to the fixed resistance, the total resistance of the circuit will be one half of the fixed resistance.
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Possibly enlightening:
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It should perhaps be mentioned that since 10k isnât that much larger than 2k, enough current will go that way also at high settings that the combined resistance wonât get close to 2k. Also, as @analogoutput points out, the resulting resistance curve is non-linear. Hereâs a plot:
The blue line is the resistance of the 10k pot as a function of the rotation (0-100%), the red the combined resistance. It ends up at 2k||10k = 1.67k.
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Right, you could maybe increase the 2k resistor to get a little more range, depending on exactly where things cut off. And as you can see from the graph, while you do get to use the full range of the pot, it doesnât really buy you that much since the variation of the combined resistance in the top 50% is quite small.
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Thank you all, I learned so much from your posts. So my intuition that the 2k are kind of an upper limit was a bit right but my explanation so wrong.
I measured the pot at the cutoff point in the original circuit and found it to be at ~2500K. So with the help of Bitnikâs formula I found that a resistor in parallel with 3333 Ohms would be optimal. I approach that with 3K and now Iâm happy with my small noisy circuitâŠ
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Hello guys et girls.
First thread for me on this great forum so I didnât want to start a new topic for a simple and maybe numb question.
Iâm quite happy for now with my first built of the simple oscillator.
The idea would be to build a few one and have a âmaster tuneâ knob. And Iâm not really sure of where I should plug the âmasterâ potentiometer and his value.
A ? :
Or B before the 1k resistor ?
Sorry guys I donât have a bredboard yet so itâs not that easy and quick to try on the go.
Cheers
Robin
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Neither diagram will work as shown, because you have only one pot terminal connected, so the pot is not effectively a part of the circuit.
In the SSO the pot wiper (middle terminal) is connected through a series 1k resistor to +V and an end terminal to the transistor. This is kind of dodgy because it means you have enough current flowing through the pot to light up the LED, at least some of the time, and pots are not meant to take that kind of current. For a pot to control multiple SSOs you could consider connecting the wiper to your battery or power supply and the end to the â+Vâ points on the SSO boards (like your second diagram, but with power connected to that pot rather than to each board), but then youâre putting enough current to light multiple LEDs through one pot. Iâd think that would risk destroying the pot.
If the âCVâ connections were really control voltages then youâd be able to use the pot as a voltage divider to create a common control voltage for all boards, but it isnât; itâs where you would connect something like a vactrol or, yes, a potentiometer to put a variable resistance in parallel with the pot on the board. But you canât connect one pot to multiple âCVâ points and expect it to work.
In Samâs Megadrone panel what he does is he uses a MOSFET to create true voltage control for the oscillators, and then has a pot as a voltage divider feeding all the oscillatorsâ CVs.
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Thanks for your response analogouput.
My bad⊠I forgot to connect the pot in my diagram.
So if Iâm not using CV I could try this :
I will defintely have a look at Samâs megadrone schematic and learn more about MOSFET.
Another question, is it ok to put several capacitor in serie to change the frequency on the way ? For exemple, if Iâm using a 50”F capacitor in my circuit. Could I use a switch to add another 50”F capacitor in serie and get something like 1oct down ?
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Capacitors should be in parallel to increase capacitance.
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Speaking of Newby questionsâŠ
So, Iâve built a super simple oscillator using ss9018 and a 9v battery. The 10k pot works great, and I added the tone/filter 100k pot per Samâs diagram, which seems to work backwards as volume control (clockwise lowers volume, anti-clockwise increases volume.)
Iâve tried reconfiguring the wiring for that pot every way I can think and it either functions as described above, or doesnât work (because wired just totally incorrectly.) Help! There has to be a correct wiring to get the volume to increase with a clockwise rotation of the pot, right? Right??
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