John Larkin's LC oscillator
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From: Winfield Hill on 8 Jun 2010 06:39 was Re: Twin T circuit wanted John Larkin wrote... ftp://jjlarkin.lmi.net/Ships_Bell.JPG > On Mon, 7 Jun 2010 George Herold wrote: > >> I loved your bell circuit John! I didn't quite get how the >> inductor was working. But still I got the idea. Thanks. >> >> George H. > > This is kind of a cute circuit. I first designed it when I needed > a very frequency and amplitude-stable sine wave to drive a Talyvel > LVDT-like inclinometer, part of the Boresight Alignment Kit for > the C5A. We had to measure level to arc-seconds of accuracy. > > It's a transformer with a resonant tank in the collector and a > positive feedback drive winding into the emitter. The emitter > feedback is just a couple of tenths of a volt p-p. > > The cool thing is that the collector swing is almost exactly 2xVcc > peak-to-peak. As the amplitude builds up, at the negative swing peak > the emitter goes a little bit negative, to get out of the way, and > the collector swings to just about ground. That forward-biases the > c-b junction and discharges the base cap, reducing transistor base > current hence gain. So it has a built-in peak detecting AGC amplitude > leveling loop with close to zero TC. All from 5 parts. Or sometimes > six. > > I tested the system on a 55 gallon drum full of sand, with a huge > steel plate on top. We built a platform that pivoted on ball bearings > and we moved a long lever arm with a micrometer, to tweak the sensor > angle. I had to tell people not to walk nearby, because their weight > would flex the concrete slab of the building. > > I learned a bunch on this project: HeNe laser power supplies, > synchronous detectors, optics. I've always sort of liked this > oscillator. With your explanation, the oscillator is much more attractive. Some folks can't stomach magnetics, perhaps that's part of the criticism. Anyway, ignore JF and JT when they get bitchy, it must be something they ate, or is age catching up with 'em? Our old friend, Tony Williams, R.I.P., would have been pleased. .. John Larkin's LC oscillator, supply-V sets amplitude .. _________________ .. | | | .. | _|_C E || L .. Rb --- E || .. | | E || .. | | * | || .. | +-----' || .. | | || .. | C gnd || .. +- B | || .. _|_ E E || .. --- | * | || .. | +-----' || .. gnd | .. '--- out Tell us more about the inductor / transformer, turns ratio, etc. Did I get the winding polarities right? I suppose you have to keep the emitter's reverse-voltage under say 5V breakdown, so 10Vpp max output? What are the prospects for making this into a high-power oscillator? Drive a speaker directly? -- Thanks, - Win
From: default on 8 Jun 2010 09:59 On 8 Jun 2010 03:39:30 -0700, Winfield Hill <Winfield_member(a)newsguy.com> wrote: > > With your explanation, the oscillator is much more attractive. > Some folks can't stomach magnetics, perhaps that's part of the > criticism. Anyway, ignore JF and JT when they get bitchy, it > must be something they ate, or is age catching up with 'em? > > Our old friend, Tony Williams, R.I.P., would have been pleased. > >. John Larkin's LC oscillator, supply-V sets amplitude >. _________________ >. | | | >. | _|_C E || L >. Rb --- E || >. | | E || >. | | * | || >. | +-----' || >. | | || >. | C gnd || >. +- B | || >. _|_ E E || >. --- | * | || >. | +-----' || >. gnd | >. '--- out > > Tell us more about the inductor / transformer, turns ratio, etc. > Did I get the winding polarities right? I suppose you have to > keep the emitter's reverse-voltage under say 5V breakdown, so > 10Vpp max output? What are the prospects for making this into > a high-power oscillator? Drive a speaker directly? > > >-- > Thanks, > - Win I'd be curious to see values. It isn't "necessary" but I would like to know what core, type, size and material you used. Did you tweak the tuning? Running with banks of them to simulate a real bell, did you calculate and tune for specific harmonics? My basic interest in the twinT was simplicity, and easy to adjust frequency and decay time, but your design is simpler. Like you said, if you were to really try for an authentic bell sound, you'd probably find some weird frequencies and their amplitudes changing as it rang. A million year ago I played drums in concert marching and dance bands. With large cymbals and gongs you can see the resonant modes fading in and out and chasing around the circumference - a blur, but visible. From the sound of large bells, I'd guess they also behave that way. (then there's generally a bell tower with its own resonant columns adding to bring out and attenuate harmonics) --
From: John Larkin on 8 Jun 2010 10:14 On 8 Jun 2010 03:39:30 -0700, Winfield Hill <Winfield_member(a)newsguy.com> wrote: >was Re: Twin T circuit wanted > >John Larkin wrote... > > ftp://jjlarkin.lmi.net/Ships_Bell.JPG > >> On Mon, 7 Jun 2010 George Herold wrote: >> >>> I loved your bell circuit John! I didn't quite get how the >>> inductor was working. But still I got the idea. Thanks. >>> >>> George H. >> >> This is kind of a cute circuit. I first designed it when I needed >> a very frequency and amplitude-stable sine wave to drive a Talyvel >> LVDT-like inclinometer, part of the Boresight Alignment Kit for >> the C5A. We had to measure level to arc-seconds of accuracy. >> >> It's a transformer with a resonant tank in the collector and a >> positive feedback drive winding into the emitter. The emitter >> feedback is just a couple of tenths of a volt p-p. >> >> The cool thing is that the collector swing is almost exactly 2xVcc >> peak-to-peak. As the amplitude builds up, at the negative swing peak >> the emitter goes a little bit negative, to get out of the way, and >> the collector swings to just about ground. That forward-biases the >> c-b junction and discharges the base cap, reducing transistor base >> current hence gain. So it has a built-in peak detecting AGC amplitude >> leveling loop with close to zero TC. All from 5 parts. Or sometimes >> six. >> >> I tested the system on a 55 gallon drum full of sand, with a huge >> steel plate on top. We built a platform that pivoted on ball bearings >> and we moved a long lever arm with a micrometer, to tweak the sensor >> angle. I had to tell people not to walk nearby, because their weight >> would flex the concrete slab of the building. >> >> I learned a bunch on this project: HeNe laser power supplies, >> synchronous detectors, optics. I've always sort of liked this >> oscillator. > > With your explanation, the oscillator is much more attractive. > Some folks can't stomach magnetics, perhaps that's part of the > criticism. Anyway, ignore JF and JT when they get bitchy, it > must be something they ate, or is age catching up with 'em? Age is a terrible thing. You have to fight it, or at least fool it, for as long as you can. > > Our old friend, Tony Williams, R.I.P., would have been pleased. > >. John Larkin's LC oscillator, supply-V sets amplitude >. _________________ >. | | | >. | _|_C E || L >. Rb --- E || >. | | E || >. | | * | || >. | +-----' || >. | | || >. | C gnd || >. +- B | || >. _|_ E E || >. --- | * | || >. | +-----' || >. gnd | >. '--- out > > Tell us more about the inductor / transformer, turns ratio, etc. > Did I get the winding polarities right? I suppose you have to > keep the emitter's reverse-voltage under say 5V breakdown, so > 10Vpp max output? What are the prospects for making this into > a high-power oscillator? Drive a speaker directly? Polarity is right. The voltage in the emitter winding is small, just a couple tenths of a volt p-p at full output, so there's no stress on the e-b junction. The collector swings to 2*Vcc, so the transistor Vce has to be rated for that. If you want a big output, take it off the collector or a third winding. I vaguely recall doing this with permalloy powder cores and with slug-tuned pot cores. I used to use a lot of magnetics for stuff like this, before active filters and DSP got to be easier. There is a tiny flat-top on the negative collector swing, when the "peak detector" works. The more base bias current, the bigger it is. If it matters (it didn't for the inclinometer) add a small resistor in series with the collector. John
From: George Herold on 8 Jun 2010 10:53 On Jun 8, 9:59 am, default <defa...(a)defaulter.net> wrote: > On 8 Jun 2010 03:39:30 -0700, Winfield Hill > > > > > > <Winfield_mem...(a)newsguy.com> wrote: > > > With your explanation, the oscillator is much more attractive. > > Some folks can't stomach magnetics, perhaps that's part of the > > criticism. Anyway, ignore JF and JT when they get bitchy, it > > must be something they ate, or is age catching up with 'em? > > > Our old friend, Tony Williams, R.I.P., would have been pleased. > > >. John Larkin's LC oscillator, supply-V sets amplitude > >. _________________ > >. | | | > >. | _|_C E || L > >. Rb --- E || > >. | | E || > >. | | * | || > >. | +-----' || > >. | | || > >. | C gnd || > >. +- B | || > >. _|_ E E || > >. --- | * | || > >. | +-----' || > >. gnd | > >. '--- out > > > Tell us more about the inductor / transformer, turns ratio, etc. > > Did I get the winding polarities right? I suppose you have to > > keep the emitter's reverse-voltage under say 5V breakdown, so > > 10Vpp max output? What are the prospects for making this into > > a high-power oscillator? Drive a speaker directly? > > >-- > > Thanks, > > - Win > > I'd be curious to see values. It isn't "necessary" but I would like > to know what core, type, size and material you used. Did you tweak > the tuning? Running with banks of them to simulate a real bell, did > you calculate and tune for specific harmonics? OK not my circuit, but try whatever they build audio transformers out of. The LC on the collector sets the freqeuncy so that pretty much determines your L. (Guess I figure a C of 0.01uF to maybe 1uF.??) Then John said that the emmiter sees only a few tenths of a volt where the collector is going +/- 12, so I'd start with maybe 50 or 100 to 1 turns ratio. Can spice do oscillators? (I remeber trying once and having a hard time getting it started.) George H. > > My basic interest in the twinT was simplicity, and easy to adjust > frequency and decay time, but your design is simpler. > > Like you said, if you were to really try for an authentic bell sound, > you'd probably find some weird frequencies and their amplitudes > changing as it rang. A million year ago I played drums in concert > marching and dance bands. With large cymbals and gongs you can see > the resonant modes fading in and out and chasing around the > circumference - a blur, but visible. From the sound of large bells, > I'd guess they also behave that way. (then there's generally a bell > tower with its own resonant columns adding to bring out and attenuate > harmonics) > --- Hide quoted text - > > - Show quoted text -
From: dagmargoodboat on 8 Jun 2010 10:55
On Jun 8, 6:39 am, Winfield Hill <Winfield_mem...(a)newsguy.com> wrote: > was Re: Twin T circuit wanted > > John Larkin wrote... > > ftp://jjlarkin.lmi.net/Ships_Bell.JPG > > > > > On Mon, 7 Jun 2010 George Herold wrote: > > >> I loved your bell circuit John! I didn't quite get how the > >> inductor was working. But still I got the idea. Thanks. > > >> George H. > > > This is kind of a cute circuit. I first designed it when I needed > > a very frequency and amplitude-stable sine wave to drive a Talyvel > > LVDT-like inclinometer, part of the Boresight Alignment Kit for > > the C5A. We had to measure level to arc-seconds of accuracy. > > > It's a transformer with a resonant tank in the collector and a > > positive feedback drive winding into the emitter. The emitter > > feedback is just a couple of tenths of a volt p-p. > > > The cool thing is that the collector swing is almost exactly 2xVcc > > peak-to-peak. As the amplitude builds up, at the negative swing peak > > the emitter goes a little bit negative, to get out of the way, and > > the collector swings to just about ground. That forward-biases the > > c-b junction and discharges the base cap, reducing transistor base > > current hence gain. So it has a built-in peak detecting AGC amplitude > > leveling loop with close to zero TC. All from 5 parts. Or sometimes > > six. > > > I tested the system on a 55 gallon drum full of sand, with a huge > > steel plate on top. We built a platform that pivoted on ball bearings > > and we moved a long lever arm with a micrometer, to tweak the sensor > > angle. I had to tell people not to walk nearby, because their weight > > would flex the concrete slab of the building. > > > I learned a bunch on this project: HeNe laser power supplies, > > synchronous detectors, optics. I've always sort of liked this > > oscillator. > > With your explanation, the oscillator is much more attractive. > Some folks can't stomach magnetics, perhaps that's part of the > criticism. Anyway, ignore JF and JT when they get bitchy, it > must be something they ate, or is age catching up with 'em? > > Our old friend, Tony Williams, R.I.P., would have been pleased. > > . John Larkin's LC oscillator, supply-V sets amplitude > . _________________ > . | | | > . | _|_C E || L > . Rb --- E || > . | | E || > . | | * | || > . | +-----' || > . | | || > . | C gnd || > . +- B | || > . _|_ E E || > . --- | * | || > . | +-----' || > . gnd | > . '--- out > > Tell us more about the inductor / transformer, turns ratio, etc. > Did I get the winding polarities right? I suppose you have to > keep the emitter's reverse-voltage under say 5V breakdown, so > 10Vpp max output? What are the prospects for making this into > a high-power oscillator? Drive a speaker directly? > > -- > Thanks, > - Win Here's a quick implementation: Vcc = +5v --+-------+------+-- | | | | | |_ || | | _)|| .-. --- L1a _)|| Rb | | C1 --- 1mH _)|| 100k | | 1uF | _)|| '-' | _)|| | | *| || | .-+------' || | |/ || +---| Q1 || | |>. 2n3904 || | | * || C2 --- +---------. || 1uF --- | L1b _)|| | | 25uH _)|| | | | === | === | '-------------> output (5KHz values shown) collector swing ~= 2*(Vcc+0.6v) emitter swing = Vc * sqrt(L1b/L1a) 1 f(out) = ------------------- 2*pi*sqrt(L1a * C1) That's a 1rst cut--I may have left L1b a little hot... Simulates really nicely--sine waves. -- Cheers, James Arthur |