John Larkin's LC oscillator
in [Design]
|
Prev: Skybuck's Universal Code Version 6 (The Fast Version)
Next: CCt to converter 24Vdc signals to 12Vdc signals
From: George Herold on 8 Jun 2010 11:04 On Jun 8, 10:55 am, dagmargoodb...(a)yahoo.com wrote: > 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- Hide quoted text - > > - Show quoted text - Cool thanks James, Say can you take it up to 10's of MHz? George H.
From: default on 8 Jun 2010 11:13 On Tue, 8 Jun 2010 07:53:24 -0700 (PDT), George Herold <ggherold(a)gmail.com> wrote: >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. > I was thinking about it from a more practical perspective - like do I really want to build 12 of these? Frequency of oscillation would be where the inductive and capacitance reactance are equal - but from a theoretical perspective that could be with any inductance like 6" of wire and large C to work in the audio range . . . in theory at least. If I have to come up with 12 laminated cores that's harder than say 12 ferrite toriod cores (which I may have on hand). But I guess all I really need is a handful of iron wires and a coil around them . . . that I could do with what is in my junk collection. >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: John Larkin on 8 Jun 2010 11:30 On Tue, 08 Jun 2010 09:59:02 -0400, default <default(a)defaulter.net> wrote: >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? After 35 years, I can remember schematics but I can't remember parts values. I do recall that a few guys stood around and critiqued the bell sound, and I changed capacitors to tweak the frequencies. I'm tin-eared, totally unmusical, so I get advice on stuff like this. I recall doing some of these kinds of oscillators using slug-tuned pot cores, to trim frequency, but the ship's bell thing was pretty crude, and once we got some cap values we just built them, no tuning. It would be interesting to Spice this oscillator. Complex things happen as the collector voltage dips down near zero, and I wonder how accurately Spice would handle that. Probably pretty well. > >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) I think a bell has several resonant modes close in frequency, and they tend to beat. And it has not-quite harmonics of those modes, which fade out faster than the fundamentals. I know a guy, a PhD ME, who owns a small machine shop as a side business. He makes handbell sets. It's hard to buy the right "bell brass" which he says is the only stuff that works right. He casts the basic forms and finishes them on an n/c lathe. He has a hammer that whacks the bells, a microphone, a lot of FFT type processing in a PC, and he closes the loop on machining. He claims his bells are as good as hand-tuned-filed ones. John
From: dagmargoodboat on 8 Jun 2010 12:47 On Jun 8, 10:04 am, George Herold <ggher...(a)gmail.com> wrote: > On Jun 8, 10:55 am, dagmargoodb...(a)yahoo.com wrote: > > > > > 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 > > > > > Cool thanks James, Say can you take it up to 10's of MHz? > > George H. Sure. You need to change transistors... Vcc = +5v --+-------+--------+-- | | | | | |_ || | | _)|| .-. --- L1a _)|| Rb | | C1 --- 2.2uH _)|| 100k | | 22pF | _)|| '-' | _)|| | | *| || | .-+-------' || | |/ || +---| Q1 || | |>. MPSH10 || | | * || C2 --- +-----------. || 10nF --- | L1b _)|| | | 100nH _)|| | | | === | === | '-------------> 22MHz output The oscillation frequency starts being greatly affected by the transistor parameters though. Much higher than this, and other circuits are used. This variation's good to UHF (100Mhz shown): Vcc = +5v --+--------+--------+-- | | |_ | | _)|| .-. --- L1 _)|| Rb | | C1 --- 100nH _)|| 100k | | 22pF | _)|| '-' | _)|| | | *| | .--+--------+ | |/ | +---| Q1 --- C3 | |>. MPSH10 --- 2.2pF | | | C2 --- +-----------' 1nF --- | | .-. | | | Re === | | 1k '-' | === Here, C3 replaces L1b in providing the positive feedback. It's made as small as possible, to avoid loading the collector tank. At really high frequencies, Q1's collector-emitter capacitance often suffices. C1 is often replaced with two caps in series forming a divider, with low-z output taken from the divider tap. Or, you can tap the inductor. -- Cheers, James Arthur
From: Winfield Hill on 8 Jun 2010 13:11
George Herold wrote... > > default wrote: >> 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. Right, it's an L, not a transformer. Inductors can be wound from the same ferrite cores as transformers, etc., but with one *big* difference: They need an intentional air gap, to set a predictable A_L value, and insure a stable inductance. -- Thanks, - Win |