John Larkin's LC oscillator
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From: Joe on 12 Jun 2010 17:59 On Sat, 12 Jun 2010 07:57:35 -0700, John Larkin wrote: > On Sat, 12 Jun 2010 08:53:20 +0100, John Devereux wrote: >>John Larkin writes: >>> On Fri, 11 Jun 2010 17:43:39 -0300, YD <ydtechHAT(a)techie.com> wrote: >>[...] >>> That's nice. It's running pretty hard class C. >>> >>> Try this: >>> >>> C2 = 10 uF >>> L2 = 0.25 uH >>> >>> That will move it to class A, with about 50 millivolts p-p drive at >>> the emitter. That's more like what I had in mind originally. Vb is >>> stiff at about +0.6, and Vc dips down to about -0.1, a little below >>> Ve, sucking a brief blip of current out of the base cap. The sine wave >>> is just slightly flattened on the bottom. Yes, those changes to C2 and L2 cut the p-p signal at emitter from about 525 mV to 50, but the currents at c, b, and e change only a little - eg peak currents (mA) Ib 1.22 vs 1.20, Ic -5.14 vs -5.34, Ie 3.91 vs 4.15. The FFT with YD's C2, L2 values is fairly clean, but with the C2, L2 that you suggest above, there are a lot of signal components only 20dB down from the 1.581kHz fundamental, vs at least 44dB down from the 1.578kHz fundamental in YD's. >>> It's useful to add a small resistor, like 1 milliohm, in the emitter >>> so that you can probe the current. It's interesting. >>You don't need to add the the resistor. You can just measure the emitter >>current by clicking on it! >> > I couldn't get that to work. Maybe my aim isn't good enough. One can click the 'Select which traces are visible' icon (just below the help button; looks like a miniature graph), or right-click in a Plot window and click 'Visible traces', and then click Ie(Q1).
From: YD on 12 Jun 2010 18:38 Late at night, by candle light, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> penned this immortal opus: >On Sat, 12 Jun 2010 08:53:20 +0100, John Devereux ><john(a)devereux.me.uk> wrote: > >>John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: >> >>> On Fri, 11 Jun 2010 17:43:39 -0300, YD <ydtechHAT(a)techie.com> wrote: >>> >>>>Late at night, by candle light, John Larkin >>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> penned this immortal >>>>opus: >> >>[...] >> >>> >>> That's nice. It's running pretty hard class C. >>> >>> Try this: >>> >>> C2 = 10 uF >>> L2 = 0.25 uH >>> >>> That will move it to class A, with about 50 millivolts p-p drive at >>> the emitter. That's more like what I had in mind originally. Vb is >>> stiff at about +0.6, and Vc dips down to about -0.1, a little below >>> Ve, sucking a brief blip of current out of the base cap. The sine wave >>> is just slightly flattened on the bottom. >>> >>> It's useful to add a small resistor, like 1 milliohm, in the emitter >>> so that you can probe the current. It's interesting. >> >>Hi John, >> >>You don't need to add the the resistor. You can just measure the emitter >>current by clicking on it! >> > >I couldn't get that to work. Maybe my aim isn't good enough. > >John > Just hover the pointer over the terminal until it looks like a clampmeter. One of those things I found quite by accident, and nicely surprised. - YD. -- File corruption detected. Select option: 1 - Call the cops 2 - Call the press 3 - Bribe it Remove HAT if replying by mail.
From: Capt. Cave Man on 12 Jun 2010 18:46 On Sat, 12 Jun 2010 19:38:42 -0300, YD <ydtechHAT(a)techie.com> wrote: >Late at night, by candle light, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> penned this immortal >opus: > >>On Sat, 12 Jun 2010 08:53:20 +0100, John Devereux >><john(a)devereux.me.uk> wrote: >> >>>John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: >>> >>>> On Fri, 11 Jun 2010 17:43:39 -0300, YD <ydtechHAT(a)techie.com> wrote: >>>> >>>>>Late at night, by candle light, John Larkin >>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> penned this immortal >>>>>opus: >>> >>>[...] >>> >>>> >>>> That's nice. It's running pretty hard class C. >>>> >>>> Try this: >>>> >>>> C2 = 10 uF >>>> L2 = 0.25 uH >>>> >>>> That will move it to class A, with about 50 millivolts p-p drive at >>>> the emitter. That's more like what I had in mind originally. Vb is >>>> stiff at about +0.6, and Vc dips down to about -0.1, a little below >>>> Ve, sucking a brief blip of current out of the base cap. The sine wave >>>> is just slightly flattened on the bottom. >>>> >>>> It's useful to add a small resistor, like 1 milliohm, in the emitter >>>> so that you can probe the current. It's interesting. >>> >>>Hi John, >>> >>>You don't need to add the the resistor. You can just measure the emitter >>>current by clicking on it! >>> >> >>I couldn't get that to work. Maybe my aim isn't good enough. >> >>John >> > >Just hover the pointer over the terminal until it looks like a >clampmeter. One of those things I found quite by accident, and nicely >surprised. > >- YD. I caught it right away. I'm a 'prober' by nature.
From: John Larkin on 12 Jun 2010 18:58 On Sat, 12 Jun 2010 19:38:42 -0300, YD <ydtechHAT(a)techie.com> wrote: >Late at night, by candle light, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> penned this immortal >opus: > >>On Sat, 12 Jun 2010 08:53:20 +0100, John Devereux >><john(a)devereux.me.uk> wrote: >> >>>John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: >>> >>>> On Fri, 11 Jun 2010 17:43:39 -0300, YD <ydtechHAT(a)techie.com> wrote: >>>> >>>>>Late at night, by candle light, John Larkin >>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> penned this immortal >>>>>opus: >>> >>>[...] >>> >>>> >>>> That's nice. It's running pretty hard class C. >>>> >>>> Try this: >>>> >>>> C2 = 10 uF >>>> L2 = 0.25 uH >>>> >>>> That will move it to class A, with about 50 millivolts p-p drive at >>>> the emitter. That's more like what I had in mind originally. Vb is >>>> stiff at about +0.6, and Vc dips down to about -0.1, a little below >>>> Ve, sucking a brief blip of current out of the base cap. The sine wave >>>> is just slightly flattened on the bottom. >>>> >>>> It's useful to add a small resistor, like 1 milliohm, in the emitter >>>> so that you can probe the current. It's interesting. >>> >>>Hi John, >>> >>>You don't need to add the the resistor. You can just measure the emitter >>>current by clicking on it! >>> >> >>I couldn't get that to work. Maybe my aim isn't good enough. >> >>John >> > >Just hover the pointer over the terminal until it looks like a >clampmeter. One of those things I found quite by accident, and nicely >surprised. > I know that, but I had a hard time hitting the emitter current. The resistor is a bigger target. Maybe I should buy more pixels or something. John
From: John Larkin on 12 Jun 2010 19:14
On Sat, 12 Jun 2010 15:10:45 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sat, 12 Jun 2010 15:28:44 -0500, John Fields ><jfields(a)austininstruments.com> wrote: > >>On Fri, 11 Jun 2010 20:04:42 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Fri, 11 Jun 2010 08:16:29 -0500, John Fields >>><jfields(a)austininstruments.com> wrote: >>> >> >>>The .wav thing is cute. But the ringdown is being caused by the LC's >>>Q, not by the transistor oscillation. The R2-C4 thing dies out pretty >>>soon, and then the tank rings on its own. That why you need R4; at >>>infinite Q, it would ring forever. >>> >>>If you can get an LC with a Q that high, you can simulate a nice bell >>>noise by just whacking it and letting it ring... like a real brass >>>bell. Much simpler. >> >>--- >> >>Speaking of real world parts and more-or-less realistic bong >>frequencies, L1 here is a Caddell-Burns 5.6mH 2.9 ohm choke (P/N >>7200-34), C1 is 10�F with an ESR of an ohm or less, and the thing >>oscillates at about 675Hz. >> > >Xl of 5.6 mH at 675 Hz is 23.8 ohms. So, ignoring core losses, the >inductor's Q is just over 8. Your model, with the 1K across L2, has an >inductor Q of about 470. > >If you model with a Q of 8, it's pretty awful. And if you play with >the base bias resistor, you can make something that looks fairly >chaotic, sort of ratty like a superregen. Oh, I see the 2.9 ohms in the box off to the side. I must be pulling the Q down to about 4. But even at 8, the oscillation is loaded pretty bad. It's hard to get good inductors at these frequencies. So what's R4 for? John |