Path: news.eternal-september.org!eternal-september.org!feeder3.eternal-september.org!usenet.blueworldhosting.com!diablo1.usenet.blueworldhosting.com!nnrp.usenet.blueworldhosting.com!.POSTED!not-for-mail From: "Edward Rawde" Newsgroups: sci.electronics.design Subject: Re: Five transistor version of the low distortion sine-wave oscillator Date: Tue, 15 Apr 2025 09:12:46 -0400 Organization: BWH Usenet Archive (https://usenet.blueworldhosting.com) Lines: 86 Message-ID: References: Injection-Date: Tue, 15 Apr 2025 13:12:48 -0000 (UTC) Injection-Info: nnrp.usenet.blueworldhosting.com; logging-data="67364"; mail-complaints-to="usenet@blueworldhosting.com" Cancel-Lock: sha1:xTI+dCGOl7qf2Hp4PEt9dobj/Mw= sha256:GP+zynGqfVmwgTIaN6fNGJms62adduK9vRgwq3YzVYo= sha1:ensKITQeAQ/P7C+mVkzvbZY5r24= sha256:rjk5AvVWKiBvCAz55TtsmFxWpDRwBDmdhqWOCJopilI= X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157 X-RFC2646: Format=Flowed; Response X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2900.5931 "Bill Sloman" wrote in message news:vtl0bc$364bt$1@dont-email.me... > On 15/04/2025 1:56 am, Edward Rawde wrote: >> "Bill Sloman" wrote in message news:vtihob$sfdm$1@dont-email.me... >>> On 12/04/2025 6:27 pm, Bill Sloman wrote: >>>> Edward Rawde posted an eight-transistor low distortion sine wave oscillator circuit recently, and John May pointed out that you >>>> could leave out half the transistors. >>>> >>>> I couldn't immediately see exactly how either of the circuits worked, though I could get the simulations to run under LTSpice >>>> and >>>> see roughly what was going on. >>>> >>>> I've now dug a bit deeper. Here is a five transistor version of John May's four transistor version. >>> >>> Out of curiousity, >> >> Is that allowed Bill? I thought that making component changes to see if the circuit works better was design by evolution? > > I didn't make the change to see whether it worked better - I did it to see if I'd correctly understood what it was doing. The fact > that it made it work better was incidental. > >>> I upped the currents through Q1A and Q1B by about an order of magnitude (R27 down to 27k, R17 down to 22kk and R28 down to 68k) >>> and the worst case harmonic became the second at 2kHz, 155dB below the the fundamental. The fourth was close behind at at about >>> 157dB down. >>> >>> Essentially, their incremental resistance has dropped by an order of magnitude, and the ripple on the gain-control signal >>> produces >>> less voltage excursion. >> > Did you mean R20? I don't see R27. > > I did indeed. > > > I think the only way forward with this circuit would be to build and > test it. > > Agreed. > > > I'd do a first prototype with everything through hole except LT1679 > and NSS40301MDR2G. > > Why? Changing almost anything in this circuit in LTSPice changes the residual harmonic levels. Assuming the same is true in reality I'd want to be able to change components easily. > > > I'd also put four more resistors in series with each 68k (maybe > reduce them to 56k) for the four diodes so I can make the current pulses in the four diodes exactly equal. > > Why? I can see an argument for removing all the 68k resistors so the current being fed through R11 is as high as possible, with > the smallest possible ripple. There is a risk that the diode current will turn off fast enough to drive them into snap-recovery, > but it is remote. > > Increasing the 68k resisitors reduces the effect of the tolerance on the forward voltage drop through each diode, but choosing > diodes with a closer tolerance on the forward voltage drop would be a better way to go. The 1N914 doesn't seem to have one at all. > > The Infineon-BAS3007ASERIES diodes at least specify 350mV typical and 400mV max at 100mA. I think NExperia had something better > back when it was Philips, but that's a long time ago. Changing to schottky diodes changes the distortion but not always down. So I'd want to be able to make changes easily on a real prototype. > > > And add a capacitor (100n min) to ground where the resistors join. > > Adding more phase delay along the feedback path and make the settling time even longer. One of us doesn't care if he has to wait 5 minutes for the purest sinewave. The other seems to put higher priority on the circuit settling in a few seconds. I think we'll just have to differ there. > > > And use the remaining LT4167 (two quad packs) as an output buffer so > that whatever is connected to the output doesn't disturb the > > operation of D10. > > What D10? The one that's D14 in your circuit. > > -- > Bill Sloman, Sydney > > >