A Crummy Commercial

I tried the booster circuit from yesterday: https://wb9kzy.blogspot.com/2025/06/giving-circuit-boost.html  Bottom line: it seems to work below 9 volts, so that is good. What wasn't good was that I spent a lot of time looking for the Seiko (now ABLIC) 1.5 volt regulator IC but no luck so far.  So I tried the circuit with an LM2931 3 volt LDO regulator with the same pinout as the old friend, the 78L05. Here is that boost circuit from the Onsemi LM2931 datasheet: With a 300 mA load the voltage only decreased about 2 mV from no load.  The circuit consisted of a 2n3906 PNP transistor (the complementary version of the 2n3904 NPN).  I also added a couple of .1 uF caps by the LM2931, decreased the input cap to 4.7 uF and increased the output cap to 47 uF.  Finally the 10k ohm resistor was reduced to 130 ohms (the LM2931 has a quiescent current much higher than the Seiko regulator I couldn't find).  After a while the 2n3906 became hot with an input voltage of 9V, so...

I mentioned trying to use an LDO regulator with an old Westclox wall clock: https://wb9kzy.blogspot.com/2025/05/failure.html  But a thought occurred to me: isn't there a simple circuit to "wrap" a transistor around a regulator to boost current capability ?  I found an example here - a TI app note for the TPS71501 LDO regulator: https://www.ti.com/lit/pdf/sbva015  But that idea appeared in 3 terminal regulator datasheets from years ago: also in this Onsemi datasheet for the 78xx regulators: same circuit but includes a couple more caps    But the SBVA015 Application Report explains the circuit and how it might be used.  The two MOSFET transistors can be eliminated to simplify the circuit.  But the text warns that it might not be suitable below 9V due to stability and transient response concerns.  Unfortunately that's what is wanted, the ability to stay stable (and thus use less current) for extended periods while supplying big pulses of current once...

Made several attempts at adding keying and may have found a winner. First, using a 2n7000 MOSFET keying transistor, pin 3 of the LM386 was shorted to ground when key up which turns off the oscillator, with a capacitor on the gate the keying is shaped.  This works but might be considered too mushy, adding weight to the code elements: blue trace is the key input Second, the 2n7000 was moved to pin 7 of the LM386 to act as a mute.  It does but was thumpy, clicky and mushy, no good. Finally, the 10k ohm feedback pot was split into two resistances in series.  A 4.7k ohm resistor in series with 2.2k ohms.  Then the drain and source were connected to both terminals of the 2.2k ohm resistor (actually still a 10 turn pot).  Then since the source (and drain) are both near DC ground, when the gate of the 2n7000 transistor is raised to 9 volts the 2.2k ohm resistor is effectively shorted out.  This shorting stops the oscillator.  When the key is down the 2n7000 tr...

Previously I mentioned mistakes: https://wb9kzy.blogspot.com/2025/06/mistakes.html  Thinking about it, one change occurred to me, make the text that mentions the potential problem RED, as in red alert ? Before: After: I dunno if that'll help, for whatever reason there are people who refuse to read the instructions, no matter what ! It reminds me of the map room scene in: Raiders Of The Lost Ark where Indy and the gang realize that the Nazis are digging in the wrong place because they didn't know that the staff length needed to be adjusted per the reverse side of the medallion. source: https://vignette.wikia.nocookie.net/indianajones/images/2/29/Staff_of_Ra.jpg/revision/latest?cb=20070623021844      "Take back one kadam to honor the Hebrew God, whose Ark this is."     ―Inscription on the Headpiece source: https://indianajones.fandom.com/wiki/Headpiece_to_the_Staff_of_Ra  Sometimes you need to read the info on both sides of the medal :) Best Regards, Ch...

Continued the LM386 Wien Audio Oscillator project by making some changes.  First, changed the feedback resistance in series with the diode pair from 16k ohms (had wrongly ID'd before as 15k ohms) to 27k ohms.  This improved the waveform under heavier output loading.  Next, tried larger output caps, started with 470 uF but then went with 1000 uF.  This made a huge difference with a speaker connected directly to the LM386 output (through the 1000 uF cap).  Finally, added a 10 ohm, 2 watt carbon comp resistor as the load.  The resistor actually gets warm to the touch after a period of tone. Here are three scope caps of the low, mid and high frequency output. . . 20 kHz is where the amplitude started to decrease also see a slight glitch on the trailing positive edge Here is an updated schematic Now to get back to keying and volume control. Best Regards, Chuck, WB9KZY http://wb9kzy.com/ham.htm 

From yesterday: https://wb9kzy.blogspot.com/2025/06/lm386-wien-bridge-audio-oscillator.html  Several items from the punchlist have been solved / changed but one big problem was spotted. 1) the waveform looks "better" - accomplished by changing the feedback resistor in series with the diode pair from 10k ohms to 15k ohms.  Using the open loop feedback resistor value of 5.7k ohms, the ratio of 5700 / 410 = 13.6 which represents a gain of about 14.6 for the maximum undistorted output.  When the diodes were in the loop the resulting gain wasn't high enough to produce undistorted output ?   2) the waveform is now tuneable - I first tried a .22 uF (10x) cap in place of the .022 uF cap connected to the LM386 output along with a change of resistor value to 4.7k ohms from 51k ohms.  This did not work resulting in either noise or a noisy square wave.  Before giving up on the 10x cap idea I tried moving the .22 uF cap to between ground and pin 2 of the LM386.  Th...

Here is my first cut at the LM386 Wien osc using diodes instead of a bulb to stabilize the waveform: the resistor in the middle of the page without a value was 51k ohms, about 10x the 4.7k ohms Here is a scope picture: Visibly distorted although certainly listenable.  The circuit is very stable, the 10k ohm pot can almost function as a volume control.  There is no big bounce as the pot is adjusted as was found with the bulb stabilized Wien mentioned yesterday. I removed the diodes and ran the oscillator open loop.  The result was touchy but visibly undistorted: it looks nice but the problem is that it won't stay this way So there are some items that remain: 0) can the diode stabilization be changed to reduce distortion ?  I know the op-amp Wien Bridge oscillators stabilized with diodes have less distortion. see item 2 1) use a different stabilization circuit with less distortion than the diodes but is more stable than a light bulb (probably a JFET or MOSFET with a di...