I built my own FM CB into a President case, and all on one PCB. It took nearly 20 years to get it working 100% ! LM380 benefits from reducing the cap on the -in to 1nF or below. Cuts out the rumble and knocks the high gain of the chip down. I am driving from an MC3371.
You can always simulate your design in something like LTSpice. This way you have the ability to optimize the circuit and make less susceptible to the component nominal variations. I am trying to do that more and actually I started to like simulations before the building hardware. Most of the time it worked out well for me.
I saw in some other videos he was already using LTspice. But I will agree. When I was designing guitar amplifiers I spent 10x the time in LTspice than I did actually building them. And I spent quite a lot of hours building them....
Great to see you designing and building again Charlie! I love the calculations and explanations. There is a lot folks can learn here. Keep up the great work and thanks for sharing. 73 Nick M0NTV
Just a brief question. In homebrew rigs I can see frequent use of AF finals with LM380 or (worse) LM386. I have been using TDA7052 instead, with very good results. It is cheap, needs very few external components, no need for a large output capacitor and RC damper, true gain control and mute, given equal supply voltage it can deliver more power output than LM386 (or any LM38x) => less distortion at the same AF output. Is there a good reason why everybody uses LM38x chips?
Hi Charlie, I really like your video's, they're very inspiring (just like M0NTV's and W2AEW's) and are the basis for our building projects with other ham's. I do have one request. Sometimes you refer to literature like SSDRA or EMRFD. Is it possible to give also a pagenumber? For example searching the books to a specific rule of thumb is just not possible. Thank in advance!! Peter ON4BDP
Depends on how much you want out! I haven't looked at the datasheet for the LM380, so I don't know how much gain is in that stage as he has it configured, but for the preamp, the gain will be approximately the ratio between the collector load resistor and the emitter resistor, for a voltage gain of about 6. Since he has the emitter calculated to be at 1V, which sets the low clipping of the output, and the high clipping is the power supply voltage, or 13V, that's an output swing of 12V, of which you don't want to use more than about half if you want to avoid the worst distortion. So that gives us 6V peak-to-peak on the output, and with a voltage gain of 6, this puts the maximum useful input voltage at about 1V peak-to-peak. This is maximum, and the minimum, again, depends on how much voltage you want at the output. Also note that since the volume control comes after the preamp, you can't just turn it down if you're overdriving the preamp. As Charlie says at the beginning, this is not meant to be a tutorial, but just documentation of how he designed the circuit, so you shouldn't treat it as a cookbook recipe. But I will add that it really should work perfectly, so feel free to use his circuit as a starting point!
Am I missing something? You want a collector current of 10 mA, which I agree is perfect for an amp that doesn't need to run at super low power, which should correspond to a base current of 100 μA. But although you said you wanted 10 times that through the bias voltage divider, which would be 1 mA, you used 10 mA in your calculations. Not that this won't work; it most assuredly will.
@@CharlieMorrisZL2CTM You are correct - I misunderstood that you had put the Ib calculation within the calculation for the resistors, so when I saw 10mA, I thought that was the current through the voltage divider.
