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RE: GitHub for Professional Beginners: From First Repository to First Release

balajivan1995 — Mon, 08 Jun 2026 16:47:17 GMT

Nice write up. But something seem to be missing and it took me a while to realise the part where git asks for password to push local commits to remote branch is missing.

RE: GitHub for Professional Beginners: From First Repository to First Release

DAB — Sun, 07 Jun 2026 19:58:56 GMT

Very good post.

RE: GitHub for Professional Beginners: From First Repository to First Release

shabaz — Sun, 07 Jun 2026 17:11:59 GMT

Just added the following diagram to help follow things.

I hope it's correct, but if anyone spots any error, please let me know!

RE: GitHub for Professional Beginners: From First Repository to First Release

genebren — Sun, 07 Jun 2026 15:35:49 GMT

Thanks for the great explanation! I have used Git in the past, but I am still rusty on all the ins and outs of the process, so this was a great review. Having started my software development on Unix environments, I have had a lot of experience using CVS. I have also used SVN (tortoise) on PCs, but I was never very impressed with that environment. I can see a lot of value in starting to use Git for my internal software development, so I have bookmarked this post to refer back to it when I am ready use it. Thanks for sharing this with the community!

RE: GitHub for Professional Beginners: From First Repository to First Release

kmikemoo — Sun, 07 Jun 2026 02:31:31 GMT

Great information! I may never get to this level, but it's noce to know that this guide is here if/when I need it. Thanks!

RE: GitHub for Professional Beginners: From First Repository to First Release

manojroy123 — Sat, 06 Jun 2026 17:03:53 GMT

Very Interesting. I was looking for such Beginners guide t GitHub.

RE: Building a Transistor Audio Preamplifier

jc2048 — Sun, 31 May 2026 09:21:04 GMT

You and Michael are way ahead of me, this is all I've done so far - just built the K2 one.

Since it's a bit cooler today, I'll try doing some measurements later.

"I’m no audio expert!" Me neither, but I seem to be slowly learning.

R13/C6 (and R8/C3) is a little more than just filtering supply noise. With ac coupling and multiple time constants clustered together down the low end of the frequency range there's potentially an issue with stability there as well as at the top end (you'd hear it as 'motor- boating', a kind of puttering at a few hertz). That can be dealt with the same way as at the top end - make one of them dominate and position the others more than a decade away - but there's probably some merit also in reducing any unwanted parasitic feedback through the supply rails (later stage affecting the supply voltage feeding to the earlier stage). In my simulation it looks fairly safe (about 40 degrees of phase margin at worst, just below a hertz) but that possibly depends on assumptions about what is driving it (I had a source impedance of 600R for the generator).

From simulation, I'd be a bit uncomfortable with C8 and C4. C8 alone is an integrator and nicely rolls of the response whilst giving an extremely safe phase margin, but C4 is then lifting the response which massively extends the bandwidth and gives an open-loop 0db point up in the multiple MHz area with next to no phase margin. Of course reality can be very different to what's in the simulation. The simulator is modelling C1 as a pure capacitor, but a real (leaded) electrolytic would probably have an srf low enough to be (perhaps massively) affecting things and is possibly what is saving the day. It would be interesting to try and measure the real open loop response, though I suspect it would be difficult to do well.

Final thought - audio designers seem to be sniffy about using ceramics as coupling caps (microphony, I think, though value change with dc voltage may also be a factor). Not sure how much that's a real concern, just thought I'd mention it. There do seem to be SMD film caps now, if the concern is to keep things compact, though you'd need to keep an eye on the voltage ratings for the smaller ones.

RE: Building a Transistor Audio Preamplifier

DAB — Tue, 26 May 2026 19:26:26 GMT

Very interesting.

That is a very good design for basic audio.

RE: Simple DCR (Direct Conversion Receiver) – Part 2: Common Emitter Amplifier

shabaz — Fri, 24 Apr 2026 15:33:06 GMT

Here's the complete intercom circuit proposal.. The simulation of the sub-circuits seems OK, but needs constructing!

I scrapped the 30 kHz alert detect circuit, I didn't have a good feeling about it. Instead, now there's DC applied when the user wants to alert the remote end. The wires need to be connected with polarity for that though (future circuit could toggle positive and negative on the line slowly to get around that), but it seemed a minor limitation.

RE: Reflow Micro Table: Compact USB PD Reflow Table with Browser Control

DAB — Sat, 11 Apr 2026 19:35:45 GMT

Great project.

RE: Simple DCR (Direct Conversion Receiver) – Part 2: Common Emitter Amplifier

michaelkellett — Fri, 27 Mar 2026 16:13:31 GMT

That's a really weird pre-amp.

R16 - R19 set up the DC biasing of Q5 with 3.3 mA of collector current.

The AC impedance at the emitter is the impedance of C13//R19, the LF breakpoint is at 0.72Hz - why !!!!!!

At higher frequencies the emitter load impedance tends to zero.

The AC impedance at the collector is more complex at low frequencies 1k//(180R + ZC12).

The LF breakpoint is 19Hz.

The input impedance will be very low (because Q5 emitter is effectively grounded for AC).

The actual gain will depend on the emitter resistance of Q5 .

Since the intention is to drive about 100mV into a 1k load a lower Q5 collector current would be fine.

I tried this (in simulation)

It has good PSU rejection (18dB worst case at 30 Hz and 90dB at 100kHz.

About 2mA current drain.

Much smaller capacitors.

It's not the best way to use two transistors but not bad. It still uses the first transistor open loop so the gain at 1kHz is lower that you would expect from the ratio of R3 to R4 because of emitter resistance.

It manages 28.7 dB of gain (you would expect 33.4) and can drive 1V pk-pk into the 1K load.

RE: Simple DCR (Direct Conversion Receiver) – Part 2: Common Emitter Amplifier

DAB — Tue, 24 Mar 2026 19:40:26 GMT

Very good post.

Excellent walk through the circuit and the changes you made.

Well done.

RE: Simple DCR (Direct Conversion Receiver) – Part 2: Common Emitter Amplifier

jc2048 — Tue, 24 Mar 2026 13:11:03 GMT

Good fun.

This is for SSB and morse?

I'm not much of a transistor circuit designer, but I've noticed that one thing they sometimes used to do in the old days was to flip the polarity of stages. As you've got it, the transistor Q3 develops its output through R10 (ie relative to the rail), but the input to Q4 is relative to GND (the BE junction). If you flip the entire 2nd stage, so that Q3 becomes PNP, then the output will be relative to GND and that then isolates somewhat from the supply noise. The input to that flipped second stage is then relative to the power rail and can come from the pot going to the rail rather than ground, which matches what the output of the first stage is doing anyway. The input of the first stage remains relative to ground, which suits the mixer output. The only potentially poor PSRR is then the output stage, but I think that one works ok because of the transformer coupling to the loudspeaker. You'd have to be careful around the pot, but you need to take care there anyway with so much gain following it and a middling impedance.

Whilst it might improve the situation, you'd probably still need to work on the power side of things.

Another approach is to transformer-couple between all the stages (which is essentially how it works going through an IF strip).

RE: A 4-zone universal transmitter node for open-drain sensors (Proof of Concept)

DAB — Sat, 21 Mar 2026 20:42:19 GMT

Interesting post.

Most of the questions you pose do not have simple answers.

In circuit design, decisions are usually based on the needs of the end product requirements.

RE: Simple DCR: Assembling a 7 MHz (40m) Direct Conversion Radio Receiver – Part 1

shabaz — Fri, 13 Mar 2026 02:49:39 GMT

I took another look at the construction, and realized that for the transistor biasing, I had set R12 to 56k, and R13 to 10k (I don’t know why; I have forgotten, since I soldered those resistors almost a year ago!). This resulted in very little current through the transistor, just a few milliamps, which is great for battery life, but not so great for generating more output.

I’ve experimented a bit, and now replaced with R12 = 18k, and R13 = 8.2k, and that results in a value closer to about 15 mA. Now with a 64 ohm load, I can drive the input to about 40 mV p-p, and see 1.35 V p-p output.
However, with an 8 ohm load, I can drive the input higher, to about 80 mV p-p, and see about 830 mV p-p output (these values are with a 1 kHz signal). Even at 100 mV p-p input, the distortion would be tolerable.

So, the conclusion now is, that the 8 ohm speaker would be better – the amplifier stage can be driven with more input, and the power output should be higher. I didn’t have an 8-ohm speaker to listen to it, but I’m going to go with those resistor values, and use an 8-ohm speaker speaker.

For anyone curious about the transformer, it has about 89 ohm DC resistance at the primary, and 3.3 ohm on the secondary. I put some impedance measurements in the table below, but I’m not sure how useful they are, I don’t think there’s much value trying to improve this circuit much further, since it is based on an AliExpress transformer which could be very different when ordered a year later that the one I measured.