Building a single stage audio amplifier

I have long wanted to build an audio amp for my regenerative receiver, so designed a simple one-stage affair around a BC547 transistor.

My calculations for the design weren’t as good as I had hoped.

I used what I had in my junk box to build the amp.

All the components in place ready for testing.

I hooked up my Hantek 6022BE oscilloscope and wasn’t impressed withe the output signal; it was cropping off the top of the amplified sine wave.

Input signal is the yellow trace with the green being the amplified signal.

I tried changing the values of the biasing resisters until I finally achieved a better result.

The amplified signal looks much better now.

Now it was time to integrate the amplifier into the receiver and turn on the power.

All ready for the smoke test.

The result was pleasing. It worked. But the sound isn’t exactly room filling. That hopefully will change when I build a second stage just the same as the first and add it to the system.

Another successful project.

2013 in review

The WordPress.com stats helper monkeys prepared a 2013 annual report for this blog.

Here’s an excerpt:

The concert hall at the Sydney Opera House holds 2,700 people. This blog was viewed about 8,600 times in 2013. If it were a concert at Sydney Opera House, it would take about 3 sold-out performances for that many people to see it.

Click here to see the complete report.

Building a 2-transistor regenerative receiver

I have always been interested in homebrewing and using parts from my junkbox. Not only is it fun, it’s also the right thing to do from an environmental or recycling point-of-view.

Regenerative receivers have also always interested me as they are a step up from the crystal set.

I came across a wonderfully simple design on Peter Parker’s website (http://home.alphalink.com.au/~parkerp/gateway/nonov99.htm) and couldn’t resist.

Anyway, to cut a long story short, I couldn’t get the thing to work. I called in the help of fellow hams Wallace VK4CBW and Jan VK4EBP; a fresh set of eyes usually does the trick and in my case it certainly did. Turns out I made a basic mistake and connected up one wire the wrong way round.

The receiver on its own produces fine audio with headphones. I wanted more, so I pulled out a little 0.5W Amp Module that I constructed and fitted into an Altoids tin some time ago. Then I connected up a small loudspeaker that I mounted in a nice wooden enclosure and now I have room-filling audio.

Wonderful little simple project that brings back the magic of radio to me.

 

OLYMPUS DIGITAL CAMERA

I used Manhattan construction for the components.

I used Manhattan construction for the components.

The audio amp fits well into an Altoids tin.

The audio amp fits well into an Altoids tin.

 

Completing the Ten Tec 1054 Regenerative Receiver

I decided I’d fit an LED to the front panel to indicate whether the internal 9v battery is on or off. This is because it is easy to forget to switch it off when shutting down the receiver, by shutting down the battery B supply, and so run the risk of depleting the battery unnecessarily.

Fortunately, there is provision for the LED, and the dropping resister, to be installed on the PCB. However, while soldering them in place, I did have to remove the earth connection that is soldered between the front panel and the PBB to remove the panel from the board so I could work on it. In so doing, I must have applied too much heat on the through-hole and it came adrift from the board. This had the effect of killing the receiver, something I discovered when I had completed the mod and turned the receiver on.

I heard nothing. It was dead.

Closer inspection revealed the problem. I soldered a jump lead to replace the damaged part.

A jumper lead was the easiest way to overcome a damaged through hole.

The final thing I had to do was to build an enclosure for the receiver. I decided wood would be the best, and easiest, to work with. It was a fairly straightforward task.

The basic enclosure looks good.

The final thing I had to do was to cut a hole in the top of the enclosure and fit a speaker. I had a 4″ 8 ohm speaker in my junk box so decided it would do fine. I also had some speaker mesh that I had saved when throwing out an old radio some time ago (I knew it would come in handy some day!). All it would take to make it fit was to use the circular piece of wood that I cut from the enclosure for the speaker and use that as a template to mould the metal mesh around.

The mesh with the wooden template and tin snips.

I mounted the template with mesh attached into my vice and began beating it to shape.

It was quite simple, really.

The speaker squeezed neatly into the hole, and the metal mesh fitted perfectly into the hole, from the top. The result I thought was most pleasing.

The speaker mesh in place.

I put everything back into place, connected up the power and switched on. Beautiful. I could pick up all sorts of stations in addition to Radio Australia. China comes through loud and clear, as does a range of others that I have yet to identify. I listen to this little receiver all the time now and really enjoy it.
So that’s another project successfully completed.

Modifying the Ten Tec Regenerative Receiver

The 10K variable potentiometers that came with this kit were not of the greatest quality and soon produced a ‘scratchy’ sound. I decided there was only one thing for it: to replace them with better quality ones.

I raided my junk box and found that I just happened to have two 10K pots of far better quality, so it was out with the soldering iron once more. I ran jumper leads to the three prongs of each pot and soldered them into their respective holes on the PCB.

The replacement 10K pots in place.

The result was impressive. Now I have smooth movement of the tuning and regen knobs and they seem to produce better results as well. Now I can easily hear loads of stations, including Chinese stations at night.

I left the volume pot as is because I only had two. In addition, the PCB is held in place up against the front panel by the pots, so it was good to have the one still secured to the board for rigidity.