Electronics
Analogue stuff
I am not only a software engineer, but I am also an electronics engineer. I graduated from Electronics Technical School before going to College. To this day, I still do some stuff in that area; it is sometimes called DIY (do-it-yourself), even though I also do some commercial work (mostly the repair of analogue audio amplifiers).
This page will feature throwbacks and new builds.
The Repairs
Here are some amplifiers I worked on. Many times, I had to fix the power supply section. Sometimes the power stage was broken (or fried). It was very rare that a more sophisticated repair was needed.
Alphrad and Ampeg
Let's go back in time. The following presents photos from the repair of the Alphrad M814 power stage amplifier and the Ampeg BA-115 guitar amplifier.
Tonsil and Randall
I had the chance to fix a very old Polish guitar amplifier, Tonsil GTX 300 Mosfet. It is a very rare model. Impossible to buy these days, let alone find a schematic. I also present below a Randall RH100 G2.
The legendary Marshall
A very well-known guitar amplifier is the British Marshall. This time, Marshall JCM-2000, with its big sound. Very loud, often paired with a 4x12 Cabinet.
Fixing the Roland
Now it's time to show a quite unusual "repair shop guest". Roland Juno-2. It is a keyboard—fully analogue, very good sound. Fairly simple fix: the non-working volume slider had to be replaced.
Guitar Amplifier - Custom Build
The following is the guitar amplifier that I designed and built myself. The ideas for a two-channel amplifier go back to 2012, with experiments with pre-amplifiers that aim to sound like Fender Twin Reverb and Marshall JMP-1.
Features:
- Output power: 50 Watt.
- Speaker: Celestion Gold 12" 50 Watt/15 Ohm.
- The power stage contains a built-in regulated power attenuator.
- Two channels: Fender (clean/crunch) and Marshall (lead).
- Fender channel: Gain, Bass, Treble, Volume.
- Marshall channel: Gain, Bass, Middle, Treble, Presence, Volume.
- Passive tone stack controlls.
- Equipped with an analogue signal level indicator.
- Equipped with with footswitch.
- Equipped with an FX Loop (Send/Return).
- Equipped with balanced lineout.
- Equipped with cabinet simulation (balanced output).
Testing - sneak peak videos follows.
Power stage test. A discrete design using transistors (no high power op-amps). I used BD149C power transistors. This is classic AB class power stage.
Treble Booster
A treble booster is an effects unit used by many guitarists to increase the high end of their tonal spectrum, whilst attenuating lower frequencies. It is intended to be used with a guitar amplifier that has no lead channel (heavy distortion channel) or a small overall gain. It allows overdriving the preamp stage for a nice, full, overdriven sound.
Whilst my guitar amplifier has a lead channel (modelled after Marshall JMP-1), I tend to use a treble booster with a clean/crunch channel (modelled after Fender Twin Reverb) to get a more Queen/Brian May-like sound. Below is a quick look at the thing.
Building Treble Booster (it gains mid- and high-frequencies and roll-offs low-end) for my guitar amplifier. This is simplified build with a universal PCB.