Over the past six years ABB has sold off the grid business it built in Finland, then started buying its way back in, this time on its own terms. Two things happened in 2026 that show where it’s going. ABB bought Finnish grid automation company Netcontrol, and it announced a joint venture with Mitsubishi Electric aimed at Asia. To see why these deals matter, start with what ABB gave up.

The Big Exit: Power Grids Goes to Hitachi (2020–2022)

In 2020 ABB completed the multi-billion-dollar sale of its global Power Grids division to Hitachi. The business first operated as Hitachi ABB Power Grids. Hitachi bought out ABB’s remaining share in 2022, and the company is now Hitachi Energy.

The deal took a lot of Finnish industrial history with it. High-voltage power transmission, large-scale utility infrastructure and grid automation software all left ABB:

• The transformer factory in Vaasa: This large, historic plant designs and builds specialized transformers for power grids, wind farms and heavy industry. Transformers have been made industrially in Finland for over 110 years.
• The MicroSCADA product line: The whole R&D team and ownership of the product went too.
• Grid automation and systems: The engineering, service and project delivery units for high-voltage substations and utility-scale systems also moved.

MicroSCADA: A Finnish Success Story Changes Owners

MicroSCADA probably has the deepest Finnish roots of anything in the deal. The Finnish electrotechnical company Strömberg Oy created it in Vaasa in the early 1980s, and Strömberg later became part of ABB. Over four decades, MicroSCADA grew into a widely used system for monitoring and controlling power networks and substations.

MicroSCADA had always been a core Power Grids product. So when that division went to Hitachi, ABB didn’t really choose to sell MicroSCADA on its own. It went along with the rest of the division.

One thing stayed the same: Vaasa. The main global R&D and product development center for MicroSCADA is still there. It now belongs entirely to Hitachi Energy Finland Oy, and the product turned 40 in 2023 under its new owner.

What ABB Kept

ABB didn’t leave Finland, and it didn’t stop doing electrification. It narrowed its focus to electrification and industrial technology, the products that sit closer to factories, buildings and the distribution grid:

• Distribution Solutions (Smart Power & Electrification): This is ABB’s large unit in Vaasa. It designs and makes medium-voltage switchgear, protection relays such as the Relion series, and smart grid components.
• Motors and Generators: Finnish factories and engineering teams build heavy-duty industrial motors and generators.
• Drive Products: These teams work on low- and medium-voltage variable speed drives, which make industry more energy efficient.

In short, ABB kept the medium-voltage and industrial side of electrification. Hitachi Energy got the high-voltage transmission side. ABB also has ABB’s Symphony SCADA and distributed control system (DCS) lineage.

Back to SCADA in Finland: The Netcontrol Acquisition (2026)

You might have expected ABB to stay out of utility SCADA after selling MicroSCADA. It hasn’t. In May 2026 ABB completed its acquisition of Netcontrol, a Northern European company started in Finland that sells grid automation solutions to energy companies. Netcontrol has SCADA software, SCADA RTUs and utility communications solutions.

Netcontrol was founded in 1991 and has about 100 employees. It is headquartered in Helsinki, and also has offices in Sweden, Norway and the UK. Before the sale it was owned by the Swedish private equity firm Procuritas Partners.

Netcontrol’s customers are mostly network operators. They include electricity distribution companies, district heating companies, power producers and energy-intensive industry.

Netcontrol’s business rests on the Netcon product family. It covers the whole automation chain, from field devices up to the control room:

• Netcon 3000 SCADA: This is the main platform for supervising and controlling power networks. It is built to handle distributed energy resources such as solar, wind and storage, which have made distribution grids much harder to run.
• Netcon RTUs and substation devices: These remote terminal units and gateways collect data from substations and secondary substations, and carry out control commands sent from the SCADA system. Netcon 5000 is sold under the ABB brand.
• Medium- and low-voltage network monitoring: Products such as Netcon 100 were developed to monitor and control medium-voltage networks and to monitor low-voltage networks. Netcon 200 is already sold under the ABB brand as a medium-voltage grid component.
• Engineering services. Netcontrol also designs, integrates and commissions complete automation systems.

Finland’s power automation scene is small, and for decades two domestic SCADA products shared it. MicroSCADA came from Strömberg’s Vaasa tradition and grew into a global product under ABB. Netcontrol, founded in Helsinki in the early 1990s, took a different path. It focused on the needs of Nordic distribution companies and offered a complete package of SCADA, RTUs and engineering from one supplier.

That focus let Netcontrol win against much bigger international suppliers. It grew from Finland into Sweden, Norway and then the UK. In 2025, Vattenfall’s UK independent distribution network business, Vattenfall IDNO, chose Netcontrol for network automation. Vattenfall hosts Netcon 3000 in its own secure industrial cloud, and Netcon RTUs connect its sites to it. The goal is faster fault detection, less downtime and better service continuity.

Developed by Netcontrol, Netcon 3000 is a prominent Supervisory Control and Data Acquisition (SCADA) and energy management software platform widely deployed across power generation and distribution networks, particularly in the Nordic region. It is engineered to provide robust real-time process visualization, comprehensive alarm handling, and detailed event history tracking for electrical power systems. While the foundational software architecture was built on the core iFIX realtime database engine and SCADA framework, Netcontrol extensively reworked and replaced major subsystems over several generations of development. Through companion hardware like Netcon gateways running Netcon NFE software, the system supports conversion across more than 50 serial and IP-based telecontrol protocols, ensuring smooth integration with legacy RTUs and modern IEC 61850 substations.

This creates a twist. In 2020, MicroSCADA, the system ABB had owned and developed for decades, went to Hitachi Energy. Six years later, ABB owns the competitor that had been bidding against MicroSCADA for Nordic utility contracts all along. In Finland, the two Finnish SCADA systems now compete under two global brands, one Japanese-owned and one Swiss-Swedish.

The reasoning is clear, though. Distribution networks are getting more complicated because of renewables, EV charging and electrified heating, and utilities want automation software that works with the switchgear and relays ABB already makes. With Netcontrol, ABB can again offer a software and systems layer to go with its hardware.

Heading East: The Mitsubishi Electric Joint Venture

ABB’s newest move is outside Europe. On the back of record Q3 orders, driven largely by surging data centre demand], ABB announced a joint venture with Mitsubishi Electric to grow in the Asia-Pacific region.

The terms, according to reports:

- ABB’s Japanese unit will buy 51% of Mitsubishi Electric’s power distribution and control equipment business for about ¥82.4 billion (approximately €467.62 million Euros)
- Mitsubishi Electric will keep 49%.
- Completion is planned for October 2027, pending antitrust and other approvals.

The joint venture fits the same pattern. ABB isn’t buying back high-voltage transmission. It’s adding to the distribution and electrification business, which is growing fast because of data centres and electrification in general.

The Bigger Picture

Put all this together and you get a company that is cleanly splitting its business:

2020–2022: Power Grids sold to Hitachi (incl. MicroSCADA, Vaasa transformers) – Leave high-voltage transmission, Keep distribution, motors, drives in Finland, Focus on electrification and industry
May 2026: Acquire Netcontrol – Add grid automation software to distribution
2026–2027: Mitsubishi Electric JV (51%) – Grow distribution in Asia-Pacific

Vaasa is an unusual case. It’s now home to two global companies whose grid businesses have the same origins. Hitachi Energy builds transformers and develops MicroSCADA there. A short distance away, ABB makes switchgear and protection relays. Both businesses come out of the same Strömberg engineering tradition (Strömberg became part of ABB in 1988), which still shapes how the world’s electricity grids are run.

Over the next few years we’ll see whether ABB’s strategy of staying medium-voltage while adding software and growing in Asia pays off. With electrification and data centre demand accelerating, its timing looks good.

About the Author: A View from Inside Netcontrol

This article isn’t written from the outside. Its editor, Tomi Engdahl, worked at Netcontrol for twenty years, from 2003 to 2023. During that time he worked on several parts of the Netcon product family described above:

• NFE (Network Front End): He has been a developer Netcontrol’s NFE software, which works as a SCADA front end, a protocol converter, and an RTU communications concentrator or gateway.
• SCADA components: He has built software components for Netcontrol’s SCADA systems.
• Netcon 100: He was the system architect for Netcon 100, a system for monitoring and controlling medium-voltage networks and monitoring low-voltage networks.
• Netcon 200: He was also the system architect for Netcon 200, which ABB now sells under its own brand as a medium-voltage grid component.
• Netcon 500: He has been one of the center persons in developing GW502 processor module running a hardened, long-term support Linux kernel. The Netcon 500 is a cybersecure, modular Remote Terminal Unit (RTU) and substation automation gateway designed primarily for primary power distribution substations, industrial grids, and utility automation.

He left Netcontrol in 2023, two years before ABB announced the acquisition, so he played no part in the deal. He did see the years and contributed to products that made Netcontrol worth buying. Over those two decades it grew from a Finnish company into a supplier for utilities in Sweden, Norway and the UK. Distribution networks also changed in that time, from basic remote control of substations to real-time monitoring all the way down to the low-voltage grid.

That background shapes how he sees this story. When MicroSCADA left ABB for Hitachi Energy, it was business news. When ABB bought Netcontrol, it was more personal. Products he designed as system architect now carry the ABB name and will be sold worldwide, while their old rival from Vaasa continues under Hitachi Energy.

Many Finnish engineers built their careers on one side of this rivalry or the other. Equipment from both companies keeps power networks running in Finland and beyond. This article has tried to cover both sides fairly. Readers should know the author spent twenty years on the Netcontrol side.

The Truth About the OSS TEAM W01 Inductance Tester
If you’ve spent any time browsing electronics repair forums or watching diagnostic videos lately, you’ve probably seen it: A sleek, pen-sized black circuit board being waved over smartphone motherboards. The green LED lights up, and—boom—the component is declared healthy (claims many videos seen on Facebook and YouTube).

Advertisements call it a “Revolutionary Motherboard Repair Tool” that grants technicians “X-Ray Vision.” Sellers claim it can instantly stop the guesswork of component failures with a clear pass/fail signal.

But is the OSS TEAM W01 Inductance Tester truly a “secret weapon,” or is it just another over-hyped online hoax? Or something in between? Let’s strip away the marketing promises and look at what this tool actually does, how much it costs, and the hidden dangers you need to know about.

What is the OSS TEAM W01?
At its core, the OSS W01 is a compact, bare-board electromagnetic field (EMF) detector. It features:
A pointed detection tip at one end.
A central detection button you must press and hold.
A small green LED indicator light.
A Type-C power input that can run off a standard 5V power bank or phone charger.

The OSS W01 Inductance Detector is a compact, black circuit board with a pointed detection terminal at one end. It features a Type-C power input port, a detection button, and a small LED indicator light. The board is labeled with ‘W01′, ‘OSS TEAM’, and ‘INDUCTANCE DETECTOR’. Dimensions: 75mm x 27mm (approximately 2.95in x 1.06in)

I came across an advertisement for such a tester online. It claims to identify faulty components on circuit boards. I guess it’s all a hoax, though? If the green LED doesn’t light up, the component is faulty. So how can it tell? The advertisement showed testing resistors and capacitors.

OSS w01 Inductance Tester What would a product with a daily sales volume of 10,000 units look like?
https://www.youtube.com/watch?v=Mi4oGukxFTo

How It’s Supposed to Work

The marketing pitch is incredibly simple: If the green LED lights up, the inductor is functioning correctly. According to the instructions, you power up the motherboard you are troubleshooting. You plug in the W01 tester, hold down its button, and bring the pointed tip close to the inductor coil (about 1 to 3 mm away).

Green light stays on or flashes: The inductor is actively processing power; the internal coil is intact.
No light: The inductor coil is broken (open circuit) or not receiving power.

OSS TEAM W01 Type-C Inductance Tester is advertised as a Professional Repair Diagnostic Tool. The marketing promise is: If the LED lights up, the inductor is functioning correctly.

Advertisements are full of promises like:
Why This Pen-Sized Diagnostic Tool Is Revolutionizing Motherboard Repair (Hint: It Gives You ‘X-Ray Vision’)
Stop guessing component failures! Handheld tester gives clear pass/fail signal. Quality components, reinforced housing.
OSS TEAM W01 Inductance Tester, a compact and user-friendly device for rapid troubleshooting and fault detection of mobile phone inductors.
EMF Detector Type-C Inductance Tester High Precision Electronic Circuit Board Inductor Detector for Electronics Repair
Features Type-C power, rapid troubleshooting, and easy operation for mobile phone motherboard
If you’re nodding your head, you’re about to discover why thousands of repair techs are calling this pocket-sized tool their “secret weapon” against the most frustrating part of electronics repair…

I have seen an AI videos advertising these, claiming they will make your multimeter obsolete. W01 does not make your multimeter or oscilloscope obsolete. Not everyone will have a use for one of these, but if you do troubleshooting on systems with buck/boost converters for current and voltage regulation, then this could be a useful tool for doing a quick check on whether an inductor is being pulsed.

The Catch: It Doesn’t Have “Magic Vision”

The fact is that the W01 can sometimes successfully detect powered coils (if they have enough power going through them and they are not too well shielded). Sometimes the detection does not work.

While the device is a functional tool, online ads often stretch the truth. Watching how they use it…just touching around at random spots on an active circuit and they say “when the light does not come on, it is a bad component”. Some commercials show technicians using it to test resistors and capacitors and diodes. Spoiler alert: It doesn’t work on them.

The device is purely an induction and EMF tester. It detects the pulsing magnetic fields generated by a working coil. If you place it near a resistor or capacitor, the light won’t turn on—not because the component is broken, but because those components don’t generate the magnetic fields this pen is looking for.

Furthermore, metal heat sinks or shielding shells can trigger false positives by spreading interference, meaning the light might turn on even if you aren’t directly over a healthy inductor.

It can be a helpful troubleshooting tool for quick reference, but it cannot mystically diagnose your entire board. They only work for inductors that are powered with high frequency pulses. For inductors you don’t need them to be out of circuit to detect the em field generated by inductors when functioning properly. If you have a working board for comparison, you can test where you see light coming on in the working board, and then see if LED lights on the not working board.

Videos:
https://youtube.com/shorts/Mi4oGukxFTo?si=gSX3gqphKXq5ZW6L
https://youtube.com/shorts/8g822XrTB9s?si=nTPWQJiYnKNCSWkW
https://www.youtube.com/shorts/faQ0mO1lOrI

Instruction pictures
https://www.aliexpress.com/item/1005010320063815.html

Manual
https://manuals.plus/m/e92f476fbf03e51ea91d75fb8bb1c70f2db89e166420bedeb4f59ea78b0eb7e8

WARNING: The Hidden Danger of An Unenclosed Board

One of the most alarming aspects of the OSS W01 is its design. It is completely unenclosed—just a bare, exposed circuit board.Instruction manuals explicitly warn: “Place the front end close to the inductor, do not touch it, as some inductors are not insulated.”

Worse yet, some promotional videos on social media show users probing live, mains-powered electronic devices with this bare board. If an inexperienced hobbyist handles this unenclosed block, their fingers can easily slip and touch high-voltage components on the live board. This is incredibly dangerous and carries a genuine risk of electrical shock.

Video where probing live main powered device (potentially very dangerous) can be seen at
https://www.facebook.com/61577839981774/videos/-oss-inductance-detector-high-precision-electromagnetic-induction-measurement-al/868769249585152/

If you use this tool, it should strictly be confined to low-voltage motherboards (like smartphones), and you should handle it with extreme care. To avoid causing any short circuits, I recommend to add insulation around the tip of the W01 sensor (for example insulating tape or heat shrinking insulation).

Circuit analysis

Circuit diagram for the sensor part. Traced from circuit board and component values measured in-circuit

Clever inductive test probe

The circuitry is strange. Like a prototype or one that has been badly copied. It has some oddities, and the button on this unit looks like a legacy feature from the original lithium cell powered version.

This is Big Clive’s video about it. Screenshot is of his traced schematic.
https://youtu.be/VsEJgODLN6Q?si=Qfxyk_JYzV4CZZpf

Price Watch: From €1 to $17?

Perhaps the strangest thing about the OSS W01 (and its sibling, like the MECHANIC DT-001) is the wild pricing discrepancy online:
The Ultra-Cheap Tier: On websites like AliExpress, you can find this exact board selling for anywhere between €0.87 and €2.85.
The Premium Repair Tier: On specialized electronics repair sites or localized storefronts, the exact same tool is repackaged or marked up to anywhere between €16.00 and $16.99.
At less than a Euro, it’s a fun, low-risk novelty gadget to throw into your repair toolkit. At $17, the price tag starts to outpace the actual utility of a bare EMF-detecting PCB.

The Verdict: Hoax or Handy?

The OSS TEAM W01 Inductance Tester is not a hoax, but the marketing definitely pushes it into “too good to be true” territory. It won’t give you “X-Ray vision,” and it won’t replace a proper multimeter or oscilloscope. However, for a mobile phone technician who needs a 2-second check to see if an inductor coil is actively passing a signal without desoldering it, it’s a functional, handy little device. Just keep your fingers away from the live components, don’t try to use it on capacitors, and definitely don’t overpay for it!

Hacker and security researcher Samy Kamkar takes a look at a variety of hacking scenes from popular media and examines their authenticity.

Video: https://www.youtube.com/watch?v=SZQz9tkEHIg

Miten hyödyntää Moderni C++ -ohjelmointikieltä tehokkaasti ja joustavasti?
https://www.tieturi.fi/webinaari-miten-hyodyntaa-moderni-c-ohjelmointikielta-tehokkaasti-ja-joustavasti/

Modern C++ Design Patterns Full Course

C++ Design Patterns – The Most Common Misconceptions (2 of N) – Klaus Iglberger – CppCon 2024

Hands-On Design Patterns with C++ by Fedor Pikus

Design Patterns in C++

Modern C++ Design Patterns Tutorial

Design Pattern Catalogue

Singleton Pattern | C++ Design Patterns

Observer
Also known as: Event-Subscriber, Listener
Observer is a behavioral design pattern that lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they’re observing.
https://refactoring.guru/design-patterns/observer

Strategy
Strategy is a behavioral design pattern that lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.
https://refactoring.guru/design-patterns/strategy

How to Create Custom Memory Allocator in C++?

Template Metaprogramming in C++

From C++ Templates to C++ Concepts – Metaprogramming: an Amazing Journey – Alex Dathskovsky

Embedded C++ : to use STL or not?

Standard Template Library (STL) in C++
https://www.geeksforgeeks.org/cpp/the-c-standard-template-library-stl/
https://en.wikipedia.org/wiki/Standard_Template_Library

In embedded systems, how much memory C++ STL uses depends heavily on:
The container type
The number of elements
The implementation (libstdc++, libc++, etc.)
Whether dynamic allocation is used
Compiler optimization settings
There is no fixed memory cost, but I’ll break it down clearly.
Heap Usage (Critical for Embedded)
Most STL containers use dynamic memory (new).

Problems in embedded:
Heap fragmentation
Unpredictable allocation time
Memory exhaustion
No control over allocator unless customized

STL within embedded system with very limited memory
https://stackoverflow.com/questions/9612588/stl-within-embedded-system-with-very-limited-memory

Understanding Memory Management, Part 2: C++ and RAII
https://educatedguesswork.org/posts/memory-management-2/

This is a bad and dangerous design

This is a dangerous design. There is potentially lethal voltage on those probe pins. ⚡️☠️
I strongly discourage to build this.

Design problems
- no isolation from mains – test probes and circuit being tested dangerous to touch
- pointless filter coil in output
- open circuit voltage can be over 300V
- output capacitor in circuit directly on probes – high current surge when you connect probe can potentially damage LED being tested

According to the latest edition of the World Happiness Report, the three happiest countries in the world are Finland, Iceland and Denmark.

Finland was named the happiest country in the world for a record 9th time in a row,

There is seen a sharp drop in youth happiness in very many countries: A key factor in the sharp drop in youth happiness, researchers said, is the number of hours young people spend consuming social media or gaming. While experts say it’s important to limit time spent with the Internet overall, some ways of spending time online are healthier than others. A key question is “if they are really social media or anti-social media.”
“The digital age is reshaping the social and emotional foundations of wellbeing in Europe”

Source:
https://www.cnn.com/2026/03/18/travel/worlds-happiest-countries-2026-wellness

Friday the 13th has a reputation as a day of bad luck mainly because two separate superstitions merged over time: fear of the number 13 and fear of Friday. When they combined, the date became especially ominous in Western culture.

The number 13 has long been considered unlucky in parts of Europe and North America (bible The Last Supper and Norse mythology).
According to Christian tradition, Jesus Christ was crucified on Good Friday. Sailors and travelers in folklore believed starting a journey on Friday brought bad luck.
Modern media amplified the superstition, especially horror films like Friday the 13th.

Read more:
Why is Friday the 13th considered unlucky? The history of the superstitious date
https://www.independent.co.uk/life-style/friday-13th-unlucky-why-meaning-history-b2919712.html

This is a classic “minimalist” single-ended Class A MOSFET amplifier. While it is praised for simplicity, it is inherently inefficient and prone to significant distortion.
​In this design, the MOSFET (IRF530) is always “on,” acting as a variable resistor that pulls current through the 15 ohms load resistor.

​Circuit Analysis

​Operating Class: Class A. The transistor conducts through the full 360° of the input cycle.
​Bias Point: The schematic shows a 12V quiescent point at the Drain (half of the 24V supply). This is achieved by adjusting the 100k potentiometer to set the Gate voltage.
​Heat Generation: This circuit is a space heater. With 12V across a 15 ohms resistor, it dissipates P = (12*12)/15 = 9.6 Watts constantly, even with no music playing.
​Output Voltage: The maximum theoretical peak-to-peak output voltage is roughly 24V, but in practice, it will be less due to the MOSFET’s saturation voltage and the voltage drop across the source (if a source resistor were present).

Original source

This is a single-ended Class-A common-source MOSFET stage using a 2SK1058 with a 15 Ω drain resistor and capacitor-coupled output.

I would not expect quality with this design be specifically good but maybe useable for experimenting. Class A avoids crossover distortion is true. But this simple class A design introduces other significant distortion sources.
1. Important: This design has NO global feedback
Notice:
No feedback loop from output to input
Pure resistor load at drain
Single-ended topology
That means:
Output impedance is mostly set by hardware physics
No correction via feedback
Strong interaction with speaker impedance curve

2. Realistic Output Impedance ≈ 3–7 Ω
Most likely around: ~4–6 Ω
Damping Factor Example (8Ω speaker) is 1.6
That is very low damping factor.
For comparison:
Typical Class AB: DF 50–500
Typical Class D: DF 200–1000+

What That Means Sonically
With ~5 Ω output impedance:
Bass will be loose
Frequency response will follow speaker impedance curve
Midrange may sound “rich”
Damping is minimal
This is electrically closer to a small tube amp than to a modern solid-state amp.

3. Bias & Quiescent Current
Drain resistor = 15 Ω
Supply = 24 V
Drain biased at 12 V
Current 0.8A

Maximum Output Voltage Swing
Because this is single-ended Class A with resistor load:
Max upward swing ≈ +12 V (until drain hits 24 V)
Max downward swing ≈ −12 V (until near 0 V)
Realistically subtract MOSFET saturation (~2 V), so usable peak swing ≈ ±10 V

RMS voltage: around 7V
Realistically: 5–6 W clean max for 8 ohms speaker

Efficiency:
That 32% is theoretical.
For resistor-loaded Class A:
Maximum theoretical efficiency = 25%
With real voltage drops and MOSFET limits:
Real-world efficiency ≈ 20–25%
The MOSFET will dissipate roughly:
~10 W at idle
~8–15 W under signal
That’s why it needs a serious heatsink.

Real Maximum Clean Power into 4 Ω ≈ 1.3 watts
Efficiency 6.8%

4. Distortion Estimate
This design:
Has no global feedback
Is single-ended
Has asymmetric transfer curve
Uses resistive load
Expected distortion at:
1W output:
~1–2% THD
Near full power (5–6W):
3–8% THD

Dominant harmonic:
Strong 2nd harmonic
Some 3rd
Very little crossover distortion (it’s pure Class A)
This is why these amps are often described as:
“Warm”
“Tube-like”
“Euphonic”
But technically:
Distortion is far higher than AB or D designs (<0.01%) Distortion with 4 Ω Because the load is heavier: Clipping starts early Distortion rises quickly At 1W expect ~3–5% THD Near max (1.3W) distortion >5–10%
It will sound:
Softer
Compressed
Less controlled bass
Very low damping factor (~4Ω / ~5Ω ≈ 0.8)

This amplifier is designed for 8 Ω or higher speakers.
Driving 4 Ω:
Wastes power
Increases distortion
Severely limits output

In this amplifier the 4700 µF output capacitor is not neutral. The 4700 µF capacitor blocks DC, passes AC to the speaker and forms a high-pass filter with the speaker. It directly affects distortion, especially at low frequencies.

How It Causes Distortion
A) Capacitor Voltage Swing Effect (Major)
Electrolytic capacitors are voltage-dependent devices.
In this amp:
The cap has ~12 V DC bias across it
Audio signal adds AC swing
So instantaneous voltage varies between ~2 V and ~22 V at high output
Electrolytic capacitance changes slightly with voltage.
That causes:
Capacitance modulation
Nonlinear impedance
Added low-frequency harmonic distortion

This increases as:
Frequency decreases
Signal amplitude increases
Load impedance decreases (4 Ω worse than 8 Ω)

B) ESR (Equivalent Series Resistance)
The capacitor has small series resistance.
At high current peaks:
Voltage drop across ESR occurs
That drop is nonlinear with temperature and ripple current
Adds small distortion
Usually minor compared to mechanism A.
C) Dielectric Absorption
Electrolytics “store memory” of previous charge.
This causes:
Slight waveform asymmetry
Mostly low-frequency distortion
Small, but measurable.

How Big Is the Effect?
For 4700 µF good-quality low-ESR electrolytic:
At 1 kHz:
Distortion from cap ≈ negligible
At 50 Hz near full power:
Can add 0.2–1% THD
At 20 Hz:
Can exceed 1–2% THD
With 4 Ω load:
Roughly doubles
And remember:
Your amp already has 1–3% intrinsic distortion.
So the cap can be a significant contributor at bass frequencies.

Why Designers Add the 10µF Poly Cap in some designa.
When you have a 10µF film cap in paraller, this:
Reduces high-frequency impedance
Bypasses electrolytic ESR at mid/high frequencies
Improves HF linearity
But it does nothing for low-frequency distortion, because 10µF is too small to affect bass.

Audible Effects
Capacitor coupling often produces:
Slight bass softening
Reduced damping
Warm character
Slight compression at high bass levels
Some people like it. Technically, it is added distortion.

Final Answer
In this amplifier the output capacitor:
Has minimal effect above ~200 Hz
Adds measurable low-frequency distortion
Increases distortion more with 4 Ω load
Slightly reduces damping factor
Contributes to the “warm” character
About 75% (est) of the power just becomes heat.

Comparison to Direct-Coupled AB Amplifier with +- power supply: A DC-coupled Class AB amp:
Has no output capacitor
Lower output impedance
Much lower LF distortion
Better bass control
That’s why modern designs avoid large output electrolytics.

Improvements ideas:

Ways to Reduce Distortion
​The primary cause of distortion here is the non-linearity of the MOSFET’s transconductance and the lack of negative feedback. Here is how to clean it up:
​1. Add a Source Resistor (Local Feedback)
​Currently, the Source (S) is tied directly to ground. Adding a small resistor (e.g., 0.47 \Omega to 1 \Omega) between the Source and Ground introduces Degeneration.
​Effect: It sacrifices some gain but makes the circuit much more linear and thermally stable.
​2. Replace the Load Resistor with a Constant Current Source (CCS)
​The 15 \Omega resistor is a “passive” load. As the output voltage swings, the current through the resistor changes, which causes harmonic distortion.
​Effect: Replacing the 15 \Omega resistor with an active CCS (using another MOSFET or an LM317) ensures the IRF530 sees a constant current, significantly flattening the distortion curve and improving bass response.

​3. Implement Global Negative Feedback
​The current design has no loop to “correct” the output against the input.
​Effect: You can take a portion of the output signal (before the output capacitor) and feed it back to an earlier gain stage or the gate biasing network. This “zeros out” the difference between what the input wants and what the output is actually doing.
​4. Use a Better MOSFET
​The IRF530 is a switching MOSFET designed for ON/OFF operations, not linear audio. Its input capacitance (C_{iss}) is non-linear.
​Effect: Switching to a lateral MOSFET specifically designed for audio (like those from Exicon) or a more linear power MOSFET will reduce high-frequency harshness.

5. Improve Power Supply Filtering
​Class A amplifiers have a Power Supply Rejection Ratio (PSRR) of nearly zero. Any ripple from your 24V power supply will hum directly through your speakers.
​Effect: Use a regulated power supply or a “Capacitance Multiplier” circuit to ensure the DC rail is perfectly smooth.

Safety Note
​The 15R 40W resistor and the IRF530 will get extremely hot. Ensure both are mounted to substantial heatsinks with thermal paste, or they will fail within minutes.