Electronic repair, restoration, and audio upgrades

 After 20+ years of IT and electronics, including some years as a professional repair technician, I decided to provide my services as a limited, "side hustle", while my career took a slightly different direction in IT. 

Details below: 

I have extensive experience repairing electronics across multiple fields. Audio is my core speciality and young love, but my background also includes work on film and digital cameras, medical equipment, automotive (from power amps to ECUs), power supplies, industrial control systems, and the whole world of IT (computers, laptops, tablets, you name it...).

If it’s electronic, and there’s a sensible balance between time, cost, and outcome, it’s usually repairable.

Audio repair, restoration, and upgrades

Much of my work focuses on repairing and restoring audio equipment that is no longer manufactured, and often undervalued or written off prematurely.

Many older amplifiers, CD players, DACs, and analogue sources were built to a standard rarely seen today. With proper servicing and some tweaks, they can perform exceptionally well, often better than modern replacements.

I regularly work on:

• Integrated and power amplifiers
• Preamplifiers, DACs, and audio interfaces
• CD players, cassette decks, and vintage digital gear
• Turntables and associated electronics

Everything from “dead” units and poor sound quality to intermittent faults — and the aftermath of previous repair attempts.

Repairs are diagnosis-led, not guesswork. The aim is to fix the root cause, not just symptoms.

Upgrades and modifications

Another good chunk of my work revolves around upgrades and improvements. A good majority of vintage amps, players or DACs have great circuit designs but their performance is reduced by cheap parts to keep production costs down. A few quality capacitors, a few power supply tweaks, some output op-amp magic and your old CD player that is now worth £30, can sound A LOT BETTER... (this is one of my specialities and is backed by customer reviews).  

• Replacement of ageing or low-quality capacitors
• Op-amp upgrades where circuit design allows
• Power supply improvements
• Reliability and thermal stress improvements

Upgrades are always discussed beforehand and only recommended where they offer real technical or audible benefit.

Broader electronics experience

If you have a strange/rare/sentimental/expensive device that needs repair, get in touch, I might be able to help. 

Beyond audio, I have extensive experience repairing:

• Cameras and photographic equipment
• Medical and laboratory electronics
• Automotive electronics with a speciality in power audio
• Industrial and automation hardware

This wider experience matters. Many audio faults originate from power regulation, control logic, or component ageing rather than the audio path itself.

How repairs are approached

Every repair starts with proper fault analysis.

1. Assessment of symptoms and history

2. Diagnostic testing using appropriate equipment

3. Clear explanation of findings and options

4. Repair, restoration, or upgrade only if it makes sense

Not all equipment is economically repairable, and I’m always upfront about that. Although I regularly work on "sentimental value" items, where cost is not an issue. 

Disclaimer: 

• My work is done selectively, I am not a shop, just a guy that loves fixing stuff (my name is Tudor by the way) 
• I have limited time and space
• I only work on 2-3 projects at a time
• I rarely do urgent work, although possible
• I take pride in my work and will not rush repairs
• I source quality and original parts, sometimes from other parts of the world, and this takes time
• Costs are discussed for each project, and are usually a lot lower than those of established repair shops. 
• I rarely charge a diagnostic fee and don't have any fixed prices. 

Enquiries

If you’re looking to repair, restore, or improve audio equipment, or need an informed second opinion, you can get in touch via the contact details below.

Please include the equipment make and model, fault description, and any previous repair history if known.

Email: lala.tudor@gmail.com 

Facebook Messenger: https://www.facebook.com/theaudiopilediy

I’m based in central London, providing audio repair, restoration, and electronic diagnostics for clients across London and the UK.

Equipment can be delivered in person by arrangement or sent securely by courier. I regularly work with clients who ship equipment from outside London. Smaller items are often easiest to handle by courier, while larger or valuable equipment can be discussed on a case-by-case basis.

Stereo vs multichannel amplifier performance

 There have been too many occasions where I’ve seen a simple stereo 2.0 amplifier run circles around an expensive multichannel receiver. This is one of those topics that tends to annoy people, especially those who have invested serious money into a big home cinema setup. But hear me out.

I’ll start with a short story.

I used to work with a guy who was a bit of an audiophile and had put a decent amount of money into his system. He was running a Denon 7.1-channel beast, packed with so much tech that it felt more like a computer than an amplifier. He had nice Monitor Audio floorstanders at the front, a Q Acoustics subwoofer, and decent bookshelf speakers for the rears and sides (I don’t remember the exact model, but it was all good quality gear).

We used to chat about music during cigarette breaks, exchange tracks, debate sound quality, the usual stuff. At some point, I asked him how he listens to music when it’s just music, no films. His answer surprised me: he runs the full 7.1 setup.

I suggested he try a few things. Turn off the rear speakers. Turn off the subwoofer. His reply honestly fired me up.

“I have no bass without the subwoofer.”

What?

I knew those speakers well. Properly placed, they have very respectable bass. More than enough for music. And they were placed correctly in his room.

After a few more discussions, I finally told him to go and buy a simple stereo amplifier. £200–£300, nothing fancy.

“But I already have a £1000+ amp, why would I buy something else?”

At that point, after months of conversations about audio and repairs, he trusted me enough. I told him that if I was wrong, I would buy the amp from him myself.

The following Friday, I saw him carrying a box to his car. He had picked up a brand-new Marantz stereo amp, open-box, discounted to around £160 from £300. He had the whole weekend to play with it.

Come Monday morning, he was almost avoiding me.

Long story short: he was blown away. His speakers suddenly had bass. The soundstage was wider. The music felt alive. Better transparency, cleaner highs, more punch. I’m trying to use his words as closely as I remember them.

At this point, you probably have the same look on your face that he had: “What is this guy talking about?”

I’ll keep this at surface level and avoid going too deep into circuit theory.

First of all, yes, there are multichannel receivers that sound genuinely excellent for music. They exist. They are also rare and very expensive. Most consumer AV receivers are designed to excel at multiple tasks, rather than being exceptional at one.

The biggest reason for the difference is power.

A seven-channel amplifier typically has one transformer and one main DC power supply feeding all seven channels. Yes, the power supply will be larger than in a stereo amp, but you are still drawing power seven times from the same source. A two-channel amplifier may have a smaller power supply overall, but only two channels are pulling from it.

It’s also far easier to design a proper dual-mono stereo amplifier than it is to build a receiver with seven transformers, seven power supplies, and all the associated space, cost, and heat problems.

Why does power matter so much?

Because power delivery is not linear. One channel suddenly needs current for a bass passage. Another needs a fast transient for a snare hit. Each of these demands pulls from the same supply. When several channels do this at once, the supply gets stressed, and the channels start fighting each other. Think of it like multitasking on an underpowered computer: everything works, but nothing works optimally.

Multichannel amplifiers are the definition of “jack of all trades, master of none”. They are incredible for films, surround effects, and convenience. Bluetooth, Wi-Fi, room correction, streaming, HDMI switching – all brilliant. But music needs two channels. Music is recorded in stereo.

Another thing I personally dislike in many hi-fi receivers is the amount of processing. The signal goes through layers of digital processing, conversions, DSP, control logic, and switching before it even reaches the amplifier stage. By the time it gets there, it barely resembles the original signal.

This is where we often joke at The Audiophile DIY: a simple valve amplifier with a handful of hand-soldered components can wipe the floor with a “smart” amplifier packed with CPUs and firmware updates.

Then there’s the marketing magic.

Manufacturers somehow managed to create energy out of thin air. A 7.1 receiver advertised as “100 W per channel” sounds impressive. Seven channels at 100 W means 700 W of audio power. Even assuming generous efficiency, losses in the transformer, heat, and the rest of the electronics, you’d expect the unit to draw maybe over 1 kW at full output.

Then you look at the back panel.

Maximum power consumption: 500 W.

That’s usually when we laugh.

To give a real-world comparison, as I’m writing this on the train, a Pioneer SA-720 Blue Series amplifier is waiting for me at home on the workbench. It’s a small, lovely vintage stereo amp rated at 65 W per channel. That’s 130 W of audio output. Accounting for efficiency and losses, you’d expect maybe 200–250 W draw. The unit is rated at 340 W.

That’s an honest specification.

If you’re using a multichannel amplifier and you have decent front speakers, do yourself a favour. Borrow a good stereo amplifier from a friend. Try it properly. You might be very surprised.

Or you might decide I’m an idiot.

Either way, you’ll learn something.

Audio Amplifiers classes explained - Class A vs Class D

When it comes to amplifier operation classes, not all hi-fi enthusiasts really understand what these classes mean in practice. We hear “Class A”, “Class D”, or “hybrid” thrown around in reviews and forums, often with a lot of strong opinions attached. In this article, I’ll cover solid-state (transistor) Class A, Class AB, Class D, and hybrid amplifiers, and explain them in a way that doesn’t require an electronics degree.

The aim is simple: help you understand how these amplifier classes behave, how they tend to sound, and which one might make sense for your system and listening habits. I’ll include simple pros and cons for each, plus some honest recommendations based on real-world use rather than marketing hype.

I’ll start with the most common and widely used amplifier class: Class AB. This has been, and still is, the most sensible and well-balanced way to run a solid-state amplifier. I won’t go into circuit theory, but rather how it behaves and why it became the reference point. To make the other classes easier to understand, I’ll compare everything back to the mighty Class AB.

Class AB is the workhorse of hi-fi. Most classic and modern solid-state amplifiers use it because it offers a very good compromise between sound quality, efficiency, heat, size, and cost. In simple terms, Class AB amplifiers keep their output transistors just slightly turned on all the time. This avoids obvious switching artefacts, but doesn’t waste huge amounts of power when there is no music playing.

In normal listening conditions, a well-designed Class AB amplifier is clean, controlled, punchy, and reliable. It can deliver real power without becoming impractically large or hot, and it works with a wide range of speakers. This is why so many respected designs from the 70s through to today are Class AB.

The good: good sound quality, good efficiency, manageable heat, reasonable size and cost, and excellent reliability.
The bad: it doesn’t quite have the purity or “magic” of Class A, and badly designed examples can suffer from crossover distortion, although this is largely a solved problem in decent designs.

For most people, most of the time, Class AB remains the best all-round choice.

Class A is the dream of many audiophiles, including me. It’s the closest solid-state technology ever got to valves (or tubes, for US readers), although valves deserve a separate article of their own. Conceptually, Class A is not a completely different animal from Class AB, it’s more like running the same engine in a very different way.

Imagine a car engine idling, and then you press the accelerator when you want power. That’s Class AB. Now imagine the same engine running flat-out all the time, whether you’re moving or not. That’s Class A. In a car, this would be madness, but in an amplifier, this behaviour has real sonic advantages.

In a Class A amplifier, the output transistors are always conducting large currents. A modest 20 W Class A amplifier can easily run 1.5–2 amps continuously through the output stage. When the music signal arrives, nothing needs to “wake up” or switch on. The devices are already fully active. This eliminates switching delays, reduces certain types of distortion, and keeps the power supply under a constant load.

The result, when done properly, can be stunning. Effortless midrange, smooth treble, a sense of flow and realism that many listeners find addictive.

The good: exceptional sound quality, especially at low and medium listening levels; very natural and fluid presentation.
The bad: terrible efficiency, lots of heat, very heavy and expensive hardware. A small Class A amplifier might draw 50–80 W continuously just to deliver 20 W of audio power, with the rest turning into heat. This means huge heatsinks, big transformers, and massive capacitor banks.

Class A only really makes sense once the rest of your system is already at a high level. You need speakers that can show the difference, space to deal with the heat, and acceptance that you’re paying for sound quality rather than practicality.

Class D is the new kid on the block, although in reality it has been around for decades. What’s changed recently is that it has finally grown up. Early Class D amplifiers were efficient but often sounded rough or artificial. Modern designs are a very different story.

A simple way to think about Class D is not “digital amplification” (despite the name), but a very fast switching power amplifier. Instead of amplifying a smooth, linear signal like Class AB or A, the output transistors switch fully on and fully off at extremely high speeds. The audio signal is encoded into these on/off patterns, then reconstructed back into music by an output filter.

Because the transistors are either fully on or fully off, they waste very little power. Efficiencies of 85–95% are common, compared to 30–40% for Class A and around 50–70% for Class AB.

The good: very high efficiency, compact size, low heat, lighter weight, and the ability to deliver lots of power cheaply. Modern Class D can sound excellent, with tight bass and very low distortion.
The bad: design complexity, sensitivity to layout and power supply quality, and a sound that some still find a little “matter of fact” compared to Class A or good AB. Poor implementations still exist.

Class D makes huge sense for high-power systems, subwoofers, active speakers, and modern compact hi-fi. It’s no longer the compromise it once was, but it still rewards careful design.

Class T is often mentioned alongside Class D, and for good reason: technically, it is a variation of Class D rather than a completely separate class. Class T was popularised by Tripath chips in the early 2000s and used a proprietary control method that adjusted the switching behaviour in a more “analogue-like” way. The result was surprisingly musical sound from very small, efficient amplifiers, often better than early Class D designs. The downside is that Tripath no longer exists, so Class T is mostly of historical interest today, but many of those small amps still have a loyal following.

Class H is less talked about in home hi-fi, but it is very common in professional and high-power amplifiers. It is essentially an evolution of Class AB that uses multiple power supply voltage rails. At low listening levels the amplifier runs on lower voltages to reduce heat and waste, and as more power is needed it switches to higher voltage rails. This improves efficiency without fully abandoning linear amplification. When done well, Class H can sound very similar to Class AB, but with better efficiency at high power levels.

Hybrids sit somewhere between these worlds. The most common hybrid approach uses valve pre-amplification combined with a solid-state power amplifier, usually Class AB or Class D. The idea is to blend the harmonic richness and character of valves with the control, power, and reliability of transistors.

Some hybrids also bias their solid-state output stages closer to Class A at low levels, sliding into Class AB as power demand increases. Others use Class D power stages with valve input stages to add a bit of flavour.

The good: flexibility, character, often a pleasing balance of warmth and control.
The bad: complexity, cost, and sometimes neither side fully delivers if the design is not well-balanced.

In terms of recommendations, Class AB remains the safest and most universally sensible choice. If you want maximum sound quality and are happy to live with heat, size, and cost, Class A can be magical. If efficiency, compactness, or high power matter, modern Class D deserves serious consideration. Hybrids are for those who enjoy experimentation and character, and who value system matching over purity.

There is no single “best” class, only the best choice for your system, your room, and how you listen.

Old jukebox or console 25 watt amplifier restoration

A vintage mono 25W amplifier saved from landfill. Cleaned, new capacitors, the old cans were checked also for leakage current and are perfect. Cleaned, calibrated and ready for a new life. 

Mission DAC 5 - capacitor service and upgrades

Another superb English DAC, in for a service and some upgrades. 

A few capacitors lost over half of the capacitance and some had high ESR. All replaced with quality caps, and solid Panasonic caps on the DAC power supply lines. 

The unit also got newer audio grade op-amps, OPA134, gold plated sockets installed, and the mute transistors were removed. 

Micromega Duo DAC - capacitors service and upgrades

A superb audio Dac, in for a service and upgrades. 

A few capacitors were out of spec, everything was replaced with quality parts. Since it was on the bench, opamps were upgraded to highes spec audio grade OPAs. 

Bose SoundTouch 300 – Power Supply Repair and Common Faults

 If your Bose SoundTouch 300 soundbar has suddenly gone completely dead, no lights, no signs of life don’t panic just yet. This is a widespread issue, and the fault almost always points to the power supply board. 

WARNING-  this work requires knowledge of electricity, safety and the dangers presented on mains-powered equipment. DO NOT TAKE THIS ON  if you don't have the basic knowledge on safety. 

Over the years, I’ve repaired a few of these, and the pattern is always the same: the SMPS (switch-mode power supply) fails, usually taking out the UCC28630 driver IC, the main switching MOSFET, and a couple of nearby resistors in the process. Sometimes on the mainboard, there are 5V regulators that short out, easy to identify by part number ( they are not op-amps 😉). There are some SMD capacitors around the chips. If you find a short on any of those caps, you remove the IC and the short goes away... the chip is dead. 

What actually happens

Parasound Zamp v3 - in service

Superb little amps with big sound. On the bench for a service: recap, and board resoldered. These amps suffer from the same issues as many others, another clear example is NAD: great circuits but cheap electrolitics. 

After a full recap and some bad solder joints, it truly sings. 

Audiophiles and Sound – Why Our Brains Don’t Like “Perfect”

 

The Idea

There’s a funny thing about sound: the more time you spend chasing perfection, the less music you actually enjoy.
After 20+ years of building, repairing, and listening to audio gear, I’ve come to a simple conclusion: our brains don’t actually like perfect sound.

We like character, colour, and a touch of imperfection that makes the music feel alive.
Before the purists start throwing cables at me, hear me out.

The Myth of Perfection

In theory, the perfect audio system would reproduce the signal exactly as recorded — zero distortion, perfectly flat frequency response, no noise, no phase errors.

In practice, that kind of sound is boring. It’s analytical and cold, and after a few minutes, your brain starts wandering off.

What keeps us listening for hours isn’t clinical precision, it’s texture, warmth, dynamics, and the subtle imperfections that make the music human.

I’ve heard expensive systems that were technically flawless but emotionally empty, and modest systems that made me smile from the first note.

 The Human Brain and “Pleasant Errors”

Our brains are not precision instruments. They’re pattern recognisers that constantly fill in gaps and add feeling to what we hear.

That’s why valve amplifiers, with their harmonic distortion, sound so inviting; they produce even harmonics that our brain interprets as musical warmth.

On paper, they “measure worse” than a cheap op-amp.
But to our ears? They sound better.

Think of it like photography: a perfectly noise-free digital image can feel sterile, while a slightly grainy film photo feels alive.

Marantz PM 151 repair - full service

A super dirty Marantz PM 151, in for a service.  These are great little amps, with a specific mellow sound. This is a "warm" sounding amp. 

After a full service and calibration- it sings nicely.

- recap with Elna and Panasonic

- sound path Nichicon Gold

- main filter caps upgraded to 10k uF 

- phono preamp opamp upgraded from 4558 to 5532

- pots and switches cleaned

- bias calibrated

Technics and Class A amplifiers

 Another crazy discussion, this was debated many, many times, no harm in presenting my experience with Technics amps that claim Class A in one form or another.

 First of all, No… Technics did not manufacture any Real Class A amplifiers (I never saw or heard about one), but they had a unique design that was quite good.

Technics used a variable biasing circuit that will somewhat modify the class of operation based on the input level.  Simple explanation: first few Watts are delivered in a Class A operation. Increasing the volume will switch the amp to class AB, and the rest of the power will be offered as a Class AB amplifier.

  Does it work?  Yes, although Technics did not focus on high-end, some of their equipment is very good. And they also have a few rare high-end series that are more Matsushita Signatures than Technics/ Panasonic consumer units.

One of the favourite amplifiers here at Audiophile Repairs is the Technics SU-V707, or for other markets the SU-V7, a 90W/ch tank that has all you ever need, sounds amazing and will drive anything. I can already hear the purists screaming about someone liking Technics, I should be hanged, right? 

Not all Technics units marked with a form of Class A operation are the same; the SU-V707 is an amp that I highly recommend to any beginner and even advanced audiophile. They require a service due to age, but the results are amazing. 

-        The unit has a small CPU that will read the speaker impedance, will preheat the output transistors and control the bias.

-        The first 10-15W  are purely amazing, it gives you the feeling that is so powerful it will blow your speakers, but once you go past that point, it just cools down and behaves normally.

The amp was the main listening and test amp for 1 year, and sometimes I miss the sound of that unit. The first time it arrived, everybody was a bit  “meh”, just another Technics. After it was recapped and calibrated … WOW,  that Technics can sing. The smaller brothers SU-V303/505 ( as above, in some markets it might be V3 or V5)  are also amazing.