Jean Hiraga’s Super Class-A Amplifier — The Legendary DIY Audiophile Design

For decades, few amplifier designs have achieved the cult status of Jean Hiraga’s Super Class-A amplifier. Even today, audiophiles and DIY builders around the world continue recreating this legendary amplifier because of one thing: its sound.

Unlike modern amplifiers that focus mainly on efficiency and compact size, Hiraga’s philosophy was completely different. The goal was musicality first — warm mids, natural vocals, smooth treble, and effortless detail.

The result became one of the most respected Class-A amplifier designs ever published.

Who Was Jean Hiraga?

Jean Hiraga was a French audio engineer, reviewer, and editor who became famous in the high-end audio community during the 1970s and 1980s. He strongly believed that simple amplifier circuits with high bias current produced more natural and emotionally engaging sound compared to heavily engineered high-feedback designs.

His amplifier projects published in audio magazines inspired thousands of DIY enthusiasts worldwide.

What Is the Super Class-A Amplifier?

The Hiraga Super Class-A amplifier is a pure Class-A transistor amplifier designed with:

• Minimal signal path
• Low negative feedback
• High idle bias current
• Oversized power supply
• Heavy heat dissipation
• Simple transistor stages

Unlike Class-AB amplifiers that switch output devices on and off depending on signal level, a true Class-A amplifier keeps the output transistors conducting continuously.

That means:

• smoother operation,
• almost no crossover distortion,
• and extremely linear low-level audio reproduction.

The trade-off is efficiency.

A 30-watt Hiraga amplifier may consume over 200 watts continuously even when no music is playing.

Why Audiophiles Love It

The Hiraga sound signature is often described as:

• Warm and organic
• Highly detailed
• Smooth at high frequencies
• Deep and natural vocals
• Excellent low-volume listening performance
• Wide stereo imaging

Many listeners compare it to tube amplifiers, but with better bass control and transistor reliability.

Even today, many builders prefer a properly built Hiraga amplifier over modern Class-D amplifiers for dedicated music listening rooms.

Famous Hiraga Designs

Le Monstre (The Monster)

Despite producing only around 8 watts, this amplifier became legendary because of its exceptional sound quality.

It proved that amplifier quality is not only about power output.

Hiraga 20W Class-A

The 20-watt version became one of the most copied DIY Class-A amplifiers ever made.

Builders appreciated:

• simpler construction,
• manageable heat,
• and excellent speaker compatibility.

Super Class-A 30W

This version delivered higher output power while maintaining the signature Hiraga sound.

However, it also introduced serious thermal challenges because of the massive idle current.

Circuit Philosophy

The Hiraga amplifier follows a very different philosophy compared to modern commercial amplifiers.

Instead of:

• complex protection systems,
• dozens of transistors,
• and extremely high feedback,

the design focuses on:

• simplicity,
• linearity,
• and stable Class-A operation.

Typical characteristics include:

• differential input stage,
• driver stage,
• complementary output transistors,
• heavy power supply filtering,
• and high standing current.

The simplicity of the circuit is one reason many DIY builders still study it today.

Heat — The Biggest Challenge

A true Class-A amplifier converts a huge amount of electrical power into heat.

For example:

P = V × I

With ±35V rails and high bias current, output devices may continuously dissipate more than 50 watts each.

That means:

• very large heatsinks are mandatory,
• cabinet ventilation is critical,
• and thermal stability must be carefully designed.

Many builders underestimate this part and end up with overheating problems.

Modern Transistor Replacements

Original Hiraga designs used transistors that are now difficult to source.

Modern DIY builders commonly use:

• Toshiba 2SC5200 / 2SA1943
• MJL4281A / MJL4302A
• MJ15024 / MJ15025

These modern devices offer:

• higher reliability,
• better thermal handling,
• and easier availability.

Power Supply Matters

One reason Hiraga amplifiers sound powerful despite moderate wattage is the oversized power supply.

A typical build may include:

• large toroidal transformers,
• massive capacitor banks,
• separate channel supplies,
• and heavy rectification stages.

The PSU is considered just as important as the amplifier circuit itself.

Is It Practical Today?

That depends on the application.

Excellent For

• Dedicated stereo listening rooms
• High-efficiency speakers
• Audiophile music playback
• Vocal and acoustic music
• DIY audio enthusiasts

Less Suitable For

• Compact installations
• Energy-efficient systems
• Small closed cabinets
• Multi-channel home theater setups
• High-power PA systems

Modern Class-D amplifiers are far more efficient, but many enthusiasts still believe the Hiraga design delivers a more natural listening experience.

Why It Still Matters

Even after decades, Jean Hiraga’s Super Class-A amplifier remains one of the most respected DIY audio designs ever created.

It represents an era where amplifier design prioritized musical emotion over specifications alone.

Today’s technology may offer:

• lower distortion numbers,
• higher efficiency,
• and smaller size,

but the Hiraga amplifier continues to remind audio enthusiasts that simplicity and careful analog design still have something special to offer.

Final Thoughts

The Hiraga Super Class-A amplifier is not just an amplifier circuit — it is a philosophy of audio design.

It sacrifices efficiency for purity. It produces heat in exchange for smoothness. And it values musical realism over marketing specifications.

That is exactly why audiophiles still build it today.