Jean Hiraga Class A amplifier
The Jean Hiraga “Super Class A” is a discrete, pure Class A amplifier circuit renowned for its sonic refinement and minimalist engineering. Operating entirely in Class A mode, it maintains constant current through its output stage, eliminating crossover distortion and preserving the integrity of low-level musical detail. Originally presented by Jean Hiraga in L’Audiophile magazine, the design employs a low overall feedback topology, carefully matched transistors, and a simple two-stage signal path to achieve exceptional linearity and phase coherence. Typical implementations deliver around 20 watts to 40 watts into 8 Ω with a warm yet highly transparent character, making it a benchmark reference for enthusiasts seeking both technical purity and musical realism.
Ampin Audio provides you PCBs and Assembled PCBs with matched Transistors and hi quality components
To Buy contact on whatsapp 8547056859 or email ampinaudio@gmail.com
Component List ( For the Ampin PCB )
Jean Hiraga “Super Class A” – PCB Assembly Guide
1. Preparation
Tools & materials:
Soldering iron (Temperature-controlled soldering iron (350–380 °C tip temp recommended)
I use this one (Amazon link )
Small side cutters, needle-nose pliers
Multimeter for continuity and value checks
Thermal paste and mounting hardware for power transistors
Workspace:
Work on an anti-static mat with good lighting and ventilation.
2. Component Organization
Sort resistors by value using a multimeter — never trust the printed color bands alone.
Group capacitors by type (electrolytic, film, ceramic) and value.
Keep semiconductors in anti-static packaging until needed.
3. Assembly Sequence
(Go from lowest profile to tallest parts to make soldering easier.)
Step 1 – Resistors
Insert all resistors into their marked positions on the silkscreen.
Bend leads neatly, flush to the board underside.
Solder and trim leads.
Step 2 – Small Signal Diodes
Match polarity to PCB markings (band = cathode).
Keep leads short.
Step 3 – Small Film & Ceramic Capacitors
Insert according to value and position.
Most are non-polar, but double-check if your kit includes polarized films.
Step 4 – Transistors (Small Signal)
Orient exactly as per PCB outline — pinouts can differ between brands.
Avoid overheating by soldering quickly.
Step 5 – Electrolytic Capacitors
Observe polarity! Longer lead = positive; negative marked with stripe.
Stand them upright unless your PCB allows for horizontal mounting.
Step 6 – Power Supply Rectifiers (if on-board)
Orient correctly according to silkscreen markings.
Step 7 – Large Film Capacitors
Often used in coupling or supply bypass — mount securely.
Step 8 – Output Stage Power Transistors
Mount to heatsinks before soldering to prevent stress on leads.
Use thermal paste between transistor and heatsink surface.
Insulate if required (mica or silicone pads).
Step 9 – Connectors & Wiring Pads
Fit input/output terminals, PSU pads, and any bias test points.
For high-current paths, use thicker solder and ensure strong joints.
Jean Hiraga “Super Class A” – Connection & Setup Guide
1. Safety First
This amplifier operates at potentially dangerous voltages — disconnect mains power before making any connections.
Use fuses rated appropriately for your transformer and mains voltage.
Class A runs hot — ensure the unit has proper ventilation before extended operation.
After soldering components make the connections as per above image. Connect a 60w light bulb in series to the primary of the transformer . Switch the power supply on, if the light bulb is glowing very bright turn the power off immediately . There is a short somewhere on the board or wiring . Check the board and see if any wrong connections are made , make sure the transistors are in right orientation .
2. Power Supply Connection
Transformer:
Typical build uses a centre tapped transformer (e.g., 2 × 18V–22V AC, rated 300–500 VA for stereo).
Use a 50Amp bridge rectifier to convert the ac to dc , use a heatsink on Bridge rectifier
Please note Bridge rectifier is not included in PCB ,
Connect secondary windings to your PSU board or rectifiers according to schematic.
DC Supply to Amplifier PCB:
Jean Hiraga “Super Class A” typically runs on ±20V to ±25V DC.
Observe polarity carefully:
+V to positive rail
0V (GND) to ground
–V to negative rail
Use heavy-gauge wire (1.5–2.4 mm²) for power rails and ground.
3. Input Connection
Use shielded audio cable for the input signal.
Connect RCA jack signal pin to PCB input pad (IN).
Connect RCA jack ground shell to PCB signal ground pad (SGND), which should link to the star ground point in the chassis.
Keep input wiring short and routed away from the transformer and mains wiring.
4. Output Connection
Use heavy-gauge wire for speaker connections (minimum 1.5 mm²).
Positive speaker terminal → PCB output pad (OUT).To Speaker protection and from there to +ve of speaker connect ground pin of speaker protection to ground pin of powersupply ( if not connected it will not detect DC )
Negative speaker terminal → Ground on Power supply
5. Grounding Scheme
Implement a star ground:
All grounds ( power, chassis, PSU speaker ) meet at a power supply ground
Mains safety earth must be securely bonded to chassis metal.
6. Initial Setup & Bias Adjustment
Pre-power check:
Verify wiring against schematic.
Ensure no shorts between rails.
First power-up:
Use a Dim-Bulb Tester
Monitor rail voltages and check for smoke, heat, or smell.
Bias setting:
The Hiraga “Super Class A” runs high bias (~1.2–1.3 A per channel for 20 W version).
Measure voltage across the output emitter resistors divide by its value to get Bias current
DC offset:
Measure DC voltage at speaker outputs with no load — should be close to 0 mV (±50 mV acceptable).
Let the amp warm for 30–45 minutes and re-check bias.
i will make a seperate post for bias adjustment
7. Final Installation
Mount amplifier boards and heatsinks securely in the chassis.
Keep AC wiring twisted and routed away from signal wires.
Install ventilation slots or fans if heatsinks exceed ~65 °C in normal operation.
Secure all wiring with cable ties or clamps to avoid movement.
8. Listening Test
Connect source and speakers.
Start at low volume, listen for hum or distortion.
Gradually increase volume and monitor temperature and sound quality.
If one channel runs hotter, re-check bias.
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