My LS3/5A Journey

Published by IWISTAO

Immersed reading—like disappearing into a novel.

When it comes to hi-fi, the British BBC LS3/5A is a hurdle almost no audiophile can avoid. If you try to list the loudspeakers that have not only survived decades but also appreciated dramatically, the LS3/5A would likely rank near the very top.

In 2004, Taiwan’s Audio Forum published a supplement titled Everlasting Classics, and one article there pointed out that the LS3/5A was among the most recommended and most frequently featured pieces of equipment. Twenty-one years have passed since then—and even today, the situation has not changed much.

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Early Research: Hong Kong and “Ah Ming”

The earliest person to conduct a dedicated, systematic study of the LS3/5A was a Hong Kong audiophile known as “Ah Ming.” Many years ago, he self-published a book titled The Immortal Legend of Loudspeakers: LS3/5A, priced at HKD 80 at that time. Although deeper research later revealed a few inaccuracies in that book, for LS3/5A fans at the time, it was practically a must-have—almost everyone owned a copy.

 

15Ω and 11Ω: Two Production Eras

From 1974 to 1987, the LS3/5A belonged to what is often called the 15-ohm era. The main producers included Rogers, Spendor, Audiomaster, Chartwell, Goodmans, and RAM.

From 1988 to 1998, it entered the 11-ohm era, with production mainly by Rogers, Spendor, Harbeth, and KEF. Among these, the two brands that truly spanned both eras were Rogers and Spendor.

The LS3/5A earned its fame in the 1980s, but it reached the broader market largely in the late 1980s— primarily during the 11-ohm period. It then became widely popular amid the early-1990s audiophile boom, continuing until 1998, when KEF discontinued the T27 tweeter and B110 mid-bass driver. In other words, during the hottest years of the 1990s, most people were actually listening to 11-ohm LS3/5A, and Rogers / Harbeth / KEF / Spendor effectively “ruled the world.”

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Why LS3/5A Became My First Target (1995)

When I planned to buy my first hi-fi system in 1995, my target was already the LS3/5A. There were two major influences behind that decision.

Influence #1: A 1994 Magazine Article That Shaped My Thinking

In 1994, while browsing the CD section of a bookstore, I discovered a magazine called Audiophile (I believe it was the second issue). Inside was a beginner’s guide article titled “A Hi-End Starter Audio System”, which had a strong impact on me.

That article was my first real introduction to the idea of the “British sound.” It argued that when choosing speakers, it is best to start with classic British designs that prioritize midrange integrity and soundstage construction—ideally BBC-derived designs like the LS3/5A. This approach, it said, is hard to get wrong, holds value well, and delivers strong musical expressiveness. It even suggested using a tube amplifier (such as 300B tube amp) and a CEC 891R CD player—spending modestly, yet establishing a correct listening philosophy.

Looking back now, those viewpoints were surprisingly solid. It really was a proper path for beginners. From then on, I developed a deep affection for the BBC-influenced British sound.

Influence #2: A Spark Audio Demo That Sounded Like Heaven

The second influence happened around January 1995. Spark Audio—newly founded at the time—held a small promotional event. If I remember correctly, there were two sessions, and I attended both.

Spark showcased two tube amplifiers: the Model 560 using FU29 tubes, and the Model 550 using 300B tubes. The event mainly used the 560. The speakers included a pair of Rogers 11-ohm rosewood BBC LS3/5A, an LS5/9, and a pair of PSB 800 floorstanders.

 

The Rogers LS3/5A belonged to the host himself—well known as a radio program presenter in the audiophile world. He wasn’t tall, wore a small mustache (a bit like George Lam), had a musical background, spoke with wit and ease, and hosted the event brilliantly.

When the 560 drove the LS3/5A, the sound was, to me at that time, simply otherworldly. I still remember listening to Zhu Zheqin’s Yellow Children. The top-end had excellent density—warm, sweet, and smooth. The musical expression was rich and deeply moving. That demonstration left the LS3/5A with an exceptionally beautiful image in my mind.

When LS3/5A Sounds Bad (Yes, It Can Happen)

Of course, I have also heard LS3/5A systems that sounded genuinely poor. For example, at the audio section of a foreign-language bookstore, there was a Rogers LS3/5A paired with an AB1 bass unit. And at a hi-fi center, I heard a Rogers 11-ohm pair. In both cases, they were driven by a Rotel integrated amplifier (the 960BX, if I recall correctly). The speakers were severely under-driven—nothing opened up, and the results were disappointing.

That’s the thing about the LS3/5A: if you don’t drive it properly, it can make you doubt the legend itself. (Laughs.)

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The Long “Knot in the Heart” (1995 → 2015)

Even in the autumn of 1995, I still didn’t manage to buy an LS3/5A. The reason was simple: the dealers had no Rogers stock. Harbeth was available, but it cost 11,500 HKD—far beyond my budget. Spendor and KEF were rare and not cheap either. Later, around 1998, a Spendor pair cost about 9,300 HKD, while a piano-black KEF version was even more expensive—around 14,000 HKD.

Still, the LS3/5A remained a “knot in my heart.” Before 2015, I owned several speakers; two of them leaned heavily toward the traditional British sound: the Castle Inversion 15 and the Harbeth Super HL5 in rosewood. Finally, in the autumn of 2015, I acquired a Spendor 11-ohm LS3/5A with a bi-wire crossover— and that long-held wish was finally fulfilled.

 

A few years later, I added a second pair: a ProAc LS3/5A in ebony veneer. At that point, I owned two pairs of 11-ohm LS3/5A at the same time.

 

Living with Two Pairs of 11-Ohm LS3/5A

I drove these two LS3/5A pairs with two amplification setups: an Exposure 15.2, and a classic Naim chain consisting of a NAC 32 preamp, SNAPS power supply, and NAP 160 power amp.

Overall, the two 11-ohm LS3/5A pairs were remarkably consistent in their character. Compared with the ProAc Super HL5 30th Anniversary (rosewood) that I had used for a long time, the LS3/5A put more emphasis on vocals—more captivating and emotionally “pulling” in a direct way. Vocals separated from the ensemble more clearly. The upper-mid and treble density was higher than the Super HL5, and female vocals had stronger penetration. The presentation felt more active and animated.

The decay was longer and more flavorful, and the treble stood out more. Naturally, the bass quantity was not as abundant as the Super HL5—after all, this is a 5-inch driver— but it still conveyed a convincing sense of scale. Imaging and localization were exceptionally strong; that advantage was obvious.

The Super HL5’s strength, on the other hand, is its ability to build atmosphere and tell a musical story— its sense of emotional narration is truly wonderful.

 

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Back to 15 Ohms (2024 → Present)

In November 2024, since I no longer had either of my 11-ohm LS3/5A pairs, I purchased a pair of Rogers black-label 15-ohm LS3/5A, paired with Yue stands. A 15-ohm pair is something you simply must own—at least that’s how it feels. (Laughs.)

Then, in September of this year, to properly match the 15-ohm LS3/5A, I acquired a Line Magnetic “Ange” AS-135 300B single-ended tube amplifier and upgraded the full set of tubes.

With the AS-135 driving the LS3/5A, everything felt perfectly “on the right track.” The black-label LS3/5A seemed to grow into a small giant: richer midrange body, longer trailing decay, extremely high mid-to-high density, and abundant detail. The overall performance clearly surpassed what I achieved with my previous solid-state amplifiers.

 

Once again, this confirmed an old belief: the LS3/5A is better suited to voltage-driven tube amplification. The saying “LS3/5A won’t sing without tubes” truly has a solid basis.

Conclusion

For veteran audiophiles, owning a pair of LS3/5A almost feels like a matter of course. As for which brand—or whether it is 11 ohms or 15 ohms—those details feel less important in the end.

Because in the world of BBC LS3/5A, there is one simple truth: If it’s an LS3/5A, it sounds good.

DIY Tube Amplifier Testing and Adjustment --A Practical Engineering Guide

Published by IWISTAO

Building a DIY tube amplifier is never just about getting sound. True performance, reliability, and tube longevity depend on systematic testing and precise adjustment.

Improper setup may lead to shortened tube life, unstable bias, excessive transformer heating, or even catastrophic failure. This article provides a complete, practical workflow for testing and tuning DIY tube amplifiers, suitable for both single-ended (SE) and push-pull (PP) designs.

 

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1. Pre-Power-On Inspection (Mandatory)

Before connecting the amplifier to mains power, every circuit must be carefully inspected. Even a small wiring error can cause:

• Output tube damage
• Electrolytic capacitor failure
• Burned power or output transformers

1.1 Visual and Wiring Checks

• Correct polarity of all electrolytic capacitors
• Proper orientation of rectifier tubes or diode bridges
• No accidental grounding of output transformer primary
• Clear separation of signal ground and protective earth (PE)
• Presence of grid-leak and screen-grid resistors

Practical experience: More than 80% of first power-up failures originate from power-supply wiring or grounding mistakes.

More details about grounding, please refer to the post below.

Grounding Design for EL34 Single-Ended Tube Amplifiers

 

1.2 Cold Resistance Measurements

With all tubes removed, use a multimeter to check:

• B+ to ground: resistance should rise slowly (capacitor charging)
• Heater to ground: low resistance, no direct short
• Control grid to ground: typically ≥ 100 kΩ
• Screen grid to ground: only through a resistor

If B+ measures close to zero ohms, stop immediately and locate the fault.

 

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2. First Power-On: Current Limiting Is Essential

Recommended Methods

• Series connection an incandescent light-bulb current limiter (60–100 W)

• Variac, slowly increasing AC voltage from 0 V

Correct Power-Up Sequence

1. Power on with no tubes installed
2. Verify heater voltage and absence of abnormal B+
3. Install the rectifier tube
4. Install output tubes last

If the current-limiting bulb stays brightly lit, a short circuit or serious fault is present.

If B+ voltage does not rise, there is a problem for rectifier or power supply.

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3. Critical Voltage Measurements

3.1 Heater Voltage

• 6.3 V tubes: 6.0–6.6 V
• 5 V rectifier tubes: 4.9–5.2 V

Excessive heater voltage shortens tube life; undervoltage degrades dynamics and increases distortion.

3.2 B+ High Voltage

A deviation within ±10% of the design value is generally acceptable.

Excessively high B+ often indicates insufficient load or incorrect rectification.

3.3 Output Tube Operating Point (Most Important)

For cathode-biased stages, quiescent current is calculated as:

I_k = V_k / R_k

Example: EL34 single-ended amplifier

• V_k ≈ 30–35 V
• I_k ≈ 60–75 mA

Plate dissipation must be verified:

P = (B⁺ − V_k) × I_k

Always remain below the tube’s maximum rated dissipation.

 

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4. Bias Adjustment

Fixed-Bias Amplifiers

• Set bias to maximum negative voltage before power-up
• Increase current slowly to target value
• Match channels within ±5% for push-pull stages

Cathode-Bias Amplifiers

• Operating point determined by cathode resistor value
• Cathode bypass capacitor affects low-frequency response

More details Bias Adjustment, please refer to the post below.

EL34 Bias Adjustment Guide (SE and PP)

 

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5. No-Signal Safety Checks

• Red-plating output tubes (bias too hot)
• Audible hum (ground loop or heater wiring issues)
• Chassis leakage voltage (incorrect PE grounding)
• High-frequency oscillation (feedback polarity error)

Never operate a tube amplifier without a load.

 

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6. Audio Signal Testing (Advanced but Highly Recommended)

Recommended Test Setup

• Signal generator: 1 kHz sine wave
• Load: 8 Ω dummy load (≥ 50 W)
• Measurement: oscilloscope

Sine-Wave Test

More details about Sine-wave testing, please refer to this post below

Understanding Output Waveform Distortion in Tube Amplifiers

 

• Clean, symmetrical waveform
• Even clipping on both halves

Square-Wave Test (10 kHz)

• Overshoot: excessive feedback
• Ringing: transformer or compensation issues

More details about square wave testing, please refer to this post below.

Overshoot and Ringing in Tube Amplifiers--Causes, Detection (Square-Wave Test), and Practical Adjustment Methods

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7. Burn-In and Thermal Stability

Operate the amplifier for 2–4 hours under load:

• Record B+ and tube current every 30 minutes
• Monitor transformer temperature rise

Typical safe limits:

• Power transformer < 70 °C
• Output transformer < 60 °C

 

Vacuum Tube Amplifier 300B Kit Single-ended Class A No soldering 6F3 Preamplifier DIY Kits HIFI

 

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Conclusion

A high-quality tube amplifier is not simply assembled — it is measured, tested, and adjusted with discipline.

A systematic testing process separates casual DIY from true audio engineering practice.

This guide just for you information, and applies to EL34, KT66, 300B, 2A3, and similar vacuum tube amplifiers.

 

Overshoot and Ringing in Tube Amplifiers--Causes, Detection (Square-Wave Test), and Practical Adjustment Methods

Published by IWISTAO

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Introduction

In tube amplifiers, overshoot and ringing are common distortion or instability phenomena.

They are typically caused by excessive feedback gain or deficiencies in output transformer design. These issues can be effectively addressed through precise adjustments focusing on optimizing the feedback loop, gain structure, and output transformer behavior.

The sections below provide a detailed, practical guide for diagnosing and resolving overshoot and ringing during tube-amplifier debugging, using a square-wave test and oscilloscope observation.

Test Method (Recommended):

Apply a square-wave signal (for example, 1 kHz) to the amplifier input and observe the output waveform on an oscilloscope across a proper dummy load.

1. Overshoot Adjustment

1.1 Identifying Overshoot

Apply a square-wave signal (for example, 1 kHz) and observe the output waveform on an oscilloscope:

• Overshoot appears as a sharp “spike” or peak at the top of the waveform, where the signal exceeds the ideal flat level.
• Overshoot usually occurs during the high-level portion of the waveform, indicating that the amplifier gain is too high or that the feedback loop is responding too aggressively.

1.2 Cause Analysis

• Excessive feedback gain: When feedback gain is too high, the amplifier overreacts to rapid signal changes, causing transient over-amplification and overshoot at the waveform edges.
• Driver stage issues: If the gain of the driver or preamplifier stage is too high, the power stage may be overdriven, especially when the input signal amplitude is excessive.
• Power supply instability: Poor power-supply regulation or inadequate filtering can introduce voltage lag or fluctuations, which can exacerbate overshoot behavior.

1.3 Adjustment Procedure

1. Reduce feedback gain: Inspect the feedback loop and reduce the amount of feedback if necessary. Lower feedback gain slows the amplifier’s transient response and often eliminates overshoot.
   • Global negative feedback: slightly reducing the feedback ratio is often effective.
   • Local feedback: ensure that resistor and capacitor values are correctly chosen to avoid excessive high-frequency gain.
2. Optimize driver-stage gain: If overshoot originates from excessive driver gain, adjust the driver stage to reduce signal amplitude and prevent the output stage from being pushed beyond its linear region.
3. Check power-supply stability: Verify that the B+ supply remains stable under load. Improving filtering—such as increasing reservoir capacitance within safe limits—can help reduce overshoot.
4. Add or adjust feedback resistors: Introducing small resistors in the feedback path (typically in the 1 kΩ to 10 kΩ range, depending on design) can help smooth the feedback response and suppress overshoot.

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2. Ringing Adjustment

2.1 Identifying Ringing

Ringing is typically visible at the rising and falling edges of a square-wave signal:

• Ringing appears as oscillations or “echoes” following the waveform transitions.
• Instead of a clean, instantaneous edge, the waveform shows several cycles of damped oscillation.

2.2 Cause Analysis

• Output transformer design limitations: If the output transformer lacks sufficient bandwidth or approaches magnetic saturation, frequency response becomes uneven, leading to ringing during fast signal transitions.
• Compensation network issues: Tube amplifiers often include compensation networks to stabilize high-frequency response. Incorrect capacitor values or time constants can result in excessive high-frequency resonance, producing ringing.
• Poor circuit layout: Suboptimal wiring, grounding, or lead dress can introduce parasitic capacitance and inductance, contributing to high-frequency instability and ringing.

2.3 Adjustment Procedure

1. Evaluate the output transformer: If ringing is prominent at waveform edges, examine whether the output transformer provides adequate bandwidth.
   • Use a high-quality transformer with appropriate low- and high-frequency performance.
   • Ensure the core does not saturate under normal operating conditions.
2. Adjust compensation networks: If ringing originates from compensation circuits, experiment with compensation capacitor values and time constants.
   • Reducing compensation capacitance or adjusting associated resistors can rebalance high-frequency response and suppress oscillations.
3. Improve circuit layout: Keep signal paths short and direct to minimize parasitic effects.
   • Use low-impedance grounding techniques.
   • Avoid ground loops and maintain proper separation between signal and power paths.
4. Add high-frequency damping: Small high-frequency suppression capacitors (for example, 100 pF to 1 nF, depending on design) at appropriate locations can help smooth high-frequency components and reduce ringing.

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3. Summary

• Overshoot is mainly caused by excessive feedback gain, overly high driver-stage gain, or unstable power supplies. It can be mitigated by reducing feedback, optimizing gain structure, and improving power-supply stability.
• Ringing is typically caused by output transformer limitations or improper compensation. It can be reduced by selecting suitable transformers, adjusting compensation networks, and improving circuit layout.
• Through careful adjustment of the feedback loop, gain structure, and output transformer design, overshoot and ringing in tube amplifiers can be significantly reduced, resulting in cleaner, more stable, and more accurate sound reproduction.

Practical Tip:

Always verify square-wave results at multiple frequencies (e.g., 100 Hz / 1 kHz / 10 kHz) and with the correct rated load. Many overshoot and ringing issues only become obvious at the high-frequency edge transitions.

Radio and the Emergence of a Synchronized World

Published by IWISTAO

Prior to the development of radio, human societies did not share a unified temporal experience. Information circulated through letters, newspapers, and telegraph networks, each constrained by physical transmission and institutional mediation. Even events of major historical significance often reached different populations at different times. As a result, social reality unfolded asynchronously: individuals and communities inhabited distinct temporal frameworks, shaped by geography and the speed of information flow.

In such a context, the notion of a universal present—of a shared “now”—had limited applicability. Time, as experienced socially, was fragmented and local rather than collective.

Scientific Foundations of Wireless Communication

The scientific conditions that enabled radio communication emerged in the late nineteenth century through advances in electromagnetic theory. James Clerk Maxwell demonstrated mathematically that electromagnetic waves could propagate through space, while Heinrich Hertz later confirmed these predictions experimentally. Although these developments were not conceived with mass communication in mind, they established the theoretical possibility of transmitting signals independently of physical conduits.

This possibility was translated into practical technology by the Italian engineer Guglielmo Marconi, whose experiments in the 1890s and early twentieth century culminated in long-distance and transoceanic wireless transmission. With these achievements, information was no longer bound to fixed infrastructures such as cables or printing networks. Communication could occur across space with unprecedented immediacy.

From Communication to Broadcasting

Initially, radio functioned as a point-to-point communication system. Its primary applications were maritime coordination, military operations, and emergency signaling. In these contexts, radio’s value derived from reliability and reach rather than from content or audience scale. It was a technical instrument designed to ensure that messages could be received under conditions where other systems failed.

The transformation of radio into a mass medium occurred in the early twentieth century with the emergence of broadcasting. Beginning around 1920, scheduled radio programs appeared in the United States and Europe. Unlike earlier forms of communication, broadcasting addressed an indeterminate audience simultaneously. Sound was no longer directed toward a specific receiver but dispersed across space to all who possessed the means to listen.

Simultaneity and the Shared Present

This shift marked a fundamental change in the temporal structure of communication.

Broadcasting introduced simultaneity as a defining feature of mass experience. Music, news, and speech were no longer encountered sequentially or retrospectively; they were received in real time by large populations. Individuals who remained socially anonymous to one another nevertheless occupied the same temporal moment. The experience of listening became, implicitly, a collective act.

In this sense, radio produced what may be described as a shared present: a temporally synchronized field of experience extending beyond local or interpersonal boundaries. This development had far-reaching social and political implications.

Political, Social, and Wartime Implications

Political communication acquired new immediacy. Leaders could address populations directly through voice, circumventing the interpretive filters of print journalism. Tone, rhythm, and presence became central elements of persuasion. Public opinion was shaped not only by argument, but by affective transmission mediated through sound.

During periods of war, radio’s capacity for synchronization assumed heightened significance. News bulletins, official announcements, and propaganda broadcasts aligned civilian perception with unfolding military events. The temporal gap between front lines and domestic spaces was narrowed, producing a sense of shared urgency and participation despite physical separation.

Radio and the Reorganization of Daily Time

Beyond politics, radio also reorganized everyday temporal practices. Broadcast schedules imposed standardized time markers on domestic life. News programs, music segments, and evening broadcasts structured daily routines, embedding institutional time within private space. Time itself became, in part, a function of programming.

Unlike later visual media, radio did not monopolize attention. Its auditory nature allowed it to coexist with other activities. Listening could accompany work, conversation, or rest. Information thus entered daily life as a continuous background presence rather than as a discrete event demanding full cognitive focus.

This characteristic contributed to radio’s pervasive influence. It did not merely inform; it habituated listeners to a mode of constant connection with distant events.

Retro Wooden HIFI Radio AM/FM 2x5W Desktop Speakers Rotary Tuning Bluetooth U Disk Playing

Retro Wooden HIFI Radio AM/FM 2x5W Desktop Speakers Support Bluetooth U Disk SD Card Playing High Sensitivity

Legacy of a Synchronized World

Although radio’s centrality declined with the rise of television and digital media, the temporal model it established persisted. Real-time reporting, live broadcasts, and the expectation of immediate access to events are direct continuations of the broadcasting logic introduced by radio.

From a historical perspective, radio did not fundamentally alter the nature of content. Its significance lies in the transformation of temporal experience. By enabling simultaneous reception on a mass scale, radio reconfigured how societies perceive events, relate to one another, and situate themselves within time.

The world ceased to occur as a series of isolated moments
and began to unfold as a shared temporal reality.

This reorganization of time, rather than any particular program or technology, constitutes radio’s enduring contribution to modern civilization.

Understanding Output Waveform Distortion in Tube Amplifiers

Published by IWISTAO

Oscilloscope-Based Diagnosis and Adjustment Guide

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Introduction

In tube (valve) amplifier design and debugging, the oscilloscope remains one of the most powerful diagnostic tools. By observing how a simple sine-wave input is transformed at the output, engineers and builders can quickly identify bias errors, overload conditions, power-supply limitations, and tube mismatches.

This article compares a reference sine wave with six typical output waveforms commonly observed during tube-amplifier testing. Each waveform corresponds to a specific electrical mechanism and provides clear guidance for troubleshooting and optimization.

 

Reference Signal: Ideal Sine Wave (Waveform a)

Waveform (a) represents the ideal input sine wave applied to the amplifier.

• Perfect symmetry between positive and negative half-cycles
• Smooth curvature with no flattening or discontinuities
• Stable amplitude and frequency

This waveform serves as the baseline reference. Any deviation observed at the amplifier output indicates nonlinearity, overload, or instability elsewhere in the circuit.

Grid Overload Distortion (Waveform b)

Waveform (b) shows flattening of the positive half-cycle while the negative half-cycle remains relatively undistorted.

This occurs when the control grid is driven to 0 V or positive voltage, causing grid current to flow and loading the driver stage.

• Excessive input signal amplitude
• Driver stage gain too high
• Missing or undersized grid-stopper resistors
• Uneven overload in push-pull stages

Audible effect: harsh highs, compressed dynamics, loss of openness.

Symmetrical Power Clipping (Waveform c)

Waveform (c) shows both waveform peaks clipped evenly, indicating the output stage has reached its maximum voltage or current swing.

• Amplifier driven beyond rated output power
• Output transformer core saturation
• Insufficient B+ voltage or rectifier capacity
• Undersized filter capacitors

Audible effect: compressed dynamics and reduced clarity at high volume.

Crossover Distortion (Waveform d)

Waveform (d) exhibits a notch around the zero-crossing point, a classic sign of crossover distortion in push-pull amplifiers.

• Bias set too cold
• Aging components causing bias drift
• Output tubes not recalibrated after replacement

Audible effect: thin sound at low volume, poor vocal smoothness.

Note: This is one of the most objectionable distortions in push-pull tube amplifiers.

Asymmetrical Distortion and Bias Imbalance (Waveform e)

Waveform (e) shows unequal positive and negative half-cycles, indicating an operating-point shift or tube imbalance.

• Mismatched or aging tubes
• Unequal quiescent currents
• Drifting cathode resistors
• Leaky coupling capacitors

Audible effect: warmer tone with increased even-order harmonics but reduced imaging accuracy.

Power-Supply Modulation and Low-Frequency Sag (Waveform f)

Waveform (f) shows collapsing or unstable peaks caused by power-supply voltage modulation under load.

• High power-supply impedance
• Insufficient filter capacitance
• Undersized choke or transformer
• High-current single-ended output stages

Audible effect: loose bass, unstable dynamics, collapsing soundstage.

Summary Table

Waveform	Distortion Type	Root Cause
a	Ideal sine wave	Normal operation
b	Grid overload distortion	Excessive drive
c	Symmetrical clipping	Output power limit
d	Crossover distortion	Bias too cold
e	Asymmetrical distortion	Tube or bias imbalance
f	Power-supply modulation	Insufficient PSU capacity

Conclusion

By observing output waveforms under controlled sine-wave testing, tube-amplifier behavior becomes visible and measurable. Each distortion pattern corresponds to a specific electrical condition, allowing rapid diagnosis and precise adjustment.

We emphasize correct biasing, proper gain structure, tube matching, and robust power-supply design to achieve both technical excellence and musical performance.

Building a High-Performance FM Tuner: A Deep Dive into a Classic IC-Based Design

Building a High-Performance FM Tuner: A Deep Dive into a Classic IC-Based Design

Published by IWISTAO

Introduction

In an age of streaming services and digital audio, there remains a unique and enduring magic to FM radio. The thrill of tuning across the dial, the serendipity of discovering a new song, and the pristine quality of a strong stereo broadcast are experiences that continue to captivate audio enthusiasts and hobbyists. For those who appreciate not just the listening but also the building, constructing a high-quality FM tuner from discrete components is a deeply rewarding journey.

This article details the design and construction of a high-performance FM tuner, built around a carefully selected set of specialized integrated circuits (ICs). Our design philosophy is to leverage the strengths of each component to create a modular, robust, and audiophile-grade receiver. We will start with a highly sensitive automotive high-frequency tuner for the front-end, followed by a dedicated IF amplification stage using the TA7302P. The core demodulation is handled by the legendary LA1235 IF system, and finally, the composite signal is decoded into glorious stereo by the LA3401 MPX decoder. Let's embark on a detailed exploration of each stage, from the antenna to the final audio output.

Component Breakdown: The Heart of the Tuner

The performance of any radio receiver is determined by the quality of its constituent parts. Our design relies on a quartet of key components, each chosen for its specific role and proven performance in the signal chain.

The Front-End: Automotive High-Frequency Tuner

The journey of an FM signal begins at the front-end. This stage is arguably the most critical, as it's responsible for plucking a single, faint station out of a sea of powerful broadcasts. For this task, we've chosen an automotive high-frequency tuner module. These modules, designed for the harsh and demanding automotive environment, offer several distinct advantages for the hobbyist.

Firstly, they exhibit exceptional sensitivity, capable of receiving weak, distant stations. Secondly, their design prioritizes strong signal handling and selectivity, meaning they are less prone to overload and interference from powerful local stations—a common problem known as intermodulation distortion. Internally, these modules typically contain an RF amplifier, a local oscillator, and a mixer, all carefully shielded in a metal can. Their job is to receive the incoming RF signal (88-108 MHz), mix it with a signal from the local oscillator, and produce a fixed Intermediate Frequency (IF), which is standardized at 10.7 MHz for FM broadcasting. The tuning is accomplished by applying a variable DC voltage (often labeled V_T) to a varactor diode, which changes the capacitance in the oscillator and RF amplifier tuning circuits.

The IF Amplifier: Toshiba TA7302P

Once the front-end has converted our desired station to the 10.7 MHz IF, this signal is still relatively weak. It needs significant amplification before it can be demodulated. While our primary demodulator IC, the LA1235, has its own IF amplifiers, we are adding a dedicated pre-amplifier stage using the Toshiba TA7302P.

The TA7302P is an FM IF amplifier and detector IC. In our specific design, we are leveraging its excellent front-end gain and limiting capabilities. By placing it before the LA1235, we ensure the signal is robustly amplified and, crucially, "limited." Limiting is the process of stripping away any amplitude variations from the FM signal. Since information in FM is encoded in frequency changes, not amplitude changes, any amplitude variations are considered noise (often from atmospheric interference or multi-path distortion). The TA7302P excels at this, providing a clean, constant-amplitude IF signal, which is the ideal input for the next stage. This two-stage IF approach contributes significantly to a high signal-to-noise ratio (SNR) and excellent AM rejection (AMR).

The Demodulator: Sanyo LA1235

The Sanyo LA1235 is a cornerstone of high-quality FM tuner design, a highly regarded and versatile FM IF system IC. After being amplified and limited by the TA7302P, the 10.7 MHz signal enters the LA1235 for the critical task of demodulation—converting the frequency variations back into an audio signal.

The LA1235 performs this magic using a quadrature detector. This circuit requires an external resonant component, typically a tunable coil or a ceramic resonator, to create a reference signal that is 90 degrees out of phase with the incoming IF signal. By comparing the phase of the incoming signal against this reference, the detector produces a voltage output that is directly proportional to the frequency deviation of the original FM signal. The quality of this demodulation is paramount for low distortion audio.

Beyond demodulation, the LA1235 offers a suite of indispensable features. It includes further IF amplification stages, a signal strength meter driver (for a tuning meter), an Automatic Frequency Control (AFC) output to help lock onto stations, and a sophisticated muting circuit to silence the output between stations, eliminating inter-station noise. Its reputation for low distortion and high SNR makes it a perfect choice for this project.

The Stereo Decoder: Sanyo LA3401

The audio signal that emerges from the LA1235 is not yet stereo. It's a composite or multiplex (MPX) signal. To understand what the LA3401 does, we must first understand how stereo is broadcast. The composite signal contains three main components:

1. The main audio channel, which is the sum of the Left and Right channels (L+R). This ensures compatibility with mono radios.
2. A 19 kHz pilot tone. This acts as a flag to the receiver, indicating that a stereo broadcast is present.
3. A sub-channel containing the difference between the Left and Right channels (L-R). This signal is modulated onto a 38 kHz subcarrier, which is suppressed at the transmitter to save bandwidth.

The Sanyo LA3401 is an FM MPX stereo decoder designed specifically to unravel this composite signal. It uses a Phase-Locked Loop (PLL) circuit to lock onto the 19 kHz pilot tone. From this stable reference, it internally generates a precise 38 kHz carrier signal. This regenerated carrier is then used to demodulate the L-R sub-channel.

With both the L+R (mono) and L-R (difference) signals now available, the LA3401 uses an internal matrix circuit to algebraically combine them and recover the original, separate Left and Right audio channels. The LA3401** is known for its excellent channel separation, low distortion, and includes a built-in driver for a stereo indicator LED, providing visual confirmation of a successful stereo lock.

 

Circuit Analysis and Integration

With an understanding of the individual components, we can now examine how they work together in a cohesive system. The proper integration, power supply design, and alignment are what transform a collection of parts into a functional, high-performance tuner.

Signal Flow: From Antenna to Audio

The signal path through our tuner is a logical progression of amplification, filtering, and decoding:

1. Antenna & Front-End: The signal is captured by the antenna and fed into the automotive tuner module. The module selects the desired station frequency and converts it down to the 10.7 MHz IF.
2. Ceramic Filtering: The output of the front-end is passed through one or more 10.7 MHz ceramic filters. These passive components are crucial for selectivity, sharply filtering the IF signal to reject adjacent channels.
3. IF Pre-Amplification: The filtered signal enters the TA7302P, where it is significantly amplified and limited, preparing it for demodulation.
4. Main IF & Demodulation: The output of the TA7302P is fed, often through another ceramic filter for even greater selectivity, into the LA1235. This IC provides final IF gain, performs the quadrature detection to recover the composite audio, and generates control signals for muting and metering.
5. Stereo Decoding: The raw composite (MPX) audio from the LA1235 is passed to the LA3401. The decoder locks onto the 19 kHz pilot tone, decodes the L-R signal, and reconstructs the separate Left and Right audio channels.
6. De-emphasis & Output: The final L and R outputs from the LA3401 pass through a de-emphasis network (typically a simple RC filter) to restore the correct tonal balance, as FM broadcasts use pre-emphasis to improve the signal-to-noise ratio at higher frequencies. The signals are then ready to be fed to an external amplifier.

Power Supply Considerations

A clean and stable power supply is non-negotiable for a high-performance audio project. RF and IF circuits are particularly sensitive to power supply noise. A well-regulated DC voltage, typically between 9V and 12V, is required. It is best practice to use a dedicated voltage regulator (e.g., a 78xx series IC) with adequate heat sinking. Furthermore, each IC (TA7302P, LA1235, LA3401) must have its own local decoupling capacitors (e.g., a 10-100µF electrolytic capacitor in parallel with a 0.1µF ceramic capacitor) placed as close to its power pins as possible. This shunts high-frequency noise to ground, preventing instability and inter-stage interference.

Alignment and Tuning

Building the circuit is only half the battle; proper alignment is what unlocks its full potential.

• Front-End Tuning: Manual tuning is achieved by supplying a stable, variable DC voltage to the V_T pin of the automotive tuner. A 10-turn precision potentiometer connected as a voltage divider provides fine control over the tuning range.
• IF and Demodulator Alignment: This is the most critical alignment step. The quadrature coil connected to the LA1235 must be tuned precisely. The goal is to center its resonant frequency exactly at 10.7 MHz, This is best done by tuning to a strong station and adjusting the coil's slug for minimum audio distortion and maximum stereo separation. A distortion analyzer is the professional tool for this, but careful listening can also yield excellent results. The point of lowest distortion often corresponds to the peak reading on a signal strength meter connected to the LA1235.
• Stereo Decoder Alignment: The LA3401 has a VCO (Voltage-Controlled Oscillator) that must be set to its free-running frequency of 76 kHz. This is done by adjusting a small variable resistor. The procedure is to tune to a known stereo station and adjust the resistor until the stereo indicator LED lights up brightly and stably. The correct adjustment point is typically in the middle of the range where the LED remains lit.

IWISTAO LA1235 FM Stereo Radio Tuner PCBA High Frequency FAE352 IF 3 Stages TA7302P Decoder LA3401

Conclusion and Further Thoughts

This project represents a beautiful synthesis of classic analog design and specialized integrated circuits. By combining a robust automotive tuner front-end with the proven performance of the TA7302P, LA1235, and LA3401 ICs, we can construct an FM tuner that rivals many commercial units in sensitivity, selectivity, and audio fidelity. The modular nature of the design allows the builder to understand the function of each stage and appreciate the intricate process of receiving and decoding an FM broadcast.

For the aspiring builder, remember that a good PCB layout with a solid ground plane is essential for stability and low noise. Shielding the front-end and keeping signal paths short will pay dividends in performance. While the alignment process requires patience, the reward is the immense satisfaction of hearing crystal-clear stereo sound from a device you built with your own hands. This design serves as both a fantastic learning experience and a gateway to high-fidelity radio listening, proving that the art of analog receiver design is very much alive and well.

 

References

1. TA7302P Datasheet – Toshiba Corporation
   Detailed specifications and application notes for the TA7302P IF amplifier.
   https://www.datasheetarchive.com/TA7302P-datasheet.html

2. LA1235 Datasheet – Sanyo Semiconductor
   Information on the LA1235 FM discriminator and related FM tuning functions.
   https://www.datasheetarchive.com/LA1235-datasheet.html

3. LA3401 Datasheet – Sanyo Semiconductor
   Data and application information for the LA3401 FM stereo decoder IC.
   https://www.datasheetarchive.com/LA3401-datasheet.html

4. Automotive FM Tuner Design Principles – Electronics Textbook and Application Notes
   Typical design approaches and technical background for automotive FM tuner circuits.  https://www.electronics-notes.com/articles/radio/radio-receivers/fm-receiver-tuner.php

 

The Role of 75-Ohm Coaxial Cable in Hi-Fi Audio Systems

Published by IWISTAO

In high-fidelity audio systems, signal integrity is just as important as circuit topology, component quality, or power-supply design. Among all interconnect options, 75-ohm coaxial cable holds a special position due to its extensive use in digital audio transmission, broadcast video, and measurement systems.

Despite its popularity, 75-ohm coaxial cable is often misunderstood—especially when it is applied indiscriminately to analog audio connections. This article explains what 75-ohm coaxial cable is, why its characteristic impedance matters, and where it is technically justified—or unnecessary—in Hi-Fi audio systems.

 

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1. What Is a 75-Ohm Coaxial Cable?

A coaxial cable consists of four fundamental elements:

• A central conductor that carries the signal
• A dielectric insulator that defines geometry and capacitance
• A cylindrical outer shield that serves as the return path
• An external protective jacket

 

The term “75 ohms” does not describe DC resistance. Instead, it refers to the characteristic impedance (Z₀) of the cable, which is determined by the ratio between conductor diameters and the dielectric constant of the insulation.

The characteristic impedance of a coaxial cable can be approximated by:

Z₀ = (60 / √ε_r) · ln(D / d)

Where:

• ε_r = relative permittivity of the dielectric material
• D = inner diameter of the outer shield
• d = diameter of the center conductor

For common polyethylene-based dielectrics, a 75-ohm design offers an excellent balance between low attenuation and wide bandwidth, which explains its dominance in broadcast and digital signal transmission.

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2. Why 75 Ohms Matters in Digital Audio

2.1 S/PDIF Coaxial Transmission

The most important Hi-Fi application of 75-ohm coaxial cable is S/PDIF (Sony/Philips Digital Interface Format) over coaxial connection.

Although S/PDIF carries audio data, electrically it is a high-speed digital signal with fast rise and fall times. As a result, its behavior is governed by transmission-line theory rather than low-frequency analog audio rules.

Using a true 75-ohm coaxial cable minimizes:

• Signal reflections caused by impedance mismatch
• Edge distortion and ringing
• Interface-induced jitter at the DAC input

Even short cable runs benefit from proper impedance control, because signal rise time—not cable length—determines the severity of reflections.

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2.2 Cable and Connector as a System

A common misconception is that “any RCA cable works for coaxial digital audio.” In reality, most standard RCA connectors do not maintain a precise 75-ohm impedance.

However, a well-designed 75-ohm coaxial cable assembly still offers significantly better performance than generic analog interconnects, particularly when cable geometry and shielding are properly controlled.

While professional systems often use BNC connectors for superior impedance accuracy, consumer S/PDIF systems still benefit greatly from true 75-ohm coaxial cabling.

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3. 75-Ohm Coaxial Cable in Analog Audio

3.1 Line-Level Analog Signals

For analog line-level audio signals (20 Hz to 20 kHz), characteristic impedance matching is not required. At these frequencies, signal wavelengths are measured in kilometers.

Therefore:

• 75-ohm impedance provides no intrinsic sonic advantage
• Shielding effectiveness becomes more relevant than impedance
• Cable capacitance may have greater impact than Z₀

In short, characteristic impedance is largely irrelevant for analog interconnects.

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3.2 Phono and High-Impedance Circuits

In phono systems, cable capacitance and shielding quality are critical, while characteristic impedance remains irrelevant.

Using a 75-ohm coaxial cable without considering its capacitance may disturb cartridge loading and frequency response, particularly with MM cartridges.

As a result, 75-ohm coaxial cable is not automatically suitable for turntable applications.

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4. Shielding and Noise Rejection

One genuine advantage of coaxial cable—regardless of impedance—is its shielding geometry. A coaxial structure provides:

• 360-degree electrostatic shielding
• Excellent rejection of EMI and RFI
• A predictable and low-impedance ground return path

This makes coaxial cable particularly effective in digitally noisy environments and mixed-signal Hi-Fi systems.

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5. Common Myths About 75-Ohm Coaxial Cable

• “75 ohms improves analog sound quality” — False
• “Any RCA cable works for digital coax” — False
• “Cable length must be long to matter” — False

6. Practical Recommendations

Use 75-ohm coaxial cable when:

• Connecting a CD transport or streamer to a DAC via S/PDIF
• Building DIY digital coaxial interconnects
• Working with digital audio or measurement equipment

IWISTAO HIFI 75-ohm Digital Coaxial Cable DAC Belden 1694A Cold Press Self-locking Budweiser RCA

 

Do not prioritize 75 ohms when:

• Selecting analog RCA interconnects
• Wiring phono cartridges (capacitance is more important)

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Conclusion

75-ohm coaxial cable is not a universal Hi-Fi upgrade, but it is technically essential for coaxial digital audio transmission.

When used in the correct context—especially for S/PDIF links—it provides measurable, engineering-based benefits. When misapplied to analog audio, its impedance specification offers little relevance.

Understanding where impedance matters—and where it does not—is fundamental to rational Hi-Fi system design.

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References

1. IEC 60958 – Digital Audio Interface Standard
   https://webstore.iec.ch/publication/6006
2. Howard Johnson, High-Speed Digital Design: A Handbook of Black Magic
   https://www.pearson.com
3. Rane Corporation – Impedance Matching in Audio
   https://www.ranecommercial.com
4. Belden – Coaxial Cable Technical Papers
   https://www.belden.com