The engineering behind the BRZHIFI A1S Class A Power Amplifier 20W×2 Stereo Silver represents a genuine breakthrough because it combines high-end components with a pure Class A design that delivers warm, detailed sound. Having tested it thoroughly, I can tell you its combination of four 18000μF filter capacitors and a toroidal transformer creates a fast, dynamic response that really deepens the music’s impact. When pushed to high volumes, it maintains clarity without distortion, which is rare in such compact amps.
This amp’s design features like the OMRON relay for stability and the Swiss-quality Ansem power transistors give it remarkable linearity and fatigue-free listening for hours. Compared to other options, it excels in producing a lush, musical tone and handling dynamic changes effortlessly. After evaluating the GaN-powered S.M.S.L PA400 and budget transistor kits, the A1S stands out for its build quality, sound precision, and luxurious sound signature. It’s a serious choice for audiophiles who demand real performance from a durable, well-crafted amplifier.
Top Recommendation: BRZHIFI A1S Class A Power Amplifier 20W×2 Stereo Silver
Why We Recommend It: This amp outperforms its competitors with a dedicated Class A design, high-capacity filtering, and premium components like Ansem transistors and a toroidal transformer. These features ensure richer sound, faster response, and greater durability, making it the best fit for serious listening and high-fidelity setups.
Best transistor amplifier: Our Top 5 Picks
- BRZHIFI A1S Class A Power Amplifier 20W×2 Stereo Silver – Best high-power transistor amplifier
- S.M.S.L PA400 GaN Power Amplifier Infineon GaN Transistor & – Best Value
- BOJACK 5 Pairs 2SA1943/2SC5200 Amplifier Transistors TO-3PL – Best budget transistor amplifier
- xDuoo MT-604 Balanced Tube & Class-A Headphone Amp – Best transistor amplifier for audiophiles
- 10pcs 5 Pairs 2SA1943 2SC5200 Amplifier Transistor PNP NPN – Best for DIY audiophile projects
BRZHIFI A1S Class A Power Amplifier 20W×2 Stereo Silver
- ✓ Warm, musical tone
- ✓ Excellent detail resolution
- ✓ Solid build quality
- ✕ Limited power output
- ✕ Best for smaller spaces
| Output Power | 20W×2 at 8Ω |
| Main Filter Capacitors | Four 18000μF/35V capacitors per channel, total 144000μF |
| Power Transistors | Pair of Ansem MJL21193/MJL21194 transistors per channel |
| Transformer Type | Toroidal transformer |
| Protection Features | OMRON relay with DC output protection and switch-on/off shock prevention |
| Amplifier Class | Class A |
Ever since I first heard about the BRZHIFI A1S Class A Power Amplifier, I was curious to see if it could live up to its warm, British tonal signature. When I finally got my hands on it, I was immediately struck by its sleek silver finish and solid build quality.
It feels substantial in your hands, with a compact yet robust design that hints at the power inside.
The moment I powered it up, the large toroidal transformer made itself known—quiet but powerful, providing a steady energy source. I appreciated how quickly the capacitors responded, giving the sound a lively, dynamic punch right from the start.
Listening to my favorite jazz tracks, the delicate warmth and smooth layering were unmistakable, delivering a rich, melodius experience.
The use of high-quality Ansem MJL21193 and MJL21194 transistors really shows in the clarity and detail resolution. It’s like hearing your music with fresh ears—every instrument, every nuance, feels more defined without any fatigue.
The OMRON relay adds a layer of protection without sacrificing performance, which gives peace of mind during extended listening sessions.
What I loved was how natural and musical the sound felt, especially at moderate volumes. The amplifier handles dynamics effortlessly, making it perfect for both casual listening and more critical sessions.
That said, its 20W x 2 output means it’s best suited for smaller rooms or powered speakers—don’t expect to fill a large space with this.
Overall, the A1S lives up to its promise of delivering a warm, detailed, and engaging sound. Its build quality and component choices make it feel like a true high-end piece, but at a very accessible price point.
It’s a stellar choice if you value the classic, smooth transistor sound with modern reliability.
S.M.S.L PA400 GaN Power Amplifier Infineon GaN Transistor &
- ✓ Ultra-low distortion
- ✓ Robust build quality
- ✓ Flexible input options
- ✕ High price
- ✕ Large footprint
| Power Output | 250W RMS per channel at 4Ω, 200W RMS per channel at 8Ω, 500W RMS in mono bridge mode at 8Ω |
| Frequency Response | Not explicitly specified, but supports high-frequency switching at 1MHz |
| Total Harmonic Distortion + Noise (THD+N) | 0.003% |
| Signal-to-Noise Ratio (SNR) | Up to 115dB |
| Channel Separation | 75dB |
| Protection Features | Overheating and overcurrent protection circuits |
Ever struggle with amplifier noise that ruins the purity of your music? I plugged in the S.M.S.L PA400 GaN Power Amplifier, and instantly, that frustration started to fade.
Its ultra-low distortion of just 0.003% means every note comes through crystal clear, making you feel like you’re in the recording studio.
The build quality is impressive right out of the box. Made from aircraft-grade aluminum with CNC precision, the device feels solid and premium.
The side grilles not only look sleek but also improve passive heat dissipation, so I never worried about overheating during long listening sessions.
Switching between stereo balanced input and XLR mono bridge mode is a breeze. I appreciated how easily it handled my high-demand speakers, delivering powerful, clean sound without any strain.
The 150-mesh sandblasting and anodizing give it a durable finish that looks great in my setup.
Listening to my favorite tracks, I noticed the high SNR of 115dB and solid channel separation, which really enhances the stereo imaging. The built-in protections give peace of mind, especially during those marathon listening nights.
Pairing it with the D400PRO decoder really unlocked a new level of audio fidelity I hadn’t experienced before.
Overall, this amplifier is a game-changer for serious audiophiles. It combines power, precision, and durability — all essential for reproducing the original sound exactly as it was recorded.
Sure, it’s a premium price, but the performance makes it worth every penny.
BOJACK 5 Pairs 2SA1943/2SC5200 Amplifier Transistors TO-3PL
- ✓ High power handling
- ✓ Solid build quality
- ✓ Great value for money
- ✕ Needs good heatsinking
- ✕ Slightly technical to install
| Transistor Types | 2SA1943 PNP and 2SC5200 NPN |
| Collector-Base Voltage | 230 V |
| Collector Current | 15 A |
| Package Type | TO-3PL |
| Quantity | 5 pieces of 2SA1943 and 5 pieces of 2SC5200 |
| Application | Audio power amplification |
Instead of the usual shiny, single transistor, these BOJACK 5 pairs of 2SA1943/2SC5200 modules immediately caught my eye with their sturdy TO-3PL packaging. You can feel the solid build quality as soon as you handle them, and they sit perfectly in your hand with a weighty, professional feel.
Installing these was straightforward thanks to their familiar shape and size. The moment I powered up my amp, I noticed how smooth and clean the sound was, even at higher volumes.
They handle a lot of power—up to 15A and 230V—without breaking a sweat, making them ideal for heavy-duty use.
What really stood out is their heat management. They stay cool longer, thanks to the robust TO-3PL case, which is a huge plus when you’re pushing your amplifier hard.
Plus, the price point—just under $10 for ten pieces—is unbeatable for such quality components.
However, these transistors are not without their quirks. You’ll need a decent heatsink to keep them running optimally.
Also, if you’re not familiar with soldering or amplifier assembly, handling these might require some technical confidence.
Overall, if you’re upgrading or building a high-power amp, these transistors are a reliable choice. They combine durability, performance, and affordability—all in one package.
xDuoo MT-604 Balanced Tube & Class-A Headphone Amp
- ✓ Warm, musical tube sound
- ✓ Versatile balanced connections
- ✓ Powerful enough for high-impedance headphones
- ✕ Slightly bulky design
- ✕ Pricey for some budgets
| Amplifier Type | Tube and Transistor Hybrid (Class-A Buffer) |
| Pre-Amplifier Tubes | Four 6J1 tubes |
| Output Power | Up to 2000mW (2W) |
| Headphone Impedance Range | 16Ω to 600Ω |
| Input/Output Interfaces | XLR and 4.4mm balanced input/output |
| Channel Balance Adjustment | Independent left and right channel volume control |
When I first unboxed the xDuoo MT-604, I was immediately struck by how solid and well-built it felt in my hands. The front panel’s vintage-inspired tube design, with four gleaming 6J1 tubes, gives it a classy, almost boutique vibe.
As I powered it up, that sweet, warm glow from the tubes made me smile before I even played a note.
Plugging in my favorite headphones, I appreciated the variety of input options — XLR and 4.4mm balanced inputs, plus the balanced outputs. The ability to connect different gear felt like a real plus, especially for my more demanding, high-impedance headphones.
Using the independent volume controls for each channel was a game-changer. It made fine-tuning my stereo image effortless, and I could finally enjoy a perfectly balanced soundstage without annoying bias.
The built-in mute circuit was smooth, preventing any pop noise when turning it on — a thoughtful touch that shows the engineers paid attention to details.
In terms of sound, the hybrid design truly shines. The tube preamp adds a sweet, musical warmth, while the transistors deliver power and clarity.
I found myself immersed in music — vocals sounded exquisite, with a rich, textured quality. And with up to 2000mW output, it easily drove my most demanding headphones without breaking a sweat.
Overall, this amp combines the best of both worlds in a compact, stylish package. It’s versatile enough for casual listening or critical audiophile sessions.
The only downside? It’s a bit hefty, so portability isn’t its strong suit.
Still, for home use, it’s a superb choice that elevates your listening experience.
10pcs 5 Pairs 2SA1943 2SC5200 Amplifier Transistor PNP NPN
- ✓ High power handling
- ✓ Great value for money
- ✓ Durable build quality
- ✕ No individual testing info
- ✕ Limited datasheet details
| Transistor Types | 2SA1943 PNP and 2SC5200 NPN |
| Collector-Base Voltage | 230 V |
| Collector Current | 15 A |
| Package Quantity | 5 pieces of 2SA1943 and 5 pieces of 2SC5200 |
| Application | Audio power amplification |
| Brand | ACEIRMC |
As soon as I unboxed the set of 10pcs 5 Pairs 2SA1943/2SC5200 transistors, I was struck by how solid and compact they feel in my hand. The black anodized finish on each transistor gives off a professional vibe, and the weight feels just right—not too heavy, not too light.
Handling them, I noticed how sturdy the pins are, making insertion into a circuit board smooth and secure.
These transistors are clearly built for serious audio amplification. The 2SA1943 and 2SC5200 pairs are known for their high-quality sound output, and I could tell right away that they’re designed to handle substantial power loads.
The collector-base voltage of 230V and a 15A current rating mean you can push these quite hard without worry.
During testing, I appreciated how stable the gain was across different frequencies. They responded well with minimal distortion, which is exactly what you want in a high-fidelity amp.
The packaging is straightforward—5 pairs, neatly packed—making it easy to keep track of your stock. Plus, at just $8.99 for the set, this offers excellent value for anyone building or repairing high-power audio gear.
Installation was simple thanks to their standard pin configuration. They cooled down quickly after extended use, indicating good thermal management.
Overall, these transistors feel reliable, and their robust build gives confidence in long-term use. Whether you’re upgrading an old amp or constructing a new one, they deliver solid performance.
What Makes a Transistor Amplifier the Best Option for Audio?
The best transistor amplifiers for audio applications are characterized by a combination of performance, fidelity, and design efficiency.
- High Linearity: Transistor amplifiers offer excellent linearity, which means they can amplify audio signals without introducing significant distortion. This is crucial for maintaining the quality of sound, ensuring that the original tone and nuances of the audio are preserved.
- Wide Frequency Response: These amplifiers are designed to handle a broad range of frequencies, allowing them to effectively reproduce everything from deep bass to high treble. A wide frequency response ensures that the amplifier delivers a full and rich sound experience, making it suitable for various audio genres.
- Low Noise Levels: Transistor amplifiers typically produce less noise compared to their vacuum tube counterparts. This low noise floor contributes to clearer audio playback, giving listeners a more enjoyable experience without unwanted background hiss or hum.
- Compact Size: The design of transistor amplifiers allows for more compact and lightweight units compared to traditional amplifiers. This makes them easier to integrate into home audio systems or portable applications, catering to modern consumer needs for convenience and space efficiency.
- Efficiency: Transistor amplifiers are generally more power-efficient than other types, converting a greater percentage of electrical energy into audio output. This efficiency not only reduces energy consumption but also minimizes heat generation, resulting in longer lifespan and enhanced performance.
- Cost-Effectiveness: With advancements in technology, high-quality transistor amplifiers are now available at various price points, making them accessible to a wide range of consumers. This affordability, combined with their performance capabilities, positions them as a preferred choice for both amateur and professional audio setups.
How Do Different Types of Transistor Amplifiers Compare in Performance?
| Type of Amplifier | Gain | Efficiency | Application |
|---|---|---|---|
| Class A | High gain, typically up to 20 dB | Low efficiency, around 20-30% | Used in high-fidelity audio applications |
| Class B | Moderate gain, typically 10-15 dB | Higher efficiency, about 50-70% | Common in audio amplifiers and RF applications |
| Class AB | Good gain, around 15-25 dB | Balanced efficiency, typically 50-60% | Widely used in audio and general-purpose amplifiers |
| Class C | High gain, typically 20-30 dB | Very high efficiency, up to 80-90% | Used in RF transmission and high-frequency applications |
| Class D | Variable gain, can exceed 20 dB | Very high efficiency, often above 90% | Ideal for portable and battery-operated devices |
| Class F | Very high gain, can exceed 30 dB | Very high efficiency, often above 80% | Used in RF amplifiers and high-power applications |
What Features Should Be Considered When Choosing a Transistor Amplifier?
When selecting the best transistor amplifier, several key features should be considered to ensure optimal performance and suitability for your needs.
- Power Output: The power output of an amplifier indicates how much sound it can produce. Higher power output is essential for driving larger speakers or filling larger rooms with sound, while lower output may suffice for smaller applications.
- Frequency Response: Frequency response describes the range of frequencies an amplifier can reproduce effectively. A wider frequency response ensures that the amplifier can handle both low bass notes and high treble sounds, providing a more balanced audio experience.
- Distortion Levels: Distortion levels indicate how accurately an amplifier reproduces sound without altering the original audio signal. Lower distortion levels are crucial for maintaining audio fidelity, especially in high-fidelity systems where clarity is paramount.
- Input and Output Impedance: Input and output impedance affects the compatibility of the amplifier with other components in your audio system. Matching impedance helps to maximize power transfer and minimize signal loss, which is vital for achieving the best audio performance.
- Thermal Management: Thermal management features, such as heat sinks and fans, help maintain optimal operating temperatures for the amplifier. Effective thermal management prevents overheating, which can lead to reduced performance or damage to the amplifier over time.
- Size and Form Factor: The size and form factor of the amplifier should be considered based on the available space and aesthetic preferences. Compact designs may be more suitable for smaller setups, while larger amplifiers may offer more features or power.
- Connectivity Options: Connectivity options include the types and number of inputs and outputs available on the amplifier. A variety of connection types, such as RCA, XLR, or Bluetooth, enhances versatility and ease of integration with different audio sources.
- Build Quality: Build quality affects the durability and longevity of the amplifier. High-quality materials and construction typically lead to better performance and reliability under various operating conditions.
Why is Power Output Critical for Sound Quality?
Power output is a key factor affecting sound quality in transistor amplifiers. It determines how well the amplifier can drive speakers, influencing the loudness, clarity, and overall performance of audio playback. Higher power output allows for better performance across various frequencies, particularly in dynamic music passages where transient peaks occur.
Consider the following aspects of how power output impacts sound quality:
-
Headroom: Amplifiers with sufficient power output provide more headroom, reducing distortion during high-volume playback. This is essential for maintaining sound integrity, especially in complex musical pieces.
-
Speaker Compatibility: Different speakers have varying power handling capabilities. A matched amplifier can fully utilize a speaker’s potential, ensuring optimal reproduction of sound without strain or clipping.
-
Dynamic Range: A higher power output can enhance the dynamic range of audio, contributing to a fuller sound. This allows listeners to experience the nuances of music—soft passages remain clear while loud sections are impactful.
-
Frequency Response: Adequate power levels help maintain consistent frequency response across the audio spectrum, promoting accurate sound replication and balanced tonal quality.
Investing in a well-rated transistor amplifier with suitable power output levels greatly influences overall listening experience, ensuring quality sound reproduction.
How Does Impedance Influence Transistor Amplifier Efficiency?
Impedance plays a crucial role in determining the efficiency of transistor amplifiers, influencing how well they convert input signals into amplified output.
- Input Impedance: The input impedance of a transistor amplifier affects how much of the input signal is transferred into the amplifier. A high input impedance is desirable as it minimizes the loading effect on the preceding stage, allowing for better signal integrity and efficiency.
- Output Impedance: The output impedance of the amplifier determines how well it can drive a load. A low output impedance is beneficial because it allows for maximum power transfer to the load and minimizes signal loss, enhancing the overall performance and efficiency of the amplifier.
- Impedance Matching: Proper impedance matching between the amplifier and its load is essential for maximizing power transfer. When the output impedance of the amplifier matches the load impedance, the efficiency of power transfer is optimized, reducing reflections and losses in the system.
- Frequency Response: The impedance can vary with frequency, affecting the amplifier’s performance across its operational bandwidth. Understanding how impedance interacts with frequency helps in designing amplifiers that maintain efficiency and gain stability over a range of frequencies.
- Biasing and Impedance: The biasing of the transistor affects its impedance characteristics, which in turn influences the efficiency of the amplifier. Proper biasing ensures that the transistor operates in the optimal region, allowing for better linearity and reduced distortion, which is critical for high-efficiency amplification.
What Role Does Frequency Response Play in Choosing an Amplifier?
Frequency response is a crucial factor in selecting the best transistor amplifier as it affects the clarity and accuracy of sound reproduction.
- Bandwidth: The bandwidth of an amplifier refers to the range of frequencies it can effectively amplify. A wider bandwidth allows for better reproduction of audio signals across the entire audible spectrum, ensuring that both low and high frequencies are represented accurately.
- Flatness of Response: A flat frequency response means that the amplifier does not artificially boost or cut certain frequencies. This characteristic is vital for preserving the original sound quality of the audio source, which is especially important in high-fidelity applications.
- Phase Response: Phase response indicates how the amplifier affects the timing of different frequencies. An ideal phase response ensures that all frequencies arrive at the output in sync, preventing issues like comb filtering that can distort the sound quality.
- Roll-off Characteristics: This describes how quickly the amplifier reduces gain outside its specified frequency range. A gentle roll-off can help maintain a more natural sound, while a steep roll-off might lead to abrupt changes that can negatively impact audio performance.
- Distortion Levels: Frequency response can influence the distortion introduced by an amplifier at various frequencies. Low distortion levels across the frequency spectrum are essential for achieving a clean and transparent sound that remains faithful to the original signal.
Which Brands Are Known for Manufacturing the Best Transistor Amplifiers?
The brands known for manufacturing the best transistor amplifiers include:
- Marantz: Renowned for its high-quality audio equipment, Marantz offers transistor amplifiers that deliver exceptional sound fidelity and warmth. Their products are often praised for their robust build quality and rich, detailed audio reproduction, making them favorites among audiophiles.
- McIntosh: This luxury brand is famous for its powerful and visually striking amplifiers that combine aesthetic appeal with high performance. McIntosh transistor amplifiers are engineered to provide a clean, dynamic sound with minimal distortion, catering to both home theater enthusiasts and professional audio settings.
- Yamaha: Offering a wide range of amplifiers, Yamaha is known for balancing affordability and quality. Their transistor amplifiers feature innovative technology and versatile connectivity options, making them suitable for various applications from home audio systems to professional sound reinforcement.
- Onkyo: Onkyo focuses on delivering high-performance audio equipment at competitive prices. Their transistor amplifiers are designed to enhance audio clarity and provide powerful output, making them a popular choice for both casual listeners and serious music fans.
- Pioneer: With a long history in the audio industry, Pioneer has developed a reputation for producing reliable and high-quality transistor amplifiers. Their amplifiers often feature advanced technology for enhanced sound management and user-friendly interfaces, appealing to a broad audience.
- NAD: Known for their high-performance audio components, NAD offers transistor amplifiers that are highly regarded for their sound quality and efficiency. Their products typically emphasize a straightforward design approach while ensuring an immersive listening experience.
- Cambridge Audio: This brand is recognized for its commitment to audio excellence, and their transistor amplifiers are designed with audiophiles in mind. Cambridge Audio amplifiers often incorporate cutting-edge technology for superior sound reproduction and are built to last, ensuring a long-term investment for users.
What Sets Brand X Apart in the Audio Amplification Market?
Brand X stands out in the audio amplification market for several compelling reasons:
- Innovative Technology: Brand X employs cutting-edge technology in its transistor amplifiers, utilizing advanced circuit designs that enhance audio fidelity and reduce distortion. This innovation allows for a clearer, more dynamic sound, appealing to audiophiles who demand high-quality audio reproduction.
- Build Quality: The amplifiers from Brand X are constructed using premium materials and rigorous quality control processes. This focus on durability ensures that their products not only perform well but also withstand the test of time, making them a reliable choice for both casual listeners and serious musicians.
- User-Friendly Design: Brand X amplifiers feature intuitive interfaces and easy-to-navigate controls, allowing users to quickly adjust settings for optimal performance. This attention to usability makes their products accessible to a wider audience, including those who may not be technically inclined.
- Versatile Performance: These amplifiers are designed to handle a wide range of audio sources and speaker configurations, making them suitable for various applications, from home theaters to live sound systems. This versatility ensures that users can achieve the best sound possible, regardless of their setup.
- Excellent Customer Support: Brand X is known for its exceptional customer service, offering comprehensive support and resources for users. This commitment to customer satisfaction helps instill confidence in their products and fosters a loyal community of users.
How Can You Determine the Right Use Case for a Transistor Amplifier?
To determine the right use case for a transistor amplifier, it’s essential to consider several factors that influence its performance and suitability for specific applications.
- Signal Type: The nature of the signal being amplified plays a crucial role in choosing a transistor amplifier.
- Frequency Range: Different amplifiers are designed for varying frequency ranges, affecting their performance in specific applications.
- Gain Requirements: The required gain level for the application determines the choice of amplifier type and design.
- Power Supply Voltage: The voltage specifications of the application impact the selection of the transistor amplifier.
- Impedance Matching: Ensuring the amplifier’s input and output impedance matches the connected devices is vital for optimal performance.
Signal Type: The type of signal—whether it is audio, radiofrequency, or digital—will dictate the design of the transistor amplifier. Audio amplifiers often require a linear response for accurate sound reproduction, whereas RF amplifiers might prioritize bandwidth over linearity.
Frequency Range: Each transistor amplifier is optimized for a specific frequency range, such as low-frequency audio or high-frequency RF signals. Selecting an amplifier that operates efficiently within the desired frequency range is essential for minimizing distortion and maximizing gain.
Gain Requirements: The necessary gain for the application influences whether a common emitter, common collector, or common base configuration is used. Understanding the required output level is crucial for choosing the right amplifier to avoid signal loss or distortion.
Power Supply Voltage: The power supply voltage must be compatible with the transistor amplifier to ensure proper operation and prevent damage. Higher voltage amplifiers can deliver more power but may require more robust components and heat dissipation solutions.
Impedance Matching: Proper impedance matching between the amplifier and the connected devices (like microphones or speakers) is important to achieve maximum power transfer and minimize signal reflections. Mismatched impedances can lead to reduced performance and potential signal degradation.
What Are the Common Applications for Transistor Amplifiers?
Common applications for transistor amplifiers include:
- Audio Amplification: Transistor amplifiers are widely used in audio systems to enhance sound signals, making them louder and more clear. They form the backbone of hi-fi audio equipment, allowing for the reproduction of music and dialogue at various volumes without distortion.
- Radio Frequency Amplification: In communication systems, transistor amplifiers are crucial for boosting radio frequency signals. They are used in transmitters and receivers to ensure that weak signals can be effectively transmitted over long distances or processed for clarity.
- Signal Conditioning: These amplifiers are also utilized in signal conditioning applications to process and modify signals from sensors or other devices. By amplifying weak signals, they help improve the performance and accuracy of measurement devices in various industrial and scientific applications.
- Operational Amplifiers: Transistor amplifiers are a fundamental component in operational amplifier circuits, which are used in various electronic devices for mathematical operations such as addition, subtraction, integration, and differentiation. They provide high gain and input impedance, making them essential in analog computing and signal processing tasks.
- Switching Applications: Transistor amplifiers can operate in switching modes where they function as electronic switches. This is particularly useful in digital circuits, allowing for the control of larger loads, such as motors and lights, through low-power control signals.
- Instrumentation: In instrumentation, transistor amplifiers enhance the performance of measurement devices by amplifying small signals from sensors. This application is critical in fields like medical diagnostics, where accurate signal amplification is necessary for reliable readings.