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LM1875 GC GainClown HIFI power amplifier using IC LM1875T. “GC” is short for GainClown, which is a very good sounding LM1875 circuit that has been repeatedly compared, verified, and optimized overseas. It has a wide bandwidth, delicate sound, durability, and stability. The principle is that the voltages at the two input terminals of the inverting amplifier circuit are always 0, and do not change with the input signal. The transistor input voltage at the amplifier input terminal remains constant and unchanged, maintaining the optimal bias state, resulting in lower distortion in the inverting amplifier.
Using the optimized version of the good voice GC architecture, with lower distortion and more durable listening, the mid-point is very stable. The output adds red oxygen-free copper hollow inductors to eliminate noise and improve sound quality.
The all-protected Omron speaker protection circuit is more reliable. The material cost is relatively high, at about $15 for a single finished product. Quoting from online sources: “GC” stands for GainClown, a very good sound LM1875 circuit optimized through repeated comparisons and verifications abroad, with a wide frequency band, delicate sound, durable listening, and stable mid-point.
Schematic LM1875T GC GainClown HIFI power amplifier
The materials include 2 large 10000uF main power supply filter capacitors, JCCON black gold audio amplifier capacitors, a large current rectifier bridge with original MDD GBJ2510 25A/1000V, and two small brown robe ELNA low-impedance audio capacitors near the LM1875 power supply pins with a capacity of 680uF.
There are also four decoupling capacitors, using 100nf Weimar audio-grade capacitors, and two ELNA low-impedance 1uF audio coupling capacitors, which can replace 2.2uF Weimar capacitors. Other components include Omron relays. The circuit also features a separate DCDC route, where dual 18V power supplies can be converted to a single route with a full rectifier bridge and 10000uF filter output, which can be used as an external preamplifier power supply (if used as an audio source power supply and output to the 1875 rear stage, please use a DCDC isolation module to avoid smoking).
In terms of operating conditions, it is recommended to use an AC dual 18V input power supply, preferably with a dual 18V Ring Bull 100W transformer. The output power is 35W-4Ω and 25W-8Ω. The dimensions are approximately 128 mm in length, 88 mm in width, and 50 mm in height (excluding solder joints).
In burning machine experiments, it is recommended to first install a heat sink before powering on, which can be temporarily attached with double-sided tape. The normal working temperature is around 57° (measured with thermal imaging). After the power is turned on, there will be a slight delay before the relay engages to allow sound transmission. When testing for the first time, connect the audio input, such as a 3.5 mm audio jack, and touch it with your hand to check for feedback. There should be no noise, and even the POP sound should not be heard once the relay is engaged.
In terms of sound quality, when comparing the highest sound quality of QQ music on author phone (iPhone 13) with the original sound on a MacBook Pro, the difference is average, with the Mac being slightly better. However, when using the Boom3D software on the MacBook Pro to enable 3D surround sound and high fidelity, the sound quality is significantly enhanced. The bass is strong, the surround sound is detailed, and the experience is immersive. When trying to install Boom3D on a desktop computer (MPG Z790 EDGE TI MAX WIFI) with a Windows system, the effect is not as good as on the MacBook Pro, but there is still some improvement. The software is available for purchase at 99 dollars.
About IC LM1875
The IC LM1875 is a high-performance audio power amplifier that is commonly used in audio amplifier circuits. It is capable of delivering up to 20 watts of power into an 8 ohm load with low distortion and high-quality sound reproduction. The LM1875 features a wide frequency response range, excellent signal-to-noise ratio, and thermal shutdown protection to prevent the IC from overheating. It is an easy-to-use integrated circuit that is popular among DIY audio enthusiasts and professionals alike for its reliability and performance in audio amplifier applications.
About IC UPC1237
The IC UPC1237 is a protection circuit designed to safeguard speakers and amplifiers from potential damage caused by short circuits, overloads, and other electrical faults. It provides a reliable and efficient way to monitor the output of audio amplifiers and ensure that they are operating within safe limits. The UPC1237 features built-in thermal shutdown and overcurrent protection to prevent overheating and damage to the connected components. This IC is commonly used in audio amplifiers and home theater systems to ensure the longevity and safety of the equipment. Its compact size and easy integration make it a popular choice for audio enthusiasts and professionals looking to protect their valuable audio equipment.
Bom LM1875 GC GainClown HIFI power amplifier
| Part | Value | Description | Quantity |
| Resistors | |||
| R1,R2,R3,R4,R13 | 10 kΩ | Brown, black, black, red, brown | 5 |
| R5,R6 | 200 kΩ | Red, red, black, orange, brown | 2 |
| R7,R8 | 10 Ω | Brown, black, black, gold, brown | 2 |
| R9 | 3.9 kΩ | Orange, white, black, brown, brown | 1 |
| R10 | 100 kΩ | Brown, black, black, orange, brown | 1 |
| R11,R12 | 47 kΩ | Yellow, violet, black, red, brown | 2 |
| Capacitors | |||
| C1,C2 | MKS2-2.2uF | Film capacitor | 2 |
| C3,C4,C6,C8 | 680uF ELNA | Electrolytic capacitor | 4 |
| C5,C7,C17,C19 | 100nF | Film capacitor | 4 |
| C9,C12,C13,C15 | 330uF | Electrolytic capacitor | 4 |
| C10 | 25V 10000uF | Electrolytic capacitor | 1 |
| C11 | 47uF | Electrolytic capacitor | 1 |
| C14 | 10uF | Electrolytic capacitor | 1 |
| C16,C18 | 50V 10000uF | Electrolytic capacitor | 2 |
| Semiconductors | |||
| D1 | KBP206 | 2A 600V KBP Bridge Rectifiers | 1 |
| D2,D3 | 1N4007-DIODE | Diodes — General Purpose | 2 |
| D4 | GBJ2510 | 25A 1kV GBJ6 Bridge Rectifiers | 1 |
| U1,U2 | LM1875T/NOPB | Audio Power OpAmps 25W | 2 |
| U7 | UPC1237HA | speaker protection | 1 |
| U8 | L7812CV | TO-220 — 12V voltage regulator | 1 |
| Miscellaneous | |||
| CN1 | ZX-XH2.54-3PZZ | 3Pin 2.54 mm connector | 1 |
| CN2,CN3 | KF301-5.0-2P | 5 mm Screw terminal 2 pin | 2 |
| CN4 | 2P PH2.54 | 2Pin 2.54 mm connector | 1 |
| CN5 | HB9500M-9.5-3P | 9.5 mm Barrier Terminal Blocks 3Pin | 1 |
| RELAY1 | G2R-2-12VDC | RELAY-TH_G2R-2 | 1 |
| L1,L2 | Air-core inductor 8.5 turns * 1.4 wire * 12 inner diameter | Air-core inductor 8.5 turns * 1.4 wire * 12 inner diameter | 2 |
| U3,U4,U5,U6 | M3 screw | M3 screw | 4 |
Download files, links, and notes
Download PCB in Gerber and PDF
- Buy LM1875 Board
- PDF datasheet IC Lm1875 — LM1875 20W Audio Power Amplifier
- PDF datasheet IC UPC1237HA
- PDF datasheet IC Lm7812
- PDF datasheet Bridge rectifier GBJ2510
- PDF datasheet Bridge rectifier KBP206
- PDF datasheet diode 1n4007
Source: https://oshwhub.com/yc_chen/lm1875-gc-lan-ya-gong-fang
