Gainclone Compact Modular Amplifier based on LM3886

Gainclone: Compact Modular Amplifier based on LM3886

 

In 1999, 47 Labs introduced the Gaincard amplifier. The Gaincard shook the audiophile community with its unconventional design. Its designer, Junji Kimura, thought that less is more and that only the simplest can accommodate the most complex. With this idea in mind, he developed a product that had fewer parts, less capacitance and simpler construction than virtually anything preceding it. Its features includes having the world’s smallest number of parts (nine per channel), the world’s shortest signal-path length (32 mm) and world’s shortest negative feedback loop (9 mm) and mounting a 56-watt chip: the LM3875.

Not everyone would agree that all of the Gaincard’s design features are desirable, in fact, these construction techniques went against the accepted wisdom of the time. But regardless of claims and espoused design principles, the bottom line, always, is the product’s sound. And the Gaincard left no one indiferent.

 

▶ Gainclone based on LM3886

Due to the success of the Gaincard, the DIY community started building replicas or “clones” of the Gaincard using the integrated circuits amplifiers LM3875 in an attempt to see if good sound could be obtained, thereby the term: “gainclone”. The design concept has expanded and become rapidly more popular over the last few years and various modifications or improvements have been made to the original application circuit.

Gainclone Compact Modular Amplifier based on LM3886 - LM3886

Figure 1. LM3886 chipamp.

Currently, the LM3886, which is the revised version of its brother LM3875, is one of the best compact HiFi amplifiers. It is capable of delivering 68 W of continuous average power to a 4 Ω load and 38 W into 8 Ω with 0.1 % THD+N from 20 Hz–20 kHz. The LM3886 maintains an excellent signal-to-noise ratio of greater than 92 dB with a typical low noise floor of 2.0 µV. It exhibits extremely low THD+N values of 0.03 % at the rated load over the audio spectrum, and provides excellent linearity with an IMD (SMPTE) typical rating of 0.004 %. It works in Class AB-A (conjugate) with a fully symmetrical structure and the reason for its popularity is due to its very low distortion, minimal external components, and low cost. With the right layout and component selection, you can build an excellent sounding Hi-Fi audio amplifier that will rival high-end amps retailing for several thousand dollars or more.

 

▶ Gainclone Compact Modular Amplifier with LM3886 chipamp

At atm-audio we designed a gainclone compact modular amplifier based on the LM3886, manufactured by National Semiconductors (now owned by Texas Instruments) with the particularity that since it is modular, you can connect in parallel, bridge or both, several units and thus be able to double, triple or quadruple the output power. This characteristic makes it ideal for basic listening systems in the near field or for home theater systems with very high performance and high sound pressure.

The Compact Modular Amplifier based on LM3886 is a 60 W(RMS) module with a frequency response from 8 Hz to 100 kHz and a signal-to-noise ratio of 110 dB that makes it the best in its category.

 

Figure 2. Compact Modular Amplifier based on LM3886.

 

Using the existing jumpers on the board, one or several LM3886 can be combined and configured in a single, bridge, parallel or bridge/parallel, thus achieving different output powers.

The different amplification circuits according to the configuration of the jumpers are shown below.

Simple configuration: up to eight individual channels.

Figure 3. Single configuration circuit.

 

Bridge configuration: up to four individual channels:

Figure 4. Bridge configuration circuit.

 

Parallel configuration: up to four individual channels.

Figure 5. Parallel configuration circuit.

 

Bridge/parallel configuration: up to two individual channels.

Gainclone Compact Modular amplifier based on LM3886 - Single

Figure 6. Bridge/parallel configuration circuit.

 

Depending on the configuration and the power supply used, you can obtain power deliveries from 56 W(RMS) to almost 400 W(RMS) which gives you enormous versatility.

Through a multipin connector, the Compact Modular Amplifier can be connected directly to a Hypex DLCP DSP to form an active two, three or four-way system, or directly to a PCB with XLR or RCA connections to form a multichannel surround system up to eight channels.

 

Figure 7. RCA input board.

 

Gainclone Compact Modular amplifier based on LM3886 - XLR

Figure 8. XLR input board.

 

▶ Measures

Different measurements with 4 Ω load and 1 kHz test tone were made on the circuit using some power outputs configurations. The results of the tests are shown below:

Frequency response: 2 Hz – 80 kHz +/- 1 dB

Figure 9. Compact Modular Amplifier frequency response.

 

THD at 10 W(RMS) output: 0,0023 %

Figure 10. Compact Modular Amplifier THD at 10 W @ 4 Ω.

 

THD at 20 W(RMS) output: 0,0039 %

Figure 11. Compact Modular Amplifier THD at 20 W @ 4 Ω.

 

THD at 40 W(RMS) output: 0,027 %

Figure 12. Compact Modular Amplifier THD at 40 W @ 4 Ω.

 

THD 60 W(RMS) output: 0,094 %

Figure 13. Compact Modular Amplifier THD at 60 W @ 4 Ω.

 

THD at 80 W(RMS) output: 0,33 %Gainclone Compact Modular amplifier based on LM3886 - THD 80W

Figure 14. Compact Modular Amplifier THD at 80 W @ 4 Ω.

▶ Where to buy

The GaincloneCompact Module Amplifier based on LM3886 is only sold as a kit or for customized equipement to custormers. If you are interested in acquiring the product or simply want to know more about its characteristics and how it works, please, do not hesitate to contact us.

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