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Power Amplifier Gainclones more Gainclones Power Amplifier

2x25 Watt LM1875 Gainclone Amplifier

2x50W LM3875 Gainclone Amplifier

2x56W LM3876 Gainclone Amplifier

2x68W LM3886 Gainclone Amplifier

2x50W Tube Gainclone Hybrid Amplifier

Build Power Amplifier LM3876, Simply and Powerfull Power Amplifier

The chip on which the amplifier is based, a Type LM3876, is a member of the Overture family from National Semiconductor, All members of this family are pin-compatible and mutually interchangeable. They are typified by an internal protection (called SPIKE). In practice, the diftection ference between them is the power output. The series was described on the basis of the LM3886 in an earlier issue*.

The PCB has been designed so what it can accommodate the LM3876 (50W) as well as the LM3886 (150W). Because of this, pin5 of the IC on the board is connected to the positive supply line. This connection is not needed for the LM3876, since its pin5 is not (internally) connected (NC).

The IC is located at the side of the board to facilitate fitting it to a heat sink as shown in the photograph.

An important aspect for optimum performance is the decoupling of the unregulated supply lines by C 7-10. All earth connections go to a single terminal on the board.

Air-cored inductor L1 consists of 13 turns of 1mm dia. enamelled copper wire with an inner diameter of 10mm. The completed inductor is pushed over R7 and its terminals soldered to those of the resistor.

All electrolytic capacitors must be mounted upright. The amplifier can be muted with a single-pole switch connected to the MUTE input (pin8). This function is enabled when the switch is open. If muting is not required, solder a wire bridge across the mute terminals on the board.

Boucherot network R6-C6 is not normally required in this application, but provision has been made for it for use in other applications.

According to the manufacturers, both chips are optimalized for a load of 8 Ohm. The output power is lower when a 4 Ohm load is used or when the supply voltage is reduced. When a 4 Ohm load is used, the SPIKE protection becomes active when the supply voltage is about 27V, resulting a in a reduction of the power output to 10W. This means that it is not advisable to use loudspeaker with an impedance < 8 Ohm.

For best result you can expand power amplifier using BPA-200 Amplifier

Part list

R1, R3 = 1 k
R2, R4, R5 = 18k
R6 = see text
R7 = 10R, 5 Watt
R8, R9 = 22k

C1 = 2.2 uF
C2 = 220 uF, 160 V
C3 = 22 uF, 40 V
C4 = 47 pF
C5 = 100 uF, 40 V
C6 = see text
C7, C8 = 100 nF
C9, C10 = 1000 uF, 40 V

L1 = 0.7 uH - see text

Integrated circuits:
IC1 = LM3876T

Heat sink for IC1 < 1.5 K W-1
Single-pole switch - see text

Schematic and PCB Layout LM3876

Build Power Amplifier LM4780 with BPA-200 Amplifier

This is design is very similar to the National Semiconductor BPA-200 (Bridge/Parallel Amplifier) which uses 4x LM3886 per channel and an input buffer:

Nothing Special in design but usefully for more watts!
My one will use 2x BrianGT LM4780 kits and a balanced line driver to bridge them, like this:


The LM4780 is a stereo audio amplifier capable of typically delivering 60W per channel of continuous average output power into an 8 load with less than 0.5% THD+N from 20Hz - 20kHz.
The LM4780 is fully protected utilizing National's Self Peak Instantaneous Temperature (°Ke) (SPiKeTM) protection circuitry. SPiKe provides a dynamically optimized Safe Operating Area (SOA). SPiKe protection completely safeguards the LM4780's outputs against over-voltage, under-voltage, overloads, shorts to the supplies or GND, thermal runaway and instantaneous temperature peaks. The advanced protection features of the LM4780 places it in a class above discrete and hybrid amplifiers.

Each amplifier of the LM4780 has an independent smooth transition fade-in/out mute.
The LM4780 can easily be configured for bridge or parallel operation for 120W mono solutions.

The total effect is (2x LM3886's paralleled) x2 Bridged and should give approx 225 watts into 8 ohm and 335 watts into 4 ohm when used with a sufficient power supply.

The line driver part is based on the DRV134 and a PCB from digi01, you can see the details here.

In the end mine was dual mono in a recycled amp case using 2x 300VA (18VACx2) toroidal transformers, 54,400uF of capacitance per channel with a snubber. The DRV134s add 6dB of gain so I set the LM4780s to about 16x gain to compensate (they are set to 33 normally). I get no DC offset, no hum, no crackle or thump on turn on or turn off, silent as.


DIY Cat5 Speaker Cables

These are perfect speaker cables for my brother speaker. I build use AMP Cat6 cables, for detail view here.

AMP Cable Cat6

TwistPair in TwistPair Cable Cat6

Ilustration wiring cable speaker using cable cat6

Perfect Sound Granite DIY Speaker Project

I have been build this speaker for my brother, these are do-it-yourself (DIY) speakers that and using granite for the speaker box. I listen this speaker, That's Great Perfect Sound, nearly linear reproduction sound. Great Job Man!. Source Perfect Sound Granite DIY Speaker Project.

DIY Granite Speakers with Seas G17REX/P and 27 TFFC Drivers

Speaker Project Summary
External box dimensions 240 x 350 x 280 mm. Internal box dimensions 200 x 310 x 240 mm. Box material 20 mm thick black granite (Nero Assoluto). Weight 35 kg.
Enclosure volume 14.9 L. Bass reflex enclosure tuned to 45 Hz. Port length 160 mm
Input power 80W. Sensitivity 87.5 dB. Transmission bandwidth 40Hz - 20kHz. Impedance 6 ohm.

Seas Granite Speaker Enclosure Plan

Seas Loudspeaker Drivers
The drivers selected for this loudspeaker system are from Seas who has been producing speaker drivers for over 50 years. The tweeter is the Seas 27 TFFC which has a fabric dome. The Sonolex lightweight fabric dome has high consistency and provides excellent stability against variations in air humidity. The stiff and stable rear chamber allows for a moderately low crossover frequency (~2500kHz). This made the Seas 27 TFFC tweeter the right choice for our granite loudspeaker project.

The woofer we used is the Seas G17REX/P. The woofer consists of a fiber glass cone, a bullet shaped phase plug and a high loss rubber surround. These are carefully matched to each other resulting in smooth frequency response.

Speaker Box and Crossover Design
The speaker box and crossover network were designed by M.Janura and K.Sýkory using the LspCAD speaker design software package. A volume of 15L (dimensions 220 x 350 x 250 mm) and a tuning frequency of 45 Hz was used for the speaker box. The dividing frequency is 2.5kHz and the drivers are connected in phase. The crossover schematic and modeled frequency response are shown below.

Calculated Speaker Box Frequency Response - Seas G17REX/P Woofer

Crossover Schematic - Seas G17REX/P Woofer and 27 TFFC Tweeter

Crossover Schematic - Seas G17REX/P Woofer and 27 TFFC Tweeter

The components used in the crossover dividing network are from TESLA. I think that the people in the former Czechoslovakia were able to produce high quality components, but you may use your favorite type. The condensers (capacitors) used in crossover are MKT type - we did not use bipolar condensers because they have disadvantages that I won't further specify. The inductors are air core.


I was knocked off my feet with the sound after the first track we played: Everlast - Folsom Prison Blues by the legendary Johnny Cash. The song tested bass response of the speakers. We didn't expect such deep and accurate bass from small speakers. The speakers deliver very detailed sound (soft treble and great imaging). They play rock music aggressively and classical music with emotion. As we say: "they play like HONEY" (it means - brilliant) and they look great too.

I would like to thank to Marian Mózer and everyone in the team for their effort and for the job well done. The loudspeaker system is designed by M.Janura and K.Sýkory - named Besie 1.

We understand that most of you will not be able to make speaker boxes of granite. If you are interested in speakers made from granite, please send me an email and we may be able to help you. Thank you and I hope you enjoyed our project.

Seas Granite Speakers

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