I finished the project of the most simplest and cheaper modular instrument amplifier. The final amplifier have output power between 70W and 300W for 4 and 8 ohm speakers. Three several modules required for this project if bridged and paralleled modes required. The 4th module is the speaker protection. The amplifier can be built as:
- Single amplifier with only one module with 1 TDA7293 or TDA7294 / channel
- Bridged amplifier with 2 modules / channel
- Paralleled amplifier with 2 modules / channel
- Combined bridged and paralleled with 4 modules / channel
- Paralleled simple or bridged amplifier, but with 2 paralleled module
The modules can be connected with 15 pin connectors instead of wires. The single, bridged, and paralleled amplifier modules are not same, one for the first and the most important "main" module, one for bridge connection, and one for parallel connection what can be used for both main and bridged modules. The last 4th module is the speaker protection, must be placed to the middle of stereo configuration between left and right channels.
The official datasheet contains all modes of TDA729x circuits. The TDA7294 is very cheap, but cannot use for paralleled mode, and no clipping led output. The recommended max. power supply voltage is +-40V. The TDA7293 have paralleled mode (where only the power stage works, the preamp stages off), the max. power supply voltage is +-47V, and clipping led output available. The maximum output power of one circuit is 70-75W of TDA7294, and about 80-100W of TDA7293.
The possible output powers of bridged application:
The V column is the power supply voltage, 1 means: 1 IC paralleled, 2 means: 2 IC paralleled with all others. Without superscripted number have no parallel connections, this is only bridged.
The possible output power with single (non bridged) application:
The V is the power supply voltage, 1 means: 1 IC paralleled, 2 means: 2 IC paralleled. Without superscripted number have no parallel connections.
The bridged or single version is very popular on "official" instrument amplifiers. Carlsbro GLX100, Marshall MG, and Marshall Mode Four contains TDA7293/7294 circuits.
I using bridged application long time ago for stereo guitar amplifications and for microphones. This is more than enough for small rooms or rock clubs for live sessions with very good (for example Eminence) speakers.
The four modules (including speaker protection) can be connected by the 15 pin connectors soldered to the edge of the PCB. This is the method to build single, bridged, paralelled, bridged+paralleled, bridged+duble-paralleled, mono or stereo applications with very simple easy to build PCBs.
The first and the most important circuit is complete 70-75W amplifier:
This circuit always be the first of the complete amplifier configuration, which can be continued with parallel, bridge, or speaker protection module.
The PCB of main TDA module:
To the Conn2 on right edge can be connected another module for bridged or parallel application. It this one main module required (for 75W output power) then Conn2 can be used for speaker protection, but this is not required. The nother side have Conn4 connector for the second (right) channel is the setup is stereo. This Conn4 connector can be connected the speaker protection only. For example the simplest stereo setup is: 1 main module for left channel, 1 speaker protection, 1 main module for the right channel.
Examples are on the PDF manual. The speaker protection will be protected bot left and right channels.
On this first PCB the Conn5 connector is the stereo audio level inputs, the right channel wired to the input of another main module on the right side of speaker protection. The output connector Conn6 is not stereo. This connector can be user for one channel only (the another output is on the second main module). The single setup uses Out+ and GND, the bridged setup uses Out+ and Out- for speaker connection.
The second circuit for bridge configuration:
And the bridge PCB:
The Conn4 connector of this bridge PCB can be used for the connection of first main circuit. This module can be continued by Conn5 connector with speaker protection (if the channel finalized) or with parallel module if more output current needed.
If the setup must be continued with parallel mode, here is the schematic:
PCB for parallel mode:
This is the simplest module, because the premaplifiers are off within the circuit, only the power FETs working. This mode controlled by Buffer Driver and Slave mode pins of TDA circuit. This module can be connected to the right side of main module, bridge module, or if required can be connected to the parallel module to duplicate the paralleled circuits within the application. The second parallel modules can be continued with speaker protection or with nothing only. The another edge of the speaker protection (if used) can be restart the full setup with main module for right channel.
The speaker protection:
And the PCB:
Here are the examples how to build complete amplifiers with several output powers with these four modules. The "Module 1" is always the first and always required main module, the "Module 2" is the optional bridge module, "Module 3" is the optional parallel module can be duplicated within the setup, and the 4th is the speaker protection.
The simplest mono setup (75W on 4 Ohm, with 8 Ohm about half):
- Module 1
- Speaker protection (optional)
Simple stereo setup (2x 75W on 4 Ohm, with 8 Ohm about half):
- Module 1
- Speaker protection (required)
- Module 1
Mono bridged application (8 Ohm only, about 150W):
- Module 1
- Module 2
- Speaker protection (optional)
Bridged stereo setup (8 Ohm only 2x150W)
- Module 1
- Module 2
- Speaker protection
- Module 1
- Module 2
Mono paralleled setup (4 Ohm about 100W):
- Module 1
- Module 3
- Speaker protection (optional)
Stereo paralleled setup (2 x 100W on 4 Ohm):
- Module 1
- Module 3
- Speaker protection (required)
- Module 1
- Module 3
Mono bridged and paralleled (4 Ohm - 300W, 8 Ohm 200W):
- Module 1
- Module 3
- Module 2
- Module 3
- Speaker protection (optional)
Stereo bridged + paralleled setup (About 2 x 300W on 4 Ohm):
- Module 1
- Module 3
- Module 2
- Module 3
- Speaker protection
- Module 1
- Module 3
- Module 2
- Module 3
The parallel module can be connected to the first parallel module for duplication. This increases the maximum current, maybe smaller output impedance possible.
Doubled parallel bridge setup:
- Module 1
- Module 3
- Module 3
- Module 2
- Module 3
- Module 3
and the upper setup can be continued with speaker protection and the another edge of speaker protection can be repeated the same setup for right channel is stereo application required.
See also:
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