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Hi All,
I built my first LM4780 7 years when I got into this hobby. I rarely used it due to the very mediocre layout, the bad solder job, and pop and hum that accompany each power up. I've always like the sound, power output and the ability to handle low speaker impedance loads of the 4780, so I decided to chuck the old amp, and redo everything from scratch. My goal was to build a simple, inexpensive chipamp that sounds good, has ample power to handle my listening style (loud, lots of dynamics), and can handle all my 4-ohm speakers.
- The PCB is on eBay and from HIFIDIY.NET. All components are sourced from Digikey, caps are "Audio" types, resistors are 1% metal film. As you can see, component count is very low. The LM4780 amp chips and LM7812 (voltage regulator) are free samples from TI.
- The transformer is the Avel 330VA 25-0-25.
- The power supply consists of a 25A/400V bridge rectifier (overkill, but I had it laying around), and Nichicon 10,000uF/50V ($3) from Apex Jr., and other components to mitigate noise from the transformer and the diode bridge.
- Soft start module was built from a TI schematic.
- Speaker protection is from an eBay kit, powered by a 12VAC/1A transformer, which output is also rectified to provide DC for the LED and fan.
- The LM4780 boards are in a parallel configuration. These boards lack the optional zobel networks, so I added the 0.1uF caps and 2.7 ohm resistors between the output and the ground. The speaker outputs are then bridged with 0.1 ohm/3W resistors. The zobels are absolutely necessary to prevent oscillation and subsequent shutdown.
This time, I think I achieved my goal of building a super quiet amp without pop, hum or buzz in a very compact Par-Metal case. Bass is very good, and detail excellent. There is a difference of about 5 to 6 degrees F between the heat sink channels, so apparently the gain is not equal. In the coming days, I will probably replace the gain resistors with better tolerance ones (0.1%).
Thanks for reading.
Hong
I built my first LM4780 7 years when I got into this hobby. I rarely used it due to the very mediocre layout, the bad solder job, and pop and hum that accompany each power up. I've always like the sound, power output and the ability to handle low speaker impedance loads of the 4780, so I decided to chuck the old amp, and redo everything from scratch. My goal was to build a simple, inexpensive chipamp that sounds good, has ample power to handle my listening style (loud, lots of dynamics), and can handle all my 4-ohm speakers.
- The PCB is on eBay and from HIFIDIY.NET. All components are sourced from Digikey, caps are "Audio" types, resistors are 1% metal film. As you can see, component count is very low. The LM4780 amp chips and LM7812 (voltage regulator) are free samples from TI.
- The transformer is the Avel 330VA 25-0-25.
- The power supply consists of a 25A/400V bridge rectifier (overkill, but I had it laying around), and Nichicon 10,000uF/50V ($3) from Apex Jr., and other components to mitigate noise from the transformer and the diode bridge.
- Soft start module was built from a TI schematic.
- Speaker protection is from an eBay kit, powered by a 12VAC/1A transformer, which output is also rectified to provide DC for the LED and fan.
- The LM4780 boards are in a parallel configuration. These boards lack the optional zobel networks, so I added the 0.1uF caps and 2.7 ohm resistors between the output and the ground. The speaker outputs are then bridged with 0.1 ohm/3W resistors. The zobels are absolutely necessary to prevent oscillation and subsequent shutdown.
This time, I think I achieved my goal of building a super quiet amp without pop, hum or buzz in a very compact Par-Metal case. Bass is very good, and detail excellent. There is a difference of about 5 to 6 degrees F between the heat sink channels, so apparently the gain is not equal. In the coming days, I will probably replace the gain resistors with better tolerance ones (0.1%).
Thanks for reading.
Hong
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