Gainclone - The most popular amplifier in the world(?)

A LM3886 from National Semiconductor. The heart of a Gainclone. 

It took a while to understand what "GC" was, or Gainclone. What a name! A couple of IC's (LM3875, LM3876 and LM3886) from National Semiconductor are very popular in the DIY community. The LM3886 is the most powerful and delivers around 68 watts and peak power of 120 watts. The IC is only 20 x 15 mm and contains a whole power amplifer with 10 A output capability. I think this IC is amazing, so much power in so small volume and few external parts.

Interesting features 

I have designed a Gainclone and it's universal in most respects? My intentions led to this:

DeLuxe version:

• Inverting or non-inverting LM3886, can be chosen
• Inverting or non-inverting input buffer, with or without gain, can be chosen
• Feedback network which can satisfy everyone, full gain at DC or gain of 1 using a capacitor in the feedback
• With or without DC-servo for both inverting or non-inverting LM3886, can be chosen
• Output filter, L//R, small handwound inductor plus a resistor.
• Inputfilter, lowpass and also highpass to block incoming DC-signals. You could also skip the filters if you want to. I recommend though to use a high frequency lowpass filter.
• Mute, the LM3886 is "dead" for a short time at power up, can be chosen.
• Bridge connection and the LM3886 can operate in inverting or non-inverting mode, can be chosen.
• Pcb for 2 separate channels, stereo, or one channel in bridge connection. It's possible to change mode easily with help from a jumper.
• Power supply be on the pcb with sufficient amount of smoothing capacitance.
• Stabilized power supply for the buffers. +-12 V is chosen (can easily be changed) so the amazing AD8620 can be used.

Normal verison (not designed yet):

• Inverting or non-inverting LM3886, can be chosen.
• Feedback network which can satisfy everyone, full gain at DC or gain of 1 using a capacitor in the feedback.
• Output filter, L//R, small handwound inductor plus a resistor
• Inputfilter, lowpass and also highpass to block incoming DC-signals. You could also skip the filters if you want to. I recommend though to use a high frequency lowpass filter.
• Mute, the LM3886 is "dead" for a short time at power up, can be chosen.
• Pcb for one channel.
• Power supply be on the pcb with a certain amount of smoothing capacitance.

Where does the name come from?

See the excellent description at Wikipedia. It began with Sakura Systems which designed a high-end (or at least expensive) power amp based on LM3875 and a minimal power supply. The product is called Gaincard. Pictures are floating around on the internet and the inside is amazing I think. Some (rather many actually) are a little bit bugged (Rod Elliott among others and I for instance) over Gaincard but others, mostly DIY'ers build their own Gaincard and then call them Gainclone. Some of the Gainclones are really beautiful, very good craftmanship.

Here are reviews of the original.

http://www.tnt-audio.com/ampli/47gaincard_e.html

http://www.6moons.com/audioreviews/47labs5/gaincard.html

The beautiful things about the LM3875 and LM3886 are that they are reliable, cheap, sounds good and are easy to get working, even if the are hardwired (no pcb).