LM3886 CHIP AMPLIFIER
Giovanni Militano 
Page 1: LM3886 Chipamp, LM3886 Chipamp Construction
Page 2: LM3886 Chipamp Construction (cont), Chipamp Sound
LM3886 CHIPAMP
So what the heck is a Gainclone? Originally, the term Gainclone meant a clone of the 47 Laboratory Gaincard. The 47 Laboratory Model 4706 Gaincard is understood to have the following general features:
- 9 parts per channel based around the National Semiconductor LM3875
- A very short signal pass and NFB loop
- PSU filter with 1000µF to 2200µF capacitors
- Voltage regulation with a 170 VA cut-core transformer
However, a Gainclone is now generally understood to mean: any low component chip amp intended for high quality sound.
Photograph 01 below shows a 47 Laboratory Model 4706 Gaincard which retails for about $3300US. Despite the high retail cost of the Gaincard, you should easily be able to build a great sounding gainclone for less than $200US.
Photograph 01: 47 Laboratory Model 4706 Gaincard and Power Humpty
OK, so now you are interested in a Chip Amplifier and you are wondering where the heck should you start? A good starting point would be chipamp.com. At Chipamp.com, you can buy kits or PCBs to build your own chip amp. A search of "LM3886 chip amp" will net you more information than you can likely digest.
For more information about this kit, see the Users Guide for the Non-Inverted LM3886 Chipamp Kit - (PDF 280KB). The amplifier circuit of the LM3886 chipamp is shown below in Figure 01.
Figure 01: LM3886 Chipamp Schematic
The power supply circuit for the kit is shown in Figure 02 below.
Figure 02: LM3886 Chipamp Power Supply Schematic
LM3886 CHIPAMP CONSTRUCTION
I purchased bare PCBs for an LM3886 and "snubberized" power supply from chipamp.com. I decided against the kit because I had several of the required passive components and the remaining components were available locally. In an attempt to get a more laid back sound, I opted to use Carbon Film resistors which I conveniently had on hand. Instead of 10000µF filtering capacitors, I used 15000µF caps for no reason other than I picked them up on sale for a few bucks. I got real lucky with the 160VA Piltron torroid and heat sinks which were given to me by Karma from diyAudio.com for the cost of shipping ($20CDN). Thank you very much Karma! :)
For myself, I always find that the most difficult portion of a DIY project is the enclosure. I had some luck using a Hammond Aluminum Chassis for my K-12M Tube Amp project, so I decided to go the Hammond route again. The 1444-32 Hammond chassis was available locally in Winnipeg from Tip Top Electronic Supply for about $33CDN.
Photograph 02: Hammond 1444-32 Aluminum Chassis
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Construction (continued), Chipamp Sound |