DIY LM3886 Chip Amplifier (Gainclone) Kit
DIY LM3886 Chip Amplifier (Gainclone) Kit
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 1 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 1: 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 1.
Figure 1: LM3886 Chipamp Schematic
The power supply circuit for the kit is shown in Figure 2 below.
Figure 2: LM3886 Chipamp Power Supply Schematic
Construction - LM3886 Chip Amplifier (Gainclone) Kit
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! :)
Photograph 2: LM3886 IC Amplifier Assembled PCB with heasink
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 3: Hammond 1444-32 Aluminum Chassis
For the mains power, I used an IEC Receptacle with 6 amp EMI filter that was recycled from a dead CRT computer monitor. The fuse holder is from my parts bin and it hold a 2 ampere slow blow fuse. The power supply wire is 14 gauge stranded copper wire.
Photograph 4 below shows the underside of the Chip Amplifier. I twisted all the AC wires together and for obvious reasons, I kept the RCA inputs and amplifier PCB close together and far away from the AC. In the Photograph, you can also see the star grounding. I had some left over real estate so one could easily fit this amp into a smaller enclosure. On the front is a small power switch with a built-in LED that is run off of the power supply board.
Photograph 4: LM3886 Chipamp Wiring
Photograph 5: LM3886 IC Chip Amplifier Wiring
From the rear view shown in Photograph 6, you can see the plain RCA jacks and binding posts. The RCA jacks I had left over from a previous project, while the binding posts were given to me by a workmate. The handles were salvaged from old cupboards. There you have it, my LM3886 based Chip Amplifier with less than $100CDN invested.
Photograph 6: Rear View of LM3886 Chipamp
Photograph 7: Front and Top View of LM3886 Chipamp
Sound - LM3886 Chip Amplifier (Gainclone) Kit
When I fired it up for the first time, I was immediately surprised with how much power was available, the level of detail and the nice bass response. It sounded much better than I was expecting and much better than it should considering the simplicity and low cost. Initially, I thought it sounded a little bright, but after about 12 hours the sound became more relaxed.
I compared the sound of this Chip Amp with my K-12M Tube Amplifier kit. I also have a Sony STR-DE585 which I use for my home theatre, but both the LM3886 Chip Amp and the K-12M Tube Amp make the Sony sound sick. The comparison between the LM3886 Chip Amp and the K-12M Tube Amp is a fair one as they are similar in price. From a practical point of view, the LM3886 Chip Amp is more flexible as it has much more available power and can easily drive a wide variety of speaker loads. I prefer the bass response of the Chip Amp over that of the tube amp. The K-12M Tube Amp has a great mid-range and a better high end over the Chip Amp. I find the Chip Amp a touch bright, but that is likely more my personal preference. Both these amps sound very good and I give the K-12M only a slight edge due to it's mid-range performance. However, at times the Chip Amp does sound more detailed to me. When I get a chance, I want to try some blind tests.