DIY LM3886 Chip Amplifier (Gainclone) Kit
4706 Gaincard Amplifier and Gainclone Amplifiers
So what the heck is a Gainclone amplifier? Originally, the term Gainclone amplifier was generally understood to be a clone of the 47 Laboratory Gaincard. The simple amplfier is based around the National Semiconductor (now Texas Instruments) LM3875 integrated circuit (IC). The 47 Laboratory Model 4706 Gaincard amplifier is understood to have the following general features:
- 9 parts per channel based around the LM3875 IC
- A very short signal pass and NFB loop
- PSU filter with 1000µF to 2200µF capacitors
- Voltage regulation with a 170 VA cut-core transformer
- 50 Watts output power (25 Watts per channel)
However as time has gone on, to many Gainclone amplifier is now generally understood to mean: any low component amplifier based around high power IC and intended for high performance audio. Photograph 1 below shows a 47 Laboratory Model 4706 Gaincard which retails for about $3300 US. Despite the high retail cost of the Gaincard, you should easily be able to build a great sounding gainclone amlifier for about $200 to $300 US.
Photograph 1: 47 Laboratory Model 4706 Gaincard and Power Humpty
The Model 4706 Gaincard amplifier was introducted in 1999 by 47 Laboratory. The Gaincard amplifier with its unconventional design that had far fewer parts, less capacitance and simpler construction than similar powered Hi-Fi amplifiers. The Gaincard amlifier stirred up trouble in the audiophile community when it was discovered that the amplifier cost less than $100 US in parts, but sold for $3300 US with its small power supply. The controversy ensued after a number of positive reviews of the Gaincard amplifier. Fast forward a number of years and now the Gainclone is probably the most commonly built and well-known DIY amplifier project amongst audio hobbyists.
LM3886 PCB from chipamp.com
OK, so now you are interested in building a Gainclone chip amplifier for yourself and you are wondering where the heck should you start? You can start at chipamp.com where you can purchase printed circuit boards (PCB) and part kits for LM1875 (20W) and LM3886 (68W) amplifiers. This leaves you with sourcing the remaining parts, power transformer and enclosure. Photograph 2 shows the LM3886 amplifier PCB and power supply PCB from chipamp.com. These are very nice quality boards with short and thick traces. I have used these PCB for a number of amplifier builds now.
Photograph 2: LM3886 Amplifier and Power Supply PCB from chipamp.com
For detailed information about this non-inverting LM3886 amplifier, see the Users Guide for Non-Inverted LM3886 Kit - (PDF 280KB). The amplifier circuit from the users guide is shown below in Figure 1.
Figure 1: LM3886 Chipamp Schematic
The amplifier circuit is built around the LM3886 IC. The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4 ohm load and 38W into 8 ohm with 0.1% THD+N from 20Hz - 20kHz. For the full details and operating parameters of the LM3886 IC see the LM3886 Datasheet - (PDF 1.2MB). The gain of the LM3886 amplifier circuit is set about 33. To adjust the gain to suit your configuration see the user guide and LM3886 datasheet.
Photograph 3: LM3886TF Itegrated Circuit
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 4: 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 $33 (May 2006).
Photograph 5: 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 6 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 6: LM3886 Chipamp Wiring
Photograph 7: LM3886 IC Chip Amplifier Wiring
From the rear view shown in Photograph 8, 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 8: Rear View of LM3886 Chipamp
Photograph 9: 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.
More Chip Amp / Gainclone Amplifier Projects
- Gobo LM1875 Amplifier Kit
- DIY TDA2050 IC Hi-Fi Chip Amplifier
- Synergy - a LM3875 Gainclone Amplifier
- DIY LM3875 Chip Amplifier (Gainclone) Kit
- Nanoo - DIY LM3875 Chip Amplifier (Gainclone)