Point to Point (P2P) LM3875 IC ChipAmp (Gainclone)
LM3875 IC Non-Inverting ChipAmp (Gainclone)
The schematic for the LM3875 IC Non-Inverting Chipamp / Gainclone is shown in the Figure below.
LM3875 Chipamp / Gainclone Schematic
Point-to-Point Chipamp / Gainclone
These are the basic point to point techniques I use for constructing a LM3875 chipamp (gainclone).
Use a 1 mm hand drill to enlarge the veroboard holes because the chip pins are too wide for the standard holes. Also some of the holes will have two components in them so they have to be quite wide.
Break off all the pins that will not be used, except pin 11, which will be soldered to the board for stability.
LM3875 with Unused Pins Removed
Add the feedback resistor. You want to keep this loop as short as possible, so the feedback resistor and chip will share the same hole. You will want to use some insulation on the resistor. Next, put the input resistor with the non-inverting input. Solder the chip-pin/resistor end. The 680R lead drops in the hole in front of the inverting input on the non-component side which also has the feedback resistor lead with it. Solder all three together and cut excess. The other end of the 680R drops directly through the board one hole across toward pin eleven. This end is solder to one of the copper rings and extended side-ways and soldered to another ring. This is your common earth lead and because it is a heavy lead it can take the load. All earths will connect to this lead.
LM3875 IC and Resistors
Add the filtering capacitors
Next, add the capacitors. Pass the positive lead of the positive supply cap through the same hole as pin one on the chip. The negative lead should just pass through at this stage to be jointed to the common earth lead mentioned above. The negative supply cap is passed though hole one forward and one to the right of pin eleven (negative lead). This will vary slightly depending on caps used and their physical size. The other lead may join direct to the common earth (positive lead). Because I have used big cheap electrolytics place a 0.1uF poly cap directly across them (see photos).
After earthing both caps, attach the positive power lead to pin one of the chip which also has the positive of the cap. Bend them to a small "U" and then solder. For the negative supply rail I strip a 2.5 cm length and put a small length yellow spaghetti on this lead to remind me it is he negative voltage rail. This lead raps around the negative lead of the cap near the eleventh pin then onto neg power of the chip. Also between the cap lead and the chip I put some spaghetti to stop it shorting other pins.
Attach Power Rails to LM3875 and Capacitors
I use heavy gauge speaker wire for the output. The positive lead now goes around the chip output which also has the lead from the feedback R. The neg of the speaker lead goes to the common earth we established earlier. The ground lead from the PS is attached to the common lead on the board. I use a heavier ground lead than power leads.