Need help: Look for bridged LM3875TF schematic

[Mrpong]

I'm looking for a simple schematic using LM3875TF in bridge mode with Burrbrown DRV134.

Thank a lot.

[tiltedhalo]

This should work for you.

[Mrpong]

Thank you so much. May I ask certain questions?

- How important are the components marked as "Optional"?
- Which roles do these optional components play in this schematic?
- For C1 (1uF), I think it's a coupling cap. If my memory is correct, a regular inverted shematic (non-bridged) uses 2.2uf or 3.3uf. Can we use 2.2 or 3.3?

[tiltedhalo]

C-1 is the input cap, to block DC offset from pre-amp, 1 uf is a round figure with the 1K, 22K, 220pf to produce a flat frequency response from 5hz to 35khz. If you are positive about your pre-amps output and C3 and C4 are used then you can leave out the input cap.
C3 and C4 are used on the sense leads of the DRV134 to prevent DC offset, these caps if used must be high quality metal poly film types.
C13 and C14 can be left out, use them if you have severe RF conditions i.e.5000watt radio station next door.
L1 and L2 are inductors made from 10 turns of #20 magnet wire on the body of the 2watt 10ohm resistor.
C11 and C12 are the negative feedback caps, these can be left out if the amps DC offset is OK. If they are used I prefer High quality 5% tolerance 16V tantalums or deposited silver micas, polorized.
The 220 pf cap should be a silver mica.
DRIVE ONLY AN 8 OHM LOAD with this amp even at 25VDC+/-, it will give you about 100watts into an 8 ohm load. Good Luck

PS layout is critical use a ground plane keep the NFB loop as close to the chip as possible.