lm3886 PCB

[AndrewT]

Move the Zobel return to the Power ground.
Break the trace between Power ground and Signal ground. Insert a pair of holes to tie these together with a link or resistor.
Where are the decoupling caps? 0u1F?
Remove pin2 & pin11 and maybe pin6.
Where is the RF attenuation?

You seem to have two extra components (R+C), that I don't recognise, from speaker to pin10.

Have another look at that other thread you could maybe share ideas.

Last thought.
Add alternative pin pitch for most or all of your caps. I just hate it when I can't find the correct pin pitch cap from stock but have plenty of the correct value and my usual suppliers don't do them either.

[13814044]

Hi Andrew

I'v made the annotations bigger so you can see whats what. I have all component indicated in the data sheet and they are labeled in the same way so it can be used as a key for interpreting my PCB.

Decoupling cap sizes have not been finalized-please advise. (I have 5*6 800uF on positive and negative supply rails located at the PS unit)

The extra components you refer to are Rf2 and C2 (fig 2-datasheet). I'm unsure of what part of the circuit is the RF attenuation-is it on the data sheet.

GNDs are now tied with res-should they still return to audio GND via separate wires?

Extra IC pins are gone.

[AndrewT]

Hi,
ref fig 2:

Cc=220pF is the RF attenuation.
C=10uF is the DC blocking cap.

Add both. They both form the low pass and high pass filters for the incoming signal. These must set the bandwidth of the power amp.

[13814044]

Hi
Have noted the other thread.

should C (the DC blocking cap) replace Rb from figure 1. Rb seems to serve the same purpose as C-prevents currents from entering the input on shutdown.

Thanks a lot for the help

[13814044]

Hi
This is what it looks like now-removed Rb, added C and Cc.

Do i need to work on getting supply rails thicker-they're 5mm at their thickest areas.

any other suggestions on the basic layout? (I'll get to adding multiple footprints for the supply caps still.)

Again should i now still run separate GND wires the the audio ground

Thanks
Chris

[AndrewT]

C and Rb should be in series for the input feed.

With the separated Signal and Power Grounds, you now have choices.

For a monobloc with transformer + PSU+Case+amplifier for one channel, connect SG to PG on the PCB, with either a link or low value resistor.

For a two channel amp with a common PSU, take all the signal and power grounds to a central Audio Ground (AG), but keep all the routes very short. This can be done with a centre tapped or dual secondary transformer and a single bridge rectifier.

For a two channel amp with separate PSUs, take each channel's SG & PG to their own AG and then connect each AG to Safety Earth with a pair of disconnecting networks. This requires dual bridge rectifiers for each channel and a dual secondary transformer.

[13814044]

Aah thanks that makes sense.

Will add Rb, make sure all component footprints are the right size etc and try submit another version some time. I would like to have the boards made on Monday so will post updated PCB as soon as i can.

Thanks again for the patient help

[AndrewT]

combining the Signal Ground with the Power ground on the PCB cripples the options when it comes to building multi-channel amplifiers.
Keep the option open and it allows for experimentation to eliminate buzz & hum.

[13814044]

Is this getting there yet?

I'll probably drill the holes for supply caps myself when i have them-I think theres enough room for experimentation (caps can be rotated slightly or shifted)

I definitely need all the flexibility i can get as the system will comprise of 6 or 8 amp modules with a single 1000VA toroidal.

3-way active crossover is already built from a kit

[AndrewT]

Move Csn (output Zobel) to Power Ground.