My Amp

[ctardi]

Here is a rather large pic of the pcb:



And attached is the ExpressPCB File so anyone can suggest some changes.

(SCH and partial design credits to bigmike216)

[ScottRHinson]

I cant look at it using the expressPCB software right now, but I did take a look at your picture.

1. I don't think you have enough bypass capacitance on that board.
2. Your power supply leads look a little long and thin.

Scott

[ctardi]

The power leads are 0.1", what should they be?

I'm not sure how much capitance I should have, can you make any suggestions?

[ScottRHinson]

Originally posted by ctardi
The power leads are 0.1", what should they be?

I'm not sure how much capitance I should have, can you make any suggestions?

Copper is free when getting a PCB made, remember it has to be etched or milled off the insulating material. Make the power traces as wide as you can.

Take a look at the LM4870 application note for a suggested board layout...study the power and grounding portions.

Each amplifier chip will typically require a large electrolytic (when I made my boards I chose 680uF) and a smaller value ceramic, say .1uF. I threw in a smaller 10uF electrolytic for good measure. The .1uF should be as physically close to the chips as you can make them, followed by the 10uF, then the large bypass.

Check out the following thread for pics of my board.


My first non-inverted gainclone circuit

Scott

[carlosfm]

Just by clicking on this thread I won a prize of 2Mb.
That's what this page takes to load.
I'll remember it next time.
Not to click.

[Mr Evil]

Indeed. For simple graphics like that you should compress to PNG (or GIF if you can't do PNG). Trim off all the excess (task bar, tile bar and anything else that doesn't interest us) and convert down to 256 or 16 colours before compressing. This will give you much smaller size than JPG and yet also better quality. JPG should only be used for high-colour, complex images like photos.

[ctardi]

Well, if i could edit it, I would. But i can't seem to find the edit button...

The larger caps, 1,3,and the two unnumbered are 3300uf. They are followed by a 0.1uf. I think that will be plenty, no? I'll also work on the power traces.

[ScottRHinson]

Originally posted by ctardi
Well, if i could edit it, I would. But i can't seem to find the edit button...

The larger caps, 1,3,and the two unnumbered are 3300uf. They are followed by a 0.1uf. I think that will be plenty, no? I'll also work on the power traces.

Maybe? Inductance is a function of cross sectional area and length. The thinner the traces, and longer the more inductance. The National parts, with their high open loop bandwidth are susceptible to such inductance, which is why the data sheets says place the bypass capacitance at the part, physically as close to the pins as possible. You should take that very seriously, that capacitance needs to be as close to the pins as physically possible using a circuit board.

I think you'd be much better off with distributing those capacitors, or making multiple boards, one for each amp.

Scott

[ctardi]

I guess i didn't mention, nor did anyone ask, but the chips are from TI, and consist of opa549, opa637, drv134, and buf634.

Also, can someone double check the power section in the botom right, i'm not too clear on how it works, and didn't design it, so am not too sure on where exactly the diodes will get solderd, as I am using MURD620CT's.

[ScottRHinson]

Originally posted by ctardi
I guess i didn't mention, nor did anyone ask, but the chips are from TI, and consist of opa549, opa637, drv134, and buf634.

Also, can someone double check the power section in the botom right, i'm not too clear on how it works, and didn't design it, so am not too sure on where exactly the diodes will get solderd, as I am using MURD620CT's.

The grounding, and bypass guidelines laid out in the National data sheet are just as valid for TI parts, in fact for all analog circuitry. They aren't chip specific, just good practice.

Scott