Lm4781 Pcb

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Looks Good;) I would like to add the soft start suggestion on page 15 of the data sheet instead of the mute switch and LR combination on the outputs as suggested under Reactive loading on page 20.

National are still sending out samples of these without charge (for now) If not PM me and I may have one.

Can you post the actual files instead of screen dumps?

Cheers


David L
 
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It's Express, I doubt he can send files.

Mastero

Can't give concrete feedback as have not looked in-depth at the files. Since it's double sided It wil be difficult to do it in one pass. However layout looks good, all parts seem to be there.

The chips are available from D-K at $11, doubt you can get them in India. Would recommend you order samples or take up Wombat's very generous offer.

The datasheet lists out the requirements for power, which varies as per load impedance. Would think about 27 volts (off a 20 volt transformer, easily available) per rail should be enough unless your speakers dip very low, in which case you need a lower voltage.

If you're cooking these up, would like to take up two boards for myself as well. We can discuss offline. I have two of these critters lying around and was planning an active bi-amped or tri-amped setup (entry level) using cheaply and locally available drivers.
 
Hello,

Samples from National is on its way.... :)

As for the pcb i have made two 4781 cuiruts on one board giving me 6ch

Each cuircut has its own BR (MUR860x 4) both the BR are connected to the 25-0-25 out from a ETD transformer rated at 5 amps..

So i et +/- 35vdc from the BR well within the specifed limits.

PCB is PTH double sided gone for making..

I ave sent for two Boards for making.. you can one if i can have one of you 4781 chips :) Boards are of top quality professionally made.

shall post image of the boards when they arrive.

Mastero
 
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Hi :D

Would love to offer you one of mine, but I only have two chips, one for left channel, one for right. I would have been willing to pay money for the boards, which we could have discussed. If you're still interested you can mail me, or else it's cool. And I'm not going to ask National for any more samples... I think I've already abused the program with my first order.

Not sure about the 35 volt rails though, they seem to be right at the limit of the chip. The datasheet lists 70 volts as the absolute maximum supply voltage, and 72 volts without signal. Sounds risky to me, but they're your chips, so you take that call. Also keep in mind the chip will be putting out a lot of heat, so dissipation will also be a challenge.

For 4 ohms the recommended supply is +/- 20 volts so I would assume they can take some abuse and be used with about 25 volt rails, or even 27-28 volts (which is the supply recommended for 8 ohm loads), but not much more.

Have fun!!
 
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