My work! LM4766 Full balanced

[bbp]

To build a stereo amp, I plan to use 8*LM4766!
I just finished PCB project with Protel DXP
Each board uses power regulator build with 5-10 mA current source and LM431 (adjust it to 32V)

Here is some PICs about it ,but I have not make real PCB out yet

 

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more pics

PCB in 3D

 

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sch

my english is so so so poor

 

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Pcb

Make this PCB out, and ...

here is the bottom side

 

[peranders]

Re: sch

my english is so so so poor

I haven't seen any signs of this yet Your english is quite alright.

Are you really usre about the parallel connection? Don't you need any resistors in series as the rest of the world does?

 

[bbp]

Re: Re: sch

my english is so so so poor

I haven't seen any signs of this yet Your english is quite alright.

Are you really usre about the parallel connection? Don't you need any resistors in series as the rest of the world does?

The post#1 shows the real schematic ,and post#3 only shows the theory,not the one I really want to build


On the PCB, I will use 4 * 0.47-1 omega resistors on each board.

 

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PCB is on

here are both the side of PCB

 

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PCB2

Get a clear view

 

[peranders]

Have you really tested to connect the inputs of LM1876 they way you do?

I really suggest you take a look at AN-1192!
http://www.national.com/an/AN/AN-1192.pdf

 

[bbp]

......

Many thanks for your suggestion,actually I have not test it before,I made the schemartic through my experience,but I will test the circuit later,and then make a report .

 

[peranders]

It will most likely not work when you connect the inputs in parallel. Why don't you try it with a couple of normal opamps first?

 

[AndrewT]

Hi,
each of the balanced inputs sees a resistance of 22k//680r=660r
Is your pre-amp able to drive 680ohm impedance to about a volt to get maximum output?
Have you considered where the input offset currents flow?

 

[bbp]

Hi,
each of the balanced inputs sees a resistance of 22k//680r=660r
Is your pre-amp able to drive 680ohm impedance to about a volt to get maximum output?
Have you considered where the input offset currents flow?

Many OP can drive 600ohm impedance easily, for example,LM4562

But I have not considered the input offset before, that's really a problem...



Thanks

 

[AndrewT]

Many OP can drive 600ohm impedance easily, for example,LM4562

I agree that many opamps can drive 600ohms but NOT easily.
I think only a few can achieve good 600ohm capability.
Check how much distortion degrades as load impedance is lowered.
Remember also that the NFB is parallel to the output and both must be driven. Then add a bit of extra current feeding any parallel capacitance (this reduces the HF impedance even further).