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Old 12th January 2005, 10:58 AM   #1
jweber is offline jweber  Germany
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Default LM3886 GC - "Simplest Ever Amplifier Bridging"

Has anyone tried the simple bridging method described by
Rod Elliot?
http://sound.westhost.com/project20.htm

Nice when it works, but I have only two LM3886 chips left and don't
like to blow them up...

Any disadvantages doing it this way?

Thanks for your comments.
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Old 12th January 2005, 11:26 AM   #2
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You can use it, but instead TL 072 give OPA 2134 and instead both 100 k resistors give there 10 k.
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Old 12th January 2005, 12:18 PM   #3
jweber is offline jweber  Germany
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Have a look at the drawing again - it is NOT a bridging adapter!

It seems you can bridge two LM3886 chips directly with two additional resistors.
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Old 12th January 2005, 12:21 PM   #4
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Default Re: LM3886 GC - "Simplest Ever Amplifier Bridging"

Quote:
Originally posted by jweber
Has anyone tried the simple bridging method described by
Rod Elliot?
http://sound.westhost.com/project20.htm
Why don't you just use the circuit shown in the LM4780/1 datasheet, you can't get much simpler.
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Old 12th January 2005, 12:36 PM   #5
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This solution is worse, have higher distortion.
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Old 12th January 2005, 08:03 PM   #6
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which solution is worse?

1) Rod Elliots
2) Rod Eliots with OPA substitute
3) The 4780 datasheet solution


The last post was ambiguous to say the least.
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Old 12th January 2005, 08:11 PM   #7
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i'd have to assume #1. it looks like distortion from amp 1 would then get distorted by amp 2, then add to the output.
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Old 12th January 2005, 08:23 PM   #8
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Rod Elliot's article is being quoted out of context...he is addressing the simplest way to bridge a couple of commercial amps.

For scratch built DIY you would be better off just building one of the different designs discussed on this forum most often.
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Old 12th January 2005, 08:42 PM   #9
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I dunno if Rod Elliots simplest bridging adaptor is worse....


The distortion products of the non-inverting amplifier are being fed to the inverting amplifier: so those non-inverting-amplifier-distorion-products will cancell out. The only distortion you are left with are the distortion products of the inverting amp (and the diustortion of the distortion products, far to low to be significant I assume).

So.. You are left with a bridged amplifier having the same distortion specs as a non-bridged amp in halve the load..

versus...

When a perfect balanced signal is obtianed from a unballanced signal and this is fed to two equal amplifiers, distrotion of each amplifier alone is like driveing halve the load but.. the even-harmonics tend to subtract from each amplifier, while the uneven-harmonics tend to sum from each amplifier... this might even be worse...


go with Elliot, that guy never failed me once....
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Old 13th January 2005, 02:37 AM   #10
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Quote:
Originally posted by tschrama


The distortion products of the non-inverting amplifier are being fed to the inverting amplifier: so those non-inverting-amplifier-distorion-products will cancell out.

Nonsense. The distortion (and noise) from the first amp will be distorted by the second amp. You will also get intermod products on the distortion. Its a non-linear process, not just add/subtract.
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