Will this design work for a LM3886 100w BR amp?? - diyAudio
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Old 18th October 2007, 08:13 PM   #1
Minion is offline Minion  Canada
diyAudio Member
Join Date: May 2006
Location: Cowican Bay , vancouver island
Default Will this design work for a LM3886 100w BR amp??

Hi ,here" is a design I came up with for a Bridged 100w LM3886 amp but I want to know if there are any Glareing errors or anything I forgot to add to the curcuit....

It uses a Dual opamp at the input , One of the duals is in a Unity gain Non-inverting Config and the other one is acting as a Unity gain Inverter...Each of the inverted and non-inverted outputs of the opamps go into a Non-inverting LM3668 IC.....

a couple of questions:

I have the gain of each LM3886 set at 20x ,Is this too high of a gain setting or should it be set to say 15x.....

Is the output inductor nescessary in this type of Bridged config??

any suggestions or comments??


PS: the PCB is about 6.7in x2 in...Also I don"t have the schematic as when I design something my self I usually have the curcuit in my head and I just go and design the PCB.....
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Old 18th October 2007, 10:51 PM   #2
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Join Date: Apr 2005
Location: In the Wild, Wild West
Gain is not too high for the LM3886 but the total gain is going to be 40x. Just depends on what level the input is and if this is enough or way too much. If too much, lower gain can improve THD but keep in mind that a gain of 10V/V is the minimum for stability with the LM3886 so maybe 15V/V on each side or something.

Not sure how the coil is in there since only a PCB. The bridge amps I have built using the LM3886 did not have any compensation like such. You know that the op amps aren't really needed, right? Check the LM4780 DS for a schematic.

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Old 18th October 2007, 11:12 PM   #3
Minion is offline Minion  Canada
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Join Date: May 2006
Location: Cowican Bay , vancouver island
Yes I know the Opamp isn"t needed but when doing a Bridged mode you need highly matched resistors to offset any Gain errors so I figured this would be easier, Pluss the Values of the resistors in the Bridged schematic are not ones I have on hand, There are also a couple less Capacitors in the signal path useing this method ,also I will be running the Preamp off of +/-15 volt rails so I have the supply allready there to run the Inverting / Non-Inverting opamp....

I will probably be useing it as a Bass or guitar amp....I might also use it to power a Subwoofer for my studio as my Brother is giveing me a 200w Subwoofer.......

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Old 19th October 2007, 11:08 AM   #4
AndrewT is online now AndrewT  Scotland
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Location: Scottish Borders
Hi Minion,
do you realise that with a bridged arrangement, each chipamp works as if driving a load of half the impedance of the actual speaker you choose to hook up?

For a target of 100W into 8ohm speaker, each amp has to try to deliver 50W into 4ohms.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 19th October 2007, 04:16 PM   #5
Minion is offline Minion  Canada
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Join Date: May 2006
Location: Cowican Bay , vancouver island
Yes I realize that....I will be useing either an 8 ohm speaker or 2 4 ohm wired in series....My PSU will be about +/-26v DC which should be OK for driveing 4 ohm loads....

Thanx Folks....Cheers
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