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Old 25th July 2004, 01:58 AM   #1
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Question Idea for switchable bridge....

Take a look at the schematic and see if you think it will do what I want it to, that is switch to a bridged amp on the 'B' side when I activate the switch. I know this has been done before, but humor the new guy tring to do it himself.

If I added some gain to the buffer/inverter stage say like a gain of 2-5 and reduced the gain of the LM3875s would this increase the performance of the LMs?Would the gains add or multiply?

Is a gain of 20 enough to get full volume from regular CD level source?

Any need to decouple OPAs from LMs?

I would also like to add a DC offset trimmer circuit and possibly DC protection (shutdown on excess offset). Any one care to show me how add the circuits or link me to some? I see poeple post about there GCs having 50-100mV DC offsets, my ol' commercial Onkyo only has 10mV at idle. So, that is my goal. Actually the goal is to make an amp that sounds better
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Old 31st July 2004, 02:26 PM   #2
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Old 1st August 2004, 02:12 AM   #3
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the lm3875 as drawn is lacking a second feedback resistor (to ground). this means the lm3875's would operate at a gain of 1. you would need a gain of at least 10. most circuits try for 20.

the upper opa opamp -- what is it doing? lets say the switch is thrown. at one moment the input to the inverting input (- in) of the opa is +1V. this causes the output to go low. this means the + input will go low. because the + input is lower then the - input, the output will stay low and you will make an inverting latch. not good...

my advise it to look into either an "inverting" amplifer or a "difference" amplifer for the phase resversal.

as shown the simplist method would be to make one buffer an inverting buffer, then wire one speaker up backwards (run the wires to the wrong colored terminals). this is how car audio amplifers are set up. note that a drv134 would also work in place of the opa opamps.
if only it could be used for good, not evil...
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Old 1st August 2004, 02:14 AM   #4
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Location: SIUE, Illinois, USA

i suggest you start in the articles section, looking at the beginners guide to opamps, then the power supply section, then the wire section, then look at the projects. lots of good stuff here.
if only it could be used for good, not evil...
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Old 6th December 2006, 10:04 PM   #5
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Tsanford, my email to you bounced. Please contact me.

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