Denon dvd-757 opamp replacement and coupling question - diyAudio
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Old 23rd July 2007, 09:35 PM   #1
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Join Date: Aug 2006
Default Denon dvd-757 opamp replacement and coupling question

hello this is my 1st post so please excuse my ignorance. i've searched this site and the web for a few days and still cant seem to find concrete information regarding this:

I'm trying to mod/improve my denon 757 cd player by replacing the generic opamp in the output/buffer stage. there is one dual opamp in the stereo output section (a 4558)
which appears to be running from a 9.6vdc single supply. I want to switch it with an OPA2134 however there're a few thing i don't fully understand. I've traced the signal back to the DSP board and it measures about 2.3vdc for both the left & right channels in reference to the PCB's ground. Next each channel hits a 10uf electro cap and a few surface mount resistors and caps to the opamp. at the opamp both input pins of both channels measure about 4.6vdc (in ref to gnd) as well as both outputs. the signal then goes through two more 10uf electros then a few transistors then the output RCA jack. at the output jack i measure only a few millivolts. Is it normal for the opamp output pins to have so much DC? Is this configuration DC coupled? I have a spare +-15vdc PSU sitting around. is it possible to run a new opamp on this supply without damaging the unit? If this setup is used would there be any DC at the opamp's output pins? I've read many sources saying any DC offset is bad but i'm still not sure in which context that applies. If anyone could post or point me to a link that might clear this up for me i would greatly appreciate it! If i haven't phrased my query well or if anyone needs more info, it's no problem. Thanks
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Old 25th July 2007, 01:34 AM   #2
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Join Date: Aug 2006

perhaps i've tried asking too much. here's the main question. can i leave the signal pins (1-3 and 5-7) of a dual op amp in the existing circuit, remove pins 4 and 8 and apply an external +- PSU to these pins and share the center tap of the PSU with the grounding plane of the PCB. can anyone foresee this doing any damage to the DVD player?
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