Denon AVR 3805 ApOmp swap

The Denon AVR-3805 (7.1 channel receiver) has a very beefy ower supply, nice power amplifiers, can be connected via Denon Link III to a compatible player for digital hi-res music (HDCD, DVD-A, SACD). I am using it with a Denon DVD-2930CI via DenonLinkIII and with a Toshiba SD-6980 via analog 5.1.
The DAC's are BB's PCM1971A (PCM/DSD, voltage output, DR 113dB, TDH+N 0.001%) followed by LM811 opamps as 3rd order filters and, only on the front channels, by a switchable 0dB/+6dB level boost for HDCD made with a NE5532.
I have some free OpAmp samples from NatSemi - LM4562. Catalog data for those shows improved (vs LM833):
- noise 2.7 nV/sq.Hz versus 4
- SR 20 V/us versus 7
- BW 55 MHz versus 15MHz
- TDH+N 0.00003% versus 0.002%
- unity gain stable (both of them)
All of them are in SMD (8-pin SOIC) and I needed my trusty magnifier glass for that. And some ChipQuick solder to lift the existing cips without damaging the pads.
After removing the cover, I found that the DAC section and OpAmps is is located on the left side of the receiver, fairly visible. But... without removing the audio board, access to work is possible only for the front, surround and +6dB OpAmps, the rest are below the edge of a metal frame. I looked into removing the audio board completelly but I wasn't sure if it worth the trouble and if I can do it safelly.
I decided to work with the board in place and the receiver sitting on a side.
I have removed the first OpAmp - below it the ground trace shields the 2 sides of the cip. Nice!
The cip is for the FR and SR channels - the don't mix R and L channels in the OpAmps/DAC's. Nice again!
The only one that shares L and R is the +6dB boost OpAmp (for the fronts).
Installed all three OpAmps that I could reach and fired the test session. Sounded nice, but something was weird... Hmmm. After a few songs I fired up Beatles Whoa! Why is some voice in the left and some instruments in the right? Wasn't supposed to sound like that.
I check the board and I notice a small pice of solder stuck on the board, not touching anything. I remove it and realise that flux was holding it in place. I didn't clean the board with alcohol... stupid. Clean it with an isopropilic pad, especially arround +6dB chip. Fired up again - all good.
I looked one more time on the board - two empty places for some capacitors on the +/- 15V rails required something to be done Mosoly. Two of 68uF/35V Nichicon - Done.
How about sound? I can compare directly between the front channels and the back ones (that have still the original LM833 and can be used as separate amplifiers). It is a definite improvement of the sound. Cleaner, darker between the songs, highs from SACD are perfect.

I am happy with this mod. Or am I? Maybe I will get some LME49722 and try them on... Hmmm, I'll see when I get them how I feel about it.

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AVR-3805(800_600).JPG241.81 KB

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