Question about Denon DVD audio stage

[Wishmaster]

I have Denon DVD-A1 with PCM1704 converters, but many others Denon DVD players have same design audio output stage. Here are 4 (for differencial DA converters) opamps. If I good understand, these are:
- IV conversion
- Differential joining
- Filter
- Buffer ?
I not understand, what exactly is last opamp? Voltage before and after this opamp is same. Line Out go to amplifier, that have high input impedance, so currents are small.
Can I bypass this opamp for saving one opamp in signal path? If Yes, what make for if? - connect pin 5 to 7, remove R635 and C657. Any other mod is need?
What exact filter is here used?

 

[stephensank]

The opamp you need to really eliminate is the one used for the horribly damaging GIC lowpass filter, IC611/IC612. While it looks harmless on paper, it does major damage to harmonic layering & much of the rest of the sound. Just removing the chip effectively eliminates it. You can also very safely eliminate the dc blocking caps on final output, which are wildly unnecessary. The final stage is the post-filter buffer, and isn't strictly needed, but the OP275 is better at driving an output line than the OP37. I own three of these players, and they have very large potential for great sound.

 

[Wishmaster]

Thank You for answer. I have all opamps replaced with sockets. My actual setting is OPA627 - Dexa NewClassD - OPA627 - Sparkos SS3601.
So best solution will be, if I going from second opamp direcly to output? Remove R617, R635, C657, IC611, IC613 and connect second opamp output to after last opamp (or after output capacitors if I want bypass these too)?

 

[stephensank]

I don't see any info on each maker's website that gives any clue as to how one can expect the Dexa & Sparkos discrete opamps to perform. I'm utterly unimpressed with the appearance of either, but without any schematics or even the most basic specs, don't know how they expect to sell them. I would add a word of caution that, just because it's discrete, it is NO guarantee of better sound, and I've seen a few, such as some of the Bursons, that are far from stable unless used with much more care than the average chip.
As for the OPA627, this is, IMO, the most overtly *colored* sounding chip in history. Having two of them in series is a recipe for pancake syrup(audio-wise). If I use an opamp(discrete or chip), which I've been getting away from, it's always the far better OPA134 series.
While I would say that generally the fewere active stages the better, I'm not entirely sure that the diff-to-singled-ended converter(second stage opamp) should also be doing final output. May work fine, with the right chip, just have a feeling it's not the best way to go.

 

[JonSnell Electronic]

Take a look at what controls TR615 and TR616. These transistors double the gain when switched off.

 

[Wishmaster]

I tested player without GIC filter, sound is brighter, tighter bass and cleaner. In combination with Dexa and Sparkos maybe little too much bright for first impression, but after longer listening it is not bad, very detailed and accurate. I bought Dexa and Sparkos after reading many reviews and these are really very good opamps. Much better than combination AD825 and AD797 what I use there before.

JonSnell Electronic: Very good reaction. These transistors are named HGAIN on bus (same are on multichannel board named AC3-H) and connect over SN74AHCT273PW chip to DVD Processor. So last opamp is not buffer, but "High gain voltage amplifier". Now is question when is this mode used? In manual is nothing about gain, only Audio output level 2Vrms. Maybe this is for any specific audio formats.

 

[samoloko]

thank you for these tips
I would like you to confirm about GIC lowpass filter tip
does It need only simply removing of chip or there Is other action needed

about dc blocking caps at output - I like to remove all caps C661 - C672 and bypass with wire but does anyone measured dc offset before caps

did you recommend to replace some of op amps I/V, differential, output buffer with newer ones like LM4562

The opamp you need to really eliminate is the one used for the horribly damaging GIC lowpass filter, IC611/IC612. While it looks harmless on paper, it does major damage to harmonic layering & much of the rest of the sound. Just removing the chip effectively eliminates it. You can also very safely eliminate the dc blocking caps on final output, which are wildly unnecessary. The final stage is the post-filter buffer, and isn't strictly needed, but the OP275 is better at driving an output line than the OP37. I own three of these players, and they have very large potential for great sound.

 

[dazzz]

Get rid that GIC filter
they Are really
Negatively affect the sound.
Just take off
The GIC op amp
I removed
them from my 2 denon project 2900 and the 3910

 

[samoloko]

thank you for reply
did you think of checking out dc offset before big white caps and eventualy bypass them
which has better sound dvd 3910 or 2900

 

[dazzz]

thank you for reply
did you think of checking out dc offset before big white caps and eventualy bypass them
which has better sound dvd 3910 or 2900

better sound overoll 2900
in cd and dvd audio
in sacd the 3910 is the best
my project the outpute dc offset is 0.1 mv
I always check the dc offset on my project

Especially on amplifiers
I have a very expensive speakers to $ 10,000 so I'm careful in this topic
Any changes I make in the machine
Before I connector to the system I'm testing the output dc
and in amp the bios

 

[samoloko]

anyone please tell me from post 1 why I/V resistor value Is 5K6
Isn't It too high even for single chip per channel