I think just choose an opamp on spec and knowledge of the device, and do the best with it. There are too many factors that effect the impression of "sound". But it's still interesting to see what people say. You just can't just plug in a replacement and say whether the device is better or not, but one can be better in a particular circuit than others.
I blame Lord High Philosopher Abraxalito Andrew, although I have some guilt in starting it off maybe by asking the subjectivists to prove their claims.
What was I thinking?
What was I thinking?
Is my title sublime enough do you think to allow me to just wave away claims imported from Guru Ethan Winer on 'Pricing out the competition' thread?
😀
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Hi
I have a cd player that uses the Burr-Brown PCM1792 DAC chip.
For the I/V section it has 4xOPA604 & for the differential circuit it uses 2xOPA604 opamps, too.
I removed the opamps, installed dip8 sockets (to easily change them) & put 4xOPA134 for the I/V & 2xLT1028ACN8 for the differential.
So far my conclusions are, that this CD player has a much much better sound. Actually everything sounds so natural. The sound before that was somehow grainy & confused.
I don't have the schematics for the circuits used in this cd player. Does anyone of you have any tweaks to share so i can get the best out of these opamps ?
Any other recommendation of which combination to use ?
Vassilis
I have a cd player that uses the Burr-Brown PCM1792 DAC chip.
For the I/V section it has 4xOPA604 & for the differential circuit it uses 2xOPA604 opamps, too.
I removed the opamps, installed dip8 sockets (to easily change them) & put 4xOPA134 for the I/V & 2xLT1028ACN8 for the differential.
So far my conclusions are, that this CD player has a much much better sound. Actually everything sounds so natural. The sound before that was somehow grainy & confused.
I don't have the schematics for the circuits used in this cd player. Does anyone of you have any tweaks to share so i can get the best out of these opamps ?
Any other recommendation of which combination to use ?
Vassilis
Not tweaks so much as basic tests,
http://www.diyaudio.com/forums/chip...g-audio-integrated-opamps-98.html#post2988476
If you don't at least do this then you are working 100% subjectively (which is fine if you are happy doing so) and you may be unaware of stability problems.
That's not to say it is unstable... but you need to check.
http://www.diyaudio.com/forums/chip...g-audio-integrated-opamps-98.html#post2988476
If you don't at least do this then you are working 100% subjectively (which is fine if you are happy doing so) and you may be unaware of stability problems.
That's not to say it is unstable... but you need to check.
details
Name of the cd player is : Original CD2008F (chinese made - but very well built).
Playing with different types of opamps turned out in the end that, best opamps for I/V are the OPA604 (OPA134 came second after hours of listening) with OPA627 for the differential. Also a very good combination was OPA604 for I/V & LT1028 for differential (there was a noticed roll-off in high frequencies here).
The circuit follows what Burr Brown is suggesting for the PCM1792. The only addition is that this manufacturer added one 10uf mkp capacitor per channel for the output bypassed with a 0.47uf one . And instead of NE5534 & LT1028 they used OPA604 everywhere.
Look at the picture.
Name of the cd player is : Original CD2008F (chinese made - but very well built).
Playing with different types of opamps turned out in the end that, best opamps for I/V are the OPA604 (OPA134 came second after hours of listening) with OPA627 for the differential. Also a very good combination was OPA604 for I/V & LT1028 for differential (there was a noticed roll-off in high frequencies here).
The circuit follows what Burr Brown is suggesting for the PCM1792. The only addition is that this manufacturer added one 10uf mkp capacitor per channel for the output bypassed with a 0.47uf one . And instead of NE5534 & LT1028 they used OPA604 everywhere.
Look at the picture.
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Do you think that changing R3/R4 (560r) with 321r or 394r will make things better?
Why does BB suggest this kind of circuit.
It is already a difficult load for the 5534 to drive.
If you change anything then you are changing the design. Are you capable of de-bugging the amplifiers when you alter components or component values.
If you ask about changing some resistors to even lower values, then I ask you:
are you sure you understand what I said in post2011?
If you change anything then you are changing the design. Are you capable of de-bugging the amplifiers when you alter components or component values.
If you ask about changing some resistors to even lower values, then I ask you:
are you sure you understand what I said in post2011?
What i ask actually is why this manufacturer has put OPA604 all over the place & did not follow BB's design. I will not change any values as i don't have proper measurement tools . I'm just wondering if this design is ok to experiment with different opamps that are compatible.
Putting 2xopa627 at the differential stage made things sonically better, but do i need to make any tweaks to this design to take full advantage of the opa627 ?
OPA627s are internally compensated, so C19 (the 33pF over-compensation cap from pin 6 to pin5 of the LT1028) becomes redundant. In fact, it needs to be removed for correct operation of the OPA627, because pin 5 of the OPA627 is one of the offset trim terminals. It's possible that it works because 33 pF is pretty small, and it probably just adds Miller stabilization on the OPA627.
Thank you very much. Do you have any link on where i can find the best optimized circuit for the opa627 for the differential section? I will discard the 33pf capacitor. I was told that a 1uf capacitor could be connected between pin4 & 8. Another thing is that the manufacturer has chosen to put a 10uf mkp capacitor connected between pin 6 and rca output. Probably they used it to cutoff possible dc. But isn't 10uf more than enough ?
There is no optimized circuit for unknown circumstances. This is very complex. You have to know a lot of things, then you have to use oscilloscope to see if it is already optimum or not.
In the I/V stage you want an OpAmp with high enough slew rate (how much is enough is debatable). In the differential stage, depending on circumstances, imo it will be beneficial to choose a low noise OpAmp. Here is for your reference:
OPAMP - SLEW RATE - INPUT NOISE
OPA627 - 55 - 4.5
OPA604 - 25 - 10.5
OPA134 - 20 - 8
NE5534 - 13 - 3.5
LT1028 - 11 - 0.85
You see? NE5534 is a cheap opamp but it has high SR, and 13V/uS is considered as "enough" slew rate for most I/V function. And LT1028 stands out in noise. So NE5534 and LT1058 is a good combo.
All of the above OpAmps are stable at gain of 1 without compensation cap (I think) except may be NE5534, that's why you see an external compensation cap. What is the function and effect of this compensation cap, that is something you have to understand to answer your previous question.
The cap, whatever the value is, may help or it may not. This is related to too many things, such that only oscilloscope can answer what the best circuit is. Next is ear.
Without going too technical and complicated, why don't you try OPA627 at IV stage? Theoretically it is the fastest. Read each OpAmp pdf for its implementation. Remember, the circuit is for voltage feedback OpAmp, not current feedback ones (Some AD OpAmps are of CF type)
How much important the OpAmp noise spec is imo dependent on the whole CD system performance (power supply, DAC chip, etc). Basic principle is to understand the weakest link of an audio chain. You have to know for example if your power supply is giving the trouble not the chip.
If you meant why it is paralleled with smaller value cap, the answer is because you want the cap to work perfectly for all frequency range. If the 10uF is cheap electrolytic you may want to parallel with 1uF MKP (if you cannot get higher value). If your 10uF is a Gold Teflon Snake Oil Cap may be you should not parallel it with any small cap at all. This also can only been seen with oscilloscope.
5534 with compensation for unity gain results in a much lower slew rate.
Both the Philips and the ONsemi datasheets show 6V/us with the 22pF fitted.
10uF MKP is big, FKP is even bigger.
These big caps likely to have higher parasitics than very small to medium size cap packages.
The decision is whether to listen or to measure to find out if the higher parasitics have any audible effect.
Both the Philips and the ONsemi datasheets show 6V/us with the 22pF fitted.
10uF MKP is big, FKP is even bigger.
These big caps likely to have higher parasitics than very small to medium size cap packages.
The decision is whether to listen or to measure to find out if the higher parasitics have any audible effect.
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I need the really really really really best opamp to replace jrc2068..
I accept browndog adapter.. i was looking at dual LME99990 but I need to know the best "replacement" opamp for jrc2068.. 🙂
discrete is also not out of the question.. (also need the best low cost solution)
I accept browndog adapter.. i was looking at dual LME99990 but I need to know the best "replacement" opamp for jrc2068.. 🙂
discrete is also not out of the question.. (also need the best low cost solution)