Decoupling/bypass & signal path capacitors for op-amps (NE5532 in Aiyima A07 vs. TPA3255evm)

[007Shortz]

Hi all,
I wanted to know if op-amp rolling is a thing. So I changed the standard NE5532 with LM4562 in my Aiyima A07. Result: I couldn't notice a difference.
But I noticed an odd op-amp decoupling in the Aiyima. There was only one 0.1uF cap close to the NE5532. So I added 10uF close to the op-amp as practiced in the TPA3255evm . My impression was an improvement in sound. Aware of confirmation biases and doubts I wonder if someone modified the amp the same way and made some measurements (THD+N or SINAD)?

 

[BR52]

The 0.1uF is good practice. More is not really necessary, but if you feel better……

 

[LTig]

I'd say confirmation bias. The 100 nF cap prevents RF instability, and for damping of power supply ripple the 220uF is good enough. Its distance adds some resistance into the power supply connection which would lead to a very small power supply voltage modulation related to the output current of the 5532. That however should be suppressed by the 5532 itsself (PSRR).

 

[DHT 845]

Hi all,
I wanted to know if op-amp rolling is a thing. So I changed the standard NE5532 with LM4562 in my Aiyima A07. Result: I couldn't notice a difference.
But I noticed an odd op-amp decoupling in the Aiyima. There was only one 0.1uF cap close to the NE5532. So I added 10uF close to the op-amp as practiced in the TPA3255evm . My impression was an improvement in sound. Aware of confirmation biases and doubts I wonder if someone modified the amp the same way and made some measurements (THD+N or SINAD)?

Very often I added 10uF (wima poly) to 0.1uF in various places in DACs, amps, op-amps, PS stabilization. In many cases improovement is easily noticeable.

 

[DHT 845]

I'd say confirmation bias.

No way. For 100% it is noticeable. In blind test 10 out of 10.

 

[007Shortz]

The 0.1uF is good practice. More is not really necessary, but if you feel better……

Texas Instruments seems to feel better

 

[007Shortz]

I'd say confirmation bias. The 100 nF cap prevents RF instability, and for damping of power supply ripple the 220uF is good enough. Its distance adds some resistance into the power supply connection which would lead to a very small power supply voltage modulation related to the output current of the 5532. That however should be suppressed by the 5532 itsself (PSRR).

It could be, that the 220uF is part of the 12V regulator and there is a small inductor between cap and 5532. Sadly I have no schematics of the Aiyima A07.

 

[007Shortz]

Very often I added 10uF (wima poly) to 0.1uF in various places in DACs, amps, op-amps, PS stabilization. In many cases improovement is easily noticeable.

A 10uF WIMA needs some space

 

[solderdude]

Very often I added 10uF (wima poly) to 0.1uF in various places in DACs, amps, op-amps, PS stabilization. In many cases improovement is easily noticeable.

Then it should be very measurable.

It is best practice to follow the manufacturer datasheet recommendations for decoupling and PCB layout when mentioned.

 

[007Shortz]

Then it should be very measurable.

It is best practice to follow the manufacturer datasheet recommendations for decoupling and PCB layout when mentioned.

In the data sheet of LM4562 the same. 0.1 + 10uF ceramics as close to the op amp as possible.

 

[solderdude]

Then it makes sense to use it that way.
Would be very easy to undo the mod and measure performance with and without the extra cap.
Such is the difficulty with observations before and after a modification when there is no reference.

 

[DHT 845]

A 10uF WIMA needs some space

WIMA MKS2 is not so big

 

[BR52]

For decoupling I prefer ceramics because lower inductance.

 

[chuckt62]

That 10uF/16V MLCC cap has 12VDC on it so needs to derated 50-75% for DC bias.

 

[LTig]

In the data sheet of LM4562 the same. 0.1 + 10uF ceramics as close to the op amp as possible.

In the datasheet of the NE5532 it's just a 0.1 μF ceramic. Hence an additional 10 μF is not required, except when the designer of the circuit thinks so and adds it.

 

[LTig]

No way. For 100% it is noticeable. In blind test 10 out of 10.

In which application?

 

[007Shortz]

In the datasheet of the NE5532 it's just a 0.1 μF ceramic. Hence an additional 10 μF is not required, except when the designer of the circuit thinks so and adds it.

The TPA3255evm was designed by Texas Instruments. It uses NE5532 in the input stage. The designers thought it would be a good idea to add 10 μF to the 0.1 μF. So why does TI think the additional 10 μF is necessary? Does it improve the performance?

 

[chuckt62]

That would depend on the power supply and PCB design. Also, the Aiyima is a consumer product in a cost sensitive market. TI is particularly concerned with the BOM cost of their EVBs.

 

[Cbdb2]

I'd say confirmation bias. The 100 nF cap prevents RF instability, and for damping of power supply ripple the 220uF is good enough. Its distance adds some resistance into the power supply connection which would lead to a very small power supply voltage modulation related to the output current of the 5532. That however should be suppressed by the 5532 itsself (PSRR).

The .1u on the power pin is not for instability its to filter RF out of the DC, the PSRR becomes low at these high freqs.
From: https://www.ti.com/lit/an/sloa069/sloa069.pdf

When a capacitor is used for decoupling, it is connected as a shunt element to carry RF energy
from a specific point in a circuit, away from a circuit power pin, and to ground. Ideally, the
impedance of the capacitor to ground should appear as low as possible to the RF energy that
needs to be rejected. It is important to know the frequencies that are causing problems and to
select the right capacitor(s) to eliminate those frequencies

 

[Cbdb2]

Very often I added 10uF (wima poly) to 0.1uF in various places in DACs, amps, op-amps, PS stabilization. In many cases improovement is easily noticeable.

So you just wilynily add caps?

Also from:https://www.ti.com/lit/an/sloa069/sloa069.pdf

Misconception number 2: Most designers think that when poor decoupling is suspected,
increasing the value of capacitance will produce more attenuation. The exact opposite is true.
When poor decoupling of high frequencies is suspected, decrease the value of capacitance (or
preferably, do the homework and look up the series self-resonance)