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NE5532 Buffer
NE5532 Buffer
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Old 27th October 2017, 08:42 AM   #71
Mooly is offline Mooly  United Kingdom
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NE5532 Buffer
If you mean the 100pF as shown in the diagram in post #2 then it could actually be very important. Its purpose is to roll off and prevent unwanted high frequencies entering the input of the chip.
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Old 27th October 2017, 08:34 PM   #72
russc is offline russc  England
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Rightly or wrongly I put 10uF from +ve to 0v & -ve to ov.
I put 0.1uF ceramic between + & - pins of op-amp on reverse of pcb.
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Old 27th October 2017, 09:13 PM   #73
doctormord is offline doctormord  Germany
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remove the 0.1uF.
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Old 28th October 2017, 03:02 AM   #74
samuelj is offline samuelj  United States
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Thanks Mooly, I intend to keep the 100pF.


Russc, thanks for sharing.

Ti datasheet for NE5532 recommends 0.1uF low ESR ceramic +V to Gnd and -V to Gnd.
10uF seems good too as it is often used in this.

Maybe it is overkill to add the 0.1uF cap across the power supply pins, but don't think it required to be removed once in place.
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Old 28th October 2017, 08:12 AM   #75
AndrewT is offline AndrewT  Scotland
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think of the decoupling as the sole charge to power the chip for a few microseconds.

The two HF decoupling capacitors are connected together.
The outers are connected to the power pins.
This +power pin > cap > cap > -power pin route must be very short to minimise inductance.
The junction between the two caps is the Power Ground.
All output current from the chip must return to this Power Ground and into the capacitor which was the current source.
The above considers the capacitor as the source of current and that current MUST RETURN to the capacitor.
One capacitor (of the pair) sources the +ve half-wave output current. The other capacitor source the -ve half-wave output current.

That HF decoupling handles the ultra short duration current transients.

Repeat the process for the MF decoupling using higher capacitance and allowing slightly longer circuit routes. The junction between the MF decoupling capacitors needs to be connected to the junction between the HF decoupling capacitors.
The amplifier now has a low impedance "point" for the HF transients and a low impedance "point" for the MF transients.
All the chip output current has to return to this low impedance "point".
So we have two HF capacitors and two MF capacitors and the output return lead all meeting at this point.

There are two more connections. The amplifier output Zobel only operates at high frequencies and needs to connect to this low impedance point.
Finally we have the PSU Zero Volts feed to make up the seventh connection.

I think of a power amplifier on the same lines. The amp/opamp outputs a current and that current MUST RETURN to it's Source.
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Last edited by AndrewT; 28th October 2017 at 08:16 AM.
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Old 28th October 2017, 09:23 AM   #76
samuelj is offline samuelj  United States
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Andrew T,

Thanks for your sharing.

For the purpose in hand, ie NE5532 unity buffer, what value would you recommend for the HF and MF decoupling capacitors.

And is a zobel network really required in this application?
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Old 28th October 2017, 12:26 PM   #77
AndrewT is offline AndrewT  Scotland
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The recommended HF and MF decoupling is usually in the manufacturer's datasheet.
It is unusual to need an Output Zobel for opamps.
Discrete opamps may well require an Output Zobel.
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Old 29th October 2017, 06:12 AM   #78
ammel68 is offline ammel68  United States
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NE5532 Buffer
I'm quite surprised that this thread has garnered 77 posts for a NE5532 op-amp based buffer that in the end will only sound "fair" at best.
Simply amazing...
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Old 29th October 2017, 07:17 AM   #79
DRONE7 is offline DRONE7  New Zealand
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Quote:
Originally Posted by ammel68 View Post
I'm quite surprised that this thread has garnered 77 posts for a NE5532 op-amp based buffer that in the end will only sound "fair" at best.
Simply amazing...
Perhaps your pockets are deeper than mine then......
If you've nothing to add in a positive way then maybe you should refrain from passive aggressive posts.....
Other posters are genuinely trying to help... pay attention and you could learn something from them...

Last edited by DRONE7; 29th October 2017 at 07:23 AM.
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