Replacement for NJM5532 (Australia)

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Hello

Nigel Goodwin

Super Moderator
If it's for an arduino, then he can used for up to 12VDC into the arduino and the on-board regulator will take care. The voltage divider to +input can be split to level-shift to 2.5vdc and gain can be set to achieve full dynamic range of the ADC.

Using a reasonably "high end" op amp ($4.00 oh, my!) will make it seem like the$6 postage is less shocking than paying $6.00 for a$0.80 chip.

Remember, he is not making a million of these, using a high end chip will set him back \$3 more than a crappy chip and he won't have to wonder where the noise is coming from.
Even a 'crappy' chip is higher quality than the circuit requires.

I don't really see the relevence of feeding 12V in to the Arduino and using that?, if you're going to add a higher power supply there's no issue with most opamps, but that wasn't the question. And of course I'm only guessing at Arduino, due to the 5V supply.

Nigel Goodwin

Super Moderator
The schematic in the first post shows an electret mic as the input. It has a 1k resistor feeding it noise from the 5V supply.
The gain of the opamp is low so that the power supply noise is not amplified too much.
The output level from the mic is low since the 1k resistor value is too low.
I'm surprised you've not commented on the pointless paralleled coupling capacitors?

rjenkinsgb

Well-Known Member
The actual performance will depend very heavily on the type and quality of the electret capsule used.

They vary tremendously in both output level and noise level; saying there is not enough gain is specious, as some capsules have high enough output to directly feed a general PA system with no extra gain; I have a couple of early electret mics [very expensive ones, back in the 70s, around £60 each] that have nothing but a cardioid electret capsule with a resistor, capacitor and AA cell. They worked very well.

A normal PC microphone socket is intended to connect directly to an electret mic capsule; no extra electronics or components involved, beyond a cable and plug.

Re. the caps, presumably the guy decided it must have 1uF coupling and only has 0.47's in his parts box...

Nigel Goodwin

Super Moderator
Re. the caps, presumably the guy decided it must have 1uF coupling and only has 0.47's in his parts box...
Except there's no reason whatsoever for it to have 1uF, a single 0.47uF is already too large.

In my experience the early electret mikes (with AA battery) gavce similar levels to a normal dynamic mike, which of course they were intended to be used alongside, with the standard 600 or 50K inputs. I too used a couple of them, alongside Shure dynamic mikes.

audioguru

Well-Known Member
The two paralleled 0.47uF coupling capacitors will pass earthquake frequencies that you can feel but cannot hear.

rjenkinsgb

Well-Known Member
Who know what the guy was thinking...

My guess is that he'd decided to aim for near flat response down to around 20Hz, which is roughly what 1uF and 47K gives.
(Though I've not had my first coffee yet, so it's possible my brain is misfiring still & that's way off...)

I doubt the capsule has flat response anywhere near that low, but it's the only reason I can think of.

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Nigel Goodwin

Super Moderator
Who know what the guy was thinking...

My guess is that he'd decided to aim for near flat response down to around 20Hz, which is roughly what 1uF and 47K gives.
(Though I've not had my first coffee yet, so it's possible my brain is misfiring still & that's way off...)

I doubt the capsule has flat response anywhere near that low, but it's the only reason I can think of.
You're missing the blindingly obvious, the 'designer' didn't have the slightest clue what he was doing

And response would be about 3.5Hz for 1uF.

rjenkinsgb

Well-Known Member
You're missing the blindingly obvious, the 'designer' didn't have the slightest clue what he was doing

And response would be about 3.5Hz for 1uF.
Absolutely, I'm just guessing!

And as you say, I was miles off on the frequency response..

Nigel Goodwin

Super Moderator
Absolutely, I'm just guessing!

And as you say, I was miles off on the frequency response..
Admittedly, if I'd got a 0.47uF in stock, I'd probably have used one - sod the silly frequency response - but putting two in parallel is just showing you don't have a clue what you're doing

In fact, I might well have stuck a 1uF in there, as it's my 'small capacitor' of choice, and I have a bandolier of 2000 of them - but I wouldn't have stuck two in parallel!

gophert

Well-Known Member
Admittedly, if I'd got a 0.47uF in stock, I'd probably have used one - sod the silly frequency response - but putting two in parallel is just showing you don't have a clue what you're doing

In fact, I might well have stuck a 1uF in there, as it's my 'small capacitor' of choice, and I have a bandolier of 2000 of them - but I wouldn't have stuck two in parallel!
A non-polarized 0.47uF is not commonly found in a junk box and 0.1uF is a more common value for that application. I am guessing some confusion and/or typo is involved and the circuit "designer" (circuit drawer?) "meant" to write 47nF, instead of 470nF. I see nF / uF conversion errors all the time in the two robotics & electronics clubs that I mentor.

It is also interesting to me how students insist on drawing schematics based on C and R parts that are in the parts drawers instead of putting the desired value in the schematic and correcting on the fly as they assemble the breadboard. In other words, I would have put 0.1uF on the schematic and used two 47nF parts on the breadboard if I was out of 0.1uF parts.

That is just the "autopsy hypothesis" I would start with if I was investigating the root cause of the part selection error.

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