[Filburt]

Alright, so I need to replace the NJM2100 op-amp in my PCDP since I'm doing major mods on it for fun. Anyhow, I need something that runs on single supply (5v), is decently quick (over 15v/usec slew), has decent bandwidth, doesn't use too much power, is not too high on input bias current, is rail to rail preferably, and is low noise and distortion.

So far I've found the OPA2350, but it's a CMOS op-amp so I'm not sure it's a good idea to use it. It isn't particularly low power, though, and the distortion looks okay though they just quote the 0,0006% figure instead of giving me the raw numbers like they do on many other op-amps (grr). Input voltage noise is fairly low, though (5nv/rhz) especially considering the tiny bias current.

The OPA6822 looks kind of cool but it's not R-to-R and requires a rather large 8uA bias current. While it looks like it has rather exemplary audio performance, this seems a bit high on bias current and I'm not sure I want to go with that when the 2100 was only 100-300nA bias current.

 

[Jazper]

hmm would it be silly to suggest building a small railsplitter and tacking it on?

 

[Filburt]

Quote:

Originally Posted by Jazper hmm would it be silly to suggest building a small railsplitter and tacking it on?

Probably, since the rest of the circuit is built around using a single supply (e.g. there is an offset being applied, decoupling caps, etc.). Any op-amp can technically be run in a configuration like this, but single supply op-amps are much better optimised for it.

 

[Filburt]

Eh, noticed the CMRR is 76db. Might be too low for this application

Although, the current op-amp in it has a CMRR of 74.

 

[nikongod]

a lot of the oem pcdp opamps are designed with lower power consumption more than sq in mind...

i will say, power consumption is a secondary concern to having a pcdp that sounds better for most. get the better sounding chips.

 

[Filburt]

Quote:

Originally Posted by nikongod a lot of the oem pcdp opamps are designed with lower power consumption more than sq in mind... i will say, power consumption is a secondary concern to having a pcdp that sounds better for most. get the better sounding chips.

Well, I'm not so worried about supply current. Mostly worried about the input bias current as I don't want to go orders of magnitude above what the current op-amp is at as I don't know how the rest of the circuit will take to it (the current op-amp is at about 100-300nA bias current). The OPA2822 looks great performance wise for use in something like a PINT, but it isn't rail-to-rail and so that may hurt dynamic range at +5v supply, and it requires an 8uA bias current which is roughly 30 times what the current op-amp requires.

I think the THD+N on this op-amp is better on the 2350 than my DAC anyhow, and it actually has pretty low input noise compared to a lot of the op-amps we use for our amps, and it swings within 10mV of its rails which is pretty sweet for +5v supply as that could help maximise dynamic range when combined with the low noise and relatively low distortion (0,0006% THD+N). I just need to make sure I'm not missing something here.

Unfortunately, it's hard to find a chip that will meet all of the requirements for a portable. I've been looking through a couple hundred datasheets and this is the best one I've found so far in terms of meeting everything, but maybe there's something better out there.

Edit: Nevermind, the typical CMRR is not 76db but ~90db for around the supply voltage it'll be at. Stupid typos in the info page >