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-   -   Recommendation for a good CMOS op-amp? (http://www.diyaudio.com/forums/solid-state/42843-recommendation-good-cmos-op-amp.html)

rruss 19th October 2004 01:51 PM

Recommendation for a good CMOS op-amp?
 
I'm trying to add pre-amp outputs to my Denon receiver. The intent is to add a buffer in parallel with the final amplifier stage in the receiver to effectively "port-out" the pre-amp signals without loading them.

I've gotten great recommendations on building an op-amp buffering stage, but the recommendation was to use a 5532 op-amp. This BJT op-amp may have an input impedance that loads the pre-amp stage more than desired.

Can anyone recommend a CMOS op-amp with excellent audio characteristics? Again, my goal is to buffer out the pre-amp signal without loading it internally...

Thanks,
-Russ

Mr Evil 19th October 2004 03:02 PM

I think a CMOS op-amp would be overkill. A normal FET-input op-amp would give a high enough input impedance. Of those, OPA604 is alright, or OPA627 if you have cash to spare.

andreas w 19th October 2004 09:32 PM

The load of ANY op amp is more than 1Mohm|| a few pf and is at high frequencies less than a few inches of cable.
Use any OP that sounds good.

djk 20th October 2004 08:36 AM

"The load of ANY op amp is more than 1Mohm"

Read the data sheet for a 5532, they say 300K typical but only guarantee 40K.

peranders 20th October 2004 08:39 AM

Re: Recommendation for a good CMOS op-amp?
 
Quote:

Originally posted by rruss
Can anyone recommend a CMOS op-amp with excellent audio characteristics?
I'm afraid but there aren't any good CMOS opamps good enough for high quality audio (correct me if I'm wrong). Why don't you choose any JFET opamp? You have tons of them.

In fact almost any audio opamp bipolar and JFET will do.

What are you demands for "loading"?

peranders 20th October 2004 08:42 AM

Quote:

Originally posted by djk
"The load of ANY op amp is more than 1Mohm"

Read the data sheet for a 5532, they say 300K typical but only guarantee 40K.

Note this is _without_ feedback. With feedback it is higher and you can't use the opamp without feedback, not for audio at least.

peranders 20th October 2004 08:47 AM

Re: Recommendation for a good CMOS op-amp?
 
Quote:

Originally posted by rruss
Can anyone recommend a CMOS op-amp with excellent audio characteristics? Again, my goal is to buffer out the pre-amp signal without loading it internally...

You need

input impedance > 10 kohms, 100 kohms is good

output impedance < 1 kohms, 100 ohms is good

Speed, 5-50 V/us is normal

Noise <10 nV/sqrHz

Many opamps will fit this description

andreas w 20th October 2004 04:51 PM

Load impedance of NE5532 is 30 - 300kohm alright, but referred to what. Of course from pos input to neg input, elemetary electronics gives that this resistance is multiplied with the
open loop gain. This means that the Real input impedance is enormous. It is one thing to read specs, yet another to understand them ; )

EchoWars 20th October 2004 08:39 PM

He knows better...he's just nit-picking.:devilr:

I happen to like the 5532, and it would work fine for what you intend. There are other options though.....


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