Recommendation for a good CMOS op-amp?

rruss · 19th October 2004, 01:51 PM

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

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

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.

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

19th October 2004, 01:51 PM	#1
rruss diyAudio Member Join Date: Oct 2004	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

19th October 2004, 03:02 PM	#2
Mr Evil diyAudio Member Join Date: Aug 2004 Location: Behind you	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. __________________ https://mrevil.asvachin.eu/

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19th October 2004, 09:32 PM	#3
andreas w diyAudio Member Join Date: Oct 2004	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.

20th October 2004, 08:36 AM	#4
djk diyAudio Member Join Date: Feb 2001 Location: USA	"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.

20th October 2004, 04:51 PM	#8
andreas w diyAudio Member Join Date: Oct 2004	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 ; )

20th October 2004, 08:39 PM	#9
EchoWars diyAudio Member Join Date: Dec 2002 Location: Left of the Dial	He knows better...he's just nit-picking. I happen to like the 5532, and it would work fine for what you intend. There are other options though.....