AD797, OPA134 or discrete buffer stage?

ventle · 11th May 2008, 06:51 PM

Hi everyone,

Im looking for a useable Op-Amp or possibly a simple discrete circuit to use as an input buffer on an amplifier I'm planning. The buffer stage should be unity gain and preferrably low noise and low distortion.

I've currently been looking at the AD797 and OPA134. Judging by the datasheets (and price...) I understand that the AD797 performs better with respect to distortion and noise. However, as the AD797 is quite costly (this is a somewhat unusual application where I'll need as much as 12 Opamps) compared to the 134, I'm wondering if it's worth the extra expense? Using AD797s will cost US$110, while the same number of 134s will get me there for around $30.

Also - I've been looking for a simple buffer stage as an alternative - does anyone know a suitable circuit that does the same job as the opamps in this context?

Horexx · 11th May 2008, 09:50 PM

Discrete OpAmp, amplification -1.

ventle · 11th May 2008, 10:31 PM

Thanks for replying, but wouldn't it be a bad idea to put an inverting buffer stage in front of a non-inverting amplifier?

Also, any idea on distortion, PSRR and other performance parameters compared to an IC OpAmp? Since it has only passive loads/current sources on the input stage, wouldn't power supply noise get quite easily injected into the signal path?

Horexx · 12th May 2008, 06:03 AM

Specs are not known to me,.
This is no opamp design for optimizing any spec. With the named transistors you could build a MM-amplifier. Because of the low amplification distortions are low. I would take a stabilized power supply anyway

It is a design to built with little effort and cost. It can be modified for +1.

john curl · 12th May 2008, 06:09 AM

The Hafler circuit looks like something we would have put together 40 years ago. It is not bad, but flawed.

peranders · 12th May 2008, 06:43 AM

Have you checked the LME49710, pretty cheap and pretty good. AD8610 is very nice also, in fact you have lot's of good opamps to choose from. OPA227 good.

peranders · 12th May 2008, 06:47 AM

Quote:

Originally posted by ventle
Thanks for replying, but wouldn't it be a bad idea to put an inverting buffer stage in front of a non-inverting amplifier?

Also, any idea on distortion, PSRR and other performance parameters compared to an IC OpAmp? Since it has only passive loads/current sources on the input stage, wouldn't power supply noise get quite easily injected into the signal path?

If you choose a modern high performance opamp you don't have to worry about much really.

The first question: An inverting amp is a bit sensitive for the signal source and it's output impedance (including a pot) and the input impedance can't be made particulary high. The obvious advantage isn't so obvoius.

john curl · 12th May 2008, 06:57 AM

Very few op amps really work well at unity gain. I usually design them out. Fet followers are better, sonically.

peranders · 12th May 2008, 07:32 AM

That might be so but I think you must also consider how advanced the PS must be and also the skill of the builder. A simple JFET source follower is rather easy to get going, hard to fail.

Mooly · 12th May 2008, 09:57 AM

Do you find any difference sonically in inverting or noninverting OpAmp configuration, and particularly at low gains ?

11th May 2008, 06:51 PM	#1
ventle diyAudio Member Join Date: Jan 2008	AD797, OPA134 or discrete buffer stage? Hi everyone, Im looking for a useable Op-Amp or possibly a simple discrete circuit to use as an input buffer on an amplifier I'm planning. The buffer stage should be unity gain and preferrably low noise and low distortion. I've currently been looking at the AD797 and OPA134. Judging by the datasheets (and price...) I understand that the AD797 performs better with respect to distortion and noise. However, as the AD797 is quite costly (this is a somewhat unusual application where I'll need as much as 12 Opamps) compared to the 134, I'm wondering if it's worth the extra expense? Using AD797s will cost US$110, while the same number of 134s will get me there for around $30. Also - I've been looking for a simple buffer stage as an alternative - does anyone know a suitable circuit that does the same job as the opamps in this context?

12th May 2008, 06:43 AM	#6
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Have you checked the LME49710, pretty cheap and pretty good. AD8610 is very nice also, in fact you have lot's of good opamps to choose from. OPA227 good. __________________ /Per-Anders (my first name) or P-A as my friends call me

12th May 2008, 07:32 AM	#9
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	That might be so but I think you must also consider how advanced the PS must be and also the skill of the builder. A simple JFET source follower is rather easy to get going, hard to fail. __________________ /Per-Anders (my first name) or P-A as my friends call me

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11th May 2008, 10:31 PM	#3
ventle diyAudio Member Join Date: Jan 2008	Thanks for replying, but wouldn't it be a bad idea to put an inverting buffer stage in front of a non-inverting amplifier? Also, any idea on distortion, PSRR and other performance parameters compared to an IC OpAmp? Since it has only passive loads/current sources on the input stage, wouldn't power supply noise get quite easily injected into the signal path?

12th May 2008, 06:03 AM	#4
Horexx diyAudio Member Join Date: Dec 2007	Specs are not known to me,. This is no opamp design for optimizing any spec. With the named transistors you could build a MM-amplifier. Because of the low amplification distortions are low. I would take a stabilized power supply anyway It is a design to built with little effort and cost. It can be modified for +1.

12th May 2008, 06:09 AM	#5
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	The Hafler circuit looks like something we would have put together 40 years ago. It is not bad, but flawed.

12th May 2008, 06:57 AM	#8
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Very few op amps really work well at unity gain. I usually design them out. Fet followers are better, sonically.

12th May 2008, 09:57 AM	#10
Mooly diyAudio Member Join Date: Sep 2007	Do you find any difference sonically in inverting or noninverting OpAmp configuration, and particularly at low gains ?

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