Required Characteristics of Buffer/Servo Opamps

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Hi there,

There has been much discussion on the required characteristics of opamps. Undoubtedly, the ultimate decisions about any opamp application is in the listening.

My question is specifically about dual opamps.

What are the required characteristics for a dual in which 1/2 is the servo and the other 1/2 is the buffer? Are settling time, lownoise and high slew rates as critical as they are in I/V applications?

The same question applies to "mix" dual opamps used to combine balanced signals into unbalanced signals.

Thanks for the info:)
servo amps

I am not sure what you are doing circuit wise, but servo amps generally operate in the sub audio range because: 1) you don't want to hear any corrections the servo is making and 2) the things sevos are trying to correct usually happen quite slowly. So your servo amp should be quiet in the sub audio range. This sort of rules out FET input opamps since their input FETs will exhibit 1/f or flicker noise. (1/f means the lower you go in frequency the higher the noise level.) But if you are servoing a low level signal you might need the hi-z input of the FET op amp. A compromise might be needed. Unless space is critical or there is some other over riding reason for using a dual opamp I sugesst you use a seperate opamp for the servo circuit. This will allow you to change the servo and the audio opamps seperately to optimize whatever you are trying to do. The problem is you basicly want the opamps optimized in different frequency bands. (audio and sub audio)

As fot the "mix" opamp if you are trying to mix audio signals I suggest using an opamp designed for audio.
Dual opamp

Hi Fet head for the info.

I have a servo/buffer combined dual opamp on my sony SCD audio board. It originally had the ad712 in there and I want to use an adaptor to use 2 different opamps in this location.

If I use a brndog adaptor, and a soic/dip adaptor, can I use an ad712 on one side for servo and a ad825 on the other side for the buffer?
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