What's the function of this?

[stef1777]

Hi Folk!

I'm analysing a circuit from a pre-amplifier. I don't have the schematics. Not all component are represented on this home made diagram.

Does someone understand the use of IC400 in this circuit?

Thanks for your help.

 

[EC8010]

It's an integrator that is performing the task of DC servo and holding the DC at the output of the second IC at 0V. Quite why they've chosen to use an OPA2134 for that function, I don't understand. The servo op-amp is usually chosen for its low DC offset rather than good audio quality.

 

[stef1777]

Great thanks. I was thinking too for a DC servo but I was confused as they use an 2114 for the "audio signal" and an 2134 for the DC...

Do you will have a recommandation to update both opamp?

I was thinking to an AD8620B for the IC400 and 2134 (or something else) for IC403.

.

 

[SY]

Quite why they've chosen to use an OPA2134 for that function, I don't understand. The servo op-amp is usually chosen for its low DC offset rather than good audio quality.

My guess is that, the way this circuit is configured, any integrator grunge will be fed directly into the non-inverting input with no attenuation. So op-amps which are particularly suitable from a low-offset and low-bias-current standpoint might not be optimal.

 

[stef1777]

What about AD822 for IC400?

 

[EC8010]

My guess is that, the way this circuit is configured, any integrator grunge will be fed directly into the non-inverting input with no attenuation. So op-amps which are particularly suitable from a low-offset and low-bias-current standpoint might not be optimal.

Good point, I've no doubt that you are right. It's a trade-off between good DC performance and LF noise.