[gavinbirss]

I come across a a circuit but need some help on what seems
to be a TO-92 component. A transistor ? Most likely, but what
value and what type and more importantly for what purpose.
(what is its function ?)

The component is connected to pins 1,4,5.

Look at the following pictures and tell me more.

Maybe PPL and PPR can help.

here is the pin out of the AD797 :

Here is a picture of the preamp board :

Here is a another picture of the preamp board :

Here is a schematic :

I had some ideas of adding to this circuit a pair of BUF634T's per
channel to have a headamp / preamp.
Gavin

 

[morsel]

The mystery component is a trim pot, connected to the offset null pins to adjust the DC offset of the opamp. The spec sheet suggests using 20k.

 

[Joobu]

The circuit doesn't strike me as particularly good. First of all, the op-amp is used in inverting configuration. Not the best choice since non-inverting configuration would be able to isolate potentiometer impedance. All the impedances are extremely close, 5.1k-15k, which can lead to interaction with the pot.

Just my 2e-4 cents

 

[gavinbirss]

Thanks morsel

I am quite surprised that it could be a pot since I was hoping
that it was a transistor.

Gavin