This is a simple circuit intended to replace any dual op-amp in dip 8 pkg.

Short question is , is there any tendency on this part (ADA4177-4) to self oscillate? Probably not but wanted to ask.


I have a new layout that is self oscillating usually around 1Mhz.

I did read the layout notes in data sheet.

Test conditions are in a known good purpose built fixture strapped in unity mode dc.

The vacuum tube is removed and a jumper placed across pins 7-8 and 2-3 which isolates the op-amp stages. No other components in signal chain, CC regulators removed...

An external 10k resistor load is across both outputs. Comp caps are 68pf. Previous Rev of board worked perfect. This rev simply adds a buffer to each to each output.

Omission of a build out resistor is intentional as the target board would supply if required. Test voltage is +- 15 VDC.

R1 and R2 may be 1k or 10k depending on which vacuum tube is used. Oscillation is with either value without a change in frequency.

The circuits (both sides ) oscillate with inputs shorted.

Injected audio range signals pass through correctly but with added osc impressed on output.

My question is, with attached schematic in a good layout do you see any condition that would cause such oscillation?