wrong opamps for phase 45?

[duck_arse]

so I'm grinding away at a p45 on the breadboard. it was working with a dual opamp for the osc, and a single + dual for the signal. to reduce the vero layout size (by 20%), I reached for a TLE2074CN, and then spent the day looking for something which wasn't on the breadboard, ie a working opamp.

circuit


datasheet
http://www.ti.com/lit/gpn/tle2074

with the fourth amp as a working V/2 buffer, the first stage passed signal, which was being phased, to the second stage input. then the signal disappeared, and the offset voltage at the output of the 2nd and 3rd stages made up their own minds as to what they should be. they weren't 4V5 like I thort they'd be.

I tried a second 2074; I lifted the fet connections, and resistored the non-inverting inputs 2 and 3 to V/2, but still no signal. well, I say no, but I mean none from the 3rd stage, and no visible phase/wobble. the only other quads I have are TL064 and LM324, both of which worked fine-ish, although the 324 showed some nasty switching spikes (?) in the output.

so, what am I not understanding in the datasheet that is causing the non-working? what needs to be done to the circuit/values to get the 2074 and all its low-noise goodness phasing or am I stuck with the noisy old (79 date code) TL074 TL064?

The devil is always in the details.  

[edit: wrong tl0 number]

[R O Tiree]

I don't know, to be honest, but I built a P45 for a friend with a TL074 and it was quiet as a mouse.

[bluebunny]

Both the P45s I've built had a pair of TL072s.  Neither seemed to care that one '072 shared LFO duty with the signal path.

[duck_arse]

well, I played about w the 2074 tonight, and got some bizarre results. it seems to want its inputs resistor isolated from any of its other inputs or outputs. when I did a voltage follower without a resistor to the ref point, the output would "latch" (dunno if that's right). with the resistor, all fine. I can't imagine how I would get it to work in the p45 though.

[duck_arse]

so, as rg was quoted in my first post, the devil, indeed.

and he is there in detail, on page 85 of 89 in the datasheet.

to cut the story short, for some strange reason, the tle2074 won't work on my 2002 vintage breadboard, but will work on my 1979 vintage breadboard. it seems to me there is some difference in the pin shoulders or dimensions of the new chip that means contact/s are lost or not made in the newer board, when the tl064 and lm324 both work when swapped in with no other changes.

so, "now we can all get some sleep", as they say in the classics, and I have an ic for my p45.

[R O Tiree]

That's dedication... trawling through nearly 90 pages and then spotting the tiny difference in mechanical specs. Good catch.

[duck_arse]

err, no, RO T, not that sort of dedication. it was just substitution on the boards. has to then be either ic pins or breadboard connections; one ic works, another doesn't in the same spot, only leaves the pins of the "bad" ic.