Dual-stacked op-amp current draw

[GGBB]

I just did the Monte Allums mod on a BOSS GE-7 for a friend. Part of the mod replaces a single 4558 with two OPA2134 stacked using an adapter. The current draw skyrocketed to ~105mA. I pulled the adapter and put the 4558 back in and the pedal drew ~12mA. With the stack adapter in with only one OPA2134 - ~20mA (I tried both chips in both positions - all the same). Pedal works and sounds just fine - in fact, I'd say it even sounds ever so marginally better than his second GE-7. What gives? Is this normal?

[PRR]

> Is this normal?

"Never" short two opamps directly together. If there is the least difference between them (and there ALWAYS is), they fight each other for control. Typically they strain to the max. The "typical" max current for each of those chips is 35mA-45mA, so 70mA-90mA for two, plus 4mA+4mA for idle current, 98mA.

The short-circuit rating is "infinite" so it "should" run this way a long time. How long? Even TI probably does not know. It is not a normal condition and may not live a million hours.

[EBK]

Here's the overdramatic Hollywood version:

PRR: There's something very important I forgot to tell you.

GGBB: What?

PRR: Don't stack the op amps.

GGBB: Why?

PRR: It would be bad.

GGBB: I'm fuzzy on the whole good/bad thing. What do you mean, "bad"?

PRR: Try to imagine all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light.

EBK: Total protonic reversal.

GGBB: Right. That's bad. Okay. All right. Important safety tip. Thanks, PRR.

[anotherjim]

This is one of those "Boutique" tricks that makes me smile.
If you're going to do it, at least insert some low value resistors to buffer each op-amp's output from the others  - I suppose 47-100R range. Of course, this isn't easy with piggy backing or a side-by adapter board. With a board, you can cut the traces from each pin 6 and place the resistors on the back between pin6 of each chip and the leadout hole the cut traces were going to.

[GGBB]

> Is this normal?

"Never" short two opamps directly together. If there is the least difference between them (and there ALWAYS is), they fight each other for control. Typically they strain to the max. The "typical" max current for each of those chips is 35mA-45mA, so 70mA-90mA for two, plus 4mA+4mA for idle current, 98mA.

The short-circuit rating is "infinite" so it "should" run this way a long time. How long? Even TI probably does not know. It is not a normal condition and may not live a million hours.

Thanks Paul. I was mostly concerned that I'd made a mistake or that this circuit doesn't play nicely with stacked op-amps. So as long as this is to be expected - so be it. I already told my friend about the current draw - I'll let him know about the potential longevity issue - I'm sure he won't care.

[PRR]

> I'm sure he won't care.

In stomp-land, that is a valid answer. Why I put "never" in quotes.