DOD FX75B - Stereo Flanger - Outputs nearly 100% out of phase

[fixproaudio]

Just had this unit come in and the stereo outputs are nearly completely out of phase even when the pedal is in bypass. Is this typical for some pedals? I see a feedback from U5A to U5B which seems like it would result in a direct out of phase signal...is this remedied some how? I just don't get it. Schematic attached.

first thing I tried was swapping the LM1458s as one is used only for the effects section in hopes that maybe I would see some change, but nothing changed.

Unsure on this one.

Any thoughts?

 

[Tubetec]

That seems to be how many of these pedals derive stereo output , One channel is a copy of the input signal but out of phase , the other effect channel has the modulation applied . Boss chorus does it the same way .By using a mono jack either half inserted or fully plugged into a balanced mixer input you can very easily flip the phase of either signal .

 

[ccaudle]

Just had this unit come in and the stereo outputs are nearly completely out of phase even when the pedal is in bypass. Is this typical for some pedals? I see a feedback from U5A to U5B which seems like it would result in a direct out of phase signal...is this remedied some how? I just don't get it. Schematic attached.

first thing I tried was swapping the LM1458s as one is used only for the effects section in hopes that maybe I would see some change, but nothing changed.

Unsure on this one.

Any thoughts?

The signal path goes through U1A (inverting), then through U5A (inverting) to OUT_BOTTOM, then from the output of U5A to U5B (inverting) to OUT_TOP.
So yes, there is an extra inverting op-amp stage between the two outputs, so they will always be opposite polarity.

 

[fixproaudio]

Thank you for you're replies and for keeping a sane man from going crazy.

Since only half of U1A is used can I feed U5B to it and flip the phase there? I know it sorta defeats the purpose, but the original design just doesn't work at all for the application the user has for it. If so, can I just do a follower? Where would I tie ground?

 

[ccaudle]

Since only half of U1A is used

There are two symbols labeled U1A, so presumably one of those is really U1B.