Eventide H90 not work properly when connected in series with other pedals

A couple of things for you to step through…
– Did you set the I/O on the H90 to line level as well (System Menu > I/O)? You said you did for the others, assuming you did, but worth double-checking

Next up is phase cancellation and unintentional comb filtering:
– What are your Kill Dry settings like through the chain? If you don’t need the dry signal back to the mixer, kill the dry signal on the H90 and go full wet-fx through the chain and blend on the mixer and deal with phase on there (assuming digital mixer) – you can do that at the algo, progam or global level; just remember if you use it for anything else and you use global/system level settings you may need to changed them.
– Are you blending the FX loop back on top of the previous dry (before send) or replacing it to output via the mixer?
On the H90
– Is it perhaps the tails (spillover) you’re missing on the delay? Try the system menu DSP Bypass against Relay Bypass.
Am assuming the chain was ok before the H90.

Just to throw something out there … have you considered adding a GFI Duophony (an extra purchase, but definitely worth it and very flexible) after the Microcosm? H90 -> Microcosm -> Duophony (LVX || or -> Mercury X)?
My stereo FX chain is Empress Zoia -> EHX Mod Rex -> EHX Super Pulsar -> H90 -> Duophony with LVX and Mercury X, but I don’t use it within a mixer send/return; I use an EHX Super Switcher (still treating it as a studio FX chain post amp/cab), and the mixer is the last touch before PA.
I would place the Microcosm in the FX insert loop of the H90 in stereo mode, but with the additional granular algorithms, the H90 and Zoia together cover most of what it can do. That H90 FX loop places it in or around the H90 algorithms.
(I have lists set up in the H90 and Zoia based on functionality and/or set requirements, some of which are specifically designed for the Meris combo, such as modulation with a short pre-wash reverb).

Alternative with what you have … if you don’t fancy a Duophony, then perhaps throw all three post-H90 pedals into the H90 insert loop and use it as the brain of that particular section, then you only have to get your I/O levels right for the H90, and the insert loop could be instrument level for the others. You can have the insert loop at instrument level (3/4) for the microcosm+lvx+mercury x and the H90 at line level (1/2) for the mixer send/return then all you’re doing is work with the H90 to get the levels right, kill the dry on the H90 and process the insert in and around your AB however you want to for each program. This would make your chain Mixer -> H90 + insert loop -> Mixer

Hello,

It is unclear what may be happening here. The H90 can be placed anywhere in the signal path without issue.

Are you sure you are sending a stereo signal to the H90? And all of the post processing is fully stereo? The effects processing may sound different if you are only hearing 1 side of the stereo image.

It may be easier to troubleshoot this issue if you email support@eventideaudio.com with some videos that demonstrate the issue. It’d be useful to see the H90 working properly as the only device in the chain, and then seeing another video that demonstrates the issue with all of the pedals in the chain.