Microphone to GuitarPedal-Looper problem

[lars-musik]

Hi folks,

I am trying to construct a little box that lets me use guitar pedals with a dynamic microphone. The basic idea is to couple a microphone preamp with a dry-blend circuit. The output would remain unbalanced, if need be, a DI box can be added offboard. Now I found this little NE5532 preamp by ESP that looks nice and I already have a board for Sabrotone's splitter mixer with a phase invert switch, so this should be used to mix the pedal fx in.
However, I cannot wrap my head around how I'd go about merging the grounding schemes of the preamp's bipolar power supply and the looper. My first attempt was this:
The 7660S power converter (to achieve the +/-12V for the preamp) and the power for the looper, both connected with their respective power ins to the 9V psu jack. Grounds of both circuits are connected via the enclosure connected. However, that doesn't work when connected. The preamps amplifies and the looper works when turned to dry but a pedal to the loop cannot be mixed in. Some DCish scratching from the pot and increasing silence.
Also, when I directly connect "SEND" and "RETURN" of the looper, signal is vanishes when the blend-pot is turned towards the loop (no matter, how the phase is switched).

I see that the "GRD" in the preamp is ½ of the supply, so this is usually my "VB". But should
Where did I go wrong?

Would it be better/easier/functioning when I convert the preamp to unipolar supply with a voltage divided "VB"?
Thanks!

[Kipper4]

I've got a headache now.
Block diagram and what you built schematic might help Lars.
What does the audio probe say.
Do the volts look right?
How you doing anyway?
Rich

[lars-musik]

Dear Rich,

first of all, congratulations are in order. My guess is, it's your birthday today and even if I am wrong: Happy DIYStompboxes anniversary. Ten years – how time flies, right 😊?



The schematic above is what I built. All the building blocks work on their own. Now I realised that the machine works if I do not connect the looper's ground to the enclosure (where the XLRs are grounded). Need to look in that a little more.

[Kipper4]

Thanks Lars.