Di buzz?

[pucho812]

First time I had to do this at the current studio spot. Producer wanted to record guitars direct to pro tools. Then reamp the pro tools outputs abs re-record them.
No biggie.
Di is an old westlake di using a utc transformer. It’s passive
It sounds quiet as a church mouse.
The reamp tracks had the usual guitar amp buzz which was deemed unusable.
So we switched it so that we had the thru on the di feeding the guitar amps. Another common thing.
Here is the puzzler.
When we did the guitars this way, we had extra buzz when the di was connected to the desk. The entire time the di path to the desk, to pro tools and back had zero buzz. The guitar amps had typical expected buzz if we plugged guitars like a strat into them without the di.
so I am pondering what would cause a different harmonic buzz when the di is connected to the desk then when it’s not?
it’s clearly audible and different frequency then the typical guitar to an amp thing.

 

[Bo Deadly]

Is there DC path when reamping or is there a transformer isolating? Is pin 1 at the desk connected to the guitar ground?

My first pass would be to run a cable from the desk to whatever line level transformer isolator at the amp and try that with and without ground lift if it has it.

 

[pucho812]

only transformers would be in the reamp box or in the DI.
Any lift of pin 1 did not elevate the issue, when swapping around passive DI's after the first sign of noise, there was vaping degrees of eliminating the buzz that was in addition to the standard guitar amp buzz. Since session was moving, I'll have to wait till after Tuesday to see if I can recreate the issue