ground loop between two unbalanced outboard gear..

[Matt Syson]

If the 'wallwart' is indeed just a regular transformer (which it probably HQAS to be if the two units use AC to derive the split supply internally, THEN the current drawn by the units will cause a voltage drop on the skinny power wires which in turn may well force some of the current through the analog connections, (made worse because they are unbalanced). Two transformers (or a single transformer with two ISOLATED outputs) is most likely the way to go. A DIY approachwould be a dual secondary 16 Volt transformer (baby cousin to JR's six output unit).

 

[Cqwet Dbdfte]

you can still check the isolation between the AC mains ground and the transformer secondary with a DMM on the AC current range. It should be microamps.
Use shielded AC mains cords. They are cheap.
Even a secondary wire from your transformer should be shield. I do not see the point of having AC fields around sensitive signal wires.
+1 for separate transformers.
In a pinch you can also use DC to power the gadget (unless it contains another transformer) as the DC will go through the rectifier.
The DC voltage should be around 1.4 times the AC value.

 

[JohnRoberts]

you can still check the isolation between the AC mains ground and the transformer secondary with a DMM on the AC current range. It should be microamps.
Use shielded AC mains cords. They are cheap.
Even a secondary wire from your transformer should be shield. I do not see the point of having AC fields around sensitive signal wires.
+1 for separate transformers.
In a pinch you can also use DC to power the gadget (unless it contains another transformer) as the DC will go through the rectifier.
The DC voltage should be around 1.4 times the AC value.

The sku probably rectifies the ac wall wart to generate split supplies.

If you feel uncomfortable probing around mains voltage DON'T... Life is short and about the only thing you might learn is what a mains shock feels like. (if you live to remember it)

JR

 

[Studiogearlover]

Thanks guys... i will skip the "probing around" and getting into the transformer etc.. lesson learned from all of you, and many thanks!

Will buy more AC supplys but maybe a better ones... not that easy to source these...i could only get one particular type here (the one pictured)...

one more thing...is it also normal that this PSU is rated 16VAC but I measure 21VAC with no load...? this is because no load there right?

 

[Khron]

is it also normal that this PSU is rated 16VAC but I measure 21VAC with no load...? this is because no load there right?

Yes and yes.

Details: https://sound-au.com/articles/xfmr4.htm#res

 

[RoadrunnerOZ]

On the 201 the Preamp input is unbalanced (Ring to Ground TRS socket) greater than 20K impedance 30dB gain, designed for guitars, bass etc low level not for line level, the Balanced/Unbalanced input is 10K impedance active balanced - the In/Out switch on the front panel bridges the Bal/Unbal TRS Input to the Bal/Unbal TRS Output. The 206 has a similar switch on the front panel. I’d test with both in bypass.
The interconnect between the two can use a TRS cable or T&S cable and the Bal/Unbal Out to Bal/Unbal In.
The 206 should not feed into the Preamp input of the 201.
If you’re getting loud hum when not having the 206 going into the 201 Preamp but the Bal/Unbal Input then it’s more than likely there is a connection to ground via the AC>DC power supply in each unit which may be out of phase causing ground currents. The 202 uses 16V AC to create a +15/-15 balanced power supply with 7805 and 7905 regulators common ground so it’s possible the 201 is similar - not sure the 206 is the same but as they all use the same type of AC supply and have high output capability it’s likely.
If you check the AC voltage on one of the spare connectors with both units connected it should not fall below 16V AC.
As previously suggested I’d be using separate supplies.