[Consigliere]

I'm finished building my AB528 and it sounds absolutely amazing. 

One thing that is weird (probably has nothing to do with this unit but) is that when I have it mounted in Bento10s it sounds fantastic but in my Bento6 (not s model) it's alot of weird noises going on. Nothing "gain related" but a constant pinkish noise and a buzz/tone sound. It's both depending on which slot in the box it is installed in (worst close to the transformer) but not constant better in the slots to further away, and also phantom power. The buzz/tone is mostly detectable with fantom power. And turning it on the sound shifts up in pitch like a spike and goes down again to aprox 185hz or so. (with an visible harmonic around 3-400 something.)

I've never heard these noises before but I only had eq's and compressors in it before. (this is my first 500 preamp)

I know I should probably ask elsewhere but I found other threads in this forum about Fredenstein Bento noise so I was hoping to se if I could get some help solving it. I want to use this bento6 for portable use. Is it a grounding issue? Transformer issue? Is it worth mod'ing or repairing? It also feels like the pcb-connection doesn't "slide in" that deep in the bento 6 comparing to my bento10s. Could that be an issue? Is it possible/worth it to try find a replacement transformer for the lunchbox, and which one in that case?

Any advice is welcome and also if you had a similar experience and how you tackled the problem. 
Thanks //Anders

[JPK]

Bento power supplies are known to be very noisy, at least for the early models.

I've never heard these noises before but I only had eq's and compressors in it before.
That is because a pre has more gain.

Is it a grounding issue?
Probably not.

Transformer issue?
They are switching mode so you won't be able to change the transformer.

Is it worth mod'ing or repairing?
Replacing the internal PSU by an external one, a lot of work. But the best solution would probably be to replace the lunchbox (sorry for the bad news).

[Consigliere]

thank you for your input JPK.

Searching the net I found a link to a document hosted by soundskulptor but it doesn't exist anymore... Is it still available and something to look in to?
http://www.soundskulptor.com/docs/cp5176-bento6-mod.pdf

thanks.

[JPK]

This modification was for the CP5176 compressor. It has now been integrated into it for a long time.

[Consigliere]

SOLVED

It was a ground issue after all. And I learned a valuable lesson
Lifting the ground on both of my Fredenstein units makes a lot of noise. (Like crazy much)

By accident the switch on my Bento6 were set to "lift ground" (which is something I usually try if noise is present to reduce it) In this case it was the other way around. With "no lift" its dead silent and I'm happy as a proud father with my two newly born AB528 twins. They are crazy good!

Thank you for all help JPK.

[JPK]