1

First Aid / Re: lunchbox help noise and buzz.

« on: November 06, 2025, 01:49:23 AM »

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.

2

First Aid / Re: lunchbox help noise and buzz.

« on: October 31, 2025, 01:50:43 AM »

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.

3

First Aid / lunchbox help noise and buzz.

« on: October 28, 2025, 12:08:46 PM »

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

4

AB528 Microphone preamplifier / Re: The T1

« on: October 13, 2025, 05:03:17 PM »

Thanks JPK

1. ok. I admit, I misread the text about the sides.
2. But why is there a step 17 that says the same thing twice? Only difference is that the headline is Back intstead of Front? (and the addon to adjust the pins) Would be less confusing if you removed that step. 
3. Ah, I'm not at home and check the pins atm. So testing on the ((solderside) (soundskuptor side) (front side)) I should have connection if I test with a DMM. But if I test on the pins on the ((connector side) (not visible side) (back side)) I would have a problem if I get a sound from the DMM testing any pin to another?

I think I got it but. The extra step and all different names for the same thing is a bit confusing. -  Back side = not visible side AND Front side = SoundSkulptor side?

The picture on step 16 Named "front side" is on the back side.
The picutre on (not needed) step 17 named "back side" is on... also the back side.

EDIT:
Haha facepalm! I thought it was the same PCB on both step 16 and 17. I didn't see the difference on the pictures.  
Home again with DMM. Have contact between every second (ie pin 1,3,5,7 etc) on both sides. I hope that is correct.?

5

AB528 Microphone preamplifier / The T1

« on: October 13, 2025, 03:08:30 PM »

I'm on stem 16 and 17 (seems to be some errors in this manual. Looks like the same step for me) and also it says:
       Insert the 90°, 13 pins headers, long tails first, into the holes, from the bottom side, marked “Not visible”.

But it has to be on the "soundskulpture side" right?

Anyway. Soldering the pins on the backside it looks like the through-hole "silver-connecting-pads?" are so wide so it's touching the next pad?
I measured and many pins seem to have connection to each other. What should I do?

How do I post pictures?

6

AB528 Microphone preamplifier / Re: AB528

« on: October 12, 2025, 12:11:54 PM »

You must skip the holes without a pad. These pins are unused. Leaving them unsoldered will make it easier if you ever need to replace the relay in the future.

Thx. Also had questions about those.