[snarfusmaximus]

Hello,

I've read another thread here where someone is having an issue with the AB528 in a Radial chassis with voltage dipping and a popping sound every second. I bought an Alctron S3MkII chassis as an interim while I save for something better, and am having the same issue. I'm just wondering if anyone has run the AB528 in a Trident Deca Dent 10-slot chassis and if all was okay? I have my eye on one but want to make sure the module works fine in it before committing.

Thanks,
Emil

[JPK]

Generally this is caused by too much inrush current at power up.
But the AB528 doesn't pull a lot of current at power up so the issue must be caused by other devices in your chassis.
Try removing an other module from your chassis to make sure your AB528 is working OK.

I just saw that you solved the issue in this thread

[foxruns]

I just saw that you solved the issue in this thread

Could anyone explain the solution snarfusmaximus describes in the above linked thread? Is this solution viable?


I have an API-8B chassis and I'm experiencing the same issue. It occurs on all channels even when there are no other units in the chassis. The noise I'm experiencing seems to be similar to what snarfusmaximus describes in that thread:

 The power dipping and popping audio at 1 second intervals occurs on the 50 and 60 dB gain settings when the output potentiometer is around the 2 o'clock position and above.

For me the popping occurs in the same settings range described and quickly shifts from 1 pop a second to a whining high pitch squeal that has a faster cyclical quality to it.. 


None of the other pres in my chassis seem to be having issues and it seems to happen fairly randomly. I've tried turning off any electronics in the house that might be introducing noise to the mains. When I remove other units the pitch of the noise seems to change. Not sure if this is an issue with the chassis or with the unit.

Are there any test procedures I could perform to isolate the issue?

Regards,
Brandon

[JPK]

Could anyone explain the solution snarfusmaximus describes in the above linked thread? Is this solution viable?
These PTC resistors, also called resettable fuses, are protective device which cut off the power when too much current is pulled and then reconnect after a while when they cool down.

Before removing them you must absolutely make sure that it is not your device that has a defect. Otherwise, you will also burn the lunchbox. 

[foxruns]

Thanks for your reply JPK. So it sounds like the PTC resistors are in the lunchbox, not the pre-amp?  Do you have any suggestions on how I might be able to determine if the issue is with the preamp vs the chassis?

Thanks,
Brandon

[JPK]

Yes, the PTC resistors we are talking about are in the lunchbox.
Some of our modules also have one or two, but not the AB528.

Things you could check on the AB528:
- Swapped power transistors Q5 and Q6,
- Reversed diode,
- With the phase  switch on center (which disconnects the out TX) check the voltage across resistor R33 at power up. It should not go over 100mV.