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Old 18th February 2019
  #19
Here for the gear
 

I'm having the same issue with my GAP Pre-73
And allot of this I can't understand...I was wondering if you would be able to explain in simpler terms?

Thanks so much!




Quote:
Originally Posted by LeeYoo View Post
Hi.
Reading through all these posts, I think it's time to eliminate things.

Some extracts from previous posts:

"hum...even with nothing other than my headphones plugged into it"
This rules out a groundloop from other gear connected to it.

"Turning the gain down or off doesn't affect the level of it..."
This rules out hum picked up by the INPUT transformer.

"I have moved it from all my other gear and even plugged it in to other outlets in the house"
This rules out hum picked up from other stationary sources.

"perhaps the outlet in my room isn't properly grounded"
The unit uses two-wire AC, without ground.

"That transformer can create a field that gives off hum"
True. Clean 50/60herz, not 100/120 with overtones.
And if you move the unit to another room, you should notice a difference, because the power brick would be in a different place.

"the only thing i have figured out is when a jack is half plugged into the line out port the buzzing goes away from the mic out"
The output transformer might drive all the outputs. If you short one by plugging a jack halfway in, the sound on the other outputs might also disappear.

"I plugged a homemade xlr cable into the mic in that was not wired right"
If a blown input causes the hum, wouldn't you be able to change the hum with the gain control?

"so the best thing i can do is get it modded?"
To me "modding" is to try to improve quality, not to fix "problems".

"Try changing the ac-adapter. It's probably the cause of the issue"
If we rule out external sources, then the external mains transformer is the only source of hum left.
The transformer's AC is most likely rectified and regulated with an internal LINEAR supply.
They are very sensitive to sagging AC.
e.g. if the supply would not output 24volt AC, but say less than 18volt AC, you would hear 100/120herz sawtooth voltage dips.

What's your mains voltage/frequency/country.
Post a picture of the label on the supply..

Leo..