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GAP Pre-73 Hum problem
Old 8th July 2013
  #1
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GAP Pre-73 Hum problem

Hey all, I've read other threads on this same issue but have yet to resolve my problem and wanted to see if there were any other ideas.

My new GAP Pre-73 has a persistent hum coming out of it even with nothing other than my headphones plugged into it. Turning the gain down or off doesnt affect the level of it nor does the output level. Its just there. I have moved it from all my other gear and even plugged it in to other outlets in the house to see if perhaps the outlet in my room isn't properly grounded.

I don't know what else to try and I dont think I can return this unit so i'm kinda stuck. Any help would be great!!!! Thanks!
Old 8th July 2013
  #2
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Jimsi's Avatar
 

I am sorry, I think the GAP line is pure garbage...I own both compresser and preamp 1st generation and I am waiting for the eternal fire coming from both... just bad build quality
Old 9th July 2013
  #3
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thanks for that.. but are there any ideas of how to fix the problem?
Old 9th July 2013
  #4
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guitarboy94's Avatar
 

Is the plug away from the preamp? That transformer can create a field that gives off hum when the unit is near the power source. My original Gap had that hum problem. My new MKII version does not. Maybe they corrected that issue?
Old 9th July 2013
  #5
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thanks but the transformer is away from it. and its an MKII to boot!
Old 10th July 2013
  #6
Try changing the ac-adapter. It's probably the cause of the issue.
Mine was causing hum when it had it too close to other adapters
Old 10th July 2013
  #7
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LeeYoo's Avatar
 

Hi.
The first thing to do if you have hum is to find out if it's pure 50/60 herz, or 100/120herz.
Clean base mains frequency hum comes from a transformer, and single and/or double the frequency with overtones comes from the electronics.
AFAIK, there is NO mains transformer INSIDE the unit that makes a mains stray field.
(Lineair) voltage regulator hum can also come from sagging mains power.
No country in your profile, but you didn't do something silly like running a 230v transformer on 110v.
Leo..
Old 10th July 2013
  #8
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Quote:
Originally Posted by deaed View Post
thanks but the transformer is away from it. and its an MKII to boot!
Try to move the preamp it self too. They are sensitive to magnetic fields. The problem is the output transformer. The same goes for a carnhill yransformer. It the same problem with all units with this type of transformer, even a neve.

Sent from my SGP321
Old 19th July 2013
  #9
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100hz

ahhh! its buzzing at 100 hz! so its the electronics? what can i do? 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 port but then i cant hear the mic. not sure what that means.. please any help would rule. this thing is a brand new $350 piece of crap if i cant fix it. thanks!
Old 19th July 2013
  #10
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also, i realized that i should mention that i plugged a homemade xlr cable into the mic in that was not wired right (the 1 & 2 wires were backwards on the female end). could this have fried something? the mic in still works there is just the buzz... this was the first cable i used so i dont know if it was like that before!
Old 19th July 2013
  #11
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Slikjmuzik's Avatar
 

I have 2, fully modded by Zen pro with tantalum caps, motorolla output transistor and Carnhill. The Carnhill in them is new, only had them like this for about a month. Neither with just the stock transformer or with the Carnhill have I heard any noise ever. My best guess is that the wal-wart has something wrong or you need to plug it into a better power conditioner. Just a guess though. I think these fully modded ones are absolutely smokin. In fact, usually, I record my GF with a Burl and from time to time a 1272. Mind you, I also have some old Telefunken pres in here too. Last night she picked the Pre73's over all of them...and as much as I wanted the chain to be 1272, Burl or Tfunk, the Pre73 beat them all out last night. Horses for courses I guess...maybe stock they suck, but tt modded they were more than usable and fully modded they hang with some of the best...easily...best of luck...
Old 20th July 2013
  #12
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hmm, so the best thing i can do is get it modded? you sure that will fix it?
Old 20th July 2013
  #13
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LeeYoo's Avatar
 

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..
Old 20th July 2013
  #14
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MarkF48's Avatar
Quote:
Originally Posted by deaed View Post
this thing is a brand new $350 piece of crap if i cant fix it. thanks!
Brand new should be under warranty. Why are you even trying to figure it out? Either contact the seller for an exchange or the manufacturer for an exchange or repair. If you mess with it you'll only void any kind of warranty you may have.
Old 20th July 2013
  #15
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Lenzo's Avatar
Quote:
Originally Posted by MarkF48 View Post
Brand new should be under warranty. Why are you even trying to figure it out? Either contact the seller for an exchange or the manufacturer for an exchange or repair. If you mess with it you'll only void any kind of warranty you may have.
If it's brand new and you can return it, do it and buy something else. On the gap I had a button broke the first time I pushed it in.....as mentioned, I think their build quality is weak.
L.
Old 20th July 2013
  #16
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MarkF48's Avatar
Quote:
Originally Posted by Lenzo View Post
If it's brand new and you can return it, do it and buy something else. On the gap I had a button broke the first time I pushed it in.....as mentioned, I think their build quality is weak.
L.
Probably regret saying this..... I have a GAP Pre73 mkII and have had no problems with build quality or functioning. (knock on wood). It perhaps isn't up to the build of a Summit 2BA-221 (more $$$) I have, but at least on the surface the GAP seems OK. I did however have an issue with a new Joe Meek 3Q, so that makes me a bit wary of their products.
Old 20th July 2013
  #17
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Slikjmuzik's Avatar
 

Quote:
Originally Posted by deaed View Post
hmm, so the best thing i can do is get it modded? you sure that will fix it?
No, not necessarily saying that. I'm saying that for me it made sense to do so. I knew that by getting it modded would make it more fail safe. Not because they fix anything wrong, but because when they open it up to mod it, if there's something wrong, they find another one that's working perfect and mod that. I knew someone here in America would touch my units if I got it modded, so for me spending the extra $99 initially, then $150 for the Carnhill, was totally worth. With that said, you shouldn't 'have' to mod it to get a good working unit with no noise.
Old 20th July 2013
  #18
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I have the MKII version, and after excitedly hooking it up the first time, I powered it on and heard a low level hum. I was beside myself, trying all kinds of things to get rid of it. I finally realized it was the damn wall wart and the way it was laying. The slightest move set off the hum, and it took a while to find the perfect delicate way to lay it so I didn't get the horrible hum.
Old 18th February 2019
  #19
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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..
Old 19th February 2019
  #20
Here for the gear
 

I went through 3 of them, some QC problem there. Then I sent the last one to Warren for the Zen mod. It came back better than ever and is still working 2 years later.
It’s worth the money.
Old 6th March 2019
  #21
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I have 2x GA Pre EQ units racked up next to each other and they both went at the same time. Think I have the Mk 1 with the metal switches, no black push buttons. I emailed their support about the hum and received this:

The LM317 regulator has probably broken down and must then be replaced. This would be indicated by the voltage output being about 32V instead of 24V.

A 47 ohm / 1W resistor should also be added before the regulator.

I hope this helps

Thanks, Stuart
Old 27th April 2019
  #22
Gear Nut
Quote:
Originally Posted by Stuart72 View Post
The LM317 regulator has probably broken down and must then be replaced. This would be indicated by the voltage output being about 32V instead of 24V.

A 47 ohm / 1W resistor should also be added before the regulator.
I got the exact same response.
I got a whiff of frying electronics, now it's got a buzz that renders it unusable, seems like a flaw in the circuit.

I got a cheap replacement PSU to try after reading about buzzing units on forums. https://imgur.com/a/EJyaj
https://www.reddit.com/r/audioengine..._the_easy_way/

Quote:
Originally Posted by zachaction View Post
Epilogue:

Bo at Golden Age sent me this photo to demonstrate where and how the resistor goes. I replaced the 24V regulator and added this resistor with the parts Tarheel mentioned, and the noise is gone! It's kind of hard to tell in the pic, but the right leg of the regulator is lifted off the board.
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