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Kustom Profile One 100w PA -loud bang!

Kustom Profile One 100w PA

Shortly after unit is switched on a loud bang can be heard through the speakers. Turning the master volume down/off does not alter this.
Alternatively there is often a continuous screeching noise but this does not persist. At other times the unit works normally for hours and at other times there is nothing at all from the speakers.
I am not too technially minded but I have been told this may indicate a ''relay fault'' (whatever that is! )
Is this reasonably easy to fix or am I looking at buying a new amplifier?

Thanks for looking.

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I have three of these in my amp repair shop. one of them does exactly this. as well, the other two are suspect to the same issue. i believe it is low quality leaky or shorting caps. are you using the xlr inputs or 1/4 inch inputs? so far, these are working good thru the 1/4 inch jacks, but the xlr inputs are squeely with feedback and i get that loud bang/pop from one of them. kustom wants me (my shop) to be an authorized repair station for them. i want to be able to resolve these three amps before i accept. if they are a nightmare to deal with, then i will tell them no way.
i will post back with in the next week with more results and hopefully i will have precise solution with parts and procedures.
yost amplifier repair

Posted on Jan 21, 2010

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  • thebrother May 04, 2010

    Anyone with these issues email me thru my website contact page The "screeching" is really called oscillating and its a simple fix. also the popping is a simple fix. the serial number of your profile head, the first two digits are the year it was made, probably close to an 03-xxxxxx. there are a few components to add on to the pcb, but its very easy. its a known issue thru Kustom. i am an authorized repair station for Kustom.

  • Jimmy Seville
    Jimmy Seville Jan 01, 2011

    What happen to the post about a possible fix?

  • nwsurfcamp Jan 25, 2011

    I dunno, man. I'm still waiting.
    Don't know what to do or where to go !
    ~ Raj


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Thebrother, thanks for helping with this issue. I also have a sick Profile One head; symptoms are a variant on what sympbrili described. I get also get a screeching noise coming through both outputs; it was intermittent at first (would appear when amp was turned on and slowly fade in volume and eventually disappear). That recenty changed: now the amp operates properly when first turned on, but after a few minutes the screeching appears and now doesn't go away. Even before seeing this Fixya discussion I suspected a leaky cap due to the symptoms, but have no clue as to where in the signal chain to look. Any insight you come up with willbe greatly appreciated!

Posted on Jan 27, 2010

  • mikeymars
    mikeymars Aug 17, 2010

    The "bang" issue is caused by the failure of two current limiting resistors in the amp power supply. They are undersized and over time weaken, to the point were they can open or drift enough to allow enough power flow to cycle the amp off and on. That casues the "bang".

    To fix this (or as I did, to prevent it from starting in the first place):

    Unscrew the four screws at the bottom of the head and remove the frame containg the amp "guts".

    Looking at the system, you will see three boards: the large one that is directly behind the controls, a small one up on top behind the controls and a third one that "tucked" inside the frame above the transformer. The area we need to deal with is in that third board.

    Looking down at the top of the frame, the area with the two problem resistors is on the right side of inside board, right in the middle. They are resistors R34 and R40 (both 100 ohm one watt). These need to be replaced with beefier parts, specifically 130 ohm 2W metal oxide resistors.

    There are two ways to do that:

    - The involved approach: completely remove the middle board to get access to the existing resistors, which are removed and replaced with new ones.

    - the easier approach: leave the middle board in the frame. On the top (trace) side of it, cut the the traces at the left (going towards rear of frame) side of each existing resistor. Then attach the new resistors on the trace side, going "around" the.existing resistors.

    Specifically, solder the right side of the new resistors to the right side solder point of the existing ones; then solder the left side of each new resistor to the point to the left of where you cut the trace.

    This results in the old resistors being disconnected from the circuit (only attached to it on one side) while the new ones fully are attached . This process takes all of five minutes and actually is better, since it allows you to place the new resistors so they are "out in the open," which helps with heat dissipation.


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I have learned quite a bit about this PA.

First, understand that the power amp is always on and always at full output (100W) to the speakers. What you adjust for volume is really a sub fader that has the 5 individual inputs assigned (hardwired) to it. You also can control the Playback volume but this is simply another source that has been summed to the output of the "Master" sub AFTER the EQ and internal FX are applied. Since the amp is always on and at max, any interruption/drift to the power supply will result in noise regardless of the input levels.

The addition of 2 caps (47uF 50V) across the input side of each of the +/- 15V regulators will take care of the squealing noise. Add one cap to each regulator across pins 1 + 2 (cap’s neg to pin 2 on each).

There are also 2 current limiting resistors that are undersized and fail. While I have not experienced the "popping" in my unit I believe it is one or both of these resistors opening, or drifting enough to open the power flow enough to cycle the amp off and on, hence the "pop". They are R34 and 40. Originally 100 ohm 1W they should be replaced with 130 ohm 2W metal oxide resistors. When I checked my original 100 ohm ones both showed the signs of excess heat and one was down to 57 ohms. I suggest you mount the replacement resistors on end so that they have better air flow around them to help with the heat dissipation.

If you need to replace components in the speaker cabinets you should look at Goldwood GW-6024 woofers and GT-1016 tweeters. I believe these will fit without needing to modify of the cabinets and their specs are very similar to the originals.

I have no affiliation with Kustom so what I say is not authorized by the people who designed this thing. I am just a guy who can read a circuit and has a brain. Hope this helps.

Posted on Jul 02, 2010

  • nwsurfcamp Dec 09, 2010

    I have a Kustom Profile One PA System.
    Have a friend that replaced the resisters to fix the 'popping sound'.
    All was good for 4 months,until last night.
    Wierd !
    The loud popping sound came back,just like before,every 4-5 seconds.
    I need to get this fixed,permanently and correctly.
    By someone that knows this system.
    Help ?
    ~ Raj


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Posted on Jun 23, 2011

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  • rccomber Aug 14, 2011

    My kustom 100 would make loud static for 4 seconds after turning on, then no sound - regardless of inputs. After reading these posts, I removed the power amp board, retouched every solder joint, plugged it back together and voila - works just like it should - great sound again. Thanks for pointing out the problems with weak solder joints. Hoping I don't have to do the other boards also as they are much harder to get to.

  • Stan Searing Jan 20, 2012

    This fix seems good on the unit we had that popped. The two 100 ohm resistors had been replaced with higher wattage ones, but the unit still popped. Raising them to 130 ohms and adding caps on the regulator inputs and outputs solved the problem. I suspected that it is the negative regulator that was having the problem, but I added caps on the inputs and outputs of both regulators. Note that the unit I worked on has 47 uF caps on the regulator inputs (factory installed on the PC board). It also had .1 uF output caps (also factory installed on the PC board). The input caps are electrolytic, and could decrease in value over time, causing problems. But output cap is also undersized per the Fairchild 7915 datasheet. Note that the datasheet for the negative regulator calls for larger caps than the positive regulator.
    One other point, when I first opened the unit, I found that the screw holding the negative regulator to the frame (a poor-mans heat sink) was a bit loose. Adding fresh heat sink grease and tightening the screw helps some, but it also needed the extra caps.
    Changing the resistor to 130 ohms is a good idea, as the voltage on the regulator inputs was 34 volts (which could easily go over the 35 V regulator spec in a high line voltage condition). The 130 ohm resistors give you a few more volts of margin.

  • Pat Finnigan
    Pat Finnigan Apr 04, 2014

    Spot on, Stan! Replaced the 100 Ohm resistors w/130's, added the 47ufd caps, and it's back among the living. Many thanx for going to such lengths in this forum, as there is NO service material out there for this thing. Kudos!


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I've had the same problem with a kustom one amp that came in to my shop. The -15v 100ohm resistor was fried and took out the .01uf film cap next to it (nice burn mark on the side). After replacing both, the unit runs fine for a few minutes, but a shorted load from the front control panel is causing the resistor to burn up again. (when i disconnect the 5pin plug to the front it runs fine and plugged in the -v drops considerably) Without a schematic I'm scrapping it, but would be nice to hear if anyone has dealt with that additional issue.

Posted on Jul 16, 2013

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The problem I've had was a static noise over powering the audio output. Bruce Collins of Mission Amps replaced the two resistors as recommended for the pop sound and touched up the solder connections. It seemed to work for awhile until two weeks ago and it completely static out. Having no schematic for this amp,
Bruce replaced the chip nearest to the main volume knob. He replaced the chip with a higher grade. ( you would to contact him at for the specific chip) Anyway, we used the Kustom last Friday without any problems. I'm keeping my fingers crossed, lol. Also Bruce put a dummy load on the amp to make sure nothing was weak on the board. Other than that, its working so far with no static sound.

Posted on Feb 20, 2013

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