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Kustom X MPA Monural Power Amp [message #26715]

Wed, 23 May 2018 13:29

jammy5152
Messages: 62
Registered: May 2018
Location: Georgia

Member

I just recenlty got a Kustom X Monural Power Amp 130 rms @ 8 ohm and when I got it hooked up through a mixer and microphone, it started good but after a while it started with a soft hiss and then gradually got louder until the hiss was LOUD and unbearable so I just turned it off...
Using freeze spray to try to isolate it did not do much good in locating a bad component...
Would like someone to given me ideas in repaing it
It uses a 5065 board which I was told
Thanks

[Updated on: Wed, 23 May 2018 13:30]

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Re: Kustom X MPA Monural Power Amp [message #26716 is a reply to message #26715]

Wed, 23 May 2018 23:53

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Welcome to the place!

I thought that the X was a stereo power amp, but I could be wrong. Is the hiss changed by the volume control? Is the hiss there when there is nothing plugged into the input? Does the hiss go away after the amp has been turned off for a while and then slowly build up again?

Hiss could be caused by many things, most often active devices like transistors, but also from old carbon comp resistors. Later versions of that power amplifier design used a number of 1% metal film resistors to help keep the noise down.

What sort of electronics skills do you have and what sorts of test equipment are available?

Again, welcome to the place.

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Re: Kustom X MPA Monural Power Amp [message #26717 is a reply to message #26715]

Thu, 24 May 2018 06:17

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Are you sure it was not the mixer producing a unbearable level of hiss that was getting into the power amp?
Was the level of hiss louder then the signal that was being amplified?
I messed up power amp with its low amount of gain I would think would not be able to produce such a level of hiss.

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Re: Kustom X MPA Monural Power Amp [message #26718 is a reply to message #26716]

Thu, 24 May 2018 13:39

pleat
Messages: 1454
Registered: June 2004
Location: Belding, Mi

Senior Member

The X MPA is the mono amp and the X SRA is the stereo version.

pleat

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Re: Kustom X MPA Monural Power Amp [message #26719 is a reply to message #26716]

Thu, 24 May 2018 16:27

jammy5152
Messages: 62
Registered: May 2018
Location: Georgia

Member

The hiss starts after it has been on for about 5 minutes.....The volume control does nothing for the hiss...
It slowly builds up until I have to turn it off
I've cleaned the connector that come from the volumn control and plugs into the board...
I have started checking the resistors out and also have used freeze spray so it's been slow

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Re: Kustom X MPA Monural Power Amp [message #26720 is a reply to message #26717]

Thu, 24 May 2018 16:29

jammy5152
Messages: 62
Registered: May 2018
Location: Georgia

Member

The mixer has been used with a Crown Power Amp and their is no problem with the mixer
Matter of fact, I have used it for two shows I have done at a music festival...

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Re: Kustom X MPA Monural Power Amp [message #26721 is a reply to message #26715]

Fri, 25 May 2018 05:57

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

There must be a preamp board in there besides the 5065 driver power amp board because that 5065 board takes way takes way more then + 4 db out of a mixer to drive the output stage to 130 watts!
Is there another board?

If it is a issue on the 5065 board then I would say that transistors Q1 and Q2 are most likely suspects!

[Updated on: Fri, 25 May 2018 06:04]

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