Phoenix Gold QX150.4 amp big problem

[Besarmatis]

Hello,

This is my first post on this forum, so sorry if I didn't write this thread in the right section.

So, I have Phoenix Gold QX150.4 amplifier. I use it to drive my four speakers. And the problem with it is kinda strange to me. When I turn on the amp and listen to the music everything works just fine. Even if I'm not listening to the music, but the amp is on everything is fine, but only for about 15 minutes. After such a while some kind of noise is getting emitted from the speakers. after 20 minutes the noise is louder, after 25 min more louder and so on. Moreover, the high frequency sounds of music is getting reduced. After few tests changing signal source and changing speakers I found out that it is definitely amplifier's problem. And now I have no idea what's wrong.

So if anyone had such problem or knows what's wrong, I would be very thankful for your suggestions.

Marius

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[helotaxi 5,000+ posts]

Probably bad components in the amp. Those are pretty old amps and PG is known for using certain components with a shelf life.

 

[Besarmatis]

I'm pretty sure it's about the components of the amp, but I wish I knew which ones. Maybe the caps, maybe the op-amps, smps components or amp components. Maybe someone already had such problem, and could remember what caused it.

 

[helotaxi 5,000+ posts]

The usual cause with the PG amps was the caps.

 

[Besarmatis]

Thanks for reply, I will try to change caps starting from supply caps and so on.

 

[Besarmatis]

Hello again,

I found the problem and fixed the amp, so I just want to share what was wrong and how to fix it.

I've tried to change capacitors starting from power supply without any luck, then I changed all remaining capacitors with still no luck, although it fixed a bit sound quality.

Then I started to check all over again if something is heating too much, and then I found one interesting thing, that then I touch input op-amps, I hear a lot of noise coming out of speakers. Those op-amps were KA4558, so I changed them with TL072 (which has more quality) and wuala, everything worked like a charm.

It looks like, that those old bad op-amps became sensitive to noise in environment, and started to catch noise from SMPS.

I hope this would help someone in the future.

 

[matt_bennett05 10+ year member]

Hello again,
I found the problem and fixed the amp, so I just want to share what was wrong and how to fix it.

I've tried to change capacitors starting from power supply without any luck, then I changed all remaining capacitors with still no luck, although it fixed a bit sound quality.

Then I started to check all over again if something is heating too much, and then I found one interesting thing, that then I touch input op-amps, I hear a lot of noise coming out of speakers. Those op-amps were KA4558, so I changed them with TL072 (which has more quality) and wuala, everything worked like a charm.

It looks like, that those old bad op-amps became sensitive to noise in environment, and started to catch noise from SMPS.

I hope this would help someone in the future.

Very informative. Glad you found and fixed your problem

 

[VWBobby 10+ year member]

This is very good to know! Most people know about the cap problem with the older PG amps, if they've been around them for a while.

I met a guy in the coast guard from Lithuania. It seems you guys are very smart and keen on tracking down and solving problems. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[helotaxi 5,000+ posts]

If you had to live with the crap build quality of a lot of things made under the Soviet Union you had to be good at fixing things if you wanted your brand new stuff to work //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif