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mike49504 5th January 2012 12:47 AM

MTX Thunder 4250 D
When i ower the amp up it will idle fine..

If i put a load on it and turn the gain up the amp will start drawing excessive current and squeal thru the speaker ..

Any ideas?

Perry Babin 5th January 2012 02:06 AM

Does the speaker push out or pull in?

Is the ground for the RCAs intact?

mike49504 5th January 2012 02:11 AM

The speakers pushes in and out when i mess with the gain control..

The RCA Shield grounds are intact.

Perry Babin 5th January 2012 02:17 AM

On some of the amps that use the THAT VCA (marked 2180, 2155... looks like an SIP op-amp) for the bass boost, the VCA would fail and cause excessive offset. You can replace the VCA with a 1k resistor (jump pin 1 to pin 8) to see if that solves the problem.

mike49504 5th January 2012 02:19 AM

Do i take the chip out of just solder a resistor between pins 1 and 8 ?

Perry Babin 5th January 2012 02:24 AM

Take the chip out.

mike49504 5th January 2012 02:46 AM

You Nailed it right on the head It takes care of the problem..

Right now i just stuck a surface mount resistor between legs 1 and 8 with a piece of wire solderd to one end and the other end solderd directly to pin 8 just for testing..

Im going to buy a 1K leaded resistor in the morning what wattage should i get??

Perry Babin 5th January 2012 02:47 AM

If the owner wants to use the remote, you'll need to replace the IC. If the amp has a limiter/compressor, it won't work without the IC. If those aren't a concern, you can leave the resistor. 1/8w would be sufficient.

mike49504 5th January 2012 02:50 AM

I have a parts amp with the THAT 2180 chip in it..

This amp the part is THAT 2155

Will the 2180 chip work?

Perry Babin 5th January 2012 02:54 AM

I think it will but I'm not 100% sure. It won't do any harm to try it.

This is common (very common) for those ICs so it's possible that the replacement will have some offset (but it may be better than the other one). Mouser had the ICs. I don't know if they still stock them.

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