Audio problem ( INTERM M700 amplifier )

[ashokkumar8226]

Hi,

when amplifier volume in mediam audio is constant and when we try to increase the volume the audio of the amplifier is coming down, I tried replacing the following.

Power capisators 4 nos replaced of value ( 10000mfd 100v ) in place of 8200mfd 80v


Can anyone helpme with this,

 

[KeepItSimpleStupid]

Look at any coupling caps in the range of 1 to 10 uf. To save cost some manufacturers use 1 uf electrolytics for what should be a polyester cap at a minimum.

 

[unclejed613]

there are several possibilities here.... are you triggering the limiter circuit? this is a common thing in PA amplifiers. there's a limiter circuit that limits the output power if the load is 4 ohms or less. in some cases it actually reduces the output power. what is your load impedance?

you could also have a problem with the inrush limiter in the power supply not disengaging. this would have an effect like reducing the power supply voltages when the volume is turned up. this would cause the amp to go into clipping sooner as one of the symptoms. if the amp uses a capacitor in the feedback loop to control DC offset, when the cap dries out it reduces the gain of the amp, but this wouldn't just happen when the volume gets turned up. i tend to lean towards the SOA limiter and the possibility you're running more than one 4 or 8 ohm speaker on each channel. so the amp to protect itself goes into limiting mode, which will reduce the volume. some amps do this by using a photocell to actually back off the gain of the amplifier and maintain a constant or reduced output level based on the amount of current in the output transistor emitter resistors.