Taramps MD 3000 clip LED blinking

[barber02]

This Taramps came in with the ground power terminal heated up a desoldered from the board and the positive speaker terminal was also separating from the board as well. I repaired both terminals, easy enough.

I powered up the amp and it booted up fine, runs nice a stable at idle and rail voltage and op amp voltages look good. However, with the gain above 50 percent and connected to a speaker and as the volume input from the head unit feeding the amp via RCA jacks is turned up the clip LED will start flashing. If it turn the gain on the above 60 percent the amp will protect. Cycling power will reset the amp.

I was playing around with it with no speaker connected, gain 100 percent and the Clip and protection LED flash as I drive a stronger signal into the amp through the RCAs but it doesn’t actually go into protection. A weaker signal does not cause the clipping LED to flash.

The output transistors and surrounding diodes all check good, gate resistors all read good. The voltage of the speaker terminals is half rail and are less than 1/2 volt of each other.

Any ideas?

 

[Perry Babin]

Does this amp have a code for the blink sequence?

 

[barber02]

It’s not flashing in a sequence. It just flashes on and off like it’s on the verge of tripping.

When the amp actually protects when connected to a load I get a solid red LED.

David

 

[barber02]

Solid Red LED according to Taramps manual is a short circuit or impedance load too low.


David

 

[Perry Babin]

If there isn't a true overcurrent fault, you need to determine what's triggering the LED. HAve you tried getting a diagram for the amp?

 

[barber02]

I now have a diagram of a similar amp. While I was waiting on that I was driving the amp pretty hard into a 4 ohm dynamic load (amp is rated for 1 ohm) and I watched the duty cycle on the outputs expand and contract but as it was doing so I noticed that the rail voltage would sag about 5 volts as the duty cycle increased. My concern is that the rail voltage will sag even more with a 1 ohm load and that will limit very much how high you can increase the gain.

Is it normal for the rail voltage to sag that much? I could see the sag on my scope and I also measured it on the secondary side of the transformer before the rail caps and rectifiers.

The amp was being fed 12.6 volts.

David

 

[Perry Babin]

The rail voltage will sag more if the 12v input sags and when the supply isn't regulated.

Noise and other irregularities on the transformer waveforms can also cause the rail voltage to be slightly higher than where it's going to be more solid.

 

[barber02]

The clip light starts flickering when the duty cycle bumps up to 100 percent.

 

[Perry Babin]

At 100% or 0% it's going to be producing the most current demand.

 

[barber02]

Ok. I fed the amp 14.5 volts and it sags even more. About 15 volts and the music becomes distorted when the clip light flickers and this time duty cycle is only about 75 percent when it sags and distorts.

 

[barber02]

Ok. I see what’s going on here. My power supply is dropping the voltage coming in as the current draw goes up. I saw drops down to 10 volts coming into the amp as the current draw hit about 35 amps.

So mystery solved. Thanks Perry for helping me figure that out.