Amplifier - Cant drive out full power

[jackdozen]

I am complete newbie to using power amplifiers. Any help/clue to this problem is appreciated. Here's my experimental setup:

I am testing Pyle PTA1000 audio amplifier in stereo mode. Currently, I am driving the amplifier from a signal generator (60Hz, 1.4V sine wave). The amplified output is connected to 600 watt pure resistive load bank (4.5Ohm). I monitor voltage (RMS) across load bank. When I vary the gain knob in amplifier, the voltage increases in resistive load bank. The maximum I can get is 17V. When I try to increase gain after 17, i can see the voltage waveform is clipping. This means that:

Max current that can be driven in this setup is: 17*sqrt(2)/4.5 = 5 A.

According to data sheet: power rating is 500 watt for 4 Ohm. So, Max current = sqrt(500/4) = 11 Amps.

Does anyone has any idea as to why I cant drive full current from my power amplifier?
Strange Observation: The amplifier has a small LED ('Clip Signal'). This light never comes ON even though oscilloscope is giving out a clipped signal.

My goal is to drive at least 10A out of amplifier. Anyone has any idea on how to acheive this?

Thanks

 

[kam1787]

Is the 17V peak to peak?

Have you measured the power supply at the point it starts to clip? Maybe the power supply is not capable of supplying the current beyond the '5A'.

Is there any DC across the load?

Perhaps there is a problem with the pre-driver stage............ Can you check the base of the driver stage with a scope?

 

[jackdozen]

I have connected the power amp directly to house wall outlet.

The output of power amp is directly connected to resistor bank. There is no DC across load.

Can you please explain whats pre-driver stage?

Thanks

 

[iop95]

"According to data sheet: power rating is 500 watt for 4 Ohm."

What kind of power is stated? There are same datasheet that show "musical power" or similar marketing expressions...

 

[jackdozen]

"According to data sheet: power rating is 500 watt for 4 Ohm."

What kind of power is stated? There are same datasheet that show "musical power" or similar marketing expressions...

Its quoted as:

Power(each channel):

8 Ohm ..................... 2x250 watts
4 Ohm.......................2x500 watts

1000 watts total power

And to add to information about my current problem, I tried to use two available channels and each of them separately is able to drive 5 Amps to resistor loads. So, no problem with the power supply to the amplifier.

 

[betwixt]

There is real power and 'market hype' power. What you are trying to measure is continuous RMS Watts but the specification may be for "peak music power" or similar. For example, my desktop speakers here each have a single 10cm loudspeakers in them, the back of the speaker is marked 8 Ohms 5W but the outside of the box says 300W.

In car terms it a bit like quoting maximum speed is 300 MPH without adding that you can only achive it briefly before hitting the bottom of a canyon.

Brian.

 

[kam1787]

There is real power and 'market hype' power. What you are trying to measure is continuous RMS Watts but the specification may be for "peak music power" or similar.

I suspect Betwixt is right. If this is the amp; https://www.pyleaudio.com/sku/pta1000/1000-watts-professional-power-amplifiers

It smells strongly like a Chinese product that is being re-marketed. That the power rating has no units (RMS, Average, Peak-to-peak, or whatever) smacks of a low-end product to impress the gullible (no offense).

Especially when the input parameters are complete, but no units or parameters for the output!

What is the power supply voltage? That gives some clue as to the maximum power. You may need to buy 50 of the amps to get 1000W[RMS] (joke).

If you are measuring the peak-to-peak voltage then the real [RMS] power is likely around 20W.

 

[audiomik]

I've seen this same question from the OP on another Forum.
Interestingly with very much the same replies.

The only difference is that for 17 Volts (RMS sine wave on the meter) at onset of clipping, this gives a whole 64 Watts into the 4.4 Ohm resistive test load.
Link: https://forum.speakerplans.com/power-power-amplifier-cant-drive-out-full-power_topic80363.html

Mik

 

[betwixt]

I watched the video on the Amazon review. Having worked in electronics, both industrial and domestic for 40+ years, I would guess 64W was a reasonable amout to expect from those components. Interestingly, even the output relay which seem to carry both channels is clearly marked as being rated at 2A. The output transistors also suggest much lower output, I would expect to see several in parallel to sustain 500W continuous output, in fact just about eveything simply looks too small for the quoted spec.

Does the user manual have wording like "specifications may be changed without notice" on it I wonder?

Brian.