Hilariously cheap car audio amp (Cougar C-300.4)

[tom66]

This amplifier is in two minds. It claims "1200W 4 channel", but apparently that's the model number, along with C-300.4. It's rated to 75W per channel, 4 channels = 300W. Price £40.

So, my manager gave me one to evaluate for an audio installation.

I connected it up to a variable bench supply set to 14.5V (nominal max bus voltage in a car.) Fed 1Vp-p audio into it. The maximum I can get it to draw is 2.8A with two speakers connected; that's 40.6W total, or about 20W per channel, a fair bit from the claimed 75W, and not even accounting for inefficiency in the amplifier. That's also hideously distorted; clipping right at the rails.

Opened it up to find two ST TDA7377's in it. Now the datasheet claims 2x30W; but that's driving a square wave, no one listens to those. With a sine wave 1kHz, 10% distortion, at 14.4V, that's 2x20W BTL. And coincidentally, about exactly what I'm seeing. 4x75W is complete crap then.

It also appears to be fake silicon as the ST datasheet claims it cuts out at 8V, but the actual amplifier dies at just 12.7V; the Iq is also 200mA per amplifier, not 150mA.

Teardown results showed several bodges too; including free-standing 7808 regulator, ready to fall right off the board especially in a vibrating car. The amplifiers were mounted squiffy, and the soldering was mediocre. Also, the gain control does...nothing? Absolutely no function. Only volume control works... It appears it may have been dropped at some point

[tom66]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Figured out the gain control. It's the volume for the rear. The "volume" is the volume for the front.

Also managed to discover a little quirk of it - if running off ~13.3V and there are heavy bass excursions it will go into UVP and not recover for half a second, meaning anything loud makes the amp silent! It only draws about 1A at those points. When I tore it apart I noticed none of the amps had decoupling; the only decoupling was a measily 1000u near the input, after a massive inductor and an input cap. All caps are off-brand Jyy or similar.

[mariushm]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Pictures would be nice...

[tom66]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Maybe I'll get them soon, it depends if I am allowed to open it again as we are going to use it anyway, even if it doesn't meet its specs and stands to last only about 30 minutes (it was VERY warm after just 30 minutes of playback at a low volume.)

[Th3_uN1Qu3]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

TDA7377? I've seen head units with more beef. And it calls itself an "amplifier"? If it had four of those instead, now maybe it woulda been worth something. Unfortunately the 7396 cannot be bridged, as it's already BTL internally.

[tom66]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

It's rated for 4 ohm anyway (minimum). Assuming 29V amplitude sine (BTL; rms=10.3V) that's a peak power of... 26.5W. Unless it had a boost converter, it would NEVER be capable of its rated 75W per channel. Maybe if it supported 1.6 ohm speakers it would work. I still haven't figured out how on earth they got 1200W though!!

Also I believe (though I may be wrong) but the peak efficiency of a class-AB is just 78.5%, so the power dissipation would not be trivial in this amp.

We have a 7W+7W homebrew amp at work which outperforms this heap of junk. Class D based around a Maxim IC. Needs no heatsink, will do 6W per channel at 12V without sweating (IIRC at 8 ohms), and sounds way better than this heap of junk.

[Th3_uN1Qu3]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Maybe if it supported 1.6 ohm speakers it would work. I still haven't figured out how on earth they got 1200W though!!

That's the peak power absorbed by the thing when the chips short, before the fuse blows.

Also I believe (though I may be wrong) but the peak efficiency of a class-AB is just 78.5%, so the power dissipation would not be trivial in this amp.

True, with 60-ish % typical.

[tom66]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

1200W is how much it draws when short circuited. Yes, the datasheet claims the amp is short circuit protected but my power supply limited to 4A when I did that so I'm pretty sure this "variant" of the TDA7377 is not so well protected. I have recently found a spare car battery at work (pretty flat though; not sure if it can be charged), so I wonder if this will run better off that, though the lab supply is very well regulated it could be limiting the peak transients.

[ben7]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

I can't wait to see what it looks like and what it looks like after it has blown up

[Th3_uN1Qu3]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

1200W is how much it draws when short circuited. Yes, the datasheet claims the amp is short circuit protected but my power supply limited to 4A when I did that so I'm pretty sure this "variant" of the TDA7377 is not so well protected.

I have found TDAs to have quite effective short circuit protection. However, most of the time their thermal protection isn't up to par.

[japlytic]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Could "1200W 4 channel" refer to PMPO (Peak Music Power Output - a bit of a magic number)?

[tom66]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Could "1200W 4 channel" refer to PMPO (Peak Music Power Output - a bit of a magic number)?

Well, how do they get that from 300W max (actually 80W)?

[tom66]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

I have found TDAs to have quite effective short circuit protection. However, most of the time their thermal protection isn't up to par.

I'm pretty sure it's fake silicon as it doesn't meet many of the datasheet's specs.

[kc8adu]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

sounds a lot like the "kombat ak-47" amp a neighbor came up with.supposed to be 2000w.
lucky to do 20w on a good day with a tailwind at 18v supply.it went to the recycle pile.

[tom66]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Well, I compared it to the 7W amp we had built (14W total.) Not only is it more efficient (barely gets warm) it sounds far louder and it doesn't clip.

[tom66]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Discovered several other little "oddities".

If you try to make a loud sound and then quiet, the amp will start oscillating. And it won't stop until you turn the volume control down, then up again... The bloody thing is motorboating! - that used to be a problem with ancient tube amps, but a modern design should NEVER do that.

I measured the bench supply for ripple; it's dead solid, never dropping by more than 50mV. Noise in an automotive environment would easily exceed that so I doubt that would be a problem. It's clearly not current limiting (that would be a drop of a volt or so), so the "going silent" is just the lack of proper decoupling, I expect.

[Th3_uN1Qu3]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

It's clearly not current limiting (that would be a drop of a volt or so), so the "going silent" is just the lack of proper decoupling, I expect.

Or garbage PCB layout.

[budm]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

It sounds like the Input circuit ground return is tied to the same high current return ground of the output stage, bad layout and bad bypass coupling between the preamp and the power output section.

[ben7]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Or garbage PCB layout.

I have noticed that cheap battery powered speakers use generic grab-bag amp chips, and they usually have their gain maxed out - maybe thats why this amp is so terrible.

[tom66]

Re: Hilariously cheap car audio amp (Cougar C-300.4)

Well, we plugged it into a car cig lighter socket, exactly the same problems. My boss has decided not to bother with it so I might take it apart again and get pictures soon. From a cursory glance the layout was really poor. Also when we opened it up the warranty sticker didn't break.

In fact the amplifier wouldn't work with the car battery idle at ~12.5V; the engine had to be running and battery at 14.4V for it to do anything. It couldn't even overpower engine noise - from a luxury Audi (which really isn't that loud) - with four speakers attached. The stock audio system was louder!