YD7377 4×10W radio amplifier, how can it output 4×25 W?

[Behemot]

I am looking into a datasheet of YD7377 chinese car radio amplifier where it says it can do 2x35 W max or 4x 10 W with 2ohm speakers. How comes they say 4x 25 W in the radio manual?

[stj]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

sales bs.

i used to enjoy pointing out the chip datasheet to people when fixing amps.

front says 50w - chips are rated at 12 or 18 was common.

[Behemot]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

Like that even 4x25 is something big - at least my rear speakers are 50W. And I think those are original which came with the car, no crazy big satellite dishes. Maybe all of them are 50 as the front ones are some interestingly shaped pioneers with strontium magnets, that's what they say…

I guess it'll ultimatelly burn?

[stj]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

why would it burn?
it just wont get the most out of the speakers.

[Behemot]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

Won't the speakers draw more current than the amplifier can provide?

[stj]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

i cant see how, if the reistance is within the allowed range.

[Behemot]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

Sould be 2 ohm which the amplifier can handle…so it is like it has limited current and won't give more on the output?

Is this the reason why the sound is heavily distorted with higher volume? The amplifier is not able to feed the speakers?

[Agent24]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

You're more likely to blow the speakers than the amp, if you drive it into clipping and end up with DC across the coils...

[momaka]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

I am looking into a datasheet of YD7377 chinese car radio amplifier where it says it can do 2x35 W max or 4x 10 W with 2ohm speakers. How comes they say 4x 25 W in the radio manual?

Ignore what the datasheets say about the maximum power of these ICs. It's BS marketing as stj noted, and it varies wildly between manufacturers. Moreover, many manufacturers will state the maximum power at 10% THD (Total Harmonic Distortion), which sounds rather ugly on a speaker. Some even do it at 30% THD, which is complete garbage.

If the IC is decent enough, then the maximum output power only depends on the supply voltage, speaker impedance, and the mode of the IC outputs - i.e. single ended (SE) or bridge-tied load (BTL).

In SE mode, the speaker will see a maximum peak AC voltage of Vs/2 (that is, half of the supply voltage), minus a diode drop minimum. So if you are running the IC at 12V, then your speakers won't get more than 12/2 - 0.7 = 5.3V peak. With a 4 Ohm speaker, that means the IC will be able to output maximum of about 3.92 Watts RMS without any considerable distortion. This agrees with the datasheet - see page 3, THD.

SE mode operation is usually not recommended, because the amp circuit will need speaker coupling capacitors for the speakers. With 4 Ohms speakers, that means you will need at least 2200 uF caps to keep the -3 dB low-cut frequency to a reasonable 18 Hz. Moreover, distortion is usually greater in SE mode, and the output power is rather limited.

In BTL mode, the speaker will essentially be able to see a little more than 2x the output voltage of SE mode, or 11.3 V peak. That should be enough to give you about 15.6 Watts RMS without considerable distortion, if the IC is capable. Note, however, that the entry for THD on page 3 of the datasheet says the IC can only do about 10 Watts @ 0.03% distortion and not 15W. This is because the IC has internal limitations. Most likely, THD will jump in the range of 1-3% at 15 Watts RMS, and then skyrocket from there.

Won't the speakers draw more current than the amplifier can provide?

Nope.
The speakers will only draw as much power as the IC can provide.

That said, Agent24 mentioned a very valid point - at high output volume, you're more likely to burn your speakers due to the IC clipping and making the output sound look like a square wave. Since square waves contain all kinds of harmonics, the tweeters usually suffer the most.

Is this the reason why the sound is heavily distorted with higher volume? The amplifier is not able to feed the speakers?

Yes.
Since you say your speakers are rated for 2 Ohms, then the supply voltage is not so much of a limitation on the output power as is the output current of the IC. If you look at page 2, you will see an absolute maximum rating for the output current Io. At 10 Watts RMS output, those 2 Ohm speakers will be drawing about sqrt(10 / 2) = 2.24 Amps. If the IC is driving two speakers, then the IC will need at least 4.5 Amps just for the speakers, which is already hitting the maximum non-repetitive limit. Also keep in mind that Class AB amplifiers will have, at best, 65% efficiency. So if you factor that in, you will probably be limited to about 6-7 Watts RMS per speaker.

[japlytic]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

The YD7377 datasheet is a copy of the ST TDA7377 datasheet, with ST logos (and other company identification info) removed.

[fzabkar]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

The datasheet specifies two standards for power ratings.

• 2 x 30W/4 ohms EIAJ
  2 x 20W/4 ohms @14.4V, 1kHz, 10%

I found an article which appears to explain the difference.

How to Compare Amplifier Power Ratings by Patrick Quilter:
http://www.soundandsong.com/Issue004...mpRatings.html

Thankfully, there are two common standards that make it easier to compare amplifier output ratings: FTC and EIA. The FTC standard, established by the Federal Trade Commission, requires a manufacturer’s stated power rating must be met, with both channels driven, over the advertised frequency range - usually 20 Hz to 20 kHz - at no more than the rated total harmonic distortion (or THD). See Example 1.

The EIA rating, established by The Electronic Industries Association, reflects the power output for a single channel driven at mid-band - typically 1 kHz - with 1% THD clipping. This standard (shown in Example 2) inflates the amplifier’s power points to 10 to 20% higher than the FTC ratings.

Of the two, the FTC rating tells you much more about the product than the EIA rating. The FTC rating gives you the average power output for both channels over a wide frequency range and lower distortion level. This is a much more conservative - and realistic - measure of an amplifier’s average output power. But in order to claim more power, some manufacturers might list only the EIA numbers; others will disclose both FTC and EIA output ratings enabling you to easily compare manufacturer’s specs.

[Behemot]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

Yeah, even that, but that's for 2 channels. And as most cars have 4 speakers plugged independently, it has to drive 4 channels.

[budm]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

Most car amp when run on 2ch mode they will do the bridge type connection for the amplifier to get more power (the speaker is not driven with ground reference).
Normal push-pull out put, the output Voltage swing will be 12V peak to peak (assume not VDrops on the output devices for simple calculation for now), then you can calculate what the power output will be in RMS based on the load resistance (power output testing is done using resistive load).
Bridge mode will give you 24V p-p (assume no V drops on output devices for simple calculation for now).
So you can tell when the manufacturer is giving you bs rate output or not, and it can easily br verified, l use AudioPrecision in my lab at work.
You can get more power if you use Dc to doc converter to boost the 12V to higher Voltages.

[Behemot]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

That's probably where the 2x35 W peak (at 14.4 V) comes from…

[momaka]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

Yeah, even that, but that's for 2 channels. And as most cars have 4 speakers plugged independently, it has to drive 4 channels.

Then you will run the IC in a 4-channel configuration, each channel being single-ended. Since your speakers are 2-Ohm, that should give you about 9 Watts max RMS per channel. However, with all 4 speakers driven simultaneously and equally, you're looking at no more than 2 Watts RMS per channel due to that Output Peak Current rating of the IC (i.e. 3.5A / 4 channels = 0.875 A/ch).

You can get more power if you use Dc to doc converter to boost the 12V to higher Voltages.

+1
That's actually how those high-power car amps do it.

However, you still have to watch the absolute maximum ratings of the IC here. According to the datasheet, maximum operating supply is 18 V and maximum repetitive output current is 3.5 A.

That's probably where the 2x35 W peak (at 14.4 V) comes from…

It's still BS, though. I get 23.6 Watts RMS maximum with that voltage. The only way I get anything reasonably close to their numbers is if I convert that RMS output power above to peak by multiplying it with a square root of 2. And even then, I only get 33.4 Watts. I guess they went with 35 W for marketing reasons. lol .

[Behemot]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

Yeah…I already got feedbeck to my feedback, the maker suggested some Toshiba and STMicro parts. $1.2 difference. Both about the same power one to other but Toshiba claimes to have much lower distortion so I suggested that one. Both will be much closer to paper ratings of the radio now over that no-name one…

It's interesting how these reputable brands actually show all the power figures for 4 channels automatically, nothing like this "peak power for half a channel" At different voltages from 13.2 to 15something, nice. Really nice datasheets.

[fzabkar]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

P = (Vrms x Vrms) / R = (Vpeak x Vpeak / 2) / R
= (14.4^2 / 2) / 4 = 25.92W

That's assuming that there is no distortion over the full peak-to-peak voltage swing for a bridged configuration.

[momaka]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

It's interesting how these reputable brands actually show all the power figures for 4 channels automatically, nothing like this "peak power for half a channel" At different voltages from 13.2 to 15something, nice.

Indeed.
The good ones will also include lots of graphs and diligently state the operating conditions for each. For example, if you see a graph for output power vs. power dissipation, it better say whether that is per channel or total all channels driven. Not giving key parameters means we have to make ASSumptions, which regularly results in unsatisfactory circuit design .

P = (Vrms x Vrms) / R = (Vpeak x Vpeak / 2) / R
= (14.4^2 / 2) / 4 = 25.92W

That's assuming that there is no distortion over the full peak-to-peak voltage swing for a bridged configuration.

Yup, that's how I calculate mine as well. Except, I also try to take into account the transistor voltage drops too (which is why I got 23-odd Watts instead of 25).

Also, if the IC has a 3.5A current rating, then 4 channels means you can push only 3.5A / 4 = 0.875 Amps RMS per channel. Since P = (I^2)*R, you can see that higher impedance speakers should give higher output power - at least until you hit the maximum supply voltage. For 2-Ohm speakers, you get 1.53 Watts RMS if all 4 channels are driven equally and simultaneously .

[budm]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

"Since P = (I^2)*R, you can see that higher impedance speakers should give higher output power"
Sorry but I have to make the correction on your statement. You cannot just change the resistor Value in the equation and still hold the current at the same value, you have to plug in new calculated Current value due to the change of the resistance value.
Higher resistance = Less current flow = less power, given Applied E is constant.
For example:
E =1V
R = 1 Ohm
So calculated current I = 1A
So P = I*E = 1A*1V
Then using P = (I^2)*R = 1W since you already know the calculated I value.
But if you change the resistor to be 2 Ohms, you cannot just put that 2 Ohms back in the formula that uses the calculated current value of 1A because you will no longer has 1A of current flowing through the 2 Ohms resistor with the same 1V source, you now only have 0.5A of current through the resistor, so the Power will be only 0.5W.
You can easily verify the above by using the power supply and resistors.
Just think the Amplifier is a constant Voltage source meaning you can use difference value of the load resistance, the amplitude (using constant 1KHz tone for example) will stay the same (think of it as AC power source). I.E. if the amplifier 10V P-P, If you connect 4 Ohms load to it, the current through the 4 Ohms load will be higher than the 8 Ohms load since the amp will still put out the 10V P-P with 8 Ohms load, the output amplitude is not affected by the load value. But of course the amplitude will change when you play music, so as power will varies, also the impedance of the speaker which will also varies with the frequency and that is why the amplifier is test with non-inductive load.
http://education.lenardaudio.com/en/05_speakers_3.html
So 4 Ohms speaker will produce more power than 8 Ohms speaker but if the 4 Ohms speaker has low sensitivity then it will not be much better than 8 Ohms speaker with much high sensitivity (http://www.psbspeakers.com/articles/...Specifications). That is why lots of car amplifiers are advertising the rated power at 2 Ohms which will show higher Wattage than showing the power at 8 ohms.

http://www.gcaudio.com/resources/howtos/spkramp.html

[momaka]

Re: YD7377 4x10W radio amplifier, how can it output 4x25 W?

"Since P = (I^2)*R, you can see that higher impedance speakers should give higher output power"
Sorry but I have to make the correction on your statement. You cannot just change the resistor Value in the equation and still hold the current at the same value, you have to plug in new calculated Current value due to the change of the resistance value.

I don't think you understood why I gave that formula. My point is to show the amplifier's maximum output power as a function of its output current (per channel). Note that I did not mention the amplifier supply voltage anywhere, which obviously DOES matter, as was shown by the formula in post #17 by fzabkar.

The whole idea is to look at all of the limitations for the IC. Namely, that's the supply voltage (which dictates what the maximum output voltage can be) and the Peak Repetitive Output Current, Io. First, you use the formula in post #17 to find the maximum RMS output power based on the amp's supply voltage and speaker impedance. Once you find that, then you can use the formula I gave in post #18 to verify if that is true or not.

Let's use Behemot's setup here as an example. You have four 2-Ohm speakers, and you are using the IC in single-ended mode to drive each channel. With a 14.4V supply and ignoring voltage drops in the amp IC, the maximum output power is 25.92 Watts RMS per channel into a 2-Ohm speaker.
But always ask yourself, does the result make sense?
So, let's check. We use the formula I provided above in post #18 and solve for the current I. With that output power we found above, the output RMS current going into a 2-Ohm speaker should be:
I = sqrt(P/R) = sqrt(25.92/2) = 3.6 Amps. This is an RMS, and it already is higher than the peak repetitive output current. Oh, and that's with just one channel driven. What about the other three channels? Forget it! No way you can push 25.92 Watts RMS into a 2-Ohm speaker. So, NO, this result clearly does not make sense.

And what if you try to drive all four channels simultaneously and equally? Then that 3.5 A repetitive peak output current rating is split into 4 channels - i.e. each channel will be able to supply only 3.5 Amps / 4 = 0.875 Amps to each speaker. With that current limitation and the same 2-Ohm speakers, the maximum peak repetitive output power per speaker becomes as I stated in post #18:
P = (I^2)*R = (0.875^2) * 2 = 1.53125 Watts per channel, with all four channels driven simultaneously and equally.