Electronics > Projects, Designs, and Technical Stuff
Texas Instruments 3116D (ClassD) amp chip
tooki:
How is it not clear to you?!?
That chip can do 100W mono into a 2 ohm load. So they’re using two of them to get stereo.
As for total power, remember that you need the voltage to reach the peaks, but that most of the signal is below the peaks. So the power supply doesn’t need to have quite as much power as you think, since capacitors are used to feed current spikes.
DW1961:
--- Quote from: tooki on August 12, 2020, 08:36:10 pm ---How is it not clear to you?!?
That chip can do 100W mono into a 2 ohm load. So they’re using two of them to get stereo.
As for total power, remember that you need the voltage to reach the peaks, but that most of the signal is below the peaks. So the power supply doesn’t need to have quite as much power as you think, since capacitors are used to feed current spikes.
--- End quote ---
Hey, sorry about the delay. I'm still interested in this topic. I just had some real life things to deal with.
I had no idea you could run a chip in mono and get stereo out of them by running two of them in mono. Pretty basic stuff, so I apologize for that.
As far as power goes, I'm always talking about continuous power. So if you're running a 24V driver, your max output is going to be 72 watts, right?
I just got this amplifier. It looks like the Chinese are upping their game. It's case is very well made with recessed, high friction knobs and the volume knob clicks as you turn it. It does have some cheesy screen printing on it--lol.
https://www.amazon.com/gp/product/B0887VX6H1
It uses two Texas Instruments 3116D2 chips (link above) and the TI NE5532 operational amplifier (link below).
https://www.ti.com/lit/ds/symlink/ne5532.pdf
I'm assuming that's an LFE sub output? It says it is an active sub output.
<-------Sorry for end of post attachments. I can;t get the inline function to work.
<-----------Not working either.
Regardless of power output, I'll bet this thing has some serious punch to it. Makes me want to get a R series Klipsch sub woofer to go with my R-51M Klipsch speakers.
tooki:
--- Quote from: DW1961 on August 15, 2020, 05:22:19 am ---
Hey, sorry about the delay. I'm still interested in this topic. I just had some real life things to deal with.
--- End quote ---
No worries, it happens to all of us!
--- Quote from: DW1961 on August 15, 2020, 05:22:19 am ---I had no idea you could run a chip in mono and get stereo out of them by running two of them in mono. Pretty basic stuff, so I apologize for that.
--- End quote ---
The channels of an audio chain are fundamentally separate. We just control them in (usually) pairs for convenience.
Class D amplifiers are a bit of an exception, in that many of them take advantage of the fact that they actually have way more power available than they need, letting them actually alternate powering the two channels, reducing the instantaneous current draw. (This is why you must only bridge class D outputs in the ways listed in the datasheet.)
--- Quote from: DW1961 on August 15, 2020, 05:22:19 am ---As far as power goes, I'm always talking about continuous power. So if you're running a 24V driver, your max output is going to be 72 watts, right?
--- End quote ---
Nope. You’re going by the math for DC, but it’s not DC, it’s AC.
Some things to understand:
1. The supply voltage is what limits the maximum power of the amp, as it is the highest voltage that be present on the output. For any given speaker impedance, it is the maximum voltage alone that limits the power. But it’s a sine wave, so the vast majority of the signal is below the peak voltage.
2. Many (most?) class D amps, including the one here, use creative switching to produce both the positive and negative sides of the output waveform from a single-polarity power supply (let’s call this VCC). This means that the output voltage can swing from +VCC to -VCC, meaning a peak-to-peak voltage of VCCx2. So if your VCC is 24V, then your output can swing from +24 to -24 volts, a total peak-to-peak voltage of 48V!
3. In a sine wave, the peak voltage is only reached for a tiny amount of time. Most of the time is less. So we measure using RMS, the value of the AC signal given as the DC voltage with the equivalent heating power. For a pure sine wave, the RMS value is the square root of 2 (about 0.707) times the peak voltage (which in an amp is at most the VCC). So for your 24V VCC, the RMS becomes 24x0.707, or about 17V. And that gives you a maximum average power of 36W into 8 ohms (a current draw of 2.125A). (You can also calculate it as VCC2/2x(impedance).)
4. Music isn’t a singular, always-full-amplitude sine wave. That’d just be a single loud tone. Nor is music multiple sine waves of different frequencies, but always full amplitude. No, it’s nearly infinitely many simultaneous sine waves of different frequencies at highly varying amplitudes. Indeed, most of them will be far below the peak amplitude (since the peak is necessarily the peak sum of all the frequencies at any instant). The consequence of this is that the average power is far lower than the peak power, easily a factor of half at full volume.
5. As such, while you will need capacitors to ensure the peak current can be supplied, the power supply only needs to be beefy enough to supply the average current. That’s why you can get away with the small power supplies commonly used in audio gear now.
And that’s all assuming you’re running it at full blast. At typical home, indoor listening levels, you don’t need but a tiny fraction the power. One of the 3116’s at just 7 volts into 8 ohm speakers is enough to be much too loud to have a conversation, and that’s just 3 watts per channel max. Nighttime watching a TV show, for instance, will have the 3116 drawing maybe 30mA at 5 volts, so 150mW total (and at 5V, the 3116’s quiescent current with no signal is about 15mA, so at most 75mW actually going to the speakers!).
A lot of info, but I hope it helps. Of course there are lots of other things that come into play and slightly increase the power needed, but this should help understand why you can’t just apply ohms law to the supply voltage to calculate an amp’s power.
DW1961:
--- Quote from: tooki on August 15, 2020, 12:54:26 pm ---
--- Quote from: DW1961 on August 15, 2020, 05:22:19 am ---
Hey, sorry about the delay. I'm still interested in this topic. I just had some real life things to deal with.
--- End quote ---
No worries, it happens to all of us!
--- Quote from: DW1961 on August 15, 2020, 05:22:19 am ---I had no idea you could run a chip in mono and get stereo out of them by running two of them in mono. Pretty basic stuff, so I apologize for that.
--- End quote ---
The channels of an audio chain are fundamentally separate. We just control them in (usually) pairs for convenience.
Class D amplifiers are a bit of an exception, in that many of them take advantage of the fact that they actually have way more power available than they need, letting them actually alternate powering the two channels, reducing the instantaneous current draw. (This is why you must only bridge class D outputs in the ways listed in the datasheet.)
--- Quote from: DW1961 on August 15, 2020, 05:22:19 am ---As far as power goes, I'm always talking about continuous power. So if you're running a 24V driver, your max output is going to be 72 watts, right?
--- End quote ---
Nope. You’re going by the math for DC, but it’s not DC, it’s AC.
Some things to understand:
1. The supply voltage is what limits the maximum power of the amp, as it is the highest voltage that be present on the output. For any given speaker impedance, it is the maximum voltage alone that limits the power. But it’s a sine wave, so the vast majority of the signal is below the peak voltage.
2. Many (most?) class D amps, including the one here, use creative switching to produce both the positive and negative sides of the output waveform from a single-polarity power supply (let’s call this VCC). This means that the output voltage can swing from +VCC to -VCC, meaning a peak-to-peak voltage of VCCx2. So if your VCC is 24V, then your output can swing from +24 to -24 volts, a total peak-to-peak voltage of 48V!
3. In a sine wave, the peak voltage is only reached for a tiny amount of time. Most of the time is less. So we measure using RMS, the value of the AC signal given as the DC voltage with the equivalent heating power. For a pure sine wave, the RMS value is the square root of 2 (about 0.707) times the peak voltage (which in an amp is at most the VCC). So for your 24V VCC, the RMS becomes 24x0.707, or about 17V. And that gives you a maximum average power of 36W into 8 ohms (a current draw of 2.125A). (You can also calculate it as VCC2/2x(impedance).)
4. Music isn’t a singular, always-full-amplitude sine wave. That’d just be a single loud tone. Nor is music multiple sine waves of different frequencies, but always full amplitude. No, it’s nearly infinitely many simultaneous sine waves of different frequencies at highly varying amplitudes. Indeed, most of them will be far below the peak amplitude (since the peak is necessarily the peak sum of all the frequencies at any instant). The consequence of this is that the average power is far lower than the peak power, easily a factor of half at full volume.
5. As such, while you will need capacitors to ensure the peak current can be supplied, the power supply only needs to be beefy enough to supply the average current. That’s why you can get away with the small power supplies commonly used in audio gear now.
And that’s all assuming you’re running it at full blast. At typical home, indoor listening levels, you don’t need but a tiny fraction the power. One of the 3116’s at just 7 volts into 8 ohm speakers is enough to be much too loud to have a conversation, and that’s just 3 watts per channel max. Nighttime watching a TV show, for instance, will have the 3116 drawing maybe 30mA at 5 volts, so 150mW total (and at 5V, the 3116’s quiescent current with no signal is about 15mA, so at most 75mW actually going to the speakers!).
A lot of info, but I hope it helps. Of course there are lots of other things that come into play and slightly increase the power needed, but this should help understand why you can’t just apply ohms law to the supply voltage to calculate an amp’s power.
--- End quote ---
Yes, understood. I read a lot about how RMS is calculated and it's the avg of the sine wave and so on.
In another thread on the same subject I posted that using the volume knob with my Klipsch R-51M speakers (93dB sensitivity), I can not get it over about half way, which if it is at all accurate is giving the speakers about 11 watts each. It's just glaringly loud at that point. (That's with a 19V power supply.)
I went to the Amazon page and asked the seller what the continuous output was at 8 ohms using their 24V power supply:
Q: The 3116D chip is only rated 100w @ 2ohms mono. Using the included power supply, what is total power output @ 8 Ohms?
A: when you use 8ohm speaker, the total power is 35-50W.
I should have asked what the continuous power is, but what he said was accurate given the oms to watts calculations, which would be 35-36 watts continuous. I think he means 35 watts continuous and 50 peak.
Back to my question, though:
So, my question, again, what is the benefit of using two 3116D chips when you get the same power output as one chip at 8 ohms?
DW1961:
Just wanted to say that the amp I posted here is not a powered sub out. It requires an active subwoofer--which is good. That leaves all power for the mids and tweets. Damn, I'll bet this thing with a 10" Klipsch active sub and the R-51M speakers as mids and highs would be incredible.
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