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Author Topic: a nice part for Guitar Amplifier  (Read 11574 times)

chejian6

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a nice part for Guitar Amplifier
« on: April 29, 2010, 05:34:58 AM »

I found a nice part to building a guitar amplifier. It's a all in one class D audio amplifier module, the size is only 0.6" x 1" x 0.15" (the size of a stamp). But the output power is 10Wx2, really amazing! No heat sink and external components (except power bypass cap) needed. I bet it's the simplest audio amplifier circuit you can find. Due to it's high efficiency there's no much heat generated even when the speaker is very loudy. It's ideal for battery powered applications.

Sound quality? pretty nice comparing to it's size and cost.

the part:


the board I made with VMA2016


reference circuit provide by v-module
« Last Edit: April 29, 2010, 05:36:30 AM by chejian6 »
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J M Fahey

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Re: a nice part for Guitar Amplifier
« Reply #1 on: April 29, 2010, 09:30:15 AM »

Nice part indeed.
Price, availability,PCB layout, Datasheet? 8|
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chejian6

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Re: a nice part for Guitar Amplifier
« Reply #2 on: April 29, 2010, 09:53:08 AM »

http://www.v-module.com is the manufacturer's website. It's seems to be a site that is being constructed.

page of VMA2016: http://www.v-module.com/info.aspx?id=20
datasheet: http://img.v-module.com/datasheets/ds_vma2016.pdf

The price is about $7 to $8, depend on the order quantity. I paid $75 for 10pcs. The system cost is quite cheaper than most ICs (such as LM1875) because there's no heatsink and other components.
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rowdy_riemer

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Re: a nice part for Guitar Amplifier
« Reply #3 on: April 29, 2010, 12:56:06 PM »

Quote
I bet it's the simplest audio amplifier circuit you can find.

Let's not forget it's actually very complex, but the IC hides the complexity. Of course, we know what you meant, but still. I guess I'm in a nit-picking mood. :)
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rowdy_riemer

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Re: a nice part for Guitar Amplifier
« Reply #4 on: April 29, 2010, 01:05:08 PM »

If you wanted more power from this, you could connect each output to a couple of complementary power MOSFET's for a power cmos invertor.
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chejian6

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Re: a nice part for Guitar Amplifier
« Reply #5 on: April 30, 2010, 01:17:50 AM »

The power can be up to 15W with 24V supply on a couple of 16Ohm speaker. This is strange when comparing with traditional analog amplifiers.
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rowdy_riemer

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Re: a nice part for Guitar Amplifier
« Reply #6 on: April 30, 2010, 09:36:58 AM »

Quote
The power can be up to 15W with 24V supply on a couple of 16Ohm speaker. This is strange when comparing with traditional analog amplifiers.

It's just an issue of impedance matching. The output impedance must be closer to 16 Ohm than 8 or 4. Remember, with matching impedance, you get you're greatest transfer of power. With an 8 Ohm load, if I remember correctly, you get 10 W at that voltage. With the lower impedance, the power stage is loaded down and though you have more current, the voltage is lowered enough that you end up with less power.
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chejian6

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Re: a nice part for Guitar Amplifier
« Reply #7 on: May 05, 2010, 05:55:51 AM »

Hi Rowdy,

Actually there's no "impedance match" problem for class D audio amplifier at all. The internal mosfet is working in on-off mode. When it's turned on the equivlant resistance is only about 0.1Ohm. The max power of class D amp is depend on the maximum current it can drive. When the current is fixed the bigger the load impandence, the bigger the power. That's why the output power is larger for 16Ohm than 8Ohm. Of course the max power is limited by some other factors such as supply voltage.
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rowdy_riemer

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Re: a nice part for Guitar Amplifier
« Reply #8 on: May 05, 2010, 09:42:44 AM »

Quote
Hi Rowdy,

Actually there's no "impedance match" problem for class D audio amplifier at all. The internal mosfet is working in on-off mode. When it's turned on the equivlant resistance is only about 0.1Ohm. The max power of class D amp is depend on the maximum current it can drive. When the current is fixed the bigger the load impandence, the bigger the power. That's why the output power is larger for 16Ohm than 8Ohm. Of course the max power is limited by some other factors such as supply voltage.

Ok, when switched on , the resistance of each MOSFET probably is about .1 Ohm. BUT, impedance is more than just resistance. The current limiting effect of the class D operation IS a type of impedance. ANYTHING that impedes current is impedance and can be measured in Ohms. Also, keep in mind that it takes time to switch from all the way off to all the way on. If you find the average resistance during this transition and multiply that by the switching frequency, you have that much more resistance to add to the .1 Ohm of on resistance. According to my calculations based on P=I^2 * R and what the data sheets shows, you have about 1.18 A of current with either 4 ohm or 8 ohm speakers, but only .968 mA of current with 16 Ohm. If it were as simple as multiplying some constant current times the speaker impedance, you would have 1.18 A ^ 2 * 16 Ohm to get about 22 W with a 16 Ohm speaker. You could also get 118W with a 100 Ohm speaker if this were the case.

Also, Class D operation is simply applying pulse width modulation to the signal and using the pulse width modulated signal to switch a CMOS or H-Bridge (or something similar) output stage. If there is some current sensing feedback to adjust the pulse width to achieve a desired output current, then this is a feature that is an addition to class D operation and not necessarily a part of class d operation any more than current or voltage feedback is a part of class a or class ab operation rather than an additional feature. Perhaps this ic is doing some sort of current sensing feedback. This does not change the fact that it has a significant output impedance. That impedance might not be absolutely fixed, but it remains higher than 8 Ohms.

The maximum output voltage at 16 Ohms would be .968 mA * 16 Ohms, or 15.5 V (Yeah, I know it wouldn't be precisely .968 mA). The output voltage at 8 ohms would be 1.18 A * 8 Ohms, or about 9.4 V. The output voltage for 4 Ohms would be 1.18 A * 4 ohms, or about 4.7 V. Regardless of class of operation or types of feedback or types of impedance, this tells me the output stage is getting loaded down more as you decrease speaker impedance, and this is not unlike what you would have with a Class A or Class AB amplifier with an output impedance significantly greater than 8 Ohm. What's great about Class D operation is that much of its output impedance is reactive rather than resistive, meaning less power wasted as dissipated heat.
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chejian6

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Re: a nice part for Guitar Amplifier
« Reply #9 on: May 06, 2010, 04:40:06 AM »

Yes you are right. The load is not a resistor. But it just OK to be a simplified way to explain why the higher the impedance the higher the power.
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rowdy_riemer

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Re: a nice part for Guitar Amplifier
« Reply #10 on: May 06, 2010, 08:55:22 AM »

Well, the .1 Ohm on resistance of a mosfet IS resistance. I'm saying that the output impedance of the amp is not all resistive. I'm also talking more about the output impedance of the output stage of the amp rather than the impedance of the load(the speaker). If you look at the instantaneous impedance of the power stage when it is on, it probably is damn small. It's also damn large when it is off. Averaging the current over time, during which it is switching on and off, will tell you what the average impedance is. Apparently, even at full output, there is enough off time to have an impedance somewhere around 16 Ohms or at least significantly more than 8 Ohms.
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Joe

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Re: a nice part for Guitar Amplifier
« Reply #11 on: February 01, 2011, 03:15:45 PM »

The small size & lack of heatsink etc is amazing!

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joecool85

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Re: a nice part for Guitar Amplifier
« Reply #12 on: February 01, 2011, 03:33:49 PM »

Wow, I somehow skimmed past this.  Really neat circuit, never seen anything like it.

Anyone else built one?

Thanks for bringing it back up to the top Joe!
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