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Class D Switching Power Amplifiers and Power D/A conversion

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Old 16th April 2010, 07:11 PM   #531
ThokN is offline ThokN  Denmark
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Okay! So you are saying that we actually shouldn't bother with trying to parallel into 2 ohms and stuff, since the battery will die very fast at such high wattage?

If that is what you are saying, then I think we will just settle with the Amp9 and 4x HP10W 4ohm, one into each channel, and then try to not turn it to the max, which would use very much power.

The high-pass you are talking about, will that function as a cut-off below 80Hz to save power? And do you have any info or link to how this is done?

It's very kind of you to help with this basic stuff
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Old 16th April 2010, 07:28 PM   #532
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4 Ohms, 4 channels is plenty of a load for that battery. I wouldn't go to 2Ohm without increasing the battery.

"The high-pass you are talking about, will that function as a cut-off below 80Hz to save power? And do you have any info or link to how this is done?"

Well, yes! Look at my previous posts in this thread. THere are even links to use.


Have fun.
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Old 16th April 2010, 07:32 PM   #533
ThokN is offline ThokN  Denmark
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Quote:
Originally Posted by Andrew Eckhardt View Post
4 Ohms, 4 channels is plenty of a load for that battery. I wouldn't go to 2Ohm without increasing the battery.

"The high-pass you are talking about, will that function as a cut-off below 80Hz to save power? And do you have any info or link to how this is done?"

Well, yes! Look at my previous posts in this thread. THere are even links to use.


Have fun.
Oh sorry, didn't see that, but thanks!

I want to mention though, that we do have 2 batteries, which we will connect in series to get 24v But it sounds like we should stick with the amp/speaker setup as mentioned. No reason to use the batteries in 2 hours or whatever. It should hopefully last all night
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Old 16th April 2010, 09:19 PM   #534
Havoc08 is offline Havoc08  Denmark
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Quote:
Originally Posted by ThokN View Post
Sorry if this is a stupid question, but bridging is where you solder some components together on the board, and parallel is just when you use two output-channels as a single output?

If so, we can parallel the outputs and leave it there, I think. We are not able to lower the speaker resistance, since they are already paralleled in pairs. (4x8ohm into 2x2 @4ohm).
By bridging you get twice the power at the same impedance as it is a kind of push-pull principle as described by other user. By paralleling you ake the amp capable of delivering twice the power, but only if you decrease the impedance.

Quote:
Originally Posted by ThokN View Post
You can see the numbers here:
Click the image to open in full size.

It is a cheap battery (249kr). I can see these numbers are for charging, so maybe that doesn't comply with drawing power from it, but I can't find any info on that.
Do you have a link to your batteries?

Ps. sorry for mis-quoting you as someone else in my last reply.
That is the same type as mine. It will do just fine. You can optionally add a capacitor of 15-20mF for better bass management. Thos type of batteries give 2-400 amps in very short bursts as that i needed for starting a motorcycle or similar. Power delivery is not an issue as ong as you use proper size cables.


Quote:
Originally Posted by ThokN View Post
Okay! So you are saying that we actually shouldn't bother with trying to parallel into 2 ohms and stuff, since the battery will die very fast at such high wattage?

If that is what you are saying, then I think we will just settle with the Amp9 and 4x HP10W 4ohm, one into each channel, and then try to not turn it to the max, which would use very much power.

The high-pass you are talking about, will that function as a cut-off below 80Hz to save power? And do you have any info or link to how this is done?

It's very kind of you to help with this basic stuff
Even at max it will last more than 30 minutes. You can't just calculate the amperage drawn as 400watt/24v = 16,7A as music signal does not behave like this. As previously mentioned music signal are way lower than you estimate it to be as only few frequencies are played at the same time.

I can assure you that no matter which amp you choose the boominator will play loud! just inherent to its sensitive design. 90dB at 1 watt is alot of sound and the boominator is above that. You will likely draw less power on account of not having to turn the volume up so far as the sensitivity is working for you.
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Old 17th April 2010, 12:19 PM   #535
ThokN is offline ThokN  Denmark
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Thank you Havoc. I do know now that playing at max volume on a 4x100w amp doesn't consume 16,7A. Do you have an approximate for how much it would use when playing electronic music on max volume?

And where should we place the capacitor? (and what does bass management actually do?).

Last edited by ThokN; 17th April 2010 at 12:21 PM.
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Old 17th April 2010, 01:53 PM   #536
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Quote:
Originally Posted by ThokN View Post
Thank you Havoc. I do know now that playing at max volume on a 4x100w amp doesn't consume 16,7A. Do you have an approximate for how much it would use when playing electronic music on max volume?

And where should we place the capacitor? (and what does bass management actually do?).

Max power consumption with music roughly equals max RMS/5, so 4x100Wrms at 24V equals 3.33A or 80W. That's still suck 2 of these 7Ah SLAs dry in under 2 hours.
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Old 17th April 2010, 02:18 PM   #537
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RMS power rating of an amplifier has more to do with continuous wave power capacity before clip. So 400WRMS means it will take more than 400W to produce the waveform through an amplifier. At that point there is no possible reduction factor, if the amp has to barf it out, it has to come from the battery and capacitors. The power envelope of an audio signal varies so much it is impractical altogether to come up with a reduction factor of peak output versus average input. Bodies have gotten together and tried but there isn't what you'd call general agreement.

Audio power - Wikipedia, the free encyclopedia

Personally I'd say you're better off to design to handle peak demand of the system, plus some continuous battery load that it can handle, which the thing at the end of the volume control will have to manually regulate, unless you add an automatic level control circuit. You could add a cheap ammeter if you really wanted to tech it out.
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Old 17th April 2010, 02:25 PM   #538
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Oh sorry, didn't see that, but thanks!

I want to mention though, that we do have 2 batteries, which we will connect in series to get 24v
Good. I was wondering how you expected to get those power figures with 24V P-P into 4 ohm. Definitely don't waste your time trying to load 2 of those batteries in series with 4 BTL switching amps channels loaded at 2 ohms. You're a bit under matched with that battery even at 4 ohm with 24 volts supply, unless you save the last 3dB for rare peaks. Like you said, if you hear clipping you have it set way too loud.

Last edited by Andrew Eckhardt; 17th April 2010 at 02:27 PM.
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Old 17th April 2010, 03:07 PM   #539
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In the past Sony used a simple RC network after a signal diode with cathode connected to the audio output. A bleeder resistor set the decay of the limiting, and the input resistor set the attack. They fed the voltage on the capacitor back to the 100Hz center on a linear voltage controlled parametric EQ IC. In other words they dialled back the bass when the overall signal got too large. So, this problem has been addressed in various ways in commercial boom box offerings. It would be fairly easy to do something like this with your input filter, but you would need some active circuitry. At this fidelity level it could potentially be pretty basic.
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Old 17th April 2010, 03:24 PM   #540
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Max power consumption with music roughly equals max RMS/5, so 4x100Wrms at 24V equals 3.33A or 80W. That's still suck 2 of these 7Ah SLAs dry in under 2 hours.
Please note this is specifically for the amp9b or amp6b which has 90% effciency, assuming the source is able to load the amp to -0 dB, and that the music roughly follows the RIAA recording standard.
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