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Old 9th July 2011, 06:26 AM   #1
epilot is offline epilot  United States
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Default Class D and low impedance load

Hello folks,

Sorry but I have a question.

I just have several load's all in Parallel with the net load happens to be just 1 ohm. I am actually a Newbie in the class D filed, so my question is if class D amplifiers are good enough to drive a such low load? Or there is a problem while doing a such job? I know that for common class AB chips like LM3886T I can not drive the sad load other than adding several other chips all in Parallel. But please enlighten me about Class D amplifiers?

Thanks a bunch
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Old 9th July 2011, 08:36 AM   #2
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I don't think it matters what class the amplifier is, a particular amp of any class will be optimised for a particular load and (usually) also able to drive lower impedances to some degree. And one ohm is not the load that amplifiers are generally optimised for.

Are you able to connect your loads in series/parallel and hence return to more standard impedances? That would ease the problems of finding a suitable amplifier greatly.
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Old 9th July 2011, 12:33 PM   #3
ssanmor is offline ssanmor  Spain
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No problem with our amplifiers, for example (www.coldamp.com). In general, as long as you don't exceed the overcurrent limit, it is fine (this means that you will have max voltage excursion limited: for example, if the current limit is 20A (approx that in our S450 amplifiers), you will go to 20Vpeak (or 200Wrms) and then it will protect itself. Some other amplifiers are not designed to handle large currents, then you will run into problems. If you need more current, you will need a more powerful amplifier with higher current limit (as our S750), and limit the supply voltage.
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Old 9th July 2011, 12:56 PM   #4
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Quote:
Originally Posted by ssanmor View Post
for example, if the current limit is 20A (approx that in our S450 amplifiers), you will go to 20Vpeak (or 200Wrms) and then it will protect itself. Some other amplifiers are not designed to handle large currents, then you will run into problems. If you need more current, you will need a more powerful amplifier with higher current limit (as our S750), and limit the supply voltage.
All credit to your amplifier that can drive a one ohm load, but I think your example illustrates the problem. We have a (presumably) 450W amplifier which can creditably work into 1 ohm loads but isn't really designed for that. So available power drops from 450W to 200W?
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Old 9th July 2011, 01:55 PM   #5
ssanmor is offline ssanmor  Spain
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Quote:
All credit to your amplifier that can drive a one ohm load, but I think your example illustrates the problem. We have a (presumably) 450W amplifier which can creditably work into 1 ohm loads but isn't really designed for that. So available power drops from 450W to 200W?
Absolutely agree with you. Amplifiers are usually designed to meet certain constraints and with typical loads. Ours are not different. They are designed to drive 4 ohm loads although they can reach full power at 2 ohm. For 1 ohm high power applications, some modifications need to be done, we have done several works of this kind for special customers (reinforcing output stage to handle larger current).
In general it makes little sense to use such low impedance loads unless you are forced to run on low rails, such as in car audio applications (where for some costs or size reasons you don't want to use a DC/DC converter to raise the voltage).
We are working on a very special (but audio) application for one customer that needs to drive 50 milliohm loads at 100-200W levels.
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Old 9th July 2011, 02:10 PM   #6
epilot is offline epilot  United States
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Thanks guys,

Before respond to your statements, I would like to know if I am able to use a transformer (something like a impedance matching transformer so that I drive my 1 ohm load by an amplifier essentially designed to work in 4 ohms?)

P.s for ssanmor,
Do you produce amplifiers? if so just what classes do you produce?
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Old 9th July 2011, 02:17 PM   #7
ssanmor is offline ssanmor  Spain
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I have heard of people using transformers for impedance matching (in fact the customer I have mentioned is currently using transformers to power his 50 mohm speakers with normal amplifiers). I don't know how that will affect sound quality, but it will for sure not help.
Yes, we produce Class-D amplifiers and switching PSUs: have a look at www.coldamp.com
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Old 10th July 2011, 12:08 AM   #8
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ssanmor, may as well short circuit your amps with that load!

i take it is some kind of VLF application, shaker motors perhaps?
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Old 10th July 2011, 12:58 PM   #9
ssanmor is offline ssanmor  Spain
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No, it is for a new speaker development, ribbon based, full audio bandwidth. First tests are very revealing.
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