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Chip Amps Amplifiers based on integrated circuits

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Old 9th October 2012, 02:06 PM   #21
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A cellphone is a terrible source. Find a real CD player.
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Old 11th October 2012, 11:05 AM   #22
AndrewT is offline AndrewT  Scotland
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I didn't spot it but I can't see a comment on 16W into 4ohms from 8Vpk.

8Vpk into 4r0 is equivalent to 8W, not 16W.

But, is 8Vpk the maximum signal that the Power Amplifier can deliver to a 4r0 test load?
You need a variable sinewave input as a test signal.
You need a 4r0 test load.
You need an oscilloscope to monitor the start of clipping and then use that to determine the maximum Vpk available without any sign of clipping.
Alternatively you can use a distortion meter and determine the maximum output that has a maximum distortion of 0.1%. But the skilled use of a scope is simpler.

P= I * V = I^2*R = V^2 / R for DC and for RMS.
For peak of sinewave
P = Ipk * Vpk / 2 = Ipk^2 * R / 2 = Vpk^2 / R / 2

You forgot to divide by 2 when using the peak signal.
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Old 11th October 2012, 02:16 PM   #23
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Alternatively you can use a distortion meter and determine the maximum output that has a maximum distortion of 0.1%. But the skilled use of a scope is simpler.
No, I don't think so.

I've already pointed out TWICE that this amplifier is only capable of maximum output for short durations, probably only a few cycles at lower frequencies, if that.

This will in all probability require a specially designed test signal and EXPERT use of a scope if the peak output is to be captured. You could create such a test signal in the digital domain or perhaps gate a high amplitude tone into a low amplitude tone in the analog domain. Problems with persistence of the sight picture will anyway mean that a digital capture scope will be preferable.

In class H it is anyway rated 10% THD @ 70W into 4 ohms
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Old 11th October 2012, 02:47 PM   #24
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a single-shot transient would be suitable, captured on a digital device.
but honestly.. would anyone realy go into all that trouble?
if its built properly and everything else is okay, then it will do 70 watt into 4r0 load.
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Old 11th October 2012, 03:33 PM   #25
Mooly is offline Mooly  United Kingdom
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Many test CD's have an "impulse response" that is easily viewed on a scope. I would imagine that would make an ideal test waveform.

Fig 3 here,
Sony SCD-C333ES SACD/CD player Measurements | Stereophile.com
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Old 11th October 2012, 05:06 PM   #26
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a single-shot transient would be suitable, captured on a digital device.
but honestly.. would anyone realy go into all that trouble?
if its built properly and everything else is okay, then it will do 70 watt into 4r0 load.
Yeah, if.

The problem is how to determine whether it has been built correctly.

A single transient is an inconvenient way to measure this, even given digital capture.

A convenient way of measuring this is to create a digital signal to output with a soundcard @ 1k (sinewave) with short bursts (say 1~3 cycles every 30 cycles, to allow the amplifier to recover) with an amplitude ratio of roughly 2. This means that when the LOW output is 18W the HIGH output will be 70W, (sqrt[70/18]). Then you set up the amplifier with a 4 ohm load and turn up the output until on the scope 'till it reaches ~<12V peak (8.48v rms) on the LOW waveform. You set the trigger to ~15V and now you will see the HIGH output if the timebase is set appropriately and the burst repetition rate is such that the trace is still visible given the persistence of the particular scope display. If you use a digital scope, no problem. The voltage should be sqrt(70*4) = 16.73v rms = 23.66V peak. The voltage is roughly doubled, because that is what you can conveniently achieve by switching in a cap (or one on each rail).
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Old 11th October 2012, 05:29 PM   #27
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why would not a single shot transient of a square wave not work, if the capture device would log the highest amplitude?
but let's assume i did not ask that.
Why do we thik its so hard to build this amp? it has everything in the package, realy needs only the minimal external components.
the original post is about having low ouput power, and using low supply voltage.
natural, supply voltage is close to minimum, can't blame the chip for not meeting specs of higher rail voltage builds.
Get a decent traffo and it will work.
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Old 12th October 2012, 09:01 AM   #28
AndrewT is offline AndrewT  Scotland
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the build does not achieve target performance because the builder has not understood the information in the datasheet. Or it is built wrong.
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Old 13th October 2012, 09:03 PM   #29
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specs say 14.4 volts.
ps psu is 12v.
difference is 1.4 volts, probably the lift supply doubles the rail.// not sure//
so it has somewhere ~4.5 volts less swing at output.
sure, it won't meet the specs. no mirracle in that.
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Old 14th October 2012, 01:22 AM   #30
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why would not a single shot transient of a square wave not work, if the capture device would log the highest amplitude?
A single shot transient may work, but how do you know that the amplitude of the transient is appropriate? You could be there half a day turning it up by increments to get it to the right level, or you could overload the device on the first shot, drive it into muting or some other fault condition and presume it was faulty.

The advantage to the methodology I have described is that it permits you to go directly to the answer in a repeatable manner. Yes, it's trouble to set up, but nobody said it was going to be easy, in fact I've warned repeatedly that testing the functionality of this amplifier is not straightforward.

Testing is about more than devising a technique that will work eventually or on a hit-or-miss basis. You have to think these things through.

How can I go directly to the result I want? Or, will the technique I have suggested really give the answer repeatably on a reliable basis, or will it perhaps lead to the (possibly inexperienced) person conducting the test wasting a lot of time and effort and still not reaching the correct conclusion?

I release tested thousands of electronic products as a student and I have seen ill-devised tests destroy expensive test equipment for which I was nominally responsible simply because the person writing the test procedure failed to account for the fact that the last state the test set was set to was a milliwatt level, and the test procedure read 'now set the DUT to full power and repeat the test'. It's all too easy to simply follow the instructions when performing an unfamiliar test under production pressures. That's why the engineer writing test procedures should have experience of performing tests and at the very least needs to think about what they are suggesting, particularly because modifications to the test procedures are cumbersome to organise under ISO 9000 etc. You would be threatened with disciplinary action simply for writing pencil annotations on the test scripts.
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