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How to connect a pico to a bridged amp?

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How to connect a pico to a bridged amp?

Postby audio_jim » Fri Jul 10, 2015 6:31 pm

Hello,

I wonder if anyone can help me figure this problem out, I have attached below an example of a bridged amplifier & the problem I can foresee is in actually connecting the Picoscope to the output of the amplifier in order to perform the usual measurements.

With a regular amplifier the speaker output consists of an output & ground, so connecting the Pico to this is very easy. The problem I can see with testing a bridged amplifier is that as soon as I connect the Pico to the output, it looks like to me that this will effectively short the negative output of the amplifier down to ground.

Image

Any help on this would be appreciated,

Thankyou!
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Re: How to connect a pico to a bridged amp?

Postby Martyn » Tue Jul 14, 2015 10:17 am

Either use a differential probe/ scope, otherwise use two channels, one for positive and one negative, and then select a maths channel to display the difference. Please ensure that you are operating within the acceptable ranges for the scope, and applying any necessary safety measures.
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Re: How to connect a pico to a bridged amp?

Postby audio_jim » Tue Jul 14, 2015 6:40 pm

Thanks Martyn,

I have never measured a bridged amp before so I have only ever used one channel, the maths channels are something I have not really used either & I noticed there are quite a few to select, which one would I use for this arrangement?

One final question, I use the 4262 for measuring THD, so if I used this method of connecting to the bridged amp using a maths channel, would the usual automated measurements still work & be just as accurate as when using a single channel?

I appreciate the help!
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Re: How to connect a pico to a bridged amp?

Postby Martyn » Thu Jul 16, 2015 10:22 am

You would need to use A-B or B-A depending upon which is the positive signal.

When using maths channels the number of samples collected is reduced to 2MS per waveform, using the release version of the software, although this has been increased to 5MS in the beta version. This may have an effect on the measurements you are taking, but this will depend upon the settings you are using.
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Re: How to connect a pico to a bridged amp?

Postby audio_jim » Fri Jul 17, 2015 6:27 pm

Thanks Martyn for your valued support as always, much appreciated :)
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