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Input voltage limitation ---post 1 of 2

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Input voltage limitation ---post 1 of 2

Postby Ben » Mon Apr 25, 2005 9:36 pm

If the maximun peak to peak input voltage is 40 Vac, then the maximum Ac rms input is 28 vac rms. Over an 8ohm load, this is 100 watts.....good for checking a modern amp at full ouput. However, I need to test alot of older tube amps which need to be adjusted with 16ohm load. At 28 volts, this only allows the amp to be tested at a 50watt load, less than the 75watt load I need. If I use a 10x probe, then pico will see a 5 volt input. In order to see harmonics to calculate a thd of say .01%, then pico would need to resolve harmonics with amplitudes lower than a 1/2millivolt. If I used a high impedance voltage divider across the 16ohm speaker and a 1x probe, I'd need to measure harmonics with amplitudes lower than 2.8millivolts. If the maximun dc input is 20 volts, then pico would need to be able to clearly see a .6millivolt peak for a dynamic range of 90dbv. Can pico do this?

Postby Sarah » Tue Apr 26, 2005 9:09 am


Thank you for your post.

I believe that using the ADC-216 this would be fine. By default 0dB is 1V RMS, this however can changed. You would need to use attenuating probes for voltages outside of the ±20V input range.

The ADC-216 is a 16-bit unit and thus would give you a good resolution. It has a dynamic range of 96dB.

Hope this helps

Best Regards

Postby Ben » Tue Apr 26, 2005 10:29 am

"By default 0dB is 1V RMS" this is handy to know, thanks.
Then -90dbv is 1/(10^4.5) volts or 31 microvolts of resolution.
Impressive. :shock:

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