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Chip Amps Amplifiers based on integrated circuits

LM1875 Amp layout
LM1875 Amp layout
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Old 7th September 2019, 04:49 PM   #151
Dunk02 is offline Dunk02  Australia
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Quote:
Originally Posted by rabbitz View Post
Got a pic of these and I assume from Jaycar.
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Old 8th September 2019, 01:01 AM   #152
rabbitz is offline rabbitz  Australia
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Thanks. Good to know that Jaycar sell the real chip.
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Old 15th September 2019, 05:58 AM   #153
Dunk02 is offline Dunk02  Australia
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One more test I want to do.

I have noticed that some music appears to have off centre vocals (Dire Straits CD).
Now considering I built the amp and the speakers, and that the music may have been recorded this way, I would like investigate but need some advice on measuring channel balance.

I know that I can do differential probing of the two channel outputs with a sine wave source signal to detect any L/R channel imbalance. How critical is it that the wires and resistive loads on the amplifier outputs have identical impedences? Is there a “best” setup for this? And if there is a difference, how is it corrected?

Cheers

Last edited by Dunk02; 15th September 2019 at 06:14 AM.
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Old 15th September 2019, 02:58 PM   #154
johnr66 is offline johnr66  United States
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Quote:
Originally Posted by Dunk02 View Post
One more test I want to do.

I have noticed that some music appears to have off centre vocals (Dire Straits CD).
Now considering I built the amp and the speakers, and that the music may have been recorded this way, I would like investigate but need some advice on measuring channel balance.

I know that I can do differential probing of the two channel outputs with a sine wave source signal to detect any L/R channel imbalance. How critical is it that the wires and resistive loads on the amplifier outputs have identical impedences? Is there a “best” setup for this? And if there is a difference, how is it corrected?

Cheers
As with any measurement, the more precise your methods, the better the results. As measured on the amp board, the damping factor of the the circuit is very high which would make the influence of any slight difference in the load impedance less critical.

Feed each channel the same signal using a Y splitter cable. This insures the exact same signal is on the inputs. Connect load resistors to the outputs and a speaker across the +L and +R output. Ideally, there will be no sound from the speaker, however, expect a small amount of signal to show.

Volume controls are the worst offenders of imbalance as they may not track perfectly.
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