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Chip Amps Amplifiers based on integrated circuits

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Old 16th August 2018, 06:02 AM   #61
FauxFrench is offline FauxFrench  France
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That it works under certain conditions is always a good start. Then the basic circuit should be correct.

The quiescent current per OPA2134 is around 10mA.
I only see one LM1875 (mono) so you only use one of the OPA2134 OP-AMPs I assume. Did you "tie" the other OP-AMP such that it does not oscillate?
Do you have an oscilloscope so you can see if there is any HF oscillation on the output of the LM1875 or on the output of the OPA2134?
What are your supply voltages for the LM1875 and the OPA2134?

My LM1875 does HF-oscillate when the peak output current approaches 3A. For initial testing I use only +/-18V. For my OPA2134 +/-15V.

The LM1875 has a tendency of HF-collapsing on one (the lower) half of the sine-wave. That will leave a resulting DC at the output. You cannot hear the HF self-oscillation as it is in the order of 1MHz (for mine at least).

Last edited by FauxFrench; 16th August 2018 at 06:12 AM.
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Old 16th August 2018, 06:30 AM   #62
Clueless but avid is offline Clueless but avid  Germany
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Hi, no, I havn't an oscilloscope, and if I had one, I wouldn't know how to use it. I am a total newbie and I'm glad, I know how to measure voltage, resistance & current with my supercheap multimeter.
I've never heard of tieing one half of an opamp, but thanks for the tipp. I'll google & try it.
The supply voltages are +/-15V & +/-26V.
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Old 16th August 2018, 07:28 AM   #63
FauxFrench is offline FauxFrench  France
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You make a simple circuit for the unused OP-AMPs (eventually a simple voltage follower tied to ground) to prevent them from HF-oscillate and thereby pulling all the OP-AMPs down. Thus, unused OP-AMP outputs to the inverting inputs and the non-inverting inputs to ground.

With +/-26V supply of the LM1875, mine would HF-collapse at higher sound levels. Try for a start to use a 10 Ohm power resistor in series with the speaker. Then the LM1875 has much less tendency to HF-collapse.
With this, can you then make the OPA2134 work?

Is your other 8-pin IC a voltage regulator?
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