Electronics > Projects, Designs, and Technical Stuff

weird opamp configuration

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wraper:

--- Quote from: stojke on January 21, 2019, 09:51:13 pm ---CD input : 440Hz test tone @ 0.207mV AC > Passes trough the Tone board : 0.207mV AC at maximum volume on output ( @ CN1 )
If I insert my (home made tm) Op Amp modification with applied gain before the volume pot I get around ~10V AC ( @ CN1 ) at max volume and the output sounds nice and loud as it should but with distortion.

Because I have* no practical nor theoretical knowledge of precise operation of amplifier circuits I had no other choice but to modify the area that seemed the most logical to be the origin of the problem.

--- End quote ---
:palm: Modifying what is not faulty and making crap out of that. No way there should be 10V AC on the output. If there is any fault then somewhere in power amplifier, not in the part of the circuit where you are making stupid experiments.

xavier60:
What were the signal levels at the input and output of the power amplifiers?

stojke:
CN1 207mV , the same as at input jacks , output I did not measure (it was loud , but not as loud as it should be. If we were to compare villager style it was like an average 30-40W amplifier).

dmills:
Preamp/Tone board is fine, it is not supposed to have meaningful gain, it is there for tone control, and some filtering for the sub.

I would be eyeballing the power amp and possibly IC6 on the input selector board, but really, stick about 1V up it from a signal generator and work your way thru it with a 'scope, where the signal vanishes you have your problem.

What are you measuring 0.207mV with? That seems awful low for the output of a CD player, they usually swing a volt or so.... 

Regards, Dan.

stojke:
Thanks for the diagnosis dan (and xavier60!) I will try that, it seems I am really off the track from all  the replies Ive read.
I am using my phone as an signal generator with some signal generator app because the voltage swing in CD player playback is trowing me off most of the time.

I am lacking some proper testing equipment at the time beeing.

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