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Per-Anders Sjöström

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QSXM2 troubleshooting!!

Started by W1DAN, January 18, 2021, 06:13:30 PM

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Per Anders:

The RIAA stage came up fine for the left channel. On the right channel RIAA section I still have some offset on the output when the preamp has 10mv at TP1. For now I inserted a 10UF capacitor in series with R93, and the main output DC is now fine.

On the preamp DC servo amp IC1, when my test oscillator is set to 20hz, I see a sine wave on the output pin 6, as well as a little at C9. Would this AC audio correction signal "subtract" the from the main signal low frequency audio? Either way I added 10uF across C9 to make the correction voltage pure DC.

I'm listening to the preamp now-sounds clean. I will then look for the cause of the right channel DC offset and eliminate the audio coupling capacitor.

Good progress this weekend! Thank you again for your assistance!!



Hej Per Anders!

I would like to increase the gain about 6dB. Would I increase R51 to do this?

I am using a MM cartridge and the preamp is working pretty well (still have an issue with the right channel DC offset without input termination).

Thank you,