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Old 25th March 2006, 04:24 PM   #1
komen is offline komen  Finland
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Default How much gain should I have?

I just finished fy first chip amp. Its little amp for PC use. I used TDA2030A chips in inverting configuration with 26 dB gain. I don't have pre-amp stage, just potentiometer. I'm happy that i don't have hum or hissing or any such newbie problems. Had some oscillations but they went away by adding input filter capasitor.

Problem i have is sensitivity/gain. Laptop computer seems to give quite low signal level even with settings turned all the way up. Doesn't bother with new music, but some movies and old recordings have lower signal level. I could of course change feedback to get more gain, but I think I'll try op-amp gain stage before the pot instead. My question is how much gain should I have? I'm thinking of 12 dB to get 38 dB full level gain. Too much or not enough? How much gain do you usually have in computer use with small amp and small speakers? I could of course try and then re-try, but it would be easier to get some suggestions to start with. Speakers are Tangband W3-871S which are not very sensitive and BSC reduces sensitivity even more.
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Old 25th March 2006, 06:48 PM   #2
Deltat is offline Deltat  United States
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Well to answer this question we need a bit more information. What voltage rails are you using? How big of an output signal can you get with that rail? What is the max output of your sourse?

The equation for gain in dB is = 20 log (Vout/Vin)
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Old 26th March 2006, 01:32 PM   #3
komen is offline komen  Finland
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I have 12-0-12 transformer and rail voltage without input signal was +/- 18,5 V. I suppose it's more like 16-17V with heavier load. I dont know how close to rail output voltage can go, but 15 V or so wouln't be bad guess for Vout.

Input voltage is more complex question. I may use this setup with different sources, and level depends also on material. That's why I wanted to hear what kind of gain is usually reasonabe. Maybe I will measure some signal levels with oscilloscope or just try adding some gain and see if it seems OK.
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