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Shaz 20th September 2003 02:51 PM

Input Capacitor
I recently built an IGC based on Peter's design and am very pleased with the results. The sound is really very good and it has a good amount of power. There was one problem I encountered that I was hoping others might be able to shed some light on.

My amp uses the recommended 4.7 uF bipolar input cap. I noticed that the overall performance was excellent including very acceptable bass response and very open and clear high frequencies. However, there was a "fuzziness" in a very narrow midrange band (affecting tenor voices and instruments in the same range). I tried shorting the input caps and that appeared to eliminate the problem. I was wondering what others have experienced with different values and types of the input cap. Also, what is the purpose of the input cap?

tschrama 20th September 2003 04:53 PM

I've had good results with a LM3886 inverted GainClone without input cap.... I sounded good, low offset (about 25mV), everything was fine ... untill ... one sad day ... I messed up the powersupply of my preamp .. without realizing that, I switched on the amp ... a big oemmpfffff ... no sound .. until after a minute or so, while I was trying to find what was wrong, suddenly a weird kind of smell appeared and smoke was coming out of my reflex ports ... my woofers where toasted.... a input cap would probably have saved my woofers.. it limits DC-gain to 1...

Goodluck to you ;) ,

analog_sa 20th September 2003 05:03 PM


a input cap would probably have saved my woofers.. it limits DC-gain to 1...
It certainly limits DC gain to zero :) So you pre was also DC coupled? Now, that's brave.

tschrama 20th September 2003 06:39 PM

Ehhhhhhh it limits DC gain to zero!! sorry about that ... you were right analog_sa .... yeehhhhhh I was brave, young and stupid... and got some ideas in my head about low frequency group delay etc ect .... actually the preamp was capacitor coupled, but I used it a headphone amp too, so I used a 4700uF output cap ... this had a DC time of 300 seconds or so .. hmmmm stupid... but I've learned.. my newest gainclone uses a 4.7uF input cap ... and it sounds good..too


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