A speaker with impedance of 8 Ohms means a DC resistance of about 4 Ohms. Driving this speaker directly with the drain of a FET to 5 Volt means a sigificant DCpower in the speaker. I would suggest to use a resistor in series, for the max power in the speaker is 0,8 W. That means you must limit the DC power (PWM on 50%) to about 0.2 - 0.3 Watt. ----- Original Message ----- From: "Dumitru Stama" To: "Microcontroller discussion list - Public." Sent: Thursday, November 05, 2009 6:53 PM Subject: Re: [EE] Amplifying a PWM signal > Hi guys, > Thank you very much for trying to help me. > The PWM frequency is about 150kHz, my sound is sampled at 22050Hz using 8 > bits. > I tried using a low pass RC filter but then the sound level is even > lower. I read somewhere on the web that if i feed the pwm signal > directly to the speaker it would be ok since the speaker cannot react > at 156kHz anyway. It works, i can say i don't have any noise except > the one generated by the fact i am using 8 bits per sample. > I thought about limiting the current from the base with R1. > The impedance of my speaker is 8 ohms, max. power is 0.8W. I can take > a few pictures with my circuit if they might help. > My power source is a bench source delivering 5V / 1.5A, i am not using > any LM7805 or other regulator. Both the PIC18F and LM386 are powered > from 5V. > > > On Thu, Nov 5, 2009 at 6:28 PM, Herbert Graf wrote: >> On Thu, 2009-11-05 at 00:59 +0200, Dumitru Stama wrote: >>> Hi guys, >>> i have a question. My PIC18F2520 is set up to output a PWM signal. I >>> want to amplify the signal's current and feed it into a speaker. >>> Right now using only a single PN2222A i can hear the sound but the >>> volume is quite low. >>> I tried a LM386 and the output is what i really want but only if i >>> select the 200x gain schematics. >>> I don't know what should i try now, i really want to use only simple >>> components and not a dedicated amplifyer like LM386. >> >> What is the impedance of your speaker? What's the frequency of your PWM? >> What's the purpose of R1? >> >> TTYL >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -------------------------------------------------------------------------------- Geen virus gevonden in het binnenkomende-bericht. Gecontroleerd door AVG - www.avg.com Versie: 9.0.698 / Virusdatabase: 270.14.51/2482 - datum van uitgifte: 11/05/09 08:37:00 -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist