Aha! That actually made me wonder if maybe one half of the opamp is dead, and I realised I was using a second-hand one. Replaced it with a new one and it runs continuous now. This thing is loud! Unfortunately the distortion is super high. It sounds more clipped than a highly distorted guitar. could it be some of the resistors need tweaking now? On 18 March 2015 at 20:13, Ryan O'Connor wrote: > Funnily enough I connected one of the caps from inverting input on > left-hand op-amp to GND by mistake, and I hear the audio with a > high-pitched squeal mixed in lol. > > On 18 March 2015 at 20:07, Ryan O'Connor wrote: >> Thanks that was a really helpful answer Robert. >> >> I've found two 0.1uF bipolar capacitors and put them in. But I still >> have the same problem. It plays distorted audio for about 0.01 seconds >> now when I plug the second cap in. >> >> Ryan >> >> On 18 March 2015 at 19:25, Robert Dvoracek wrote: >>> In this case, no, accuracy does not matter. These are DC blocking caps= to prevent the DC bias from leaking back into the signal source. As long = as they are at least 10nF, any film caps will work. The reason I am recomm= ending film is because they are guaranteed nonpolar, they don't dry out lik= e electrolytics, and they don't drift, piezo, or have noise like ceramics. = Film is always the best when you are dealing with audio. >>> >>> Cheers, >>> Robert >>> >>> ---------------------------------------- >>>> Date: Wed, 18 Mar 2015 19:14:15 +1300 >>>> Subject: Re: [EE] simple opamp amplifier problems >>>> From: rocifier@gmail.com >>>> To: piclist@mit.edu >>>> >>>> Hi Robert, why does it have to be 10nF specifically? What do those >>>> caps do? I have a professional audio mixer circuit here that uses >>>> in-line 47uF polarized caps at the signal inputs. Does the accuracy >>>> matter? >>>> >>>> Cheers >>>> Ryan >>>> >>>> On 18 March 2015 at 18:42, Robert Dvoracek wrot= e: >>>>> 10nF, use film caps. >>>>> I would have also connected the feedback resistor after the totem pol= e instead of before it to correct for some of the distortion in the final s= tage. >>>>> >>>>> Cheers, >>>>> Robert >>>>> >>>>> ---------------------------------------- >>>>>> From: bobblick@ftml.net >>>>>> To: piclist@mit.edu >>>>>> Subject: Re: [EE] simple opamp amplifier problems >>>>>> Date: Tue, 17 Mar 2015 22:01:18 -0700 >>>>>> >>>>>> Actually I take back that thing about the third diode, just the pull= down >>>>>> resistor should fix things. >>>>>> >>>>>> Bob >>>>>> >>>>>> On Tue, Mar 17, 2015, at 09:46 PM, Bob Blick wrote: >>>>>>> Hi Ryan, >>>>>>> >>>>>>> The LM358 will require a pulldown resistor on its output, otherwise= it >>>>>>> runs class B and will distort real bad. >>>>>>> >>>>>>> Also you will need to get the bases of your transistors a little fu= rther >>>>>>> than 2 diodes apart. Put a third diode in there, and it should soun= d >>>>>>> great but use too much current. Make that third diode a Schottky an= d you >>>>>>> should be golden. >>>>>>> >>>>>>> Cheerful regards, Bob >>>>>>> >>>>>>> On Tue, Mar 17, 2015, at 09:36 PM, Ryan O'Connor wrote: >>>>>>>> Hi guys, I've bread-boarded the following circuit, but its not pla= ying >>>>>>>> audio. I get only DC current at the base of the 2N4401. I've had i= t >>>>>>>> playing audio briefly while screwing around. For example if I remo= ve >>>>>>>> the 0.01uF cap from the non-inverting input of the left-most opamp= and >>>>>>>> plug it back in, I hear a distorted version of the song I am playi= ng >>>>>>>> as input for about half a second (actually the cap value is polar >>>>>>>> 47uF). Then silence, DC voltage. Could it be because I am using >>>>>>>> electrolytics for these two caps? I can't find any "103" bipolar l= ying >>>>>>>> around, or even close to it. I tried a 0.47uF bipolar but I only h= ear >>>>>>>> about 0.05 seconds of audio when I plug/unplug that one. Have doub= le >>>>>>>> checked all the wiring twice. >>>>>>>> >>>>>>>> Circuit below: >>>>>>>> >>>>>>>> http://www.techlib.com/electronics/graphics/audioa14.gif >>>>>>>> >>>>>>>> Cheers, >>>>>>>> Ryan >>>>>> >>>>>> -- >>>>>> http://www.fastmail.com - Choose from over 50 domains or use your ow= n >>>>>> >>>>>> -- >>>>>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >>>>>> View/change your membership options at >>>>>> http://mailman.mit.edu/mailman/listinfo/piclist >>>>> >>>>> -- >>>>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >>>>> View/change your membership options at >>>>> http://mailman.mit.edu/mailman/listinfo/piclist >>>> -- >>>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >>>> View/change your membership options at >>>> http://mailman.mit.edu/mailman/listinfo/piclist >>> >>> -- >>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >>> View/change your membership options at >>> http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .