Audio Amp question - Page 1
Forum section: electronics / projects

author: nick.sek
author_rank: Regular Contributor
timestamp: June 28, 2012, 11:27:36 am
content: I'm trying to design a small audio amplifier just for fun and it isn't working - so here is a small attached file of my design can you see the fundamental mistake that I'm over looking? I really want to get this working - and on a side note the op amp are 741 as I have no other amplifiers and I want to keep this extremely basic. Any input would be awesome.Thanks so muchNick

author: Rerouter
author_rank: Super Contributor
timestamp: June 28, 2012, 11:33:18 am
content: try flipping it and reattaching it to your first post,

author: DarkPrince
author_rank: Regular Contributor
timestamp: June 28, 2012, 11:33:44 am
content: No comment just a less upside-down image.

author: nick.sek
author_rank: Regular Contributor
timestamp: June 28, 2012, 11:37:20 am
content: Thank You Dark Prince

author: olsenn
author_rank: Frequent Contributor
timestamp: June 28, 2012, 11:50:16 am
content: The ua-741 will SOUND LIKE SHIT! Actually, you probably won't even hear anything that resembles music. Try the design in the below thread. This is my design which works very well, but there's also a site for an alternative if you prefer called the O2 amp, which several people are raving about. Don't sweat the higher end components... you can get them as free samples and overnight delivery.https://www.eevblog.com/forum/projects-designs-and-technical-stuff/headphone-amplifier/msg120754/#msg120754

author: Stephen Hill
author_rank: Regular Contributor
timestamp: June 28, 2012, 11:58:59 am
content: What does your power supply circuit look like?

author: nick.sek
author_rank: Regular Contributor
timestamp: June 28, 2012, 12:28:54 pm
content: Its is just a dual power supply that produces which both sides produce 9 volts. I have it configured to produce a relative negative voltage, that is why the guitar ground is going to earth ground, same with all the other small components.

author: Stephen Hill
author_rank: Regular Contributor
timestamp: June 28, 2012, 12:32:28 pm
content: I'm just curious how clean the output of the power supply is and if you've used bypass capacitor at all the power pins of the op amps.Also, what have you developed the prototype on? If it's breadboard, there might be a brake in the circuit somewhere.Finally, have you simulated the circuit in something like LTSpice and did it work in that?

author: nick.sek
author_rank: Regular Contributor
timestamp: June 28, 2012, 12:55:51 pm
content: I'm going to ad the by-pass capacitors - my power supply is pretty good, but as always never ideal. And it was developed on a bread board, and no I have not simulated it. Now I'm trying to get use to the program you suggested do you know if there is a place with a sample tutorial?

author: Stephen Hill
author_rank: Regular Contributor
timestamp: June 28, 2012, 01:05:09 pm
content: Just search YouTube for LTSpice Tutorial and quite a few are available covering different topics. Once you've simulated the circuit you might find the problem

author: Tube_Dude
author_rank: Regular Contributor
timestamp: June 28, 2012, 01:55:06 pm
content: Take out, or substitute for a voltage follower the last amp before the output. The way you have it is completely wrong...

author: T4P
author_rank: Super Contributor
timestamp: June 28, 2012, 01:58:51 pm
content: 1)Trust me the ua741 is going to be a POS, use a proper opamp, like a TL072

author: Tube_Dude
author_rank: Regular Contributor
timestamp: June 28, 2012, 02:01:19 pm
content: Quote from: DaveXRQ on June 28, 2012, 01:58:51 pmEven a "proper" opamp, will not work when there are fatal design faults...

author: Stephen Hill
author_rank: Regular Contributor
timestamp: June 28, 2012, 02:08:42 pm
content: Why not go all out and buy an AD843 or OPA627... *sigh*

author: T4P
author_rank: Super Contributor
timestamp: June 28, 2012, 02:39:56 pm
content: Quote from: Tube_Dude on June 28, 2012, 02:01:19 pmYeah...

author: Hideki
author_rank: Frequent Contributor
timestamp: June 28, 2012, 09:56:27 pm
content: Using 741 is the least of your worriesWhat is this circuit supposed to do?Each lowpass and highpass filter has adjustable gain upwards, but it doesn't go below unity. The two potmeters are effectively both just adding more gain to the entire bandpass signal (the filter curve will change a little bit as well), so why have two adjustments that do almost the same thing?I assume you want to sum the three outputs. For a proper virtual earth mixer you need three separate 1k resistors -- not a single one. You have now shorted all opamp outputs together, so they will have to fight each other when the three signals are different at any point in time. See figure 4 inhttp://sound.westhost.com/articles/audio-mixing.htmfor a better solution.It looks like the last opamp is there to invert the signal, but it won't work that way. Study the schematic. You have shorted the output directly to the output of the mixer opamp before it. An inverting amplifier with no gain needs two resistors of the same value. One into the negative input and one in the feedback loop.If you intended it to work like a typical three band EQ with cut and boost, I would advise you to use the extremely common Baxandall style EQ, like figure 2 inhttp://gilmore2.chem.northwestern.edu/projects/equal_prj.htmor this onehttp://electroschematics.com/6201/3-band-equalizer/