Single Supply vs Dual Supply Opamp's   - Page 1
Forum section: electronics / beginners

author: Anonmis
author_rank: Contributor
timestamp: June 20, 2012, 08:11:51 pm
content: Hello everyone,I was recently trying to put together a circuit that my brother successfully put together for a class project (specifically it is an audio preamp). On his board he uses an LM324 and a LM386. I built it the exact same way but all I had was a mc1458c and a LM386, the rest was built with the same components. If I hook his up to an ipod for example I can hear the music just fine, mine on the other hand sounds VERY VERY quiet and alot of distortion. These are hooked up with a 9V battery on positive rail and gnd on the respective VEE or gnd rail.I looked at the data sheets and noticed the LM324 is a single supply opamp where as the mc1458c is a dual supply. Which brings me to the following questions. Could this be the reason why my circuit is not working properly? Also, what are the differences in single supply vs dual supply and what difference can it make?

author: m12lrpv
author_rank: Regular Contributor
timestamp: June 21, 2012, 12:03:43 am
content: I'm new to this myself however looking at the datasheet for the MC1458 the input and output range is well clear of each rail while with the LM324 it can go to ground on both input and output.The things I looked for in the datasheet areCommon Mode Input Voltage Range and Output Voltage SwingI compared them to the input +/- supply voltage (rails) to see how close to the it can get.

author: Anonmis
author_rank: Contributor
timestamp: June 21, 2012, 02:18:28 am
content: Thanks for the info. I bought a few LM358 opamps and replaced the MC1458C and voila... it started working. Was it a matter of Single supply vs Dual or something else that made it work?

author: T4P
author_rank: Super Contributor
timestamp: June 21, 2012, 02:22:16 am
content: Quote from: Anonmis on June 21, 2012, 02:18:28 amALL opamps are dual supply. it's the CMIVR you want to think of

author: m12lrpv
author_rank: Regular Contributor
timestamp: June 21, 2012, 03:12:20 am
content: Quote from: Anonmis on June 21, 2012, 02:18:28 amThe something else...You're using ground as the negative rail. The LM358 can get to ground (it's negative rail) on input and output.The input/output range from a 9v battery for the LM358 is 0V to 7.5V give or take.For the MC1458C in a single supply circuit you're probably looking at about 4V min to 5V max I/O operating range from a 9v battery.

author: Zero999
author_rank: Super Contributor
timestamp: June 23, 2012, 05:33:47 am
content: The LM358/MC1458 are very poor choices for an audio amplifier - they have too lower bandwidth, insufficient slew rate and too much distortion.

author: Unclegummers
author_rank: Contributor
timestamp: June 23, 2012, 07:52:52 pm
content: Quote from: Anonmis on June 21, 2012, 02:18:28 amSingle supply op amps are usually found in those crappy little portable speakers that run on 9 volts for example. The op amp, according to the datasheet will have common mode voltage range that will be your output range. If you were to hook your guitar up to say an inverting style op amp, it would clip the bottom half of your guitar signal off. You need to bias the signal (DC offset.)"Google biasing" A dual supply op amp is something you might find in a solid state guitar amp for example, as the pre amplifier. The values obviously vary quite a bit for source supplies, but for example +-12V could be used. This doesn't require pre biasing, because the amp can go negative.Please correct me if I'm wrong (I know you would anyway!)