Author Topic: op amp spitting out input voltage instead of amplifing signal ?  (Read 2233 times)

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Offline Dantali0nTopic starter

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Hey all so I have an op amp an mc4558d dual op amp to be precise. And i hooked it up but it dosent actualy amplify the signal it just spits out a slightly lower voltage then is on the vcc.

Ive included an image of my setup. now my question is did my op amp die, certainly can't image that this is normal behaviour.

The input is an 1 volt source so with times 2 amplification i expect a 2 volt signal however its 11.4 ?  :-//
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Online Andy Watson

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Re: op amp spitting out input voltage instead of amplifing signal ?
« Reply #1 on: March 27, 2014, 04:16:55 pm »
The input is an 1 volt source so with times 2 amplification
I make it a gain of 1.5.

The 4558 is an old design and it does not operate rail-to-rail. The datasheet seems to suggest that the input (and output) operating range is typically 1 volt above -Vee to 1 volt below +Vcc, (although it could be as much as 3 volts above and below). If you have another power supply available try adding a negative supply to Vee, or else try moving the input voltage range to 1/2 of your power supply voltage.
 

Offline cravenhaven

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Re: op amp spitting out input voltage instead of amplifing signal ?
« Reply #2 on: March 28, 2014, 02:57:13 am »
Isnt that OpAmp designed to run from a split power supply?. Try biasing the inputs to a virtual earth at half the Vcc voltage.
 

Offline Dantali0nTopic starter

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Re: op amp spitting out input voltage instead of amplifing signal ?
« Reply #3 on: March 29, 2014, 12:55:33 pm »
Thanks for all the support, ive tried both suggestions. sadly neither worked and now I think the op amps death. ( it gets very hot )

Im just gonna try using another op amp, any suggestion on a op amp that can amplify a one volt signal to 5 volts. its for audio but dosen't need be anything of high power since it will be used as signal input for a transmitter.
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Online Zero999

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Re: op amp spitting out input voltage instead of amplifing signal ?
« Reply #4 on: March 29, 2014, 07:38:25 pm »
The virtual earth should work but you need to know what you're doing.

Use a single supply op-amp such as the LM358.
 


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