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op-amps

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conchord

New Member
Hey guys,
I'm building a circuit for my class but I'm not totally sure how I go about choosing the best amp for the job.

all I want to do is amplify the input from 3mV to about 3V.

Is there a spec I should work off or is it just a case of looking at data sheets and trial and error?

any help would be great!

cheers,

Iain
 

crutschow

Well-Known Member
Most Helpful Member
Is this signal dc or ac?

If ac, what is the frequency range.

If dc, are you concerned about dc offset?

Do you care if it inverts the signal polarity?

What is the amplifier output load?

What is the signal source impedance?

What power supplies do you have?
 

Hero999

Banned
Is that peak-to-peak or RMS?
 

conchord

New Member
signal is DC

not really concerned about DC offset

signal source impedance is 500 Ohms

power supply is 5V from USB source

not sure about inverting polarity or amp load

cheers
 

unclejed613

Well-Known Member
Most Helpful Member
signal is DC

not really concerned about DC offset

signal source impedance is 500 Ohms

power supply is 5V from USB source

not sure about inverting polarity or amp load

cheers

for a 5v rail voltage, best to use a TL062 or other low voltage op amp, or even better a rail-to-rail op amp (sorry, can't think of the number for one right away). try searching the TI, Analog Devices, or National Semiconductors websites for "rail to rail op amp" or "low voltage op amp"

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Analog Devices, Inc. |Converters Amplifiers Processors MEMS A/D Converters Analog to Digital Video Converter Temperature Sensors Analog Device RF Amplifiers Differential Amplifiers Digital Signal Processing Thermal Management D to A Converters Micro,

www.national.com
 
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ericgibbs

Well-Known Member
Most Helpful Member
I went out and bought an LM324.

was this a huge mistake?

haha
hi,
A LM324 with a +5V supply will give an output of Vs-1.5V = 3.5V, so it can amplify a signal to +3V.
 

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Mikebits

Well-Known Member
Are you sure about that 3mv input level? That is really small, and you will have to worry about outside noise. What is your source that only produces 3mv?
 

conchord

New Member
that was an estimate.

The input is between 0.01V - 5V

It’s not a consistent source

it's a piezo transducer used as a drum trigger
 

ericgibbs

Well-Known Member
Most Helpful Member
that was an estimate.

The input is between 0.01V - 5V

It’s not a consistent source

it's a piezo transducer used as a drum trigger
hi conchord,
Dont want to twitter, but why couldnt you put this information in your first post.??

You cant amplify 0.01Vin and 5Vin to give you +3Vout on the same OPA
 

conchord

New Member
hey eric,
apologies, I just was trying to concentrate on op-amp.

Do I need to amplify at all, I just assumed I would. I saw the schematic on edrum.info (http://edrum.info/files/analog8_v06.gif) and that led me to choose the LM324.

I was considering using a schmidt trigger to change the signal to a digital signal
 

Nigel Goodwin

Super Moderator
Most Helpful Member
hey eric,
apologies, I just was trying to concentrate on op-amp.

Do I need to amplify at all, I just assumed I would. I saw the schematic on edrum.info (http://edrum.info/files/analog8_v06.gif) and that led me to choose the LM324.

I was considering using a schmidt trigger to change the signal to a digital signal
If you look at the edrum circuit you posted, that doesn't hardly amplify at all, why not just copy that exactly as you're doing the same thing?.
 

unclejed613

Well-Known Member
Most Helpful Member
I went out and bought an LM324.

was this a huge mistake?

haha
piezo transducers have much higher source impedance than 500 ohms, and the input bias current of an LM324 is high, and it's not a rail-to rail op amp. a TL062 would have been a better choice because of the lower input bias current. although an LM324 will work at 5V, i suspect you will be "underwhelmed" with the results
 

Nigel Goodwin

Super Moderator
Most Helpful Member
piezo transducers have much higher source impedance than 500 ohms, and the input bias current of an LM324 is high, and it's not a rail-to rail op amp. a TL062 would have been a better choice because of the lower input bias current. although an LM324 will work at 5V, i suspect you will be "underwhelmed" with the results
I think you're rather missing the point?, it's to get a trigger from a drum pad to connect to a drum machine, the 324 is perfectly suited to the job, and the edrum has been made in fairly large numbers. It's a tried and tested design.
 
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