Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

resistor ladder network or op-amp for output attenuation?

Status
Not open for further replies.

Neil Groves

New Member
I just started using my home built function generator and discovered the outputs are way too large for what i need, funny when i built it i thought only 3v sinewave.....thats no good, well as it turns out i need 10mv-100mv output to test amps and filter circuits lol

So my question is can i use a simple resistor ladder network as my attenuator or is it better to use an op amp on the output stage so i can make the output variable?

i don't know how to use an op amp as an attenuator though, maybe someone can advise?

I'm not an engineer, just a lowely backroom hobbyist so go easy on me :)

Neil.
 
I just started using my home built function generator and discovered the outputs are way too large for what i need, funny when i built it i thought only 3v sinewave.....thats no good, well as it turns out i need 10mv-100mv output to test amps and filter circuits lol

So my question is can i use a simple resistor ladder network as my attenuator or is it better to use an op amp on the output stage so i can make the output variable?

i don't know how to use an op amp as an attenuator though, maybe someone can advise?

I'm not an engineer, just a lowely backroom hobbyist so go easy on me :)

Neil.
Neil,
Do you want it to be continuously variable between 10 mV & 100 mV?

If so, then all you need is a potentiometer & 2 resistors.

What output resistance do you want? eg. 50 Ohm, 600 Ohm?

I'll await your reply & draw a circuit for you once I know exactly what you want.

Len
 
i hadn't thought about continuously variable, i was going for selective outputs if i went the resistor route, i'm assuming 2 resistors from +v and 0v respectively then with a pot in the middle, with the wiper going to the output socket....good idea Len, i'll knock it up when i get time next week.

thankyou

Neil.
 
Sorry Len, i meant resistors from the output to ground with a pot in the middle not the v+ supply, it was late when i wrote that lol

Neil.
 
Neil,
No problem, I knew what you meant. However you did not comment on my point about the output resistance.

With the simple resistor and pot arrangement, the output resistance will vary as the pot is moved.

For example, if you used a 1 k pot is series with a 29 k resistor, the output resistance will change from from zero when the pot is set to 0V volt to almost 1k when it is at the maximum. (To be precise, it will be 1k//29k = 967 Ohm) (// is my shorthand for "in parallel with")

This won't matter for your application provided that the input impedance of the amp is much greater than 1k.

But if you want to minimise this effect, you would need a pot & 2 resistors. I can draw it & post if you wish.
 
Last edited:
I don't want to take up your valuable time with drawings Len although much appreciated, i think i will tinker with putting a resistor from the output to a pot, the other side of the pot i will take to 0v via another resistor then take the wiper of the pot to my output jack, i'm not sure about output resistances, thats a bit beyond my knowledge but if i play with the resistor values i'm sure i can knock something useful together.

thankyou so much for your help.

Neil.

p.s ok then, a drawing would be nice please :)
 
Neil,
Here is the drawing.

Drawn with a finger nail dipped in tar.
 

Attachments

  • Audio atten.jpg
    Audio atten.jpg
    67 KB · Views: 122
I thought a spider had got drunk, staggered into your ink pot, then wandered aimlessly across the paper ;)

just kidding!

Thanks very much, this is a cicuit i want to experiment with when i finish my current project.

I played around with a different config of resistors at the output and found i couldn't just control the output amplitude but could also adjust the D.C level that the waveform sits on, i am getting the bug again, totally fascinating, i am stoked!!

Neil.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top