Function generator & Scope set-up

[paulrichards7]

Hi,
Im not sure if I have this figured out correctly
I borrowed a scope from my friend and bought myself a funtion generator to see if i could test my circuits
I dont seem to be having much luck though
I made the probes myself(not sure if that is the problem)
OR
How I'm connecting everything
See pics for equipment and set-up
Thanks
Paul

http://i390.photobucket.com/albums/oo345/paulrichards7/Scope.jpg
http://i390.photobucket.com/albums/oo345/paulrichards7/Scopediyprobes2.jpg
http://i390.photobucket.com/albums/oo345/paulrichards7/Functionandprobes2.jpg
http://i390.photobucket.com/albums/oo345/paulrichards7/Boardconnections2.jpg

 

[Ptownkid]

not having any luck how?

Have you started by hooking the scope directly to the generator? Off the top of my head, i see you have the gen set for 5ish volts and the scope to .3V

 

[rodabod]

Yep, test either piece separately. Say, function gen. into a line input, and line output with some programme material into your 'scope.

 

[paulrichards7]

Yeah, its ok if i put the function directly into scope
its just that i can hear there is a lot of noise within the channel when a use an earpiece
but this doesnt seem to be showing up on scope
so i thought maybe i had it hooked up wrong
thanks though
paul

 

[gswan]

The scope only has a 30mV/div vertical, so you would need quite a bit of noise to be present in order to see much. You are more likely to pick up induced noise through your home-made probes. Scope probes are made of coax and have a trimmer in the end to calibrate them for overshoot (caused by probe capacitance).

Your home-made probes will act as a nice loop antenna and pick up loads of induced noise (and probably inject it back into the board under test). The least you can do is to make probes using shielded cable, and minimize any loop area between the ground connection and the probe tip.

I'd suggest (as rodabod did) to inject your signal into the line input at line level and measure it along the signal chain. It's likely to be at the input circuit, since you mentioned that EQ affects the 'tone' of the noise (so it's pre-eq).

 

[paulrichards7]

Hey gswan, thanks for that
that explains why i havent been able to see the noise
i will go about knocking up some shielded cables next
as of the noise, it seems to be between the collector of 1st transistor and the power supply to board
even with the channel switched off?
so im just wondering what kind of signal to inject into line input and what am i looking for at various points in circuit?
i thought it was caused by a bad cap, but when checking with a square wave they seem fine/
thanks
paul

 

[Ptownkid]

sine wave, 1k, 1V

 

[paulrichards7]

Ptownkid, thanks for that
paul