Please help me build an audio probe for my mic preamp

I just finished a vp26 and it's not pasing signal.  i want to build an audio probe that will help me troubleshoot.


1/8" male from my ipod

I've tried to wrap my head around this and looked quite a bit on the net, but to no avail.  Any help would be greatly appreciated. 

Thanks

Your ipod could be the *source* of an audio signal, but you will need amplification to probe the circuit.  If you send the ipod out (turned down a good bit) into the preamp input, you can then probe at different points to see where the signal disappears.  The probe can be as simple as a small capacitor going to the tip of an instrument cable which is plugged into a guitar amp.  The capacitor blocks DC voltage from the preamp but lets AC audio signals through.

I am not familiar with VP26 but to inject audio you want to use a pad to drop down the level of line level source to mic level.

To mimic a mic I'd use a 150 or 200 ohm resistor connected across pin 2 and 3, with say 2k ohm resistors in series with pins 2 and 3, connect one 2k to the line level source, the other to ground.

An audio probe to sniff for signal by listening is a different animal. You need to use a series cap to block DC and series resistance so you don't destabilize the circuitry..

Of course be careful when probing around a powered circuit so you don't damage it or you.

JR

I just spotted this site that features videos showing the construction and use of a simple audio probe like the type others have mentioned above.

http://billmaudio.com/wp/?page_id=1254

Personally, I'd use a film type blocking capacitor rated at 600V for the audio probe to be on the safe side. This would allow you to use the probe to carefully sniff around in solid state as well as most vacuum tube audio circuits (with one hand behind your back, or in your pocket,  in the case of vacuum tube gear).

Regards,
Frank

Definitely 600v if you are going to use it on vacuum tube gear!  50v would be fine for 500 series modules, but higher is safer.

Thanks for the help everyone.
I think I understand how the probe works now.

nice link there thanks