Connecting oscilloscope

Jari Jokinen · Posted: Wed May 30, 2007 1:24 pm Post subject: Connecting oscilloscope

I am just starting to use an oscilloscope with my Eurorack modular. I wonder how should I connect it with the minijacks.

I did a brief test using a multiple (in the system) and a probe with 10X attenuation. Connecting probe tip to patch cord tip and ground lead to patch cord ground works as expected, although there is some noise and spikes. However, this connection was difficult to make and seems very unpractical. What is the standard practice? Are special (minijack) adapters used? Are the probes necessary or can one make a direct connection with a custom audio cable (miniplug-BNC)?

Lots of questions. Thank you for help.
Jari Jokinen

doctorvague · Posted: Wed May 30, 2007 1:38 pm Post subject:

Jari
I made up a couple of cables with BNC on one side and miniplug on the other from an old BNC word clock cable I wasn't using. Very convenient. Not sure if there's an adapter for that but probably is somewhere. In a pinch you can open up a miniplug and clip your probes onto the solder connections. Some guys have them wired from the back to a panel or mult right in their modular too.

I would use good shielded cable if building your own.

HTH
Phil

blue hell · Posted: Wed May 30, 2007 1:46 pm Post subject:

The usual probes are meant for high frequency measurement and for that they have some caps included to keep the signal edges OK. For audio rates this is less important, I'd try to make one or two custom cables so that you can plug 'm in where ever you want.

Don't know what the max scale is for your scope, but when you have 5 or 10 V/div the 10:1 attenuator could probably be left out as well. You might want to experiment a bit, try to look at a known good square wave (or the scope's calibration output, if it has one), see if it's reasonable.

BTW, keep your existing probes OK, they are quite expensive :D

Some noise is almost inevitable especially on a high bandwidth scope. Try to experiment with how you connect the ground connector and try to avoid ground loops. You could try to run a separate earth connection and not use the probe cable's shield for it (and have the cable shield connected on the scope side only).

Try ground lifting.

Jari Jokinen · Posted: Thu May 31, 2007 1:09 am Post subject:

Thak you. I will try your suggestions.

My oscilloscope has a quite loud fan. If I was shopping for a new oscilloscope for audio use, I would definitely check this feature before buying. I wonder, if the fan is there to protect parts from melting or to stabilisize measurement conditions. In the latter case I might try to disable the fan...

Best regards
Jari Jokinen

Jari Jokinen · Posted: Thu May 31, 2007 5:32 am Post subject:

I haven't noticed any disadvantage after switching the probe to 1X. Is there some special situation I should test?

Best regards
Jari Jokinen

blue hell · Posted: Thu May 31, 2007 8:29 am Post subject:

Clack · Posted: Sat Jun 23, 2007 2:59 pm Post subject:

BNC to phono ( rca jack? ) are quite common ( I can buy them in the street in the uk which means its pretty common!!! ) if you cant be asked to solder - this is what I use