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Subject: Re: [motm] Scope question

From: Dave Manley <david_l_manley@...>
Date: 2009-01-30

You can always put a series resistor in the plug body if you're really
concerned.  Most scopes have a 1M input impedance.  The method
I described is really a X1 probe with some pF's of capacitance/ft due to the
coax.  For audio frequencies it probably isn't going too matter much.
Put a 9M resistor in series in the plug and you have a X10 probe.

Note many Tek scopes aren't going to recognize it as a X10 probe
due to the autosense mentioned earlier.

(If you really want to compensate it, you can put a little (variable)
cap inside the plug body as well.)

--- On Thu, 1/29/09, Richard Brewster <pugix@...> wrote:
From: Richard Brewster <pugix@...>
Subject: Re: [motm] Scope question
To: lists@...
Cc: motm@yahoogroups.com
Date: Thursday, January 29, 2009, 4:37 PM

I've been getting by with the simple approach of just clipping a 10x
probe to a 1/4-inch plug without its housing. I like the idea of
preserving the impedance features of the probe, rather than just
connecting directly to the scope BNC input.

Richard Brewster
http://www.pugix. com

Adam Schabtach wrote:
> Aside from all of the suggestions that have been aired for connecting
> a 1/4"audio plug to a BNC connector, there's another solution that's
> somewhat more flexible: buy a scope probe with a clip-on probe
> cover, then clip it to a 1/4" plug with its shell removed. This will
> give you hands-free operation with both the 1/4" plug and anything
> else you need to look at with a scope.
>
> Here's a random example of what I'm talking about:
> http://www.testpath .com/Items/ Passive-Oscillos cope-Probe- 15MHz-X1- 110-564.htm
> (No, I've never used that particular probe. It was just the first
> example I found.)
>
> --Adam
>
> ------------ --------- --------- --------- --------- --------- -
> ∗From:∗ motm@yahoogroups. com [mailto:motm@yahoogroups. com] ∗On
> Behalf Of ∗jneilnyc
> ∗Sent:∗ Wednesday, January 28, 2009 8:25 PM
> ∗To:∗ motm@yahoogroups. com
> ∗Subject:∗ [motm] Scope question
>
>
> I finally sat down tonight at got my Tektronix to give me some
> waveform views of one of my oscillators. There was more than a little
> trial-and-error at first, but once I got in the ballpark I was able to
> zero in on clear, static waveforms that changed shape in predictable
> and expected ways, which was immensely satisfying (and will no doubt
> impress my musical buddies, for whom a MOTM cabinet is already like
> seeing something out of Close Encounters - this now adds that last mad
> scientist touch).
>
> And I got the onboard frequency counter working, which is a nice plus.
>
> All this was done using a rather painful method whereby I clipped the
> ground to one exposed terminal on the end of a phone cable and touched
> the probe to the other. While this worked, it was not at all easy to
> do one-handed, and clearly not a long-term methodology. What I really
> want is to make this kind of connection permanent, ie just have some
> sort of probe terminating in a phone plug that I can tap into any jack
> without worrying about fiddly connections. Does such a thing exist,
> either ready-to-use or in some combination of probes+adaptors?
>
> What do people who know what they're doing do? (he said, and not for
> the first time...)
>
> Thanks!
> JN
>
>