bjoneson

In line BNC 10x attenuator
« on: January 31, 2017, 11:30:18 PM »
Maybe this is a silly question, but here goes...

I'm trying to measure the output of a power amp for clipping level, and am using a dual banana plug adapter to go BNC straight into my Tektronix 434 scope.

The issue is, the max scale is 10V / div. Obviously, could use a 10x probe, but it's a little less convenient.

Do they make such a thing as an in-line 10x attenuator for straight BNC connections?



joaquins

Re: In line BNC 10x attenuator
« Reply #1 on: January 31, 2017, 11:59:44 PM »
Why not to stuff a banana plug with a 10M inside and label it 10X banana wire?

JS
If I don't know how it works, I prefer don't turn it on.

bjoneson

Re: In line BNC 10x attenuator
« Reply #2 on: February 01, 2017, 12:04:39 AM »
This makes perfect sense. I knew I was missing something obvious.

Thanks for the suggestion!

joaquins

Re: In line BNC 10x attenuator
« Reply #3 on: February 01, 2017, 03:33:53 PM »
If you want 10X it's actually 9M resistor and you could select a cap to stuff in parallel for best HF response on one particular scope or add the trim circuit which is probably a PIA for you, unless you have a fixed 10X donor probe, to take the BNC from.

I guess this is the more reasonable one for audio use, instead of the trim cap you could select a fixed one for your scope.


This is a nice one if you get a donor probe, one which has the trim on the BNC, not on the probe.


This is in case you get serious into HF and you need to start from scratch.


JS
If I don't know how it works, I prefer don't turn it on.

Re: In line BNC 10x attenuator
« Reply #4 on: February 10, 2017, 07:44:42 AM »
If you want 10X it's actually 9M resistor and you could select a cap to stuff in parallel for best HF response on one particular scope or add the trim circuit which is probably a PIA for you, unless you have a fixed 10X donor probe, to take the BNC from.

I guess this is the more reasonable one for audio use, instead of the trim cap you could select a fixed one for your scope.


This is a nice one if you get a donor probe, one which has the trim on the BNC, not on the probe.


This is in case you get serious into HF and you need to start from scratch.


JS
Would it not be more simpler just to get a new scope probe that is x1/x10 switchable?  Does everything for you.

Mike


joaquins

Re: In line BNC 10x attenuator
« Reply #5 on: February 10, 2017, 12:01:01 PM »
Would it not be more simpler just to get a new scope probe that is x1/x10 switchable?  Does everything for you.

Mike

  Usually fixed X10 probes are better than switchable, if you are working up to a few MHz it's fine and practical the switchable ones, of course. Not having the switch means having the 9M resistor physically closer to the tip, so less capacitance loading the DUT and more control over the resulting filter, as usual the 9M needs a cap in parallel, and at some point compensation trimming is needed, but now you can do that at the other end of the probe, and as there isn't a switch anymore the filter can be much more elaborated and precise. Switchable probes are a compromise, and generally speaking using X1 probes is a compromise, for bandwidth and safety, and should only be used when the 10X more gain are required to measure very low level signals (and limited bandwidth).

  In this case bjoneson didn't need a probe but banana plugs, I suggested just to add a resistor inside of one and in the case to need extra bandwidth add the proper compensation, and then the various approaches depending on the expected results, just adding the resistors would seriously compromise even for audio range, ~1M impedance of the 9M-1M devider and just 20pF means -3dB @9kHz, and depending on the wire it's likely to have more than 20pF combined with the scope's input capacitance.

JS
If I don't know how it works, I prefer don't turn it on.

Andy Peters

Re: In line BNC 10x attenuator
« Reply #6 on: February 10, 2017, 03:00:12 PM »
  Usually fixed X10 probes are better than switchable, if you are working up to a few MHz it's fine and practical the switchable ones, of course.

For standard audio work, the switchable probes are just fine. Hell, they're fine with my 200 MHz analog bandwidth TDS2024. For high-frequency work, the 3" ground wire is more of a problem than the switchable attenuation. (The DPO3034 on my desk at work does not have switchable probes.)
"On the Internet, nobody can hear you mix a band"

joaquins

Re: In line BNC 10x attenuator
« Reply #7 on: February 10, 2017, 08:01:40 PM »
For standard audio work, the switchable probes are just fine. Hell, they're fine with my 200 MHz analog bandwidth TDS2024. For high-frequency work, the 3" ground wire is more of a problem than the switchable attenuation. (The DPO3034 on my desk at work does not have switchable probes.)

  Is very common to see very cheap switchable, not so much expensive ones and the other way around with fixed. I'm aware there are very good switchable ones.
  My point was, banana, 10X, just add a 9M resistor inside the terminal, that without any compensation is really bad HF response even for audio, so a cap in parallel, selected for the specific scope and setup or with a compensation trim. It makes no sense at all to make a switchable banana plug!

JS
If I don't know how it works, I prefer don't turn it on.

Audio1Man

Re: In line BNC 10x attenuator
« Reply #8 on: February 11, 2017, 11:18:01 PM »