Proper way to use DS1054Z to measure balanced amp and preamp, please? - Page 1
Forum section: electronics / beginners

author: beady
author_rank: Newbie
timestamp: October 31, 2015, 12:54:53 pm
content: Hello,First technical post so I apologize for the newbie question(s).I have a Rigol DS1054Z and would like to measure the signals at the input and output of my balanced preamplifier and amplifier (separately) and see if there is anything out of the ordinary going on. My biggest concern is that I will damage the amp or preamp by probing the wrong pins on the input/output connections.My balanced connections follow the wiring scheme in this cable:http://www.monoprice.com/Product?p_id=4777&utm_source=criteo&utm_medium=retargetting&utm_content=633x328&utm_campaign=q4_2015_testI have a set of these cables. I also have an HP201C signal generator to use as a source. To power the Rigol I plan to use a battery powered inverter so that the oscilloscope is not tied to the amp/preamp through the ground.Could someone please help me understand which XLR pins I should attach my scope probes to so that I don’t damage anything? I *think* Pin 1 should go to the alligator clip on my probe and then I can probe Pins 2 and 3 looking for a signal?Also, how would I attach the output of the HP201C to the XLR pins on the input of the amp/preamp? (i.e. the HP only has 2 output connections and the XLR 3 input connections)Final question, is it possible to view the input signal from the HP201C on one channel of the scope, and then with the preamp and amp tied together with their normal XLR cables, to view the output of the amplifier after the signal has traveled through both the preamp and amp? So basically see the combined effect of both units on the original input signal?Thanks for helping me learn,Mike

author: Paul Price
author_rank: Super Contributor
timestamp: October 31, 2015, 04:26:05 pm
content: Outside of a prolonged accidental short circuit on the amp output by misplaced probes, there is practically no chance of damaging the amp or preamp using your scope, especially since you are running the scope on isolated power.You could us tiny enameled (AWG 34, sand off the insulation at the ends) and insert them into the female XLR pins before inserting the male connector into the sockets. The balanced line connector uses one pin to the metal shield ground, you needn't connect to the pin, connect the input and ground leads of your scope probe to the other two to view the input signal to the preamp.Since the output of your amplifier has a higher amplitude signal that is not referenced to the input pins, you cannot view the output at the same time since the preamp connection to the scope is a floating isolated ground terminal. Your only hope is then to make separate scope measurements. If you have a pair of ground isolated scopes or a pair of differential probes you can see amp input and output signals at same time.

author: beady
author_rank: Newbie
timestamp: October 31, 2015, 05:59:10 pm
content: Thanks Paul.I realized my preamp has unbalanced RCA inputs and output also. Will probing the XLR connectors tell me anything more than the RCA’s? As I’ve read, both the amp and preamp are “real” balanced circuits, and not just XLR inputs into an unbalanced circuit.Mike

author: beady
author_rank: Newbie
timestamp: November 02, 2015, 12:55:43 am
content: Quote from: blueskull on November 01, 2015, 06:32:14 amThanks for the idea. I assume you mean I’d run the ground from each channel to Pin 1 and then probe Pins 2 and 3 on the input and the same for another 2 channels on the output?Mike