Oscilloscopes - Questions, Comments and WTF?

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#23
Mark does a fine job of detailing the setup. Referring to the trigger, most signal generators have a trigger output. This is the same signal as the output that is taken before the level control. I connect it to the external trigger input on the scope and set the scope's trigger switch to external. I prefer this arrangement. It works for me.

Scope probes are a PITA for connecting to amplifiers. Instead I use BNC-banana jack adaptors on the scope. I connect the amp to a load bank with 12 guage speaker cables fitted with stacking daul banana jacks (Pomona MDP's) on each end. I use short jumpers with stacking dual banana jacks from the load bank to the scope.

Ground loops between signal generators, a scope, and an amplifier can destroy an amplifier including the P/L's. It's essential that the amplifier input and output are not both grounded to the scope via the ground on the generator. Since I use the external trigger from the signal generator which grounds the scope to the generator, I lift the ground lead between the speaker cables and the scope input. The dual banana jacks on the speaker cables make this easy. I also lift the ground wire on power cord for the scope.

Mark also refers to 10:1 probes. Since I don't use scope probes I have a switchable 1x/10x voltage divider between the load bank and the scope. When I built this, about 30 years ago, it seemed like a no brainer to use 10k and 100k resistors for the voltage divider. Wrong. A 10:1 divider needs to use some multiple of 9K and 1K.

Ed mentioned the article that suggests that analog scopes are better than digital scopes. Until I came across that article I thought I was the only person on the planet that felt that way. The R&D lab at my day job uses the popular Rigol DS1054 which is a really nice 4 channel, 50mhz, digital storage scope. It can be cracked to make it 100mhz. It only costs $350. I bought one and sent it back for a replacement because the trace was awful compared to the 30 year old Hitachi I use. The trace was so fat it left out details that are important such as oscillations riding on waveforms. The second Rigol scope was the same. I ended up keeping it because it's nice to have a digital storage function, but the Hitachi beats the pants off of it for quality of trace.

I used the Rigol last week at work to track down a cold solder joint on an inverter at work. The inverter would run anywhere from a few minutes to several hours and then suddenly take out a 300 amp fuse. I had all 4 channels set up and was able to track down the cracked joint after 4 fuses. FWIW, blowing 300A high speed fuses is far less dramatic then 10A fuses on an amplifier.

When using a scope probe that is 10:1 or 100:1 it is essential to calibrate the probe if looking at square waves. All scopes have a square wave signal source, usually on the front, that the probe is connected to. The probe will have an adjustment to make sure the leading and trailing edges of the square wave are not rounded off.

The attached images show the scope setup for triggering and the cable connections I use.
 

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laatsch55

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#25
Well, this thread has made me get the book out and do more studying...that's a good thing..
 

BlazeES

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#26
Ed mentioned the article that suggests that analog scopes are better than digital scopes. Until I came across that article I thought I was the only person on the planet that felt that way. The R&D lab at my day job uses the popular Rigol DS1054 which is a really nice 4 channel, 50mhz, digital storage scope. It can be cracked to make it 100mhz. It only costs $350. I bought one and sent it back for a replacement because the trace was awful compared to the 30 year old Hitachi I use. The trace was so fat it left out details that are important such as oscillations riding on waveforms. The second Rigol scope was the same. I ended up keeping it because it's nice to have a digital storage function, but the Hitachi beats the pants off of it for quality of trace.
You're not. Just like in vintage audio, there's actually a lot of old school techs & engineers out there that know the value of a good phosphor CRT based scope.

And by the way, I like your contributions to discussions around here.
They are lucid and valuable, making them (and obviously you) a good source of learning - whether you intend it not.
 

orange

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#29
You gotta be careful, my late uncle once grounded himself to his Cantenna.

No, leukemia got him later.
 

oldphaser

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#30
Don,

I see that you have a Loftech TS-1 Audio Test Set.

Did you by any chance get a copy of their book:
"Audio Measurements: Their Importance and How to Make Them" by Larry Blakely, John H. Roberts Phoenix Audio Laboratory (Loftech) 1982 87 pgs


This book was a free companion piece for the Loftech TS-1 audio test set or could be purchased separately.

I've been looking for a copy.

Ed
 
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#31
Ed, I bought the TS1 around 1983 and it’s served me well. I added a synk output on the back of it You can’t beat being able to cover 2o -20 kHz with one controll. When I bought this it came with the book.

I’m tied up for the next 10 days or so. At first chance I’ll get the book scanned and make it available
 

mlucitt

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#32
It's one volt RMS, 2.88 peak to peak.....
Lee, If you are using a 10X probe, like it says on the display; that is a 30V P-P signal sine wave represented on the display at around 1KHz. UNLESS your scope compensates for the 10X probe to change the display to reflect the probe in use. Then it would be a 3V P-P sine wave. Digital scopes do weird things. Nice display, with notations right on the screen; but I like the old school analog display with the controls to change the display.

To me, VOMs or True RMS Voltmeters are for measuring DC or RMS AC. O'scopes are for measuring Peak-to-Peak AC. We need to see those peaks for noise or distortion, if any.
 

Gepetto

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#33
Lee, If you are using a 10X probe, like it says on the display; that is a 30V P-P signal sine wave represented on the display at around 1KHz. UNLESS your scope compensates for the 10X probe to change the display to reflect the probe in use. Then it would be a 3V P-P sine wave. Digital scopes do weird things. Nice display, with notations right on the screen; but I like the old school analog display with the controls to change the display.

To me, VOMs or True RMS Voltmeters are for measuring DC or RMS AC. O'scopes are for measuring Peak-to-Peak AC. We need to see those peaks for noise or distortion, if any.
Lee's Tek scope automatically compensates to show the correct voltage whether in 1X or 10X mode. The probes have a switch on the side and the scope detects that and changes the on screen scale. It is like my 2024B
 

BlazeES

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#34
A TDS1001C edu is from the mid-to-late 2000's. As Joe correctly states, it's smart scope and it's obviously displaying 1v per division ...not rocket science ...
Turn them cursors on Lee !


Would anyone be offended if I paid entirely for a Geritol group-buy ? :laughing8:
 
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laatsch55

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#35
Easy now guys . That is a 1 volt RMS sine wave from the AP. Verified with my Fluke at 60hz. And at 1 khz.
A little reading and it made sense..
 
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