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The importance of a good MM

post #1 of 7
Thread Starter 
I've always used a small analouge multimeter for just about everything I do that concerns electronics. I used this mm on my DIY amp and power supply for everthing from matching resistors to setting the voltage on the regulator. In a lower thred I was worried about my amp not getting hot, well now I've found out why.

Apparently my mm was off, a lot. It was reading 15V when it was only 9, and the resistance values were just nuts. I discovered the problem by accident. I was setting up to check how much current the amp was drawing with a nice digital mm I had stumbled upon (it had a higher current rating), and a fuse was missing in it. I was bored so I checked a few things, including the outpuit of the power supply.

Anyway, my amp is now at the proper voltage (as checked by 3 mms), and I've learned a lesson. Make sure your equpment is up to snuf, this could have led to a bad ending, such as a fire if too much voltage was applied. Oh, how accurate are these digital mms? Will they eventualy drift from accuracy like my old one did?
post #2 of 7
well, accurate enough. Each one is different, depending on the quality of the parts used.

but typically, the absolute value is within 1%, and if you're just making comparasons, they are even more accurate. There are no parts that will drift, though temperature changes might have a small effect.

For the average amp, i don't think the absolute values are as important as you think. Even a 5-10% error is unlikely to be over the maximum ratings of the parts, and even less likely to be dangerous.

For matching resistors, the accuracy is more important, but generally digital multimeters are VERY accurate for comparasons. Way more accurate than they are capable of displaying...
post #3 of 7

the price of sanity...

Much more than any of us need (for this stuff) but since we're about "the best" and all that... just so you know, Apheared wants one: a Fluke 189. $400 for a multimeter, OW that hurts... but it's sooo nice.

post #4 of 7
ah... you haven't used their scope meters?

at an electronics competition my school entered me in, one of the judges was the pres. of fluke electronics, and they let us use their 200mHz portable scopes/multimeters... now those things are sweet ($4g a pop?)

post #5 of 7
Analog Volt ohm meters can be quite usefull in situations when you need to monitor changing voltages Digitals are just to slow. Try monitoring the Audio output of any Audio component using Music. A digital unit is just made the reading by the time the next Peak has arrived. If your going to use Analog Vot ohm Meters Called (VOM) then get a vacuum tube voltmeter that we all used to use in the Old days. Digital multimeters (DMM) are great for like you say resistance and DC voltage measurements. I use A Fluke 70 somthing and evean radio shack meters at times. the Thing i like about Fluke is that DC reeds the same regardless if the Leeds are reverced unlike most others that can show 0.6 - 1.5 volts of difference depending upon polarity. Also the Fluke has an Analog type bargaph that will come in handy more times than you might think. Then i recomend a good scope and it need not be a wideband one it just helps if it is. Oscilation can be observed on lowbandwidth scopes if you Know what to look for. just my 2C Worth
post #6 of 7
I use a digital cheapie from ebay for $7 shipped. Claimed accuracy is 0.5% and I found it's true. Boy is it an ugly plastic case!

Remind me cheap Casio watch beat up very expensive Swiss watches in terms of accuracy. Therefore, if function is all what matters, go for the cheapest digital MM.
post #7 of 7

my local surplus store has really old (suposedly still working) scopes on sale for $20... They're the really old type, with 1 channel, and a round glass screen. Its bandwith is probably less than 100khz, but fine for audio...

Do you think somthing like that is necessary, or just another piece of junk that i'll never use?
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