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spooney 3rd November 2007 03:06 PM

Where to find a decent somewhat inexpensive DMM?
I've had the same radio shack DMM for years.I'm not even sure how much it cost me when I got it but it has served me well and helped me make several repairs.The more I get into amplifier repair the more I fear my dmm is losing some accuracy or that it was never there to begin with.I'd like to find a new unit preferably under 100 dollars that will be a nice piece of equipment for years to come.I would appreciate some
suggestions from you guys with first hand experience with these things.

SY 3rd November 2007 04:29 PM

Harbor Freight. They had some perfectly good ones for $3-4 or so- I bought ten. You can never have too many multimeters.

Conrad Hoffman 3rd November 2007 04:44 PM

What's that saying- A man with a watch knows what time it is, but a man with two watches is never sure.

It's handy to have several DVMs for simultaneous measurements, but IMO you should have at least one decent meter. Look for a used Fluke, HP, or Keithley meter on eBay. You should be able to get a not-too-ancient 4.5 or 5.5 digit meter for under $100. I like a bench meter, but most go for portable. Something like an old Keithley 175, or a Fluke 8050A, an HP 3478A, or if you have the bench space, even an HP 3455A or Fluke 8502. There are about a dozen variations on those numbers, depending on age and features.

SY 3rd November 2007 05:12 PM

I get your point, but... the meters all measured DC volts, 60 and 120Hz AC sines, and resistance within a percent or two of one another, and within about 3-4% against my beloved Fluke. As a dedicated hobbyist, a Fluke is a nice thing to have, but for more casual work, the cheap spread is surprisingly capable. The multiple meters mean I can monitor several voltage points at once, very useful for amp start-up, adjustment, and troubleshooting.

Perry Babin 3rd November 2007 06:17 PM

Find a used Fluke meter if you're looking for something inexpensive. I probably have a dozen handheld meters (mostly Fluke) but I use a lowly Fluke 11 for day-to-day troubleshooting. It's perfect for repairing car audio amplifiers.

Conrad Hoffman 3rd November 2007 06:59 PM

Sy, as I've said before, I'm a test equipment snob. It just has to say Fluke, HP, or Keithley. OTOH, we buy the cheapies at work just to be able to clip them on lots of points, and they work fine. I'd also make the case that in an environment where bad things can happen to good meters, like automotive sound systems, the cheapies are a better bet. IMO, there are no audio related measurements where absolute accuracy better than 5% makes any difference. Relative measurements maybe, but not absolute to NIST standards.

I Am An Idiot 3rd November 2007 09:13 PM

As Perry stated the cheaper of the older Flukes are my favorite too. The 10 11 or the 12 are the easiest to use. You can find them in pawn shops for 20 to 40 dollars.

spooney 4th November 2007 12:44 AM

is a "true rms" meter a necessity for amplifier repair?

Perry Babin 4th November 2007 01:07 AM

You rarely need a true RMS meter. The only time I use mine is when I'm trying to accurately measure
RMS output power. I can't remember a time that I needed one for any repair work.

If you do buy a true RMS meter, you should realize that not all true RMS meters will read the same. All meters have a finite bandwidth. For many true RMS meters, the bandwidth is only ~500Hz. Others go much higher. You need to buy one that suits your needs.

Conrad Hoffman 4th November 2007 01:47 AM

You pretty much never need a true RMS meter. Anything you measure will likely be a sine wave, so any RMS calibrated averaging meter will be fine. You need true RMS when measuring non-sinusoidal waveforms, usually for 50/60 Hz AC work with a severely distorted waveform. For audio the issue rarely comes up.

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