Are these multimeters good for audio work?

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lloop9

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Joined 2004
#1
#3
The BK spec sheet does not really show the specs, or wether it has frequency and capacitance function. So I would choose between the Amprobe and Instek. The Amprobe has temperature measurement, the Instek not. The Amprobe spec sheet reads "professional ..." but they messed up voltage and current units.

If still in doubt, buy a cheap one at a local store. After a while you will know what to look for and what to appreciate.
 
#4
I've got two. One was over £100 from Fluke and the other less than £30 from a highstreet store. (Maplin in UK).

TBPO there is not a lot between them. They are as accurate as each other and the Maplin one has many more functions like Hfe and capacitance testing.

For audio use they are as good as each other.

A $10 special from Wallmart may be stretching this ideal. But you don't really need to go stupid with a professional device costing a lot of money.

http://www.ebay.co.uk/itm/New-VC97-..._Measurement_Equipment_ET&hash=item45f6bd1f03

http://www.ebay.co.uk/itm/FLUKE-77-..._Measurement_Equipment_ET&hash=item2a19c10a38
 
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#5
lloop9 said:
Heya fellows,

I'm considering getting a DMM. I've narrowed down three models but can't decide which to get. I would like to hear some advice from you guys. What are your thoughts?

Amprobe AM-250
Amprobe AM-250 Professional Electrical Multimeter. New in Box.

BK Precision 2407A Mini-Pro
BK Precision 2407A Mini-Pro, Autoranging. New in Box.

Instek GDM-394
Instek GDM-394 3.75 Digits ( 3 3/4 Digits) Handheld Digital Multimeter (3999 Counts) Single LCD Display. Brand New.

cheers
Click to expand...

Maybe I am getting old. I have 4 multimeters that work right now -- two digital and two analogue. The small analogue I can slip into my pocket and head over to someone's house to fix the electrical whatever that is broke. Possibly the best $12 ever spent. A rather nice and modern digital one that I use when I am around the house or if someone has something a little more complex going. That one is probably the more flexible one with respect to ranges, temperature probe, and audible continuity (yes, set it to resistance and go from there, but sometimes checking a lot of wires and traces for breaks, a simple beeeeep is nice). The other digital one was got at a garage sale (Mastercraft for Canadian Tire) and it has a PNP NPN transistor plug in area which I have used about three times, but $5 is something you have for pocket change.

However, the one that I have used on everyone else's amps checking transformers and voltages going in and out, checking the voltage on a single phase 700V line into an HVAC turbine motor (this is where I learned that lower the amps, higher the voltage, smaller the size motor, the equivalent the torque, and less the heat... the motor was the size of a loaf of bread!) is a Simpson Model 955. This is the close cousin of the Simpson model 260. The upside is that this one can do it all. The downside, is that it is heavy and bulky as the body is thick cast aluminum.

I got mine for $30 -- it should have been more, but I don't think that the antique shop knew what they were selling. I would recommend this one or any of the older Simpson VOMs (Volt-Ohm-Milliameter) out there. It reads AC, DC, and the rage is from something like 2.5 V to 1,000 V AC or 1 V to 5,000 V DC (I don't think I will ever try that 5,000 V DC, c'mon... really, where am I going to find 5,000 V DC anyway?). Only problem is the unique 30V battery for the 10,000 ohm resistance range as I have to order a now one on-line. I have always wanted a Simpson 260 or a Hickok 215, but this one came up.

Do a google search on Simpson 260 as these are more plentiful. It ain't pretty, but it is pretty amazing. All my friends look at me and wonder what decade I time traveled from when I pull that one out, meanwhile the older guys (like my HVAC repair guy think that it is one of the best finds ever, but he has a Simpson 260 he still uses).

I have used auto-ranging and did not like the way the numbers danced and finally settled on a number that was close to my better meter. I like analogue more than digital because I can read scale and nothing jumps up and down in the AC.

I have broke or burnt out maybe 4 or 5 multimeters because they were cheap (made in China) or I let my father use them (who decided to check the AMPERAGE in the wall socket with my very nice Fluke -- I can safely say it ends with a shower of blue sparks).

If you really want digital multimeter and have cash to spend, then go Fluke. They make a dependable product, but not cheap and I have always wanted on before. Go check Greenlee (mentioned up there) as I have one and it has been reliable and comes with a lifetime warranty if that means anything for a company that has been around longer than I have been living.

That's the news and the way I see it.
 
#6
Hi
If you do not have a multimeter already I would start with a modest priced one; Maplin, Greenweld etc, at around £30 or $40.
If you find you get serious about electronics you will need more then 1 meter anway and you can buy an expensive one at that time such as a fluke, megger or avo etc.
Expensive meters are different than the cheaper ones. For example the accuracy, especially over time, will be better, particularly at low resistence values. For example you will find it difficult to measure resistence with any accuracy below 1 ohm with a cheap meter. But I would leave an expensive meter till later when you know for sure what you want.
Don
 
#7
One of my meters is the AM-240. Works fine and the accuracy seems OK. I have a 25 year old aging 4.5 digit and the 2 compare well. It also does better than I expected checking capacitors. Only thing I do not like about it is the auto-off function. It will beep that it is shutting off even if it it is being used. Seems to me, an auto-off should respond after 15 minutes of no input, not just 15 minutes! (there is a manual override procedure that I perform almost every time I turn it on)
I paid around $50 on sale from one of the big suppliers 2 years ago. Also note that on mine anyway, the physical size of one of the internal fuses is incorrectly listed.
So measures well but has a few minor user issues.
 
#8
Thank you so much for the advice guys. I think I'd rather spend my money on two for the price of one DMM, so I can use them for measuring voltage & current during amp construction. I'll check out your recommendations & try to get a good deal on ebay.

If not, I'll probably go for this $15 Instek, I would have like at least a 3 3/4 digit count, but I guess for the price 3 1/2 will do. It looks kind of cute too. 😀

Instek GDM-350A
Instek GDM-350A 3.5 Digits ( 3 1/2 Digits) Handheld Digital Multimeter (1999 Counts) Single LCD Display. Brand New.

An externally hosted image should be here but it was not working when we last tested it.
 
#9
For audio work, you would like to able to accurately set the idle (bias) current, most often measured as a voltage drop across the power resistors in the output stage. This can be very low for Class B amplifiers, down to 5~10 mV or so. In other words, a DVM for this adjustment works should have a resolution (accuracy) of at least 1 mV (which ain't terrific) and preferably much better (say 0.1~0.2 mV).

You can determine the resolution looking at their specs. For example, if it is 1% of full scale, and the lowest DC voltage range is 400 mV (typical for these handheld DVMs), then it's resolution is 4 mV, not really sufficiant for adeqaute bias adjustments.

I could recommend to purchase a decent second hand Philips/HP/Fluke workbench (lab) DVM from that auction side; you'll find nice quality ones for way below $/€ 100, and which will do easily 0.1 mV.
 
#10
AmpliFire said:
You can determine the resolution looking at their specs. For example, if it is 1% of full scale, and the lowest DC voltage range is 400 mV (typical for these handheld DVMs), then it's resolution is 4 mV, not really sufficiant for adeqaute bias adjustments.
Click to expand...
You are confusing resolution with accuracy.

The resolution is strictly the smallest possible difference between two readings, almost always simply one "count" or least-significant digit. So on a 3.5 digit meter (+/-1999 display), set to the 200 mV scale, the resolution is 0.1 mV (and it can read from -199.9 mV to +199.9 mV). That absolutely does not imply it can take a reading to within 0.1 mV accuracy.

The accuracy spec (e.g. "1%") nearly always means "1% of the reading", not "1% of full scale". So, for example, if the reading is only 100 mV, then the tolerance is 1 mV. The catch is that there is usually an extra fixed inaccuracy specified, commonly +/- 1 or 2 counts for most ranges, and sometimes +/- a few counts at the lowest range. So if your reading is at the low end of the range, that extra 1 or 2 digits creates big % of inaccuracy. e.g. If you have a meter spec'd to "1% of reading +/- 5 counts" in the 200 mV range, and you are reading about 20.0 mV, then you have an inaccuracy of 0.2 mV (1%) + 0.5 mV (5 counts), or 0.7 mV, which amounts to 3.5% of 20 mV.
 
#11
Yes you are fully right, thanks for putting it right. I could just add that often 'x% of full scale' is often quoted by meter manufacturers, which is mainly the fixed inaccuracy as you mention. But it does mean that an inaccuracy of 4mV at 400mV range still stands, even if you measure 20 mV at a given moment.
 
#12
Thank you for all the valued input guys.

If one were to use a handheld DMM for matching mosfets, jfets, etc, what is the minimum digit count to aim for? Cheap units are mostly 2000 counts, I heard someone said that a 10000 is the minimum?

cheers
 
#13
Well, it depends on how close you want to match them. The hFE option on DMMs is at one given (low) current only, while close matching rather requires comparing BJT/FET over a wide range, and for power devices preferrably under load.

There is a curve tracer design thread by locky_z going here, with an excellent group buy organised by LazyButt here. You can still order.

Or, an alternative device which allows you to connect any case style (even TO-3 and TO-66), is something like this, but it's not a curve tracer.

And measuring an hFE upto 2000 would be very sufficiant....
 
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#15
Unless i missed it no ones mentioned accuracy when measuring AC signal voltages , for the purpose of gain calculation etc . Its been my experience to be wary of the result when measuring any signal voltage whos frequency is below 50Hz or above 3Khz with an ordinary dvm . Cant give any comparisons between different makes however .
 
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