Trying to learn how to use a multimeter in SF Bay Area...

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greatmagnet
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Trying to learn how to use a multimeter in SF Bay Area...

Post by greatmagnet » Tue Jul 03, 2007 9:22 am

Hey All,

I'm nearly finished on my very first 7th Circle Audio kit...the API-style preamp. Everything's going great but I'm at the point now where I'm supposed to start using my digital multimeter to check for shorts and then on to initial power-up and fine-tuning which requires even more dimm work.

I own one, but have absolutely no idea how to use it! I've done internet searches and found loads of tutorials, but they all seem to assume one has a basic knowledge of electronic theory and application which I do not have. So I'm lost from the first sentence. I'm really just following instructions and soldering shit to the board...which I am pretty damn good at but only gets me this far...

I live in Petaluma...about 45 minutes north of San Francisco. Are there any DIY-savvy TapeOppers out there in my area that would be interested in a little face-to-face confab time to help me wrap my brain around this?

I'd be happy to buy you many beers or even trade some studio time!

Cheers,
Adam
"All energy flows in accordance with the whims of the great Magnet"
?Raoul Duke
www.greatmagnetrecording.com

philbo
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Post by philbo » Tue Jul 03, 2007 3:46 pm

Checking for shorts -

The idea is to make sure that nothing is connected together unless it's supposed to be. The method: Depending on your DMM, use the Ohms range (looks like an upside-down U) or the diode checker (looks sort of like this: -|<|- ).

- - - - -

If using the Ohms range, touch your test leads together and note the reading (it should be something like around 0.5 or 1.0 or so). This is what a short will measure. Anything that should not be shorted should read more than this. Coils, transformers and low-value resistors might have pretty low readings, but everything else should be high.

The numeric display might be a little confusing - - if it says 'k', that means thousands (like, 4.7 k = 4700 Ohma). If it says 'M', that means millions (like 0.150 M means 150,000 Ohms).

- - - - - -

If you're using the diode checker, you will get a steady beeeep when you touch the leads together, and when you find any two points that are shorted (or which have very low resistance, such as the coils/transformers/etc. mentioned above). Also, you might get a momentary beep, which means you are connected across a diode or other semiconductor. If that happens, the DMM displays the voltage needed to force 1 mA (a small current) through the device. Don't worry about it too much, unless the number is very close to zero, (like 0.1 or less) which indicates a short.

- - - - -

For measuring voltages, you need to know whether you're looking for an AC or DC measurement. Generally, when checking out a newly built circuit, you are interested in DC voltages. For amplifiers, hese measurements are generally made with no signal fed in. The voltage measurements tell you whether the components in the amp are properly setting up the transistors/tubes/ICs to operate properly. If the voltages are very far off what is expected (like more than, say, 5%), the amp will not work correctly and may fry up the parts, either immediately or after a while. So the cause of bad readings should be investigated and resolved.

AC voltage measurements come into play only in 2 situations.
1) When the device is powered from the AC wall plug, and you are trying to make sure that the power supply (which converts the AC into the DC which runs the amp) has proper input from the wall. This voltage is life-threatening, and should be treated with utmost respect.
2) Tracing signals as they pass through the various parts of the amp and are, well, amplified into bigger signals. A DMM is generally fairly useless for this because all but the most exotic and expensive won't accurately measure AC voltage above about 300 or 400 Hz.

When measuring DC voltages: The Black lead, which plugs into the NEGATIVE socket on your DMM, is normally connected to the circuit ground, while the RED lead, plugged into the POSITIVE socket on the DMM, is connected to the point of the circuit that you want to measure.

(For AC voltages, you need to sort out in advance where the black lead reference point is - - sometimes it's circuit ground, some times it's somewhere else. But, as mentioned above, DMM AC measurements are fairly useless, and I'd recommend not doing any at all unless you know what you are doing and why and how).


ALWAYS make sure neither of your hands is touching any part of either test lead. If it does, it can possibly load down the circuit and give you a false reading, or, if the voltage is above around 50V, possibly kill you. (50V is the OSHA limit for safe voltages in a non-medical environment.)

I hope you find this helpful.
________
Honda Cr250M Specifications
Last edited by philbo on Sun Mar 20, 2011 12:14 am, edited 1 time in total.

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Post by greatmagnet » Mon Jul 09, 2007 1:42 pm

Thanks guys for all the tips!

Over the weekend I actually unearthed the manual that originally CAME with my specific multimeter, and that turned out to be the "rosetta stone" for me as it was relevant to the specific dial and inputs to that model.

All worked out well and I now have my very first fully-functional hand-built API clone with no issues...it sounds GREAT! The first of many DIY pres to come for me no doubt.

Cheers,
Adam
"All energy flows in accordance with the whims of the great Magnet"
?Raoul Duke
www.greatmagnetrecording.com

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calaverasgrandes
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Post by calaverasgrandes » Sat Jul 28, 2007 1:54 am

wow see I was actually hesitant to take the jump on building one of those because I doubted my abilities. I guess I still think of myslef as that 8th grader that couldnt solder sometimes? I'm actually pretty good now. What did you do for the racking? did you go with his chassis or something else? I like his whole concept and its pretty cheap AFTER you get the chassis and PS. Which togehter cost about the same as an API chassis.
I'm looking at the N72's and the A12's. But I gotta finish 1 or 2 other projects before I start anything else.
Hmm looks like I live not too far from this guy. Maybe he could be in to some barter?
??????? wrote: "everything sounds best right before it blows up."

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greatmagnet
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Post by greatmagnet » Mon Jul 30, 2007 3:00 pm

calaverasgrandes wrote:wow see I was actually hesitant to take the jump on building one of those because I doubted my abilities. I guess I still think of myslef as that 8th grader that couldnt solder sometimes? I'm actually pretty good now.
Yeah like I think I said finding my original multimeter manual got me halfway there and then there was a bit of fiddling with settings on it until the numbers that registered on the readout looked to be in the range they were supposed to be. Which I guess is kind of like backwards engineering and would not have worked out had I actually fucked up my build and created a scenario where the multimeter settings were all wrong!

But don't be afraid of these kits if you have a little bit of experience populating circuitboards, doing clean solders on small objects, and looking over materials lists. My first DIY project ever was one of the build-your-own-clone (BYOC) stomp boxes, which is REALLY easy to follow...their directions offer even more hand-holding than the 7th circle stuff and without the sometimes-vague word mangling. If you are just now jumping into this world that is the place to start.

It's also worth downloading all the build instructions off the 7th Circle website before you order and going through them just to see how much you understand as a way of testing the waters. And you can look at their forum before you buy as well. The guy that runs the show is notoriously (by his own admission) lousy about returning calls and emails, but is crackerjack about responding on his forum. As are a lot of other folks.

Start with the API kit as it's pretty basic. If your API rocks, then move up to the Neve which has more complicated doodads on it.
calaverasgrandes wrote:What did you do for the racking? did you go with his chassis or something else? I like his whole concept and its pretty cheap AFTER you get the chassis and PS. Which togehter cost about the same as an API chassis.
I did indeed go with his rack and power supply, which I highly recommend...he doesn't really state it on his site but it seems these days he's not only providing the power supply pre-built, but if you buy a PSU, rack, wiring harness, and preamp kit from him at the same time, you get the rack already built as well and the PSU already installed in it! Which is just a huuuuge shortcut to being finished.

Also if you didn't notice, there are MASSIVE price reductions if you buy all that stuff together. Do yourself the favor of filling out his online order form and hitting the "calculate" button and watch your overall costs come waaay down...

Adam
"All energy flows in accordance with the whims of the great Magnet"
?Raoul Duke
www.greatmagnetrecording.com

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calaverasgrandes
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Post by calaverasgrandes » Mon Jul 30, 2007 4:01 pm

hmmm maybe I didnt do it right. I am only getting a 35 disc when I populate the api and teh opamp.
his stuff is still a good deal. And I am pretty sure I can bang it out in no time.
I am just wishing his stuff was 500 series compatible. i am really likeing the idea of getting a 500 series rack and a couple api a couple OSA a couple A sound etc.
are there any 500 series kits out there?
??????? wrote: "everything sounds best right before it blows up."

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