List your favorite(cheap) test tools for audio systems

[clm811]

AC Line sniffers...Better ones have adjustable sensitivity...

Yep.
Tried this one as well- great for checking all of the wiring and cables in your setup! But look for the adjustable version.

Ref:
http://www.psaudio.com/ps/tips/15-noise-sniffer

[jtsaudio]

My "pen-type" digital multimeter has this feature (non-contact voltage detection). It works best when adjusted so that you get a reading from 4-6" away from a known AC source.

[Pano]

Very clever on the AC sniffers guys. Will have to give it a try!

[gmphadte]

A crystal receiver, as audio tracer.
Comes handy to find which stage of the amp is faulty

An injection needle comes very handy to probe the pcb.

Gajanan Phadte

[jackinnj]

Originally posted by gmphadte
A crystal receiver, as audio tracer.
Comes handy to find which stage of the amp is faulty

An injection needle comes very handy to probe the pcb.

Gajanan Phadte

Eico 147 Signal Injectors were a collector's item several years back.



There were also models by Heathkit and Knight

[clm811]

Following is Part One of the results from scanning my system wiring with the various AC "sniffers":

A while back I'd tried the polarity indicator and one of my wall outlets(on a side wall, where I plug in my subwoofer) had to be corrected for reversal of "Hot" and "Neutral". I don't know what (if any) effect this had on the sound, but at least I know that all of the components are seeing similar polarity at the mains.

I tried out the AudioPrism "Noise Sniffer" setup,
http://www.soundstage.com/revequip/db04.htm
which indicates non-60Hz noise at the AC outlet. Each and every one of my outlets had a high level of noise indicated, except for the dedicated 20 amp circuit I had installed for my components.

Turns out that the "Line Conditioner" (a Monster Power unit) I had plugged in was mostly responsible for cleaning up that circuit (measured both from the L.C.'s outlets and the adjacent one at the wall plate). When I tried unplugging the L.C. from the outlet, the AudioPrism unit "went crazy", signalling the return of much noise. My investment in the line conditioner having been justified, I turned to the other outlets in the room.

At each outlet I tried plugging in one of those two-prong "wall wart" noise filters and, while it certainly helped reduce the noise, it wasn't as effective as the Monster Power (some noise was still indicated).

I made up a three-prong filter from a diagram I found on the web* :
http://www.tnt-audio.com/clinica/mains_e.html
This made a much greater difference. The indicated noise was reduced nearly as much as with the expensive Monster unit!

I decided to install the two and three-prong filters at the spare outlet and the subwoofer outlet, respectively. Powerline noise has been considerably reduced, if not eliminated, in my listening room as a result.

-Chas


*Be careful to use only 'X' and/or 'Y' rated capacitors to reduce risk of fire!

[clm811]

Part Two:

Next I tried the “non-contact” AC voltage Detector designed for sensing 50-600v AC when its probe is placed near a suspected (or even unexpected!) source.

I was very surprised when the AC detector gave a reading when held near a group of interconnect (shielded twin-axial) cables at the rear of my preamp! Normally any AC voltage(signal) here is very small. I suspect some inductive coupling was present.

Subsequently, I've rearranged my cables a bit. I had used wire ties to bundle the cables for neatness, as many people have recommended, with similar cables tied together(AC with AC, interconnects together, speaker wires together, etc.).

I found that separating the interconnects of one component from one another and especially keeping them away from the AC cords(which I've replaced with shielded cords), has eliminated that AC reading. I have also done the same for my speaker cables).

While I believe I can hear an improvement (clearer sound/lowered noise floor), at least I know I've improved the measured performance.

Very cool diagnostic check for a minimum invested!

I’ve purchased a pen-type multimeter which includes a non-contact voltage detector. This will replace a couple of items in my test kit.

Another great tester for under $20!


-Chas


P.S. I'll be listing the non-contact voltage detector in the “Marketplace”, along with some other extra items I have lying around.

[clm811]

Part Three:

Next I tried the (Rat Shack) Mini Amp/Speaker. Apparently this is a very sensitive indicator for noise at your components' outputs!

First I connected it to my (15 years old) power amp's speaker terminals using alligator clips, with the preamp muted. There was a shocking amount of 120Hz hum and some buzz as well that vanished into silence as soon as I turned off the amp. Note that this hum/buzz is normally unnoticeable unless I place my ear very near the speaker, and then it's just audible over normal room noises.

This might indicate a need to replace the main filter caps, which may have become leaky over years of use.

Using an adapter with RCA plug, I also checked the outputs of my disc player and preamp. There was a tiny bit of hum (but no buzzing), which was present regardless of which output I checked. I tried reversing the interconnect cables(which have the shield connected at one end) end-for-end, but this didn’t seem to make a difference. Next I tried reversing the orientation of the preamp's two-prong AC power plug, which made a very small change in the noise. I left the AC plug in the orientation which produced the least noise. My other components use shielded 3 prong power cords, so I wasn't able to reverse them.

Note that this test was performed after I had rearranged my leads using the AC detector. I will want to experiment more in the future with different interconnects and cables as a result.

Overall, a very sensitive tester that reveals any system hum!

Not bad for less than $20 !

-Chas

[clm811]

Interestingly(or maybe not), there has been a buzz over at Audio Asylum the past week about the tweak of placing a 1.5"copper pipe union over the IEC plug end of a power cord (butted up against the chassis/rear panel of your component). If it makes you feel better you can even attach a wire to the union, connected to a chassis screw or ground connection.

Back when I tested the "non-contact" voltage detector I had noticed that even on shielded power cords I got a reading at the plug end(s), and this sounds like a handy solution.

This is a cheap tweak that costs maybe $3-4, and it DOES noticeably reduce the EMF at the plug.

Heres a link to a Youtube video demonstrating the use (Please note that I'm not endorsing the other tweaks shown)

http://www.youtube.com/watch?v=piPI_ByD0Q0

As usual, YMMV

Thanks, WJH, for the tip!

-Chas

[walter2]

Having done audio design and troubleshooting for about 30 years, I think the hands down "ultimate tool" remains a good analog scope. Digital scopes are of no value to me (USB or otherwise, including the $5K DSO's) because quantization error makes everything look noisy, hardly a feature for analog design, although the FFT/spectrum analysis features can be interesting, even if they never help you.

You can get a good cheap analog scope from many sources (the 20Mhz goldstar OS-9020A is excellent for audio, and is under $100 on ebay), and while I personally prefer a Tektronix or Phillips /Fluke scope (with a bigger price tag, but better features), I can only advise that whatever the make, it remains the one weapon that that can reveal literally every type of audio related problem, and do it very quickly. Along with a good fluke DMM, and suitable low distortion signal source like an HP 651A or other (now) low cost generator, you can do almost anything.

having said that, ears and noses find a lot of problems, too. It's just that sometimes one is looking for a finer level of accuracy or discrimination than they can provide

all for now,
walter