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loonatron 19th March 2005 07:59 AM

Safety when testing headphone amp for muso's

At work yesterday, I had to test headphones at a really loud level, to check a supposedly distorting headphone amplifier. As I half expected, the distortion was within the performance that you would expect... it only distorts at levels above what is a safe listening level. I felt really anxious afterwards, as I was testing the amplifier by listening through headphones (two different types, with different impedances, both worked fine) and almost blasted my head off.

What is a safer way to test them? Should I use a dummy load and check test tones with a CRO, and compare the results with the spec sheet? (which may not always be available)

many thanks, from Steve

Bill Fitzpatrick 19th March 2005 09:00 AM

It appears you already tested them with a dummy load.

pinkmouse 19th March 2005 10:33 AM

Foam earplugs. Or mic them up and run through the main desk.

loonatron 19th March 2005 11:14 AM


It appears you already tested them with a dummy load
yes, but I was looking for some useful advice here, more like what pinkmouse had to say ;) (I see your humor!)

DigitalJunkie 19th March 2005 11:37 AM

Seriously,NEVER test headphone amps with headphones on your ears!
If something went wrong,and the amp went into a full-power oscillation or something wierd,that LOUD screeching sound might be the last thing you ever hear. :att'n:

Use a dummyload,small speaker,or just leave the headphones sittin on the desk,you'll still hear them okay... Just NOT on your ears.

(A very useful tip I learned the hard way while working on a 1Wpc tube headphone amp.) :hot:

loonatron 19th March 2005 08:56 PM

Thanks, I won't be that silly again! ::clown:

This is what I will do next time...

1) make a dummy:clown: (resistive) load
2) put a test tone through amp
3) measure output on CRO
4) when output distorts, measure output with AC voltmeter, calculate power output, compare with specifications. Tell those who reported it faulty that it works within the design limitations. (if that is the case)

I will also put a pair of headphones (via an attenuator) in paralell with the dummy load, for an objective sound quality test. (That is what most of us identify with!)

When I did the att'n: 'dangerous' :eek: testing I actually found that with some songs on the CD (a Daft Punk CD) the bass just deteriorated completely, even though the volume wasn't really that loud. The only way I could think of checking that this was normal performance for this amplifier was to check it against another identical unit. Both performed the same. This is where it becomes subjective, as I'm sure that the manufacturer's specs are only going to specify the power output at the frequency at which the power output is the highest. (for marketing reasons)

Has anyone got any more suggestions?

Many thanks, from Steve

pinkmouse 19th March 2005 09:02 PM

Just play around with the patch panel, tell the muso you swapped the channels to a good one, but don't actually change anything. That fixes the problem 95% of the time...;)

loonatron 20th March 2005 12:22 AM

:D Good idea! I like that one! :D But the headphone amp was sent back to me for 'repair' from a live gig.

sam9 20th March 2005 04:07 AM

Here's something I'm going to order from digikey along with regular stuff.

I want to see if a headphone amp can drive them. They might be an answer to safely listening to headphones amps. I've idea what they will sound like. They are cheap and maybe I'll end up with "minim-Magnepans" beside my PC.

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