Components producing AUDIO?!!!!

[Dubka]

With my (broken) 1176 on full input/output I can hear the audio coming from inside the unit!

Where is it coming from?!!

 

[MicDaddy]

Transformer(s)?

 

[Dubka]

I had a feeling it was coming from the output transformer...  is that normal?

 

[Kamel]

Gremlins?

 

[ncoak]

Gremlins?

yep, they set up shop in there and are singing along. check around for teeth marks on wires, suspicious "cold" (sabotaged) joints, things like that.

 

[ruckus328]

Anyone ever see Cat's Eye?  I keep picturing that little troll guy in there.

Cue: "Every Breath You Take"

 

[MicDaddy]

How is the thing 'broken'?


gremlins....  :

LOL

 

[Dubka]

It's broken in that it doesn't sound good, like my other 1176..

It's driving me mad trying to find what's wrong with this thing....

I can stop the distortion by touching various points (with my finger) like the solder tags on the attack pot.
Any ideas?

 

[JohnRoberts]

It is pretty common in high power circuits for components to vibrate in response to current, but it's worth considering that excessive noise is energy that should be signal or simple waste heat. I have even seen power resistors make noise in response to audio signal.

I recall one small transformer used in a dual output switching power supply that made so much racket I was asked to redesign the power supply, to make it quiet. I ended up using a potted inductor that was completely silent.

Too much noise is often evidence of a questionable part... but it depends on the context. For low power audio paths I wouldn't expect much audible noise.

JR  

PS: to help trouble shoot maybe use a small wood dowel with one end held close to your ear, the other end touching various components, until you find your gremlin.

 

[0dbfs]

I've found that the meters make audible audio when driven really hard. Can't be "good" for them.

Cheers,
jb

 

[gemini86]

I've found that the meters make audible audio when driven really hard. Can't be "good" for them.

Cheers,
jb

My G1176 meter makes noise when pegged... at least I THINK it's the meter... When running a 1k sine through it, it'll sound like a headphone can on medium loud volume, then as you crank it, it hits a certain threshold and clips hard, creating a distorted 2k tone along with the 1k tone. It only did this during initial setup and testing. During normal use, I never have the output at half the level needed to make anything make noise inside.

 

[Slenderchap]

Audio transformers make noise when they are in operation because of magnetostriction of the core.... the steel expands and contracts in "sympathy" with the audio.... usually you will only hear it in output transformers because of the signal levels involved.... bigger the signal, bigger the noise.

It is the same process which makes mains transformers hum.

I guess that the same thing will happen to a VU meter if you drive it hard enough.

Colin
www.audiomaintenance.com

 

[RuudNL]

Believe it or not: I once had an amplifier that produced audio. There were no audio transformers inside, but after a close examination I noticed that the power transistors (AD149) produced sound!

 

[0dbfs]

Yeah I'm gonna run the drums through the RevA, peg it hard, mic up the vu meter out in the live room, bring that up on my parallel drum bus, eq out all the highs, and send it through the plate with some pre-delay...

Only in the chorus.

Just what I've been looking for !

Cheers,
jb

 

[MicDaddy]

LOL, somewhere I read where a fella played a melody with some kind of synth... might be onto something here.

Flea circus PA system  LOL  http://www.youtube.com/watch?v=gauReGP_Tps&feature=related