Amp Hiss Causing Speaker Excursion

[ViperDom]

Harmon Kardon 3390 Stereo Receiver
Noticed she has begun to output a hiss/whitenoise to the right channel.

You need to be closer than 6 ft to faintly hear it and right up on it to really notice so at first was thinking no big deal... UNTILL I ALSO NOTICED IT IS CAUSING THE WOOFER TO BE HELD FOWARD IN EXCURSION.

First question: I don't know how long this has been going on but i regularly leave the receiver on for days at a time so am concerned at the possibility this may have caused speaker damage. While playing music the speaker remains in forward excursion which i assume causes it to be pushed a bit further than it typically would. Thoughts?

Next, Not really interested in fixing it because ive had the itch to switch to a dedicated amplifier for some time now. Just Curious what yall think might have happened to her. The following is what I have done so far to troubleshoot.

0 = Noise remained in Right speaker
X = Noise was silenced
------------------------------------------------
0 – Swap RCA inputs L/R
0 – Switch RCA cables/input from CD to Vid1
0 – Turn off source
0 – Swap L/R speakers
0 – Swap in different/sparer speaker
0 – Plug Receiver into alternate dedicated outlet without surge protector.
X – Unplug Receiver
TBD - Switch the speaker outputs from Speaker '1' to Speaker '2'

The following are pictures of the speaker with the Receiver ON at idle with source removed, speakers +/- switched, and Receiver OFF

Receiver ON

ON +/- switched

Receiver OFF

 

[fpitas]

That has to be a DC offset problem.

 

[ViperDom]

Thanks fpitas, I'll measure the voltage at all four pairs of speaker outputs when i get home from work.
In your experience is this something that would be linked to the one channel(prior to the speaker outputs) therefore effecting both Speaker 1 & 2?
or is there a chance that i might have some life in her by utilizing the 2nd set of outputs?

 

[tomtoo]

The noise comes togheter with a DC offset problem. Thats serious, keep it off until repair if you like your speaker.

 

[DonH56]

You swapped L/R speakers but the hiss/offset stayed with the right amplifier output? That implies a bad amplifier channel. As @fpitas said, the static excursion is a DC offset problem. The hiss/noise is likely a symptom of a bad coupling capacitor or other problem in the amp, which could be related to the DC offset. Static offsets (excursions) in speakers can cause problems like higher distortion/limited dynamic range, surrounds breaking down or being "molded" into new positions, degradation of the magnets from the constant DC current, and so forth. It also is likely to get worse. I would get the amp repaired or replaced.

The second set of outputs almost certainly goes to the same amplifier channels since it is a stereo (two-channel) amplifier so would not help. You can always try it and see. Be sure the amp is off before swapping wires.

 

[antcollinet]

am concerned at the possibility this may have caused speaker damage

I agree that your amp is putting out DC - which is generally thought to be a bad thing.

Hopefully your tweeters are protected from this internally to the speaker.

If the woofer is still working, and no magic smoke has been emitted, or horrible mechanical (cone reaching mechanical end stop) been heard, probably it is still OK.

But I would not connect this amp to the speakers anymore.

 

[dasdoing]

perfect 0Hz square wave. there is another topic where people desperately try something like that lol

 

[ViperDom]

Here is the Voltage readings at L & R the terminals.
Checked my AVR's as well for comparison...

HK Receiver in question:
-5mV
140-160V

Onkyo AV #1
-50mV
-30mV

Onkyo AV #2
-60mV
-40mV

So, yea i'd say the HK is shot.
I wander if the loudish on/off pop its been outputting to the speakers for the past year was telling of the condition?
Perhaps the combo of these speakers having high excursion split-gap woofers and being 90Hz X'd w/Subs hid this flaw?

 

[DonH56]

Here is the Voltage readings at L & R the terminals.
Checked my AVR's as well for comparison...

HK Receiver in question:
-5mV
140-160V

Onkyo AV #1
-50mV
-30mV

Onkyo AV #2
-60mV
-40mV

So, yea i'd say the HK is shot.
I wander if the loudish on/off pop its been outputting to the speakers for the past year was telling of the condition?
Perhaps the combo of these speakers having high excursion split-gap woofers and being 90Hz X'd w/Subs hid this flaw?

You're lucky the woofer is not blown. You'd best check it as well... Split-gap magnets do nothing to protect the voice coil, and the crossover would not stop a DC offset like that (as you've measured).