speaker noises when spooling down

[TomReceiver]

I asked this question over on the Polk Forum years ago and got some interesting responses. Whenever I shut down my Adcom GFA-555 I get a type of balloon letting out air sound as the the amplifier spools down and shuts off completely. Usually one speaker and then the other then silence. I got it that maybe the caps are discharging but what actually is causing this or did I answer my own question ?Also similar but different per each set of speakers. Do tube amps do this and what's your own experience w/ this. Some described it as a pleasantly farting sound ..lol

 

[bowtie427ss]

Agree with Inductor, oscillation caused by assymetric decay of the power supply. I doubt many solid state amps did this when new which suggests minimally that something has drifted in spec.

Do tube amps do this and what's your own experience w/ this.

Depends on the tube amp. Some tube amps continue to play normally for up to several seconds because there is plenty of B+ stored in the filter caps, and fully heated tubes will remain in their thermal operating range for several seconds after the heater voltage is cut. Some tube amps will use muting circuits or other methods to cut B+ or otherwise mute the output when mains power is switched off.

 

[soundmig]

Having played with numerous GFA555's since the mid-late 1980's I can attest that this beast plays on for quite a while after you turn it off. I don't recall for absolute certain, but it seems to me that even when new these amps (I had several back then) gave out a bit of a groan at the end of shut down even when new. The one that I have currently for driving woofers does this and it has never alarmed me as it is something that I've come to expect from 555's.

 

[SoCal Sam]

No speaker relay means stuff like this gets through. In fact, much, much worse can get through which will fry your speakers. If you have to go with a 555, get the SE or get your vintage modded with speaker relay.

 

[Chris Brown]

My Yamaha P2200/P2201 amps usually keep going for over 30 seconds after I turn them off. The first 10 seconds or so sounds pretty normal, then it gets increasingly crackly and faint, before settling into more of a hiss, and then eventually becoming quiet. They have behaved that way ever since I got them, and all 4 of them exhibit the same behavior. I can make it stop considerably quicker if I turn the volume up and/or purposefully play bass-heavy content.

 

[Audi0]

I've had a few amps with no protection relay. Atypical there is a pop noise on shut off with the woofers moving quite drastically back and forth. Same with start up does your amp do anything weird on start up?

My dynaco tube amp does not do this. No protection relay here either. On shut off you here the sound slowly fading away. One side shuts off twice as fast as it is powering a extra tube.

A Ballon noise is weird. Maybe it's the caps losing there charge through a circuit with a bleeder resistor? With one side turning off quicker then the other it's about circuit design.

 

[SoCal Sam]

Or get an Adcom speaker switch and switch the speakers off before powering the 555 on or off. A pain but necessary.

 

[TomReceiver]

Hey AudiO, to answer directly my amp has no sound upon power up and never gets or even has been warm in back by the fins w/ a multi speaker load on it. I used to say I had the cleanest Adcom ever made coming from Audio Classics slippery clean for the regular going price of a few hundys. The noise which really now doesn't concern me just sounds like a balloon letting go. Yes it's one side then by the time the other side lets go it's considerably softer and fizzing out. From the responses I got from Polkies it seemed that quite a few brands did this and not sure if the common thread was no D.C. protection circuit. Another point was that it never blew speakers that were fused or not like my former Polk Monitor 7s.

 

[Hak Foo]

I noticed a weird "dragging the speaker around" noise a few seconds after powering down the PC attached to my JVC JR-S300... but it only started after I put a ground-loop elimination transformer in line with the line that was going to my PC (I was getting a 60Hz hum) Maybe it inbalances the system somehow.

 

[goodolpg]

My Rotel RB-990BX has/had* a high pitched squealing sound out of one channel shortly after shutdown.
I asked about it on here and the consensus was capacitors discharging.

I had it checked out for slightly high dc offset in one channel, did not ask the tech to look into the squealing noise.
He found a couple minor issues and addressed those.
Have not used it since the trip to the repair shop so don't know if it's still making that noise.