[Jukebox-list] ami continental sound problem

[Daniel Gray]

Thanks for your responses.

The noise disappears when I lift the tone arm off the record. The hum/rumble 
starts almost immediately on the lead out groove, you can hear it fading in 
when the song fades out. The cut off switch is adjusted correctly.

I still had the bolts holding the mech down in the cabinet. I didn't know 
they are supposed to come out. I took them out, but it hasn't made any 
difference the noise is still there.

Do you think it could be the rubber mounts?


>From: Ron Rich <ronnnrich at yahoo.com>
>Reply-To: Jukebox mailing list <jukebox-list at lists.netlojix.com>
>To: Jukebox mailing list <jukebox-list at lists.netlojix.com>
>Subject: Re: [Jukebox-list] ami continental sound problem
>Date: Sun, 9 Sep 2007 10:03:14 -0700 (PDT)
>
>Jay is correct, but I might add that the "trip-off switch" adjustment may 
>be off, allowing the AVC more build up-time, prior to record trip-off. If 
>the hum is electrical ( present with the needle off the record), check out 
>the tone arm/cartridge grounding circuit. Ron Rich
>
>Jay Hennigan <jay at west.net> wrote:  Daniel Gray wrote:
> > Hello again!
> >
> > So I have sorted the crossover problem. I have another problem I need to
> > sort out. When the jukebox is at a high volume during lead out section
> > of the record, the jukebox hums really loud. Sometimes it sounds like
> > its going to take off! The woofer shakes really violently, I turn it
> > down because it can't be good for it. It doesn't happen on the lead in
> > section of the record. Do you know what could be causing this?
>
>Hello, Daniel and welcome to the list! I had somewhat of the same thing
>with my Wurlitzer 1900. The underlying cause is probably mechanical
>rumble coupled to the stylus. It could also be magnetic hum pickup from
>the motor to the cartridge, or even acoustic feedback from the woofer.
>Try carefully lifting the arm just off of the surface of the record
>right at the end of the record and hold it there for a few seconds to
>see if the hum appears. If so it is electrical or magnetic from the
>motor. If not, it's mechanical.
>
>There's a reason for waiting a few seconds, and it is why you don't hear
>the hum at the beginning of the record or while it's playing. The
>amplifier has AVC, automatic volume control. To compensate for records
>of different loudness and have the jukebox volume relatively constant, a
>circuit in the amplifier boosts the volume for quiet records and lowers
>it for loud records. There is a time constant of about one to four
>seconds for this to adjust so it doesn't obviously "breathe".
>
>The muting circuitry forces the AVC to be at its lowest volume during
>record transfer and immediately after it unmutes. This plus the time
>constant brings up the volume up slowly at the beginning of the record,
>hiding any crackle in the lead-in groove.
>
>At the end of the record, however, the lead-out groove will have a few
>seconds of silence. The AVC treats this silence as very low volume
>music and turns up the amplifier to compensate. Thus, any problems with
>rumble or noise that exist are amplified.
>
>You'll want to find and fix the source of the noise, of course, but it
>may also be worthwhile to make the AVC a little less aggressive. The
>aggressiveness is adjustable on Seeburg amplifiers, but I don't think it
>is on the AMI. This might require some component changes in the
>amplifier. Depending on your expertise you might want to look into
>this. Fix the cause of the underlying noise, as well.
>
>--
>Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
>Impulse Internet Service - http://www.impulse.net/
>Your local telephone and internet company - 805 884-6323 - WB6RDV
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