[sdiy] Kurzweil K2000 Query continued

[Doug Terrebonne]

K2000s are well-known for blowing their outputs due to static electric shocks. They used to warn you never to touch the output jacks.

Doug
--- On Mon, 7/13/09, John Loffink <jloffink at austin.rr.com> wrote:

> From: John Loffink <jloffink at austin.rr.com>
> Subject: Re: [sdiy] Kurzweil K2000 Query continued
> To: "DTK" <aurastar at cox.net>
> Cc: "Synth DIY" <synth-diy at dropmix.xs4all.nl>
> Date: Monday, July 13, 2009, 7:48 PM
> Kurzweil K2000 have FETs in the
> output circuitry to mute them when powering off, so you
> don't get audible pops on your speakers.  Since both
> channels have failed, it sounds like the circuitry that
> controls the mute has failed.  The control circuitry is
> a few transistors and resistors, if I recall
> correctly.  It detects a dip in the voltage rails as in
> a power off situation and then turns on the FETs to a low
> resistance path to ground, muting the signals.
> 
> Look for three terminal transistors connected to the output
> signals.  Then track the gate signals for these FETs to
> find the control circuitry. 
> John Loffink
> The Microtonal Synthesis Web Site
> http://www.microtonal-synthesis.com
> The Wavemakers Synthesizer Web Site
> http://www.wavemakers-synth.com
> 
> 
> 
> DTK wrote:
> > A bit more information on this:
> > 
> > First, for those who suggested changing the
> batteries:  There are actually no batteries in this
> machine.  The owner uses the synth as a controller, and
> for stock sounds.  According to him, he removed the
> batteries long ago.
> > 
> > The volume loss has continued, but there is still no
> noticeable change in sound quality.  I'm thinking that
> maybe something is going out in the final output
> stage.  Anyone have any suggestions?  I'll be
> googling for schematics momentarily, but if you know where I
> can get them, or the service manual, feel free to chime in.
> > 
> > Thanks
> > 
> > 
> > 
> >   
> >> I'm taking a look at a K2000 for a friend. 
> It's exhibiting a strange
> >> problem... at least, I think it's a problem. 
> If I hadn't been there when it
> >> happened, I might have thought it was nothing.
> >> 
> >> We were playing, and suddenly the K2000 lost
> volume...  It wasn't a dramatic
> >> loss, the patch was still audible, but there was
> *definitely* a loss in
> >> volume.  The patch wasn't changed or edited,
> mixer settings weren't changed,
> >> etc.  It just got quieter all of a sudden.
> >> 
> >> At first we thought it might be some sort of
> mechanical failure in the
> >> output jack... A solder joint on the way out, or a
> worn out center
> >> connection.  However, that doesn't seem to be
> the case.  The problem
> >> persists on the L, R, and Headphone jacks, and on
> different patches as well.
> >> 
> >> I'm a bit puzzled by this one, frankly. 
> There's no difference in the audio
> >> quality, which leads me to think that the output
> circuitry is ok.  Anyone
> >> have any thoughts?  Suggestions?
> >> 
> >>     
> > 
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