[sdiy] Kurzweil K2000 Query continued

[John Loffink]

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?
>>
>>     
>