[sdiy] Re: [AH] Resolution(?) of Siel DK600 trouble..interrresting

[Bob Weigel]

Hehe.  Yeah I wiggled them and listened and watched for response 
changes.  I also checked grounds with my HP and there were a few tenths 
between posts but nothing that would cause something like that.
     .  I'm still to see a problem with the cables in these units 
(worked on about 4 of them now)  but it could happen. Especially if the 
boards get bent up and down enough time without disconnecting them. .  
Seen it in a lot of other things...like the crimp onto plastic ribbon 
things these guys did for us on an RV jack controller...tons of Peavey 
things, some Fender things, Mackie things galore, one Behringer thing .. 
(amazing..some guy told me the 'dumpsters were full of that stuff in 
Nashville'.  I asked him for the address :-) With the cable 
record..you'd have thought the dumpsters would be full of something 
else..especially now that mackie charges 100 bucks for a set of them for 
a 16 channel mixer! ) -Bob

felixkrull2u wrote:

>  My tech has told me in the past that the ribbon cables in the DK 600 
> can cause a whole variety of erratic behavior and replacing them can 
> solve a multitude of troubles. I hesitate to offer this overly 
> simplistic advice to the esteemed Mr Weigel, but there you go.
>   Thanks,
>           Paul Tillotson
>
> ----- Original Message ----- From: "Bob Weigel" <sounddoctorin at imt.net>
> To: "analogue list" <analogue at hyperreal.org>; "synthdiy" 
> <synth-diy at dropmix.xs4all.nl>
> Sent: Wednesday, June 08, 2005 2:07 AM
> Subject: [AH] Resolution(?) of Siel DK600 trouble..interrresting
>
>
>> Ahh you guys give up too easy. :-)  One hint that I didn't 
>> mention...the 'bumps' in apparently all the S+H signals that were 
>> introduced when you began hitting keys with max velocity...were at 
>> around 60 cycles in frequency it appeared.  That would have just sown 
>> more confusion though.. as it turns out the refresh frequency for the 
>> cells is actually around 20msec=50cps.  But..recall with me the 
>> 'bumps' only appear when keys are hit hard..not when anything else 
>> like a bunch of high notes gets hit.
>>      You'd think they'd all contribute equally.   But the hint was 
>> that the top of the waveform was showing a little sawtooth when we'd 
>> hit a max velocity on the sample/hold cell that stores that voltage. 
>> BUT NOT when it was at the voltage below that. (Turns out there are 8 
>> different velocity voltages on the Siel...if anyone had ever wondered 
>> :-) )  Anyway the 5V supply sagged to 4.8V as it warmed up 
>> consistently over about the same time frame as our little noise 
>> appeared.  The 470 ohm resistor in the bias leg of the regulator 
>> (which has no adjustment on the 5V ONLY on DK600..) had gone low..to 
>> 420 or so.  Putting in a trimmer and getting the voltage up a hair 
>> over 5V fixed the problem.  It was consistently warming up and doing 
>> it in the room temp I had and that quick change, reboot and play for 
>> hours without that scrambled sound.   So...apparently the problem was 
>> that the DAC was generating a signal that pushed a little beyond the 
>> rail on the 4051 chip and..they don't like that...it forward biases 
>> the switch junction or something as I recall and I couldn't see the 
>> tiny difference in voltage between the peaks on the velocity and the 
>> peaks on say the key value..but it was there just enough to cause the 
>> problem it seems.  This is a great example of a problem where you 
>> think you've found a cure and it gets you thinking that it must be 
>> something related to something that seemed to bring some success 
>> before when it resurfaces.  But it was a great study for me. Ahh..I 
>> learn to fix one more time...:) -Bob
>>
>
>
>
>