[sdiy] 4051 spikes

[Dave Brown]

I have seen crosstalk between pins not addressed on CD4051s on some vintage
synth stuff I have repaired.  Replacing the parts with modern did not fix
it.  I ended up hanging some small value capacitors on the outputs (inputs)
to quiet things down.  Does termination on the unused outputs (inputs)
change anything (such as the previous email suggested)?

My SCI 700 page at http://modularsynthesis.com/SCI/700/m700.htm has a
comment about the 4051 with the same behavior so I know I saw it there.

Dave

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of florian anwander
> Sent: Saturday, April 25, 2015 2:38 PM
> To: SDIY List
> Subject: [sdiy] 4051 spikes
> 
> Hello,
> 
> I have setup today a simple test circuit for a batch of 4051 (HEF14051BCP
to
> be exact), which I received for free. While testing I found that all 4051
I own
> (not only the ones from the received batch) show some short feedthrough
> of the common signal at outputs 3 and 5 at not addressed times.
> A picture of the scope image can be found here (signal from output 3)
> http://fa.utfs.org/diy/CD4051_1.jpg
> The test setup can be seen here:
> http://fa.utfs.org/diy/CD4051_2.jpg
> It is simply a 4069 as oscillator, a 4520 as address counter and the 4051.
> One has to turn down the clock rate into the audiorange, to make this
vanish.
> 
> Is this normal? Is it caused by the breadboarding setup?
> 
> Thanks for any insight.
> 
> Florian
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