Cgs synth

--- In cgs_synth@yahoogroups.com, sasami@h... wrote:
>
> >I'm getting ready to put the Sequential Switch together (on the
> >breadboard first). I noticed that there are diodes at the power
supply
> >and ground inputs. Can someone shed some light as to what their
> >function is? Are they essential to the circuit? I'm very curious.
>
> They are essential. What they do is more the 4051 so it is
operating in the
> -0.6 to +14.4 volt range instead of the 0 - 15V range. This is
needed
> because the chip is coupled to a summing null (virtual ground) of
an op-amp.
> WHen operated in this mode, the voltage across the active 4051
channel is
> always zero, held there by the op-amp. This means positive and
negative
> voltages can be switched, without the positive negative voltage ever
> actually having to pass through the 4051. All the diodes at the
inputs
> prevent the not-selected channels from being taken negative.
>
> This is also explained in the article.
>
> Ken
>
______________________________________________________________________
_
> Ken Stone sasami@h... or sasami@c...
> Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
> Australian Miniature Horses & Ponies
<http://www.blaze.net.au/~sasami/>
>

> Ahhh. I see. I don't know how I missed it. Thanks Ken. One more
>question. The LM324 is powered from 14.4V and -0.6V. If I use a TL074
>instead, should I be aware of any special considerations? Can I power
>the TL074 with + and - 15 Volts?
>
>Thanks,
>peng
>
>
>--- In cgs_synth@yahoogroups.com, sasami@h... wrote:
>>
>> >I'm getting ready to put the Sequential Switch together (on the
>> >breadboard first). I noticed that there are diodes at the power
>supply
>> >and ground inputs. Can someone shed some light as to what their
>> >function is? Are they essential to the circuit? I'm very curious.
>>
>> They are essential. What they do is more the 4051 so it is
>operating in the
>> -0.6 to +14.4 volt range instead of the 0 - 15V range. This is
>needed
>> because the chip is coupled to a summing null (virtual ground) of
>an op-amp.
>> WHen operated in this mode, the voltage across the active 4051
>channel is
>> always zero, held there by the op-amp. This means positive and
>negative
>> voltages can be switched, without the positive negative voltage ever
>> actually having to pass through the 4051. All the diodes at the
>inputs
>> prevent the not-selected channels from being taken negative.
>>
>> This is also explained in the article.
>>
>> Ken
>>
>______________________________________________________________________
>_
>> Ken Stone sasami@h... or sasami@c...
>> Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
>> Australian Miniature Horses & Ponies
><http://www.blaze.net.au/~sasami/>
>>
>
>
>
>
>
>
>
>The CGS Modular Synth home page: http://www.cgs.synth.net/
>
>Yahoo! Groups Links
>
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