[sdiy] 555 vco (electronotes)

[TheMysticSatin]

Yeah I was wondering about syncing problems from using 2 timers on the same
chip.  Figure only way to find out is to try it (also I only have the dual
timers around right now), I can't get the thing to do anything right now all
I get is a -5v at the square outs and a -3 at the saw outs so the syncing
problem will have to wait till I have something to sync (or swim)...
----------
>From: Scott Gravenhorst <music.maker at gte.net>
>To: "TheMysticSatin" <elmystico at earthlink.net>
>Subject: Re: [sdiy] 555 vco (electronotes)
>Date: Fri, Nov 9, 2001, 10:33 PM
>

>My guess is that it's a second source for the same
>part.  To be sure, get the data sheet PDFs for both
>parts and compare.  You might also want to get the
>data sheet for the bipolar part and compare it to
>the part you want to use.  It's *probably* the same,
>but only the data sheet can clear that up.
>
>Also, I'm not real sure how well the two timers on
>the dual will be isolated.  You may wind up with
>soft synch problems anyway due to coupling within
>the IC.  (via internal power connections).  I've
>never used the dual, so I'm no authority on that.
>
>"TheMysticSatin" <elmystico at earthlink.net> wrote:
>>After running into 555 power supply drain in a sequencer I was working on I
>>opted to use what I've found labelled as a C555 ( actually I'll be using a
>>C556 to make a dual vco) Is that the same as the ICM chip or a reasonable
>>equal? It IS a CMOS chip.
>>----------
>>>From: Scott Gravenhorst <music.maker at gte.net>
>>>To: synth-diy at dropmix.xs4all.nl
>>>Subject: Re: [sdiy] 555 vco (electronotes)
>>>Date: Fri, Nov 9, 2001, 7:03 PM
>>>
>>
>>>I would not use a bipolar 555.  I would look at using
>>>an ICM7555 which is a CMOS 555 clone, pin compatible.
>>>I've replaced 555s with ICM7555s in 4 fatman VCOs.
>>>Work perfectly, no change in component values and there
>>>was no change in the sound.  (The stock FatMan comes with
>>>bipolar 555 timers.)
>>>
>>>The main reason to use the ICM7555 instead is the fact that
>>>a bipolar 555 allows both the upper and lower TTL totem pole
>>>transistors to be on at the same time for an instant while the
>>>output is transitioning from low to high or high to low.  This
>>>causes a high current path between the supply and ground pins.
>>>This brief high current pulse WILL appear on your power supply
>>>rails and it WILL cause problems with other things on that
>>>supply.  Most notably, the VCOs in the FatMan will "soft synch"
>>>when you try to get them close together in pitch.  Simply 
>>>replacing them with the ICM7555 makes it much harder to get
>>>the VCOs to lock together.  This is because the ICM7555 does
>>>not do this.  (It's declared so in the data sheet).
>>>
>>>AFAIK, timing values for the ICM7555 and the 555 will be the
>>>same.  I am not sure about the differences in output (pin 3)
>>>drive current, but in a VCO, pin 3 is not usually used to 
>>>drive anything of significant current requirement.  I use pin
>>>3 to clock a suboctave, which needs only a very tiny current to 
>>>do, well within the spec for either part.
>>>
>>>"TheMysticSatin" <elmystico at earthlink.net> wrote:
>>>>Has anyone out there built the 555 based "Dirt Cheap Utility" VCO from
>>>>electronotes #67 and can give me any troubleshooting pointers, especially if
>>>>there are common problems or critical areas that might need fine tuning as
>>>>far as values.  This is my first VCO... what else can I say?  Any general
>>>>555 timer VCO tips would be appreciated as well.
>>>>Thanks in advance
>>>>Gavin
>>>
>>>=========================================================  
>>>- Government: The other religion.
>>>- The media's credibility should always be questioned.
>>>- Lambs who lie down with lions are lunch.
>>>
>>>-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>>>-- Linux Rex         | RedWebMail by RedStarWare
>>>-- FatMan: home1.GTE.NET/res0658s/TekLab_FatMan_WebSite/index.html
>>>
>>>
>
>=========================================================  
>- Government: The other religion.
>- The media's credibility should always be questioned.
>- Lambs who lie down with lions are lunch.
>
>-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>-- Linux Rex         | RedWebMail by RedStarWare
>-- FatMan: home1.GTE.NET/res0658s/TekLab_FatMan_WebSite/index.html
>
>