[sdiy] 555 vco (electronotes)

[TheMysticSatin]

Hold on let me get you straight, just add a resistor along the CV input line
so there would be my standard 100k input impedence resistor and then  a 10k
in series with that before it?  Or am I misunderstanding?
----------
>From: Scott Gravenhorst <music.maker at gte.net>
>To: "TheMysticSatin" <elmystico at earthlink.net>
>Subject: Re: [sdiy] 555 vco (electronotes)
>Date: Sat, Nov 10, 2001, 7:18 AM
>

>Hmm.  I don't have EN, so I can't look at it, but this
>ought to be a fairly straightforward circuit.  Other than
>the CV input, there should be very little different from
>a plain 'ol multivibrator circuit.  If you can, try to
>replace the CV input current source with a resistor, I'd
>guess to start around 10K.  That will tell you if your
>problem is in the CV input or in the basic sawtooth 
>oscillator.
>
>"TheMysticSatin" <elmystico at earthlink.net> wrote:
>>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
>>>>>
>
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