[sdiy] First DIY synth (555 osc.'s)

[Scott Gravenhorst]

Most of the bad press over the 555 issue is related
to the older bipolar version which does, indeed,
have problems.  The ICM7555 is a whole lot different.
The main issue with the ICM7555 would probably be
that it produces saw and pulse only, but I think
that's not so bad since waveshapers can be used
to do PWM and others.  (This factor is no different
for the bipolar 555).  I'm convinced that the 555
(read BIPOLAR) sucks, but the 7555 is fine.  The
ICM7555 works FAR better in a FatMan than does the
bipolar 555.  The FatMan is a dual VCO unit and with
the ICM7555 chips installed, I can get the VCOs within
better than 1/10 hertz of each other with no soft
synch lockup; without modifying the power supply 
bypass arrangement.


"Seb Carr" <star at all-carrs.demon.co.uk> wrote:
>I've never heard a fatman in the flesh but people seem to rate them okay 
>with a 555 based osc. but the basic homemade synth suggested below seems a
>bt wrong e.g. cem chips for lfo but 555 for osc. With all the recents
>arguments over whether 555's are any good for vcos or not, the outcome
>appears to be "alright, but not great" but for an lfo i'm sure their
>stability id fine , and they output square which can be integrated to give
>triangle (ideal for most lfo uses). am i right?
>
>----------
>>From: Scott Gravenhorst <music.maker at gte.net>
>>To: synth-diy at node12b53.a2000.nl
>>Subject: Re: [sdiy] First DIY synth (555 osc.'s)
>>Date: Mon, May 7, 2001, 2:22 pm
>>
>
>> IMHO, an easy and good way to use a 555 as a
>> musical VCO is the PAiA FatMan way.  Even
>> better if the 7555 is used instead.  It produces
>> a saw and a pulse waveform as is, although
>> the pulse wave is not routed to the mixer
>> in the FatMan unless modified to do so.
>>
>> The oscillator in the datasheet which uses
>> pin 5 as a CV input has very limited pitch
>> range and may also cause saw amplitude variations
>> depending on pitch.  This is because the pin 5
>> input changes the threshold value to control
>> pitch instead of supplying a controlled current
>> to charge the cap (leaving the threshold constant).
>> The latter method (controlled current) is what
>> is employed in the PAiA circuit.
>>
>> "Seb Carr" <star at all-carrs.demon.co.uk> wrote:
>>>I looked at the link to geocities, and the sample of the 555 osc is very
>>>cool, but is there a schematic for it, or is it just the osc from the
>>>datasheet?
>>>
>>>Seb Carr
>>>
>>>----------
>>>>From: perpetual <perpetual at uswest.net>
>>>>To: synth-diy <synth-diy at node12b53.a2000.nl>
>>>>Subject: Re: [sdiy] First DIY synth (555 osc.'s)
>>>>Date: Mon, May 7, 2001, 5:37 pm
>>>>
>>>
>>>>
>>>>> > I wanted to build a bear bones system for more of a learning experience
>>>then
>>>>> > anything else.  I planed to build the VCO and ADSR from simple circuts I
>>>>> > found based around 555 timer chips and I was going to use CEM chips for
>any
>>>>> > or all of the VCA,VCF and LFO (if I included one).
>>>>>
>>>>> Huh? VCO with 555, but LFO with CEM chip?
>>>>>
>>>>> > I would use batterys in lue of a powersupply.
>>>>>
>>>>> If you do so, use a VCO that is unsensitive to power supply voltage. Or
>>>>> you'll have to re-tune all the time when the battery goes weak...
>>>>
>>>> so i was playing with a 555 oscillator last week.  more info here:
>>>> www.geocities.com/aurelialuz/shadow.htm
>>>>
>>>> what i've found is that all this talk about instability is true.  this
>>>> thing is really temperature sensitive.  and we're not talking like a
>>>> couple cents over an hour, i'm talking like octave flucuations from
>>>> minute to minute.  this thing is powered off a battery too, so i've got
>>>> both demons of instability working against me.  if i was really
>>>> interested in creating some sort of stable oscillator, i'd look
>>>> elsewhere.
>>>>
>>>> but lucky for me, i care not a whim for stability.  and what's really
>>>> cool about this thing is when you feed a wave output from another
>>>> oscillator into the CV input.  it becomes something like a sub-osc., but
>>>> instead of creating a low note, it gives all these weird overtones, sort
>>>> of like an "effects" oscillator.
>>>>
>>>> also, i've always read that 555's put out a pretty weak tone, but i put
>>>> a pretty big poly cap in it (.18uf) and i was suprised how thick it
>>>> sounds.  so if you go the 555 route, the bigger the cap the better.
>>>>
>>>> best,
>>>> alex
>>
>>
>> =========================================================
>>   If children are unable to read by the 4th grade,
>>   then one must ask:  What is being taught?
>>
>> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>> -- Linux Rex         | RedWebMail by RedStarWare
>> -- FatMan: www.teklab.com/~chordman
>> -- NonFatMan: members.xoom.com/_XMCM/chordman/index.html
>>
>> 


=========================================================  
  If children are unable to read by the 4th grade, 
  then one must ask:  What are the teachers doing?

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: www.teklab.com/~chordman
-- NonFatMan: members.xoom.com/_XMCM/chordman/index.html