[sdiy] pseudo-random tone generator

[Dan Snazelle]

yep

i looked into the past and there was a topic called

"555 cv level?/Psuedo Random Generator Circuit..wow/questions‏"
this topic covered this very circuit


here is a qoute from TIM about the voltage issue:


>
> I suspect part of the reason for this (only working with 5v) is that essentially all the devices in
> the circuit are working on/giving out 'unipolar' signals, i.e. they only
> swing positive, between 0 and 5V (apart from the 556 and op amp, the rest
> are really digital devices, or wired as such). Most other synth circuits
> will be 'bipolar', i.e. swing both pos and neg, perhaps +5 to -5V. Thus if
> you tried driving 4024 u2 from another VCO, and not the 556 pin 5, the 4024
> will see signals going below its own supply (0-5V), and won't like this -
> whether it would be enough to stop it working completely is another matter.
> Thus your driving VCO needs (ideally) a squarewave output, and you could
> hook up a transistor or two to make it unipolar.
>
>> 2. WHAT IS THE VOLTAGE RANGE OF CV IN ON the 555/556555? (pin
>> 5) He mentions that the single supply opamp (would a 324
>> work?) is biasing the voltage for the 555's cv Input. if i
>> knew more about what the range is, i might be able to get
>> this working better.
>
> Personally I find remembering the way a 555 works hard to do, so I always
> reach for a book with it in, almost always 'Practical Oscillator Circuits'
> by A.Flind, Babani publishing, as the description on page 2 is very simple
> and tells me most of what I want to know! In this configuration, with the
> control pin unconnected, the cap will switch to charging when the level
> drops below a third of the supply, then charges up till it starts to
> discharge when it gets to two-thirds supply. If the control pin is connected
> to a low-impedance source (like u7), then this 'overrides' the top third of
> the voltage, so the cap waveform will then switch between the applied CV
> voltage, and one half of it, hence the way voltage control is achieved. I'm
> guessing you probably haven't got an oscilloscope, but if you did this would
> be easy to see! Thus the effective 'range' of the applied CV can be pretty
> much anywhere from ground to the positive rail.
>
> Another thing you could do (if you haven't already) is do the calculation
> for the u7 output, given the off/on nature of the inputs, so that you get
> some idea of what the range actually should be - if you have a DVM, and you
> can get the thing running slow enough, you could probably see the output
> changing in discrete steps as the inputs change. (u7 is basically a standard
> inverting op amp set up, a little complicated by the fact that it is working
> around the 2.5V point, rather than ground.)
>
> That's probably enough to overload you for now - have fun, and if I can help
> any further, I'll try and do so!
>
> Regards,
> Tim



--------------------------------------------
check out various dan music at:

http://www.myspace.com/lossnyc


http://www.soundclick.com/lossnyc.htm


http://www.indie911.com/dan-snazelle
(or for techno) http://www.myspace.com/snazelle


> From: subjectivity at hotmail.com
> To: music.maker at gte.net; synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] pseudo-random tone generator
> Date: Tue, 14 Oct 2008 19:04:21 +0000
> CC:
>
>
> no no no
>
> i did NOT mean the chips wont RUN on 12 or 15 BUT this circuit in particular wont make SOUND on 12 or 15.
> something to do with the way it is setup.
> if you read the circuit description,,,he explains why.
>
> check my old post on sdiy about this (from about 6 months ago)
>
> sorry for the confusion
>
>
>
>
> --------------------------------------------
> check out various dan music at:
>
> http://www.myspace.com/lossnyc
>
>
> http://www.soundclick.com/lossnyc.htm
>
>
> http://www.indie911.com/dan-snazelle
> (or for techno) http://www.myspace.com/snazelle
>
>
>> Date: Tue, 14 Oct 2008 11:26:54 -0700
>> From: music.maker at gte.net
>> Subject: Re: [sdiy] pseudo-random tone generator
>> To: synth-diy at dropmix.xs4all.nl
>>
>> Tom Wiltshire wrote:
>>>
>>>On 14 Oct 2008, at 18:48, Dan Snazelle wrote:
>>>>
>>>>
>>>> IMPORTANT...these buggers ONLY seem to work with +5 volts. i tried
>>>> it on + 12 and +15 and got nothing. ALSO when i tried interfacing
>>>> certain VCO's and other modular stuff to them that was being
>>>> powered by 12
>>>
>>>I can't speak for the specific circuit in question, but I used to run
>>>a lot of 4000-series CMOS circuits and 555 timers off a 9V battery
>>>when I was a teenager. Seemed to work fine.
>>>CMOS has pretty wide tolerances for supply voltage.
>>
>> same here, I have a bunch of CMOS mods on my FatMan synths. They use as high as a
>> 15 volt supply.
>>
>> Is it possible Dan's part is not a 4000 series, but rather a 74HC equivalent? I
>> believe those parts are limited to +5v. All of my 4000 series logic datasheets have
>> a Vdd range of 3 to 15 volts.
>>
>> -- ScottG
>> ______________________________________________________________
>> -- Scott Gravenhorst
>> -- GateManPoly - FPGA-based Polyphonic MIDI LA/FM Synthesizer
>> -- GateMan-III - FPGA-based Monophonic MIDI LA/FM Synthesizer
>> -- PolyDaWG/8 - FPGA-based 8 Voice Polyphonic MIDI Synthesizer
>> -- FatMan: home1.gte.net/res0658s/fatman/
>> -- NonFatMan: home1.gte.net/res0658s/electronics/
>> -- When the going gets tough, the tough use the command line.
>>
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