[sdiy] understanding this one transistor F to V

[Dan Snazelle]

 	<BAY144-W256E5CD9693B812047B706C8B20 at phx.gbl>
 
 <4AF06FA0.10809 at cox.net>
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thanks so much for the analysis!!

i really appreciate it

you wouldn't believe how many people have told me it IS an F to V converter

so=2C....this leads me to my new question

ARE there any low parts counts (primitive) F to V converters around?

i have searched every electronics book I have and only one or two even ment=
ion F to V=2C and when they do it is
in a TACHOMETER circuit using an LM3900 or using an A to D

i would love to find a circuit that doesnt need any special chips.



----------------------------------------
> Date: Tue=2C 3 Nov 2009 11:00:00 -0700
> From: ebrombaugh1 at cox.net
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] understanding this one transistor F to V
>
>
> Yes=2C it's driving the supply lines of the oscillator. Basically any
> waveform applied to the input gets amplified up to a fairly large AC
> signal that appears on the base of the middle transistor (the one with
> the diode across the E/B). This modulates the supply of the astable
> flip-flop on/off at the input frequency. If you modulate faster than the
> natural frequency of the oscillator (about 100 Hz here) then every time
> the flip-flop is turned on it comes up in the opposite state as on the
> previous cycle=2C so there will be a slight 1/2 frequency variation on th=
e
> output.
>
> I actually built the circuit up and observed this on the 'scope. The 1/2
> frequency modulation is fairly minor compared to the amplitude of the
> supply modulation=2C and the primary frequency dominates. Judging by the
> waveforms it probably sounds pretty harsh too=2C but sometimes that's jus=
t
> what you want I suppose...
>
> So=2C no=2C this isn't an F/V converter. It's more like a suboctave
> generator via a modulated astable flip-flop.
>
> Eric
>
> On 11/03/2009 10:07 AM=2C Dan Snazelle wrote:
>>=20
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>>
>> ok but it is driving the supply lines of the oscillator? so isnt it then=
 cr=3D
>> eating a voltage? when i made a few adjustments to the circuit=3D2C i wa=
s get=3D
>> ting some interesting results. a plucked note would make my scope rise f=
rom=3D
>> 0 to around 5 volts (roughly) and then it would slowly swoop back down. =
i =3D
>> hooked it up to a transistor/40106 setup and was able to get sweeps out =
of =3D
>> the 40106 oscillator but it was hardly in tune with the guitar!! anyway.=
..y=3D
>> our explanation makes sense as i have certainly never seen such a simple=
 F =3D
>> to V before. i was sort of hoping that I could tweak it enough to get th=
is =3D
>> to drive a VCO thanks>> On Nov 3=3D2C 2009=3D2C at 4:24 AM=3D2C Ren=3DE9=
 Schmitz wr=3D
>> ote:>>> Eric Brombaugh schrieb:>>> Sure looks like a simple flip-flop di=
vid=3D
>> er to me.>>>> But thats not a FF but an astable oscillator.>> Well=3D2C =
yes. =3D
>> I've heard the cross-coupled circuit on the right called an> 'astable fl=
ip-=3D
>> flop'=3D2C so let's split the difference. My point though is> to clarify=
 for =3D
>> the OP that the way this circuit is set up there is no> explicit convers=
ion=3D
>> from frequency to voltage. Instead=3D2C the input> signal is amplified a=
nd d=3D
>> rives the supply lines of the astable flip-> flop in such a way that the=
 re=3D
>> sult is to divide the input signal's> frequency by two.>> At least that =
was=3D
>> my thought based on a quick glance at the circuit.> If you've got a diff=
er=3D
>> ent interpretation I'd be interested to hear it.>> Eric> _______________=
___=3D
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.xs=3D
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