[sdiy] VCR - Voltage Controlled Resistor

[Scott Gravenhorst]

harrybissell <harrybissell at prodigy.net> wrote:
>Actually the vactrols are known for being able to process ANY amount
>of voltage... up to hundreds of volts. But they are dog-slow !
>
>I think I was looking at some phaser stuff over at Osamu's site. Didn't
>you see the linearization stuff ???

Just did, I think this is what you mean:
http://www5b.biglobe.ne.jp/~houshu/synth/PhaseFet0205.GIF

OpAmps... Bad kharma.  4069UB inverters don't have + inputs...  But it is the shunt
thing you were talking about.  In this case, he's using a voltage contolled hipass
stage.  Which is why my original question was about using a hipass in the feedback
loop of an opamp (or a 4069UB) to make a lowpass.  Even at that, I don't see the FET
VCR as high enough performance to allow a 3 volt input signal which would be needed
to get a 4069UB integrator to distort when powered at 5 volts.  Heck, powered at
only 3 volts, the input would have to be about 1.8V for that.  I'm barely able to
push 100 mV without nasty distortion.  I want distortion, but not through the VCRs,
I want it as a result of using the 4069UB as an integrator.  Perhaps I'm going to
wind up with a WASP clone of some kind???  Not what I wanted to do really.


>
>H^) harry
>
>Scott Gravenhorst wrote:
>
>> harrybissell <harrybissell at prodigy.net> wrote:
>> >Hello Scott (et al)
>> >
>> >You are now getting there. The FET distortion is why they are seldom used.  If
>> >you add the linearizing resistors, the impedance drops a lot.
>> >
>> >Usually the more successful FET designs use them in shunt mode... with a fixed
>> >series component and a linearized FET to ground. Most FET phasers do this.
>> >Guitar waves have very low amplitude after a huge peak... the distortion will
>> >be very short and no one will be the wiser. VCO waves are constant amplitude.
>> >
>> >I suggest you hie hither to Osamu Hoshuyama's site. He has some ideas there on
>> >FET linearization iirc.  One of them is truly a new idea that has not been
>> >commonly used !
>>
>> I've been there, he has an SVF using 4069UB integrators, but with an M5222 dual
>> expo OTA (unobtainium), essentially as WASP type filter.  He also has a 4069UB
>> integrator SVF using MOSFET OTAs built from more 4069UB (but says they are tricky
>> to make them work).  He doesn't seem to use FET VCRs in any of his filters.
>> Perhaps I know why now.
>>
>> >Now take two VAC-TROLLS and call me in the morning   :^P
>>
>> God I don't want to do that.  For one thing, I don't have any, unless you call an
>> H11F1 a vactrol, and those don't look much better for even 3 volts P-P of signal
>> (unless I'm reading the spec sheet wrong).
>>
>> >
>> >H^) harry
>> >
>> >Scott Gravenhorst wrote:
>> >
>> >> Ok, well I still have the H11F1 option, I've got a couple here that I can
>> >> use, but I will first try to get the best I can out of a 4007, since I really
>> >> would like to see that work if it can.  The H11F1 also eliminates the need
>> >> for a bastardized ground/powersupply thing, but the large signal spec seems
>> >> to suck for that one too, the V-I curve is linear only from about -50 mV to
>> >> +50 mV.
>> >>
>> >> I was hoping to be able to drive the filter with around 3 volts of input, but
>> >> it's not looking good for that.  Perhaps this is why the WASP uses an OTA...
>> >>
>> >> "Theo" <t.hogers at home.nl> wrote:
>> >> >I experimented a bit with those but found other FET like the BF245 behave
>> >> >too similar to the special VCR FET to jump even half a inch.
>> >> >
>> >> >Could not find the home of Siliconix the gallier but he lives in Vishay now,
>> >> >thanks for the tip.
>> >> >The FET as VCR application note AN105 should be at the Vishay website.
>> >> >
>> >> >Theo
>> >> >
>> >> >----- Original Message -----
>> >> >From: Magnus Danielson <cfmd at bredband.net>
>> >> >To: <synth-diy at dropmix.xs4all.nl>
>> >> >Sent: Sunday, July 18, 2004 3:41 AM
>> >> >Subject: [sdiy] VCR - Voltage Controlled Resistor
>> >> >
>> >> >
>> >> >> Hi!
>> >> >>
>> >> >> There should be folks enjoying this!
>> >> >>
>> >> >> Vishay Siliconix has Voltage Controlled Resistors in their productrange.
>> >> >> Their VCR2N, VCR3N and VCR7N does this. They dynamics may not be much to
>> >> >jump
>> >> >> high for, but at least something.
>> >> >>
>> >> >> Cheers,
>> >> >> Magnus
>> >> >
>> >>
>> >> ---------------------------------------------------------
>> >> - Where merit is not rewarded, excellence fades.
>> >> - Hydrogen is pointless without solar.
>> >> - What good are laws that only lawyers understand?
>> >> - The media's credibility should always be questioned.
>> >> - The only good terrorist is a dead terrorist.
>> >> - Governments do nothing well, save collect taxes.
>> >>
>> >> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>> >> -- Linux Rex         | RedWebMail by RedStarWare
>> >> -- FatMan: home1.gte.net/res0658s/FatMan/
>> >> -- NonFatMan: home1.gte.net/res0658s/electronics/
>> >> -- Autodidactic Master of Arcane and Hidden Knowledge.
>> >
>>
>> ---------------------------------------------------------
>> - Where merit is not rewarded, excellence fades.
>> - Hydrogen is pointless without solar.
>> - What good are laws that only lawyers understand?
>> - The media's credibility should always be questioned.
>> - The only good terrorist is a dead terrorist.
>> - Governments do nothing well, save collect taxes.
>>
>> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>> -- Linux Rex         | RedWebMail by RedStarWare
>> -- FatMan: home1.gte.net/res0658s/FatMan/
>> -- NonFatMan: home1.gte.net/res0658s/electronics/
>> -- Autodidactic Master of Arcane and Hidden Knowledge.
>

---------------------------------------------------------
- Where merit is not rewarded, excellence fades.
- Hydrogen is pointless without solar.
- What good are laws that only lawyers understand?
- The media's credibility should always be questioned.
- The only good terrorist is a dead terrorist.
- Governments do nothing well, save collect taxes.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: home1.gte.net/res0658s/FatMan/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- Autodidactic Master of Arcane and Hidden Knowledge.