[sdiy] VCR - Voltage Controlled Resistor

[Scott Gravenhorst]

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.
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>>
>> -- 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.