How is a Fairchild jfet identified from fakesters?

[lowvolt]

Yea ... heheh ... I'm a fan of opamp circuits, if I had my way I'd make everything out of 741s, 072s and 074s.  But, we all know about that "ideal world" that pretty much is nonexistant.

Every synth module I have that uses TL074s sounds just great .. transparent as all hell, and stone dead quiet.  I WISH I knew of a good compressor that was based on opamps only (no BJTs and definitely NO OTAs).

[PRR]

> I WISH I knew of a good compressor that was based on opamps only (no BJTs and definitely NO OTAs).

Look outside the field. LA2-A (opto) is loved in the studio. So are Fairchild 660, Altec(?) 175 and other vari-mu tube compressors. UA-1176 is a very lovely FET comp/limiter. CBS sold VoluMax and AudiMax(?) dynamic processors (diode bridge), THE standard radio rig for a decade. Later radio-rigs use PWM. The RNC is a very nice budget studio dynamic tool based on THAT Corp chips.

But "opamps only"? What is the defining property of opamps? The gain is controlled only by EXternal parts. So to vary gain you need some external NON-opamp part(s). Starved tubes. Biased FETs. PWM. VCAs.

Of all of these, the Resistor+FET scheme is by far the simplest and most suited to simple low-voltage pedals.

But even an FET needs voltage. Specifically you should be able to drive the Gate all the way to Vgs(off). Vgs(off) is available in w-i-d-e sorts from 0.5V to 8V.

Vgs(off) is critical another way. If the signal approaches a fraction of Vgs(off) it distorts.

So we need high Vgs(off) for low distortion, low Vgs(off) for easy drive from 9V supply.

And in simple designs, the output level is directly related to Vgs(off) (by the sidechain gain). So different pedals with different Vgs(off) will have different output levels.

If, say, you wanted to make several "all the same" FET compressors, you need to sort for Vgs(off). It needs to be more than a Volt but much less than 8 Volts. Tolerable values depend a LOT on the circuit. Let's say you find that a Vgs(off)=3V part works nice. For excellent pedal repeatability you probably want to stay within 10% of that. Buy a tub of JFETs and sort for Vgs(off)=2.7V-3.3V.

If you were building stereo limiters, or many-stage phase shifters, you would also have to sort for On resistance, or Idss (a very related parameter), to get left/Right or stage-stage matching.

And BTW: this seems to have NOTHING to do with Fairchild or "fakesters". Indeed the "rejects" from amplifier FET sorting can sometimes be just-fine FET attenuators.

[lowvolt]

Yea, I know that "opamps only" aren't possible ... just dreaming.  It was just a "if the world were perfect according to me" statement that some of us dreamers spew from time to time.  Hence the statement about the ideal world we all know doesn't exist in my post there (wink wink) ...    

Yea ... heheh ... I'm a fan of opamp circuits, if I had my way I'd make everything out of 741s, 072s and 074s.  But, we all know about that "ideal world" that pretty much is nonexistant.

Every synth module I have that uses TL074s sounds just great .. transparent as all hell, and stone dead quiet.  I WISH I knew of a good compressor that was based on opamps only (no BJTs and definitely NO OTAs).

I THINK I created a workaround to my immediate problem last night.  Thanks to inspirations by yourself and a few others here.  To summarize what I did, I SIMPLY DID What Was SUGGESTED AND DESIsigned the circuit around the limitations of the components used.  A simplt modification, and BLAM, one again I AM IN CONTROL!.

(pardon the capitalization issues ... wonky keyboard.  Odd thing is that this only happens when I come to DIY Stompbox forum!  I HAVE ZIP_CLUE WHy my shift key seems to stick when I'm on this forum.  I GOTTA WHAck the hell out of it to get it to unstick - but only in this forum.  Dunno ...)

PRR please check your inbox.  Thanks.