[sdiy] MC1495 multiplier chip discontinued completely

[patchell]

    Well, just to throw my 2 cents in...

http://www.oldcrows.net/~patchell/archives/ca3280_12.html

    This is a 4-quadrant I built from a CA3280...however, with the price of a
CA3280 being what it is, it might be more ecconomical to use an AD633.

Ian Fritz wrote:

> Hi folks --
>
> I'm not sure how this fits in exactly with the discussion of class A or B
> operation, but I once made a switchable 2-quadrant/4-quadrant multiplier
> using linearized 13600's.  It's in Electronotes #113 (just before the
> famous Serge T. article on the "new" OtA's).  What was interesting to me at
> the time was that I figured out how to make a switchable mode module, with
> independent trimming for each.  I never made a permanent version, so I
> can't compare noise and distortion with my 1495-based unit, but at the time
> I thought they were pretty decent.
>
> It would be something else to look at, anyway.
>
>    Ian
>
> At 10:41 AM 4/24/2003, jhaible wrote:
>
> > > The 13600/13700 do have the problem that they are only two quadrant.
> > > You can overcome this with using two vca devices, each for two quadrants
> > > will make four quadrants. The problem is then, like in B type output
> >stages,
> > > the crossover distortion. This kind of distortion will not go away
> > > if the signal gets smaller, so no good prospect.
> >
> >Come on: forget about the second VCA device, and you're forced to go for
> >"class A" (stretching the terminology to the mixing part, not ´peaking
> >of the OTAs interior), so you kill two birds with one stone.
> >Here's the circuit:
> >http://www.oldcrows.net/~jhaible/tonline_stuff/jh1_ring.gif
> >It is not clean either, and not temperatire compensated, but you can
> >overcome both problems if you use a linearised VCA instead of the
> >3080.
> >
> >
> > > Perhaps there is a possibility to have a tricky bias scheme,
> > > similar to A/B or A operation of output stages. However, a lot of mirrors
> > > are involved, much more circuitry than the normal gain cell
> > > has, I do not like that idea.
> >
> >The most funny thing in terms of RM design is that there is a circuit
> >which deliberately uses class B (a real gap, though ever so tiny) instead
> >of class AB or whatever. That's from ARP (as used in the 2500
> >or 2600, maybe in both, I don't remember), and it has a reputation
> >of being especially *clean* !!
> >
> >Why? Because clean can mean two different things: No higher sidebands
> >from nonlinearity and/or no carrier bleedthru when you stop playing.
> >Obviously the latter can be achieved even without perfect trimming
> >if the *signal* (not the modulator) is fed into the input that suffers
> >from the dead band.
> >
> >
> > > The problems of symmetry also applies to the last one, RC4200.
> > > They are still around at Farnell, but I need to try them.
> >
> >You need a lot of resistors, and a lot of trimming, if you want to make this
> >a decent 4Q multiplier. And be careful about the impedance match of
> >signal inputs and the other inputs used for trimming. These are bipolar
> >devices, and you can ruin all the trimming with drift of offset _currents_.
> >If you really want the trimming to be good, you need 3 resistors and a
> >capacitor in addition to the trimpot, and this all x3.
> >(Two resistors to divide down the trimpot voltage, the 3rd resistor
> >to increase the impedance of the divider, as seen from the IC's pin,
> >and a capacitor to make the pin a GND for high frequency.
> >(I know that the MS-50 and also the circuit in Barry Klein's book
> >uses a simpler approach, but you loose some of the chip's specs
> >that way.)
> >
> >JH.

--
 -Jim
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