[sdiy] MC1495 multiplier chip discontinued completely

[Ian Fritz]

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.