Four quadrant multipliers:Results of my searching

[harry]

Hi Kids:

I like the "matter of taste" comment. The advantage of the "no trim"
solution
is if you are building a commercial lot, you do not have to run units
through
very expensive "calibration" department where everything must be done just
so
by high-priced employees... or done poorly or not at all by low priced
employees.

I have trouble with getting cals on a 4-20 mA current loop output. This has
a
Span and Zero cal... which interact. Sound familiar ???  ;^)
I can do one in about a minute. Less skilled people take over 5 minutes.
This is from
my VCO "cal" training. Hitting a 4-20mA is easy compared with tracking
multiple
VCO over many octaves.

My Rev3 Prophet V  had a reduction from 160 trims (earlier units) to only 80
!!! I added
40 trims back in because I insisted that the Poly-mod section track from
note to note so
I could do "bagpipes" and other calibrated offset bends.  It was a bitch to
calibrate.

Yo Magnus and JH. Face it. You are just like me. You will buy the laser
trimmed part
because it is tighter tolerance to start with, and you can hear, want,
deserve, and can afford ? the best. Then you will decide that it is not
"good enough" yet.... and add the
trims because it can be BETTER.  So you will have an awesome result and few
will
follow in your footsteps... or even see your footsteps....   ;^)

If you want fun... modify one of Bob Moogs designs. I think he gets perverse
pleasure
out of making every component do THREE things at the same time, so you can't
change
one parameter without screwing up two others !!! ARRRGGGHHHH!!!

PS:
Hey Magnus: when they come out with a "Divide by Zero" be sure and let me
know...
(or divide near zero, through zero...etc.)   ;^)

H^) harry

Magnus Danielson wrote:

> From: jhaible at t-online.de (jh.)
> Subject: Re: Four quadrant multipliers:Results of my searching
> Date: Sun, 24 Dec 2000 01:55:05 +0100
>
> > > For a DIY yes, but when in commercial buissness, no. Each trimmer is
> > > expensive then. Laser-trimming reduces the need.
> >
> > Does this mean the 633 requires no trimming ?
>
> "no trimming" is a matter of taste. The laser-trimmed version would
> mean no trimmers for more applications than non-trimmed
> versions. Then, when you are really picky, then you would need
> trimmers again, but then covering a much smaller range and then that
> would be less prone to aging of trimmer positions, so there is added
> benefit right there anyway.
>
> > I thought there was an expensive no-trim version, and the "cheap"
> > one needed trimpots. Maybe I mixed that up with another device.
>
> Possibly. Analog Devices calls this "Low Cost Analog Multiplier".
>
> Their high-spec would be AD534 and AD734 multipliers. The fun part
> with those is that they include divide functionallity.
>
> > Now what's the remaining offset voltage (in dB's or % from full range)
> > of a trimpot-less 633 circuit ?
>
> They claim it to be within 2 % of full scale, and then we are talking
> about "guaranteed total accuracy".
>
> This means output offset voltage of +/- 50 mV maximum and +/- 5 mV
> typical. The input offsets have similar numbers (30 and 5 mV).
>
> The benefit of using a device like the AD633 is that if you add
> trimmers, you can directly adjust the inputs and output separately and
> that by taking only 3 trimmers and 6 resistors. The datasheet gives
> suitable values for these to give the +/- 50 mV trimming range.
>
> Looks like a nice little 8-pin chip to me. If only AD could deliver
> their backlog that is...
>
> PS. Christmas calibrating my OB-8... ;)
>
> Cheers,
> Magnus