Wiardgroup

Awwww.. Grant!

-- In wiardgroup@yahoogroups.com, "Grant Richter" <grichter@...> wrote:
> The simplest method to determine power supply stability is to have a
VCO attached to a 
> tuner. Add modules to the power supply until the VCO reaches the
level of instability you 
> can accept. 
>

a good rule of thumb...to be sure

but you should take care to specify that said VCO's should be nice
well-behaved storebought Oscillators (like the Wiard 'Classic') and
not surly bolshevik DIY contraptions!
Hell Professor!, My VCO's are unstable when i run 'em off BATTERIES!
;'>

but seriously ...
Thanks for not  being too sqeamish to shine a light on entropy. The
craving for simple answers has become a modern plague ....and to
'Marketing Professionals' (an oxymoron of epic proportions) this
plague has been a positive boon.**
 'Published Specs' has become my favorite genre of fiction! Specs have
been so pervasively subverted by 'marketing engineers' that no layman
consumer in his right mind should trust them. This sad state of
affairs has polluted even as deeply as chip manufacturer data sheets.
The old proverb "Lies, Damned Lies, and Statistics" says it best.

As you point out, current consumption is a graph , not a number,  and
this is why i advise anyone who asks me to plan some 'headroom' into
their power supplies. If you run a PSU very close to it's limit, it is
just --possible-- that a condition could occur that lights all the
LED's  in the rack at once and the fuse pops.  My experience is that
the module manufacturer is always blamed (and the angy message always
contains the perennial fallacy: "It never failed before") And if the
hapless maker published a current consumption number, there's always
one user who will try to treat it as a NIST certification.

This issue is exaggerated in this new, modern, a-go-go modular era of
mix & match systems. In the old modular days, Dr. Bob made sure to
install a power supply with sufficent current reserve (and then some)
 to supply all the Moog modules you ordered in your cabinet at
simultaneous peak conditions. This luxury has been laid aside in order
to bring the cost of modules down. (and the synth cabinets tend to
weigh less than a B3 nowadays too)

My own hard-knocks lesson in this came during my primordial DIY
fumblings when i'd augment an Odyssey and try to run my boards off the
'surplus' current in the on-board power supply. The upper left corner
of the panel kept my tea warm while i worked in that cold basement! 

-doc

**
ie: Sunn's tests demonstrated that their Coliseum power amp COULD
actually perform at it's published output spec. The marketing folks
just felt that it was delving into too much techie detail to mention
that during the  test , the unit was submerged in liquid nitrogen, the
fuse was bypassed, and amp was only required to sustain the rated
output for 4 milliseconds..... 
The only truthful THD spec is 'Yes'


> There are technical problems with talking about power draw. It is
similar to the problems 
> in the old days with amplifier power. How do you measure it? If
different manufacturers 
> use different methods, one may look better than another, but it can
be a mirage.
> 
> Power draw in a module is not a constant. It fluctuates with usage.
So what power do I list? 
> Peak, average, RMS? With all inputs and outputs connected or not? If
not all then how 
> many? If I list the peak power it may be 10 times what the avarage
power is. That is a sales 
> liability.
> 
> Then stop. This is bound to be less than the full rated power of the
supply. But 
> forms a FUNCTIONAL maximum draw.
>