[sdiy] CMOS Synth

Mon Feb 3 18:11:51 CET 2003

Hi Magnus:

My reply was not 'strictly' a comment on the 4069... but 
was to address the concerns of those who wanted to limit the
power dissipation of CMOS linear circuits.

Other ways would be to lower the supply voltage to the minimum
possible...

Using fewer inverters per package would help as well... not on overall
power consumption, but at least in temperature rise per package.

The "all 4069" might be a fun project but I doubt I'd try it
anytime soon. (well maybe if I was stranded on a desert island
with nothing BUT 4069).  There would not be too much benefit from
cost, performance, etc.

As you correctly observe... the entire exercise would be mental...
to think "outside the box".  I think that engineering already
provides the same pleasure of making the choices and trade-offs
involved in making a good design.  It might be more fun to try and
meet some other challenge like a synth that runs so some very low power
(9V battery, solar power ???) or design to maximize on some other
parameter.

There might be some fun in making a parts list for what I'll call
the "Apollo 13" challenge... where you have to engineer some circuits
using only the parts in that kit. You assume that you are 100,000 miles
from home... and you simply cannot get ONE more resistor, transistor, etc. no matter how hard you wish.

Or maybe an absolute minimum component synth ?

Anyway, for me I don't have the time to pursue synth circuits that are
likely to perform less well than more traditional approaches.

And I bet you don't have time either, Magnus...  ;^P

(but its nice to dream...)

H^) harry

PS: I would consider the 4007 seriously. Because when I was a tech
(just starting out) we had to fix a circuit that had failures of the 4007 very often. It was VERY early in the CMOS process, and the 4007
was used as an analog gate.

There were so many failures (I think now, related to ESD pretection being inadequate) that the 4007 got a very bad reputation.

I 'solved' the problem by taking a fresh tube of 4007, and remove ONE chip. (all other techs were watching - what is this crazy guy doing?)

and drop the brand new chip into some clear exoxy they were parching the floor with.  I then gave a 'lecture' to the remaining chips in the
tube "If you chips cause us any more trouble, we will bury you ALIVE like I just buried your brother here..."

And there was never any problem after that. Voodoo electronics.

After that, whenever some tech had a problem with his circuit, he would
go to the burial site (floor) with a rag and wipe the dirt from the floor... so that everyone could see the chip again....  This was thought to cause 'good luck' for the repairs...   ;^P

So I would not rule out the 4007 as being NO fun. I think it is a
LOT of fun...   :o)

H^) harry

>Subject: Re: [sdiy] CMOS Synth
>Date: Mon, 03 Feb 2003 00:12:20 -0500
>> Why not try the CD4007... where you could use "emitter resistors"
>> (well I know they are not emitters... but I mean like in the output
>> stage of a bipolar audio power amp.
>If you *really* think about it (I know it is hard) emitters is best understood
>as a word when thinking about tubes, ain't it? Collector is equalently obvious
>then, ain't it? Both NPN-transistors and N-channel FETs have the correct
>directions for electrons in this analogy. In a similar sense is both source
>and drain (source of electrons and the drain down which used electron goes)
>equalently obvious, ain't it?
>So if you *really* think of it (instead of just nitpicking about conventions)
>where you using it incorrectly?
>No. ;O)
>In tubes it's so obvious where the electron goes. The irony in it all is that
>I can never recall which is the anode and which is the cathode... but gate I
>darn well understan... if you open the gate, you can go though... right ;O)
>> These could limit the 'shoot through' current to a manageable level,
>> allow the output to still be centered in the supply range... and not
>> cause all the devices in the package to be unfortunatly coupled as in
>> the case of resistors in the power supply legs.
>> 
>> The inverter in the 4007 could not use this method...
>You are correct in that 4007 is better since it allows access to individual
>transistors even if they sit on the same chip. However, if you leave your
>ordinary engineering sense behind and think about geeky odd-ball solutions, you
>realize that the 4069UB is the optimum since it is a digital gate which allows
>all kinds of analogue tweaks. So, there's the motivation for the challenge, to
>use all kinds of ways to bend the digital gate to do quite usefull analogue
>properties. The challenge of creating a full synth with no other active
>components than the 4069 is there not for the extreme high quality aspect of it
>but there for the mindbending needed and challenge of getting decent
>performance out of a "dead matter" as digital gates can be.
>So, yes, the 4007 is to some degree more optimum, but is it as much fun?
>Cheers,
>Magnus