One thing to be thankful for [OT]

[Scott Gravenhorst]

Alan Podjursky <alan.p at clear.net.nz> wrote:
>At 03:06 PM 11/25/00, daniel stocks wrote:
>>>Just think, if analog synths were like computers...
>>then we'd all be hanging on to those xt's wouldn't we..
>>TB303.. new$$$.... thousands taken to the tip later as they didnt sell... 
>>1991 - $50... 1995 $1500...
>>XT $1269...   few years later $50.. now?? anyone want a XT retro computer? 
>>really cool with analog 5" floppy drive! I got a few but better hurry they 
>>gonna go fast! $2000 ea or swap for ARP, MOOG, MS20 etc
>>:>
>
>How closely linked are analog synths and analog computers?

Very closely.  The "op amp" or "operational amplifier" is an
analog computer function block that helps perform the arithmetic 
operation of add (or subtract) with an additional operation 
of multiplying by a constant by using a resistor for negative 
feedback.  The ratio of input current to feedback current is
the multiplier.

Many analog synths use opamps to perform a variety of "operations".  
A mixer can be an opamp with summing resistors at the input, summing 
the currents of each and then multiplying the sum by some fixed amount 
(which can be 1) to produce a mixed output with some gain.  
Oscillators and filters can be cobbled from this basic 
building block.  An OTA (operational transconductance amplifier) 
is an extension of an opamp in that the multiplier is controllable 
by a voltage.  Even more fun things can be done with an OTA, 
including voltage controlled oscillators, filters and amplifiers
(plus more).  

Note that these basic building blocks are not the only way that
VCOs, VCFs et al can be built, many people here on this list 
have done these things without ICs so named, but rather with
discrete components.  However, controllable gain, summing, 
subtracting etc are still present in these musical analog 
circuits.

My own personal experience was with analog computers before
I ever saw a synth circuit.  I was pleasantly comfortable with
much of what I saw as a result.

What I have described scratches only the surface.

>
>>Dan
>
>-AlanP
>

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