questions from a newbie

[Harry Bissell]

Ill pass on #1

2) Opamps differ in many ways. Important specs include

Open Loop Gain... sometimes but not always, bigger is better. Too high a 
loop gain can make a circuit not stable at all frequencies

Gain Bandwith Product... This means that an op-amp can be used for a low 
frequency signal with very high gain, or a high frequency at low gain 
(1 * 
1000  =  1000 * 1) again, bigger is sometimes better

Input bias current. Usually lower is better... for citcuits like 
sample/hold, some filters, integrators... lower is a MUST.

Slew Rate... How fast can the output actually move ??? Higher values
mean faster, but could be less stable...

Input offset voltage. Usually lower is better. Not important in all
applications...

Single vs Dual supply... some opamps need a plus/minus supply, some are 
happy with one...

Output Voltage swing... some opamps only work up to a couple of volts
less 
than the supply voltage... some go very near the supply (these are
called 
rail-to-rail)

Output Current... Can it drive the load you will be using ???

Output Short Circuit current protect... will it blow up if you shory it 
out... This can be real important in a modular synth, where you cannot 
predict what will be connected...

So I guess that you could say all op-amps are not created equal. Often
a very low offset voltage and low input bias current will go along with
a 
low gain bandwidth product (like accurate but slow)...

You will find discussions in the archives about everyones favorites.
I like the 741 (1458) if I need a slow, but very rugged opamp. I like
the TL081 (82,84) for higher speed and low bias current. For the lowest
bias current I use CA3140 (if I can stand the voltage offset)

H^)  harry

#3 Light Dependant Resistor (aka Photoconductive Cell, Photocell etc...)



>From: matti at devo.com
>To: <synth-diy at node12b53.a2000.nl>
>Subject: questions from a newbie
>Date: Thu, 20 Apr 2000 16:32:20 -0500
>
>ok, I'm hoping someone(s) can help me with these....
>
>1)Fatman :
>I've recently soldered together the Fatman kit. Naturally, something went 
>wrong,
>and I'm now in the process of figuring out how to get the sucker working. 
>The
>symptoms : the gate LED doesn't lite when I send in a MIDI note (the MIDI 
>LED
>does, however), and there is no output, beyond what sounds like two out of 
>synch
>saw waves playing some middle-end note (very faint, and audible only when I
>crank the output all the way up). I've done quite a bit of probing, and 
>both
>oscillators are working fine, and I'm getting the output from the VCF pots 
>that
>I should be (lug two of R56, the 1/2 mixer gives me nothing though). Any
>thoughts, anyone?
>
>2) concerning different op-amps...: is there any difference between 
>different
>op-amps, other than gain? If this is so, then it seems to me that any 
>op-amp can
>be used anywhere, certain ones are simply more efficient.
>
>3)just what does an LDR do?
>
>
>
>Many thanks....
>
>6669the RaabidMuttn Speaks6999

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