[sdiy] Op-amp to boost VC signal with +5V/GND?

[Harry Bissell]

If i need a non-inverting amplifier, I'd use two NPN transistors. The first one can
have a divider at the base to get any trigger level you want, take to output from the
collector, then invert with a second NPN. Needs two transistors, four resistors.

You might use an unbuffered CMOS inverter as a linear gain stage, but with no input
they queue up to 1/2 the supply and usually oscillate there... (nasty)

H^) harry

----- Original Message -----
From: Thomas Strathmann <thomas at pdp7.org>
To: synth-diy at dropmix.xs4all.nl
Sent: Mon, 23 Aug 2010 11:47:02 -0400 (EDT)
Subject: Re: [sdiy] Op-amp to boost VC signal with +5V/GND?

On 8/23/10 17:23 , Harry Bissell wrote:
> Many classic synths use CMOS (4000 series) and 12 or 15 volt supples, which would
> require a gate voltage of between 6 to 7.5V minimum to trigger, possibly more if
> a schmitt trigger gate was used.

Tell me about it. I have build two with 4000 series Schmitt triggers on 
the front end and had to amplify the input signal quite a bit to get the 
circuits to work. In retrospect I could probably have used a discrete 
two transistor Schmitt trigger instead and done away with an additional 
gain stage.

That reminds me of a question I've wanted to ask: What's your favourite 
Schmitt trigger or way to drive CMOS ICs from a gate or trigger signal 
in modern (i.e. probably low gate voltage) synths?

> 5V is too low for a good gate imho. I think the 10V level would be best.

Yes, better save than sorry when it comes to interfaces. The little 
extra current won't hurt.

	Thomas
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-- 
Harry Bissell & Nora Abdullah 4eva