[sdiy] 4049/4069 linear mode

Scott Nordlund gsn10 at hotmail.com
Sun May 31 17:16:24 CEST 2009


> Hi everyone and thanks for the feedback on this particular IC!
>
> Scott, you mentioned biasing the input of the gate for use as an
> amplifier, but all the single supply circuits I see using this technique
> such as the Anderton "Tube Fuzz" (and I *think* in the Wasp filter,
> although I'm not sure...) do not bias it at all.

It seems slightly weird to me since there's no virtual ground (like an op amp) but the negative feedback should take care of it.  The signal will still be centered around 1/2 Vdd.

> To be more specific, I'm using this in small battery powered synths
> based on 4093 gated square wave oscillators, and I'm trying to get the
> best use of it as both gain control and overdrive. Should I worry about
> biasing in this case? Would I get better performance out of it if I do?

I'm not really sure how you're going to be using this, but you know you can't really overdrive a single square wave, right?  If you're only using straight square waves, I don't think there's any need to play with linear stuff until you start filtering or mixing signals.

Anyway you should also be able to play with the 4007 in a similar way.

> Hadn't considered driving an LED with it, was using discrete transistors
> for that as I have a ton of 4069 rather than 4049.

The 4069 may be able to drive more modern (high efficiency) LEDs, as long as you don't exceed the maximum source/sink current.  Or you could use open collector/open drain chips...

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