[sdiy] Simple clickless FET mute switch?

[Mattias Rickardsson]

3 answers in one:

Dave wrote:
> You might want to go look at the Rane website.
> They might have a product with a similar function,
> and they have a lot of schematics online.

Thanks, good point  -  but I didn't find anything else than mechanical
& IC switches in their designs, though.

Nicolas wrote:
> To avoid the click it needs to be either zero-crossing.
> Or be a gradual fade over at least 10ms.

Well, switching a signal instantaneously at a zero crossing also gives
a click, albeit a mufflier one. Otherwise, triangle waves would be
silent, you know! :-)

The reason for using a FET instead of a mechanical switch was to
introduce a short fade via the suggested RC network, otherwise the
question would never arise. So:

Loscha wrote:
> I recommend  checking out Boss guitar pedals. That's how they mute and
> unmute the effect, using complimentary switching of FETs.

Great suggestion! I wasn't even aware that they use this. At
   http://www.schematicheaven.com/effects.htm
all the five Boss choruses (for example) uses FETs for their on/off
switching. In the bigger CE-300, as well as in the schematics on this
audio switch page,
   http://www.pic101.com/audiosw/index.html
they tend to use electrolytics both before and after the switch... but
since I want to keep my 32 switches as over-simplistic as possible,
I'm wondering if the following suggested circuit sketch would do?

   http://www.analogue.org/mr/sas/temp/mixer_send_mute.jpg

The majority of the components would sit together at one circuit board
in the mixer, and be connected via wires to the audio inputs & on/off
switch situated at each channel strip. Would it work decently? Without
more capacitors etc?

I'm also curious about how many dB of attenuation it is reasonable to
get in mute mode from a single FET... it would be nice not to have to
add 32 more FETs shunting to ground to make it more silent.

The less, the merrier. ;-)

/mr


>>> On Sun, Sep 14, 2008 at 6:49 PM, Mattias Rickardsson <mr at analogue.org>
>>> wrote:
>>>>
>>>> Hi gurus,  :-)
>>>>
>>>> I need to build a couple of extra effect sends in all the 16 channels of
>>>> an old mixer, and I plan to use toggle & momentary switches to easily switch
>>>> on/off the signals live, and I want this switching to be clickless.
>>>>
>>>> Perhaps a FET and some C and R could do the trick?
>>>> What is the simplest way of building a decent clickless mute switch?
>>>> Hifi-ness is not important, but money is. :-)
>>>>
>>>> I've searched the Intarnets but found remarkably few schematics here.
>>>>
>>>>
>>>> /mr