Re: Can I do this with a uProcessor?

On 28 May 2007 13:13:13 -0700, the renowned MooseFET
<kensmith@xxxxxxxxx> wrote:

On May 28, 1:03 pm, Eeyore <rabbitsfriendsandrelati...@xxxxxxxxxxx>
wrote:
Rich Grise wrote:
Eeyore wrote:
Rich Grise wrote:
Eeyore wrote:
Rich Grise wrote:

I'd use something like CD4053s, like a SPDT switch at the input
and output of each effect stage, one on the input and the other
on the output, with NC of each going to the circuit and both NO's
going to each other.

NO NO
C o-----------------------o C
------o o--> to next stage
o----[effect circuit]---o
NC NC

(The switch "wipers" (actually analog switches) are invisible in this
view.)

There's a problem with this Rich.

The CMOS IC switches can only tolerate signals that stay within their supply rails.
Since the guitar pedals are AC cooupled, the audio signal will want to swing 'below
ground'. No dice with the above unless you now introduce a negative rail to supply Vss.

Jfets don't care though. They'll be fine.

I'd expect an "effects" string running off 9V to be using line level,
which would be AC coupled at a volt AC or so, AFAIK. So, with the signal's
bias zeroed at, say, 4.5V, and only a volt or two peak, I see no problem.

The ins and outs are biased at ZERO volts.

That's how ac coupling works !

Well, yes, of course - let me fix my suggested circuit:

NO NO
C o----------------------------o C
--+----o o----+---> etc.
| o--||--[effect circuit]--||--o |
[1M] NC NC [1M]
| |
GND GND

This shows the caps around the cct, and the 1Ms are pop suppressants. :-)

Actually, the 'pop suppressor' 1Ms need to be on the terminals you denoted NC.

However, as I described, an audio signal referenced to ground spends about half its time at
a negative voltage.

A negative voltage that the 4000 series CMOS swich can't cope with. That was my point.

The CD4051..3 switches handle swings below ground. They have a minus
supply connection you need hook up. The 4016 does not handle negative
voltages.

You can run an XX4016 from +/- supplies (within the overall limit of
supply voltage) but you have to do level translation for the logic
inputs so they swing +/- as well. There's a similar part that has the
level translation built in.. the 4316.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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