[sdiy] mults and mixers

[Oren Leavitt]

My own two bits:
I do like to buffer anything that may go to the 'outside' world or drive alot of inputs.
Such as a 100K attenuator pot that may be connected to an amp with a 5K input impedance.
I buffer anything that outputs a control voltage.

Oren

-----Original Message-----
From: john mahoney <jmahoney at gate.net>
Sent: Aug 15, 2003 9:53 AM
To: synth-diy at dropmix.xs4all.nl, Dave Magnuson <resfreq at hoohahrecords.com>, 
	Paul Maddox <P.Maddox at signal.qinetiq.com>
Subject: Re: [sdiy] mults and mixers

Thanks Dave and Paul Maddox (off-list reply) for your help.

> Although buffering is ideal, it's not that common.
I assume that some builders (DIY and commercial) tend to build more
conservatively than others, meaning more buffers and bypass caps and so on.
I'd be interested to hear some more builders' opinions, i.e. do you tend to
use buffers liberally or sparingly?

To buffer, or not to buffer? That is the question. Is it safe to simply use
one's ears to make that decision, or should perhaps a voltmeter be used to
check V levels? I'm mainly wondering if a voltage drop (due to
lack-a-buffering) can hurt the electronics in any way.
--
john


----- Original Message ----- 
From: "Dave Magnuson" <resfreq at hoohahrecords.com>
To: "john mahoney" <jmahoney at gate.net>; <synth-diy at dropmix.xs4all.nl>
Sent: Friday, August 15, 2003 12:19 PM
Subject: Re: [sdiy] mults and mixers


> At 11:01 AM 8/15/03 -0400, john mahoney wrote:
> >
> >What are multiples, 4-input control voltage mixers, and attenuators? (An
> >easy point of reference is the Moog CP-251, it has all those:
> >http://moogmusic.com/detail.php?main_product_id=12)
> >
> >Is an attenuator just a pot? (1 Meg linear taper?)
>
> Yes, and attenuator is typically just a pot.  1M would work, but I tend to
> use 100K.  Buffered ins and outs are nice, but not necessary.  The buffers
> let the modules on either end see a constant impedence, where an
unbuffered
> pot will change the loading as you adjust the pot.  Without buffers you
may
> notice some odd behavior with certain modules (waveform distortions, etc).
>
>
> >Is a mult just 4 jacks wired together, or do you need buffers/etc.?
>
> A mult is generally unbuffered.  It takes one signal and allows it to be
> patched to multiple destinations.  Buffering is ideal, since plugging in a
> new cable won't effect the load that the other modules see.  If you have
an
> unbuffered mult you may notice a pitch shift when patching to a VCO CV,
for
> example. Although buffering is ideal, it's not that common
>
>
> >Is a 4 input mixer just a mult with attenuators?
>
> A mixer is the reverse of a mult.  It allows 4 sources to be mixed and
sent
> to a single destination.  This is almost always an "active" module with an
> opamp stage or two (where mults are generally passive with nothing but
> inter-connected jacks)