Path: utzoo!attcan!uunet!mcvax!ukc!reading!cf-cm!cybaswan!eegauthe
From: eegauthe@cybaswan.UUCP (o)
Newsgroups: sci.electronics
Subject: Re: Guitar Sound Effects
Summary: Sound effects and impedance
Keywords: effects, impedance
Message-ID: <444@cybaswan.UUCP>
Date: 16 May 89 08:48:48 GMT
References: <496@hwee.UUCP> <4458@ncrcae.Columbia.NCR.COM>
Reply-To: eegauthe@cybaswan.UUCP (Olivier Gautherot)
Organization: University College of Swansea, UK
Lines: 49

In article <4458@ncrcae.Columbia.NCR.COM> wte@ncrcae.Columbia.NCR.COM (Bill Eason) writes:
>
>I am also interested in such sound effects and think they might be of enough
>general interest to post to the net.  If you don't think so, then at least
>be kind enough to E-mail me a copy of replies, too.  TIA!!!

If you have a look at your local electronics shop they must have books full of
projects to build including sound effects (I bought one recently from MAPLIN
in UK but there must be some others all over the world. If you're interested
in the title just send me a mail and I will check it). The one I have include
chorus, flanger, vibrato, tremolo, parametric equaliser and an analog
synthetic drum. Everything is explained clearly (how it works and how to build
it).

>For my own questions, what are the standard impedances for "high-Z and low-Z"
>audio inputs?  I know that there are matching transformers to convert from
>the three-pin microphone connectors (low impedance) to 1/4" plugs (high),
>but what impedances are they matching?  

The 2 impedance standards are 600 ohms (low impedance) and 50kohms (high).
Actually most equipment designed for low impedance input has an impedance of
2kohms to gain some level, and a 50kohms input is 100kohms (except
transformers which match more closely to optimise the power transmission).
What you'll have to check is the type of application you have: a high
impedance will be ok for wires up to 5 feet but might give some problems for
longer ones. You won't have this problem with low impedance, especially with a
symetric low impedance link (I have description of a symetriser/desymetriser
if anyone is interested. The design is very easy).

>If I wanted to design some sort of
>sound effect box, would I need to match my input impedance with some
>external impedance, or would there be any problems using the textbook
>op-amp principle of really high input impedance and really low output
>impedance?  (I'm not talking about a passive box.)  

A compromise is designing your effect with a high impedance (which will even
be compatible with your HiFi equipment) and put a switch and a resistor if you
want to use it with a low impedance.

>Bill Eason   (803) 791-6419    ...!ucbvax!sdcsvax!ncr-sd!ncrcae!sauron!wte
>NCR Corporation		       ....!rutgers!mcnc!ece-csc!ncrcae!sauron!wte
>E & M Columbia   3325 Platt Springs Rd.   West Columbia, SC  29169


-- 
Olivier GAUTHEROT,// Postgraduate // Electrical Engineering Dept.
University of Wales // Swansea, SA2 8PP, U.K.	(+44 792 205678 ext 4564)
UUCP  : ...!ukc!pyr.swan.ac.uk!eegauthe    JANET : eegauthe@uk.ac.swan.pyr
	Usual disclaimer. Who shall I send the copyrights to?