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Subject: RE: [motm] Balanced vs. unbalanced I/O (was: External feedback...)

From: "Adam Schabtach" <lists@...>
Date: 2007-09-27

Larry,
 
I'll have to confess that I probably don't understand voltages and dB descriptions of signal levels any better than you do. The best answer I can give is "it works for me." :-)
 
I made some measurements with an oscilloscope to verify that the signal levels I'm working with make everything happy. I started by taking the SINE output of one of my MOTM-300 VCOs, running it through my DIY quad VCA/mixer (which has unity gain) and then through my unbalanced->balanced converter. I ran the balanced output into one (balanced) input of my Apogee interface.
 
According to my oscilloscope, the VCO's signal was 10.3V peak to peak as it entered the unbal->bal converter. The signal level once it arrived in my DAW software (i.e. after passing through the Apogee and my RME ADAT PCI card) was -1.1dBFS (that is, -1.1dB on Cubase's channel meter). This means that the system is providing a hot enough signal for the Apogee, and in fact you'd have to attenuate it a bit if you were outputting something louder than just a single sine wave. (I usually use a MOTM-830 mixer as the last module in my synth patches so that I can easily reduce the signal level if necessary.)
 
Going the other direction, I generated a full-scale 0dBFS 1kHz sine wave in Cubase, ran it out through the Apogee, into my balanced->unbalanced converter, and measured the unbalanced output with the o'scope. It read 10.5V peak to peak. Hence I'm satisfied that signals originating in the DAW end up at an appropriate level for running through my synthesizer's filters and stuff.
 
So, in short, it works well enough for my purposes.
 
--Adam

From: motm@yahoogroups.com [mailto:motm@yahoogroups.com] On Behalf Of Larry Troth
Sent: Thursday, September 27, 2007 12:08 AM
To: motm@yahoogroups.com
Subject: [motm] Balanced vs. unbalanced I/O (was: External feedback...)

Adam (or anyone else)

I get totally confused and lost on this one. What is the line level of our
modular synths (10vpp) vs. typical digital synths/samplers/ effects units and
1/4 I/O mixers? I have the old Roland M-160 rack mixers which have both
1/4" and xlr in/out connectors.

Referring to the 1246, it is listed as -6DB gain. Will this give me the
+5/-5 volt swing on processed signals? Will the 1646 properly take the
+5/-5 signals and make the balanced output happy?

Larry (dazed and confused) T.

--- In motm@yahoogroups. com, "Adam Schabtach" <lists@...> wrote:
>
> Hi Richard,
>
> There's really nothing to post. I copied the circuits directly from the
> application notes for the THAT 1646 and THAT 1246 chips. You can find PDFs
> of the app notes at THAT's website. Arguably if I did post my circuits it
> would be a copyright violation. :-)
>
> The chips are dead-simple to use. The only external components you need
are
> some caps that are actually optional but improve performance somewhat (if
I
> remember correctly). You can order the chips from Mouser although they
don't
> seem to carry the entire THAT line.
>
> --Adam
>
> _____
>
> From: motm@yahoogroups. com [mailto:motm@yahoogroups. com] On Behalf Of
> Richard Brewster
> Sent: Tuesday, September 25, 2007 5:29 PM
> To: lists@...
> Cc: motm@yahoogroups. com
> Subject: Re: External feedback; was Re: [motm] Stuck in a rut (help)
>
> Can you post a circuit schematic diagram, Adam?
>
> Thanks,
>
> Richard Brewster
> http://www.pugix. <http://www.pugix. com> com
>
> Adam Schabtach wrote:
> > Not long ago I built a module for my MOTM system that has four
> > unbalanced-to- balanced line drivers/converters and two
> > balanced-to- unbalanced line receivers. The latter act as outputs from
the
> > synthesizer; the former are inputs. This lets me make balanced
connections
> > between the synth and my Apogee converter. I did this mostly because my
> > studio layout makes it necessary to run longish cables between the synth
> and
> > the converter, but I think that it improved the sound quality of the
> > connection a bit also. Thanks in part to the excellent support for
> external
> > hardware in Cubase, this module lets me use my synthesizer as both an
> > instrument and an insert effect within my DAW.
> >
> > The module was pretty easy to build. I just used balanced line driver
and
> > receiver chips from THAT Corp. and followed the design suggestions in
> their
> > app notes.
> >
> > --Adam