Just adding another source to the discussion. The Gold Book, in the 5Overall.pdf states that these are 'the three kinds of voltage':
"Audio Voltages: Black Jacks. 20 to 20,000 Hertz. Output voltage typically -2.5 to 2.5 volts. Audio voltages produced by blue jacks typically 0 to 5 volts. However, any voltage range, so long as it oscillates in the audio range can be used as an audio voltage. Black inputs are typically AC coupled, meaning that the slow or non-changing aspects of the voltage are blocked.
Control Voltages: Blue Jacks. Typically 0 to 500 Hertz but can be higher particularly in the case of FM and AM. Usually either -5 to 0 or 0 to 5 volts but can range over -10 to 10 volts. Blue inputs are DC coupled meaning they respond to the full range including negative voltages.
Trigger or Pulse Voltages: Red Jacks. Either 0 volts or 5 volts with a fast rising edge between 0 and 5 volts. Some red outputs can hold the high level indefinitely, others fall back to 0 in a set time. Red inputs are triggered by the rising edge and therefore other voltages, such as inverted saw waves, can be used to trigger. Some red inputs control certain functions of a module as long as the voltage remains HI. In these cases and 5 volt level will sustain the function."
Just to add to that, according to another list post, the CUPL OUT on the SSG is 0-10 volts.
The top picture in the serge-fans gallery shows an 80's Serge panel that was re-faced by STS. The jack's (different) color scheme remained.
Matt
On 12/6/07, randaleem <randaleem@...> wrote:Hi,
Thank you all for the answers so far. There seems to be some confusion
or overlap in some of these based on conflicts in answers? (No wonder
I've been wondering!)
I hope others will continue to answer to either confirm or contest the
answers so far given. It would be nice to have this info as accurate as
possible and posted somewhere readily available to all of us?
Meanwhile, I'll try to answer the questions posed below.
>In SergeModular@yahoogroups.com, "riluttante" <riluttante@...> wrote:
>I know what AC and DC stand for, but can someone explain the
>functional difference in the Serge system between these two?
AC coupled means there is a capacitor at the input which the signal
must go through to be further processed. The functional effect of this
is that DC will not be passed. Therefore if you place an AC signal at
this input, its DC component (its offset from gnd, above OR below, or
both!) will be removed. This can help in "converting" CV's into "audio"
or "signals". It may also be used to eliminate a CV "carrier" from an
audio signal.
Words like signal, CV and Audio are necessarily limiting in a
discussion like this. When does a fast changing CV become a signal?
When does a slow moving "audio" signal become a CV? best to simply know
that there is a capacitor there, and then seek to learn enough about
capacitors to understand what will happen to various types of inputs
applied there.
Other capacitor effects may be present at AC coupled inputs, such as
input resistance changes due to capacitive reactance. (A fancy way of
saying that a capacitor acts like a resistor to a greater and lesser
degree depending upon its size in uF and the relationship between that
size and the input frequency.) Usually the circuit designer in most
general synth audio paths will attempt to minimise these kinds of "side
effects" for the expected signal frequencies to be encountered, by
careful selection of the capacitor size chosen for AC coupling. Other
times a capacitor may be chosen to take advantage of this effect, and
instead of attempting to be "transparent" to the signal going through,
it is acting as a consciously applied filter of the incoming signal.
DC coupled means there is no capacitor. Just a direct wire. Therefore
the DC component of the input is allowed to pass through maintaining
its "height" above or below ground. AC signals are not affected in any
way. This can cause problems when an AC signal is not centered about
ground equally. Because then the DC components do not cancel out and we
may hear their potential differences expressed as nasty clicks, pops,
or other (usually!) undesirable artifacts in the sound output. (Which
is one reason why we are given the option of AC coupling!)
>I understand from the above description that a bipolar, -5v to +5v
>output may still be DC coupled?
Yes. DC or AC coupling does not limit the inputs you can use, it
affects what gets passed on to the next stage in sound or CV processing.
Put a DC CV into an AC coupled input and nothing gets through, unless
the CV is changing fast enough in voltage level to be considered as AC
by the capacitor at the input. Conversely, if you have summed(mixed) CV
into your audio, and you put this through a DC coupled input; further
processing may not behave as expected due to the fact that the audio is
no longer centered around ground.
So there are reasons to use these AC and DC coupled inputs as intended,
and also reasons to go against their originally intended functions.
Just know that there is a capacitor on the AC coupled inputs and
experiment from there!
>Thanks for the questions and answers, good to see some of the basics
>explained!
Yes, thank you as well.
Kind regards, Randal
> > Very early Serges sometimes used Green for sync and
> > white for CV, and I've seen white used for the coupler
> > on SSGs (which swings -10v to +10v).
> > Steve