Serge Audio and CV Levels?

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Serge Audio and CV Levels?

Post by Isaiah » Tue Apr 21, 2015 2:48 am

Sorry if this has been asked many times before.
I've tried to find a definitive answer, but it seems there's a lot of conflicting information about the Serge signal levels.
Some sources state 0-5V and +/- 2.5V, others state 0-10V and +/-5V.
Which is correct?

Also, regarding the blue and black bananas, it seems that one of a few sets of rules applies depending on the module.
Blue and black could mean DC and AC-coupled respectively, or unipolar and bipolar.
Looking at the schematic for the VCFQ (CGS112), it looks like all the blue inputs could accept negative voltages providing their associated controls provide enough DC offset that their sums don't go below 0V.
Is that correct?
Looking at the schematic for the SSG (CGS92), it looks like the blue inputs could just as easily be black, or the output could be blue.
Other modules like the TWS (CGS85) completely ignore any negative voltage present at their VC inputs.

I ask because I'm slowly planning a Serge panel for the future.
I'm thinking about using grey bananas for the majority of inputs and outputs (red for gates) and labelling the appropriate inputs with something like "AGC IN (AC)" on the VCFQ for example.
It makes sense to me to differentiate this way since most Serge inputs that aren't explicitly audio are DC-coupled.
For example, the DCSM is only used for audio so I automatically assume it's got AC-coupled inputs, but the VCFQ and middle Wave Multipler are both capable of processing DC so the AC-coupled inputs should be labelled as such.
Any thoughts on this?
Maybe I'm thinking about it too much... :hihi:

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Post by livefreela » Tue Apr 21, 2015 5:09 am

hey isaiah, i'm no serge authority, but i do have a few of the modules you've listed. trigger outputs are usually 5v but there are a few instances (the coupler in the ssg for example) that can swing close to the power rails. those are usually designated by a "special" color jack (grey, yellow etc.) there is a 5v option for the coupler on the cgs board however, and i believe sts builds them that way these days too. re: the blue/black jack paradigm, also take notice of the associated panel graphics with pots associated with those jacks. the black swoops are usually unipolar (or attenuating) controls whereas the half black, half white indicate an attenuverting input. to simplify things, i generally interpret the black jacks as inputs or outputs for the signal being processed in the circuit (audio or cv) while the blue are for cv control over that process (cutoff of the filter, or the rate of the ssg for example). in modules only intended to process cv (like the cv processor) ins and outs are also usually blue. i know it sounds confusing, but i promise it all winds up being pretty easy to grasp when using the system. hope that helps!

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Post by Isaiah » Tue Apr 21, 2015 9:45 am

Thanks for your reply.
Yes, the Trigger and Gate signals seem to be the only signals that all sources agree on - 5V.
The CGS92 SSG PCB provides both the 5V and ~+/-10V Coupler outputs, the latter being used for patching the SSG as a Random Source with a Noise Source. I plan to include both when I get around to it.

Still, the question remains though: What is the Serge standard? 0-5V and +/-2.5V, or 0-10V and +/-5V?

Also, with modules like the DCSM do the VC Pan inputs ignore negative voltages?
What I mean is, if the Pan pot is set in the middle for a channel, will modulating the panning with a bipolar LFO of sufficient amplitude move the signal all the way left and right?
I understand that the channels are set up to respond to the same Panning CV inversely.

Your thoughts on black and blue bananas make more sense than what I've read in some Serge literature. Thanks for sharing.
More food for thought! :tu:

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Post by Borellus » Tue Apr 21, 2015 1:26 pm

AC coupled outputs (black) are +/- 2.5v
DC coupled outputs (blue) are 0-5v
Gate/trigger outputs (red) are 0v (low) or +5v (high)

There are a few exceptions, like the coupled output on the SSG, though the current versions from STS are a lot closer to 5v then the +/-10v of the older versions.

For panning purposes, start with the pot at 12:00 for CV signals from black outputs, and the +/- 2.5v CV is sufficient for very wide left/right swings. Doubling a CV by patching it into two inputs of a CV processor will allow you to pan "wall-to-wall", but you only gain slightly more perceived stereo space, and it's easy to introduce unwanted clipping.
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Re: Serge Audio and CV Levels?

Post by skkatter » Thu Apr 23, 2015 3:32 pm

Isaiah wrote: Maybe I'm thinking about it too much... :hihi:
I've got a four panel Serge and I've never needed to check any of this. You won't fry anything when patching any one connection to another. I've never had any problems. Just make sure to connect the grounds if you've got other banana gear you want to patch it with, I've got a Fenix II+III all patched into the Serge and it works great.

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Post by johnstilton » Sun Jun 09, 2019 8:29 am

apologies for following up on such an old thread.

I’m trying to wrap my head around something in Serge systems:

I believe that from what I have read is that one of the noteworthy attributes of the Serge system is that AC coupled and “Audio” signals are interchangeable.

I read here on this thread that AC coupled signals are 5Vpp (-2.5/+2.5)

These two statements lead me to believe that audio levels are also expected to be 5Vpp.

Now, the Doepfer manual reads that their audio signals typically are 10Vpp (-5/+5), which I understand is more-or-less the Euro standard.

Does this mean that the new Random*Source “EuroSerge” offerings are 10Vpp ? Does this mean that the classic and Euro Serge platforms will not play with each other without attenuation/amplification of AC signals?

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Post by Gandalf » Sun Jun 09, 2019 6:31 pm

If you read 'The Gold Book' you will find that basically all signals are 5Vpp. Typically that means AC/Audio are +/-2.5V and DC/LOGIC are 0-5V. Of course there is nothing to stop an AC signal going 0-5V or a DC signal going between -2.5V and +2.5V. All inputs can generally accept full power range swings without damage and most modules will function with inputs outside of these ranges.
The main reason for uniformity is to simplify inter-mixing of signals and the fact that that there is no need to differentiate between the different types.
The lower extent of these signals when compared with Eurorack is the greater potential for mixing multiple signals without the need for attenuation and remaining comfortably within the bandwidth of the power supply ie MUST stay within +/-10V.
As for colours. The Serge defined standard is Black = AC/Audio, Blue = DC, Red = Logic. Unfortunately (!) it dodesn't differentiate between IN and OUT. ELBY Designs augmented this by keeping these 3 colours as INputs and adding White (AC), Green (DC) and Yellow (Logic) for OUTputs. The colours Grey (AC), Violet (DC) and Orange (Lofic) are used to define special signals within these groups.
R*S went totally against the Serge convention (which is amazing).

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Post by JesperP » Mon Jun 10, 2019 9:35 am

johnstilton The R*S euro modules also run 5Vpp so you often need attenuation to get it to work properly with other Euro modules. I myself went the other route and build a complete R*S Euro Serge :hihi:

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