AC and DC signals

If a module has an AC input and also a DC input...could another AC signal be routed using the DC input?

it depends, which module are you thinking of?

From my limited knowledge of electrical engineering, I'd say yes. DC coupling means both AC and DC current can pass through. It has no bearing on the polarity of the current (positive or negative) which I'm suspecting might have been why you asked? The opposite would be a problem though: DC signals can not pass through AC coupled inputs, because AC coupling has no direct path between input and output and will only allow AC current above a certain threshold frequency to pass through.

Yeah my understanding is "DC coupled" generally just means not AC coupled.

https://noiseengineering.us/blogs/loquelic-literitas-the-blog/ac-vs-dc-coupling-what-is-it

EDITED Jul 20th 2022, 11:44

"AC Coupling" often has a filter to remove DC signals...

it depends, which module are you thinking of?
-- JimHowell1970

Hey Jim, I was looking through all the Make Noise modules the other day and noticed this one:
https://www.modulargrid.net/e/grayscale-make-noise-mmg-multimode-gate-grayscale-panel

Shows an AC in and then a DC below it and just wondered if an AC signal could also be routed to the DC input. I still have a big 'learning electronics' curve to get over but it seemed to me that I've heard you can run audio signal via DC (and having a DC coupled audio interface also made me wonder).

helps to RTFM... which is on the original module and not included on 3rd party panels

https://www.modulargrid.net/e/make-noise-mmg

"The AC coupled Input has an attenuator to adjust signal levels. An un-attenuated DC input is also offered as this was the type of input utilized on the original QMMG. Together these inputs allow for mixing audio signals or combining a control signal with an audio signal to yield asymmetrical behaviors in the circuits that follow."

Which definitively answers the question - yes you can send AC signals through the DC input

Clicking on the link on the product page leads to an error... so module discontinued... good luck finding one!

From my limited knowledge of electrical engineering, I'd say yes. DC coupling means both AC and DC current can pass through. It has no bearing on the polarity of the current (positive or negative) which I'm suspecting might have been why you asked? The opposite would be a problem though: DC signals can not pass through AC coupled inputs, because AC coupling has no direct path between input and output and will only allow AC current above a certain threshold frequency to pass through.
-- theneweuropa

Thanks @theneweuropa my electronics learning curve is a bit steep as well. It makes sense that it would be the case considering I believe that is what DC coupled audio interfaces are capable of?

Yeah my understanding is "DC coupled" generally just means not AC coupled.

https://noiseengineering.us/blogs/loquelic-literitas-the-blog/ac-vs-dc-coupling-what-is-it
-- adaris

Thanks for posting that link, that was a great read @adaris

Clicking on the link on the product page leads to an error... so module discontinued... good luck finding one!
-- JimHowell1970

Thanks @JimHowell1970 wasn't considering buying/trying to buy one, just looking through the various modules that Make Noise does and noticed MMG...hadn't seen a module really like that before.

EDITED Jul 20th 2022, 18:22

"Coupling" refers to which signals can or cannot be passed through a given patchpoint. "AC coupling" means that the point can be used for anything in the audio range, which can vary from manufacturer to manufacturer, but in general it implies a cutoff that blocks DC signals (or anything in the range below subsonics, such as modulation). "DC coupling", however, means that the patchpoint can accept any signal, all the way down to DC (offset voltages, y'know).

And this can get interesting when you've got a bunch of DC-coupled devices in your voicing, but NO AC-coupled ones after that to strip DC, then you send it on out to your amp. And this can result in............

Yeah. Always try to eliminate any and all DC in your audio path, because once it hits your amp, things WILL get ugly.

And this can get interesting when you've got a bunch of DC-coupled devices in your voicing, but NO AC-coupled ones after that to strip DC, then you send it on out to your amp. And this can result in............
Yeah. Always try to eliminate any and all DC in your audio path, because once it hits your amp, things WILL get ugly.
-- Lugia

So for the MMG by Make Noise, could it cause this type of issue if you passed an AC signal to the DC input?

So for the MMG by Make Noise, could it cause this type of issue if you passed an AC signal to the DC input?

-- jb61264

no it's potentially the other way round - using the DC input to add DC to the AC signal...

So for the MMG by Make Noise, could it cause this type of issue if you passed an AC signal to the DC input?

-- jb61264

no it's potentially the other way round - using the DC input to add DC to the AC signal...

-- JimHowell1970

Right. The usual culprit there is DC offset voltages finding their way onto the audio signals. In some cases, you might want that, but you DON'T want DC getting out of the modular, which can easily result in the above video atrocity. Even Uli didn't go with that on B's 2600, despite the ARP 2600 having that. Uli left it on the 3.5 mms, but the TRS 1/4" jacks are AC-coupled. This is one of the main reasons why I toss in one of Happy Nerding's Isolators on builds that I do, since that module also acts as a DC block (transformers no habla DC), allowing NO DC to get past it. Plus, transformers always beef your sound up when you push 'em a little.

Hi Lugia,

Ha, ha, I love that video! I watched it many times however it still is very entertaining and educational too :-) Hence the reason I have several audio interfaces (those Eurorack modules that "export" (sometimes "import") audio to the Eurorack outside world like for example a mixer or in other words these modules transform the higher/hotter Eurorack voltage audio signals into lower audio line level and DC gets filtered away too, if the module is of a certain quality), to make sure this is not happening to my monitors ;-)

Regarding the B. 2600, you only tell me now that those TRS 1/4" jacks are AC coupled... I bought that Lehle 7013 DC filter to make sure non-unexpected-DC-signals from that B. 2600 of mine reaches my monitors ;-) So actually that was not needed, to buy that Lehle DC filter I mean?

Don't get me wrong, I am not regretting to buy that DC filter from Lehle, it's a little nice little box, even stereo! But if I knew this upfront, perhaps it wasn't necessary to buy it :-)

It would be actually interesting to see one testing its monitors, see them going in up in smoke, especially a 2 or 3 way monitor would be interesting to see how that "smokes up" ;-)

Kind regards, Garfield.