Norns - Audio In/Out Specs?

bmoren · 2020-11-19T14:32:00.068Z

Question for those with a bit more electrical knowledge than me:

For attenuating modular levels for input into norns, could you use a voltage divider on the modular signal to bring it down to line level?

If I’m correct in this:
Vout = Vin * (R2 / R1 + R2)

Vin: 5v (10v peak to peak)
R1: 2200Ω
R2: 1000Ω

Vout = 1.56v (3.12v peak to peak?)

This would be a super simple thing to build into a cable or a small box or 2 HP module.

Not sure how this would affect audio quality, but would love input from folks who know more than I do.

I’ve always been a bit mystified by Line vs Modular vs Headphone vs Mic levels…

corpusjonsey · 2020-11-19T14:45:32.264Z

A transformer is more appropriate.

bmoren · 2020-11-19T14:49:36.863Z

Sure, do you have any technical info you could share on this?
I understand this is what RIP & others do, but I don’t have transformers sitting on my bench atm

corpusjonsey · 2020-11-19T15:01:49.593Z

I like this site. It has some great audio circuit examples with the math behind them.

bmoren · 2020-11-19T15:08:58.849Z

This look like a great resource! thank you!

I suppose in the mean time, I’m curious if a voltage divider will work in a pinch / as a cheap stop-gap, and what the impacts / characteristics of it might be – if anyone has tried it. (I’ll probably have a go this afternoon and I can report back too).

I’ve used a simple potentiometer attenuated signal into my H1 recorder for ages and have never had an issue, but I’d love to have something that is ‘fixed’ to make it all a little more consistent in my recordings (and in this case norns input).

anon60283851 · 2020-11-19T15:16:30.770Z

I’d actually argue that a simple potentiometer based volume control, or a fixed resistor divider (both having the same effect), would be more appropriate than a transformer - unless you specifically need galvanic isolation or want to hear transformer coloration in which case you already know what you want.

Why? It’s both vastly cheaper, and does the job as well as you’d want to with an unbalanced, line level (or hotter than standard line level) signal and modern gear. Fixed resistor pads are ubiquitous, and you’re likely to have and use attenuators / mixers in your modular anyway. Low distortion, no discernible change in sound quality, just a quieter signal.

(Edit: I see transformers used for balancing and impedance matching a lot, but it’s pretty rare to see them used in circuits for attenuating a line-level signal. There’s nothing inherently wrong with that either, but a resistor divider will just be neutral, effective and super cheap, so there’s not much reason to use anything else unless you know you need something else than simple attenuation.)

jlmitch5 · 2020-11-19T16:27:57.808Z

A voltage divider or pot, for a single channel should be totally fine I’d think…not 100% sure but I think you’d want to use a pot so that your input impedance isn’t too low and your output impedance isn’t crazy high. My guess is 25-50k…as all the devices your working with are buffered, active (not like a guitar).
Source on the impedance question as it relates to volume pedals:

missionengineering.com

Volume Pedal Q&A – Mission Engineering

When you get into mixing is when active circuits should come into play. Mobenthey/Ciat-Lonbarde (synthmall) thread

I have the EXI[S]T which combines RIP-style cinnemag transformers with a passive volume attenuator. It seems to works great for me, I haven’t noticed any sort of tone suck when the attenuator is down (and sometimes that lift is definitely necessary.

desolationjones · 2020-11-19T16:40:52.984Z

You’re totally in the clear with that concept. A simple voltage divider attenuator is called an “L-pad” in the audio world. There are fancier configurations for passive attenuation if you are concerned with impedance matching and coloration.

bmoren · 2020-11-19T17:13:23.706Z

I haven’t had a chance to read everything yet, but I put this together since I posted as a possible idea for a a super simple passive modular/norns aux send box.

I realize that this is kind of strange since it uses 2 dual gang pots to control vol from each input instead of using a wet/dry knob (panning mixer). But from my quick test, that approach resulted in too much loss of signal in a passive setup. I think it would have to be active for that.

My approach is kind of like a pre-configured matrix mixer with the voltage divider built in.
lmk if I’m missing anything big, and I’ll try to build it this afternoon

update, working version:

Screen Shot 2020-11-20 at 11.51.16 AM2364×904 89.3 KB

RNI-Films-IMG-53F60FCF-D39F-47DB-B85E-E6354890A8FE3640×1380 951 KB

RNI-Films-IMG-3CDF1979-D4D7-4216-956E-9C64CDAF61842471×2470 1.16 MB

RNI-Films-IMG-F94246BA-CC4F-45D7-8538-AA832C0BEDE52608×2607 1.49 MB

I’m going to switch this to 2 dual gang A10k pots like these when I get a chance

I’ll probably also lay this out onto a PCB / kit soon

bmoren · 2020-11-19T19:40:27.682Z

update:

Voltage divider confirmed working as per discussions above.
I put together a little schematic in case anyone else wants to make a version for themselves.

Screen Shot 2020-11-19 at 1.37.13 PM1190×898 7.68 KB

RNI-Films-IMG-397C0416-E7EB-4CFC-9C1F-BE729E7B6E251658×2210 646 KB

I may continue to work on the more complex version from above, but will likely break it out into its own thread in that event.

ngwese · 2020-11-19T20:33:24.972Z

Not to dissuade folks from going DIY but figured there might be some interest in the BLN module from Michigan Synth Works. I’m hoping it will provide me with a way to squeeze norns I/O in my main case.

Hopefully it does the trick when it arrives.

bmoren · 2020-11-19T22:51:28.700Z

That looks really nice – and much better cost and size than most of the IO modules out there. nice one!

secondratemachine · 2024-05-15T14:21:24.488Z

Just wondered if anyone out there uses the BLN and if so, do you configure the dip switches for balanced/unbalanced and what types of cables do you use?

crunchyave · 2024-05-19T21:22:45.626Z

I use the BLN in my modular case, it’s perfect for the use case of integrating Norns into the audio path of your modular. $85 and 2hp, what’s not to like!

I have actually never played with the DIP switches , but I don’t use anything fancy cable wise to do it. Just a few pairs of 1/4” to 3.5mm TRS, basically.

andrew · 2024-05-20T18:26:13.428Z

I’ll try to remember to snap a pic next time I’m unscrewing stuff to confirm – but I’m using unbalanced mono cables w/ norns (both shield + factory) and I believe the dip switches are set to the unbalanced modes

no issues at all with levels or noise, they work great! I have two of them currently

graymazes · 2024-05-20T19:07:24.261Z

Use TS cables and unbalanced I/O by default.

TRS and balanced I/O will work though; ring will be internally shorted to tip rather than left floating, resulting in 1/2 amplitude compared to a true balanced source.

secondratemachine · 2024-05-21T06:14:15.916Z

Thank you @crunchyave , @andrew and @graymazes for your responses.
I can’t seem to get my head around line level, balanced vs unbalanced etc. so thanks for the help.

I ended up emailing MSW as I couldn’t work out what the positions of the switches relate to.
They said, “There is no balanced/unbalanced, just signal level. . . . Its automatic depending on the signal/cable used with the exception of an unbalanced signal over a TRS cable where you will lose signal since your cold pin will be floating. . . . The switches just set the gain levels so just try both settings and see which works better.”

I’ve ordered some TS and guess I’ll just put the switch in whichever position is loudest.

graymazes · 2024-05-21T09:56:04.842Z

as far as levels, i long ago measured factory norns output as peaking around 1v (with a very high impedance sink), meaning i’d treat it as +4dBu “pro line level” source, but not a particularly hot one. hope my memory is correct, i think it was posted on here. not sure about shield.

setfield · 2024-05-24T15:17:51.227Z

In lieu of adding a Listen IO or BLN to my case, is it safe to say that I can run my norns into my Strymon AA.1 so long as I turn down the output levels on my norns?

graymazes · 2024-05-24T18:50:50.002Z

i assume that’s the “AA.1 Amplifier Attenuator?” it says it does +/- 18dB, which seems about right to me.