Weird saturation when feeding from RadioMusic?

Hi there,

Just starting digging (LATELY) my ER301.
0.3.02 Unstable 48kHz version

Feeding IN of my channel 1 with a signal coming from my RadioMusic.
Files playing are ok, signal coming from RadioMusic too BUT when I feed my ER301 and just passing the signal from input to output, it appears to be a bit saturated.

I check preamp settings, 1x is selected and still saturated a bit.

any ideas of something to check ?

It sounds like the signal is too hot? I have this problem with Rings and Plonk, they both have hot signals (though you can decrease volume internally on Plonk). I get around this by using the Limiter unit.

actually, if signal is too hot (which I don’t think as the exactly same signal connected to the same interface where connect the output of my ER301 sounds totally ok. the sound is modified by the ER301 (WHICH can be GREAT :slight_smile: ) but not that way actually.

you mean a hardware limiter …?

Yeah, it sounds like I experience the same thing as you. Something where the 301 inputs will clip hot signals. The ER-301 has a basic Limiter unit. That should definitely help, or at least help you troubleshoot if it’s something else.

I have built more Radio Music than I can remember and always make a point of adjusting the trim for the output volume - it’s the only trimmer on the back of the module - probably worth adjusting! It sounds like all your problems will disappear!

:slight_smile:

Actually, if the signal input is too hot, it is already too late if you put a limiter after that input in the chain…

I’ll try.
But how could I explain why that module outputs a signal totally okay if I send it to my other modules, interfaces etc?

I think that is maybe just a question trimming a very bit. I read here and there that the ER301 inputs were a bit “warming” the signal… So maybe the radiomusic one is just a little bit too much which is okay with 99% of models except those warming a bit…

Thanks for your inputs!

Without knowing what the other modules are it’s an open ended question, each circuit has it’s own tolerances, some are more tolerant than others, the E580 for example is incredibly easy to overdrive with a rather unfriendly Audio Input: -5V to +5V maximum, 18KHz bandwidth (clean mode) anything you put in there must be attenuated first.

To be fair, I have always thought Radio Music modules tend to play hot, probably fine for most things, but running through a ADC with limited headroom… I can see a need to be a little more careful.

And yes, just a little bit of adjustment will probably sort it :slight_smile:

Let us know how you get on…

Haven’t noticed it with the Radio Music so much, but my Shapeshifter is a little too hot for the ER-301. Typically I’ll need to attenuate it just a touch before bringing it in.

Hi Joe. Thanks for your answer.
Actually, if I have to do that especially for several modules and not for the others, that would mess globally the whole setup… I could “trim” down all modules too… wow.

If that’s the DSP handling part that is concerned, as for preamp settings, wouldn’t it be possible to add an option x 0.9 for instance beside of the 3 other settings?
btw, I suppose that’s the hardware part involved in that “issue” (which is not necessarily a “real” issue. Anyway it distorts my incoming signal)

What is the peak-to-peak output voltage of your RadioMusic?

Sorry. This is not possible. The hardware provides only these 3 settings.

this is most the approach I’d have too.
and indeed, that’s currently the only module giving me this with the ER301 (didn’t test ALL mine, but a lot)

I’ll first trim it (not in the studio at the moment).

How do you want me to measure this ?
Let me know.

Also, if anyone knows the output impedance of the Radio Music or at least a visual of the schematic, that would help also.

I guess this means you don’t have an oscilloscope? If not then, I suggest:

Prepare a normalized 440Hz (or similar) sine wave WAV file. Load it into your Radio Music and play the file into one of the INx inputs on the ER-301. Look at the signal in the ER-301 scope mode and take a screenshot (SHIFT+CANCEL). You will find the screenshot in ER-301/v0.3/screenshots. Please post the screenshot here.

All the details of the radio music are here:

I looked at the schematic PDF but unfortunately the IC4 (TL074) is not included in the schematic.

I see, just had a look at one of the ones i have here which has this printed on it

6BAKLKM TL074CN

The Mouser part number leads me here:

https://www.mouser.co.uk/productdetail/texas-instruments/tl074cn?qs=sGAEpiMZZMtCHixnSjNA6NVXWo9AXLOeoUCxMTuUhxw%3D

With it being open source any compatible TL074 chip could be used and there may be some variance in the specifications, but I wouldn’t expect there to be any great differences for obvious reasons.

Ah sorry for being ambiguous. I was trying to determine how exactly the op-amp was being powered but that information is not in the schematic as far as I could tell. Probably right in front of my eyes…

Assuming it is powered from +/- 12V rails then potentially the output could have 23V peak-to-peak swing depending on the setting of the output trimmer. The INx inputs only support 14V peak-to-peak. (A typical eurorack oscillator is 10V peak-to-peak.)

Also apparently there was a distortion problem in on PCB rev2 (Red Thonk):

That’s interesting, not experienced this myself, I wonder why some do it and some don’t.

I might have to check my builds for much longer periods of time before sending them out - that’s quite annoying! Regardless, my own RM is happily sat in my rack playing happily with no distortion, although I often run it through, wait for it, a distortion module so maybe it is and I’ve just not noticed hehe :smiley:

but yes, the RM can get VERY loud, the trimmer is there for a reason :smiley:

Thanks a lot for all your inputs.
I’ll trim it and test ASAP and will also do the screenshot as you suggested. Just for checking it, globally.

Yeah, I hear you. In my case, the Shapeshifter is the only thing I’ve noticed it with. If I send in a sine wave, it gets very slightly clipped. It hasn’t risen to the top of my list of things to try to work out a fix for at this point. I’m not even sure the SS has a trim pot for attenuation - I think maybe just for offset, but will have to look further.

Sounds like the radio music does though, so good luck!