distortion

[observer]

Hi, I'm new to this so I truly apologize if this has been covered. I searched the forum but didn't find a clear answer to this.

I bought my preenfm2 prebuilt, second hand. I absolutely love this thing! The build seems legit and everything functions as it should and firmware is up to date. There's the slight 15khz noise that others have mentioned. That I can live with for now, and soon I will attempt the mod to deal with that.

But I'm experiencing a noticeable fuzz on pure sine waves. Even with the gain turned down, running a single op sine wave, there is a little hairiness that is driving me nuts. It's not noticeable with other waveforms or on complex patches, but it's definitely there. I'll try to post an audio recording soon. Just wanted to see if anybody had any quick info on the matter.

[served]

See if you are delivering enough voltage to the unit. Voltage Overhead distortion.

See if you have a correct opamps used.
See if you have the same distortion with a 9V PSU.
It might be related to many different things, but theese will be a first easy check.

[observer]

thanks for the tip, I'll give it a try. 

[Xavier]

A pure sin played alone can be noisy at low volume.

Set voice to 1 in Instrument 1, chose algo 1, and Mix1 to 1.00
Set it to 0 for instrument you don't use. I2, I3, I4.
And set Velo to 0. So that the wave is always at max volume.
If the sin is now OK then you have a normal behaviour.

All is digital and done on 18bits....
So the more voice you add the lower definition you'll have per voice or per carrier operator.
What you hear is the limit of the DAC.
But if you optimize by reducing the voices to the number of voices you really use, it should be fine.

[clément]

Hey, just to let you know that I do have the same issue, though I wouldn't call it distortion at first, I think it's the same thing. I believe it's not exactly the same on the Left and Right output.
But yeah it's been a bummer for me sometimes, when trying to achieve smoother sounds.
I built several PreenFMs for various people and I believe there always was an issue like this, by that I mean, I don't know if it's possible to create a true pure sine.

I'll check Xavier's tip though