That is definitive enough for me, thank you very much.
Yes, it is not too much of a problem, as with higher inputs the noise is all but suppressed or masked and with the filter types you mentioned it is not at all so bad, only in the quieter passages that I may create does it become a bit of an issue, but then I tend to just use another filter module for those parts.

I was only concerned that it may have been a fault that may have got progressively louder over time.....but, your answer puts that worry aside.

Thank you again and best wishes.

--- In Doepfer_a100@yahoogroups.com , <yahoo@...> wrote:
>
> > Thank you for your replies Florian, perhaps Dieter will have the
> > definitive answer.
>
> I don't know the "definitive answer" but indeed the XP filter design
> generates a bit more noise than other filters (the A-107 is nothing but an
> expanded XP filter). The reason is that the original signals of the four
> filter stages (CEM3379 filter chip) have very low levels and have to be
> amplified by about 100 to obtain the audio level used in the A-100. This
> causes a higher noise floor because even the noise is amplified. And in
> addition some filter types are composed from up to 4 filter stages. This
> increases the noise additionally. The filter types that use only one filter
> stage (i.e. 6, 12, 18, 24 dB low pass) should be a bit less noisy because
> for these only one of the filter stages is used.
>
> But with max. audio input level (i.e. just before clipping) the noise floor
> should cause no problems.
>
> Best wishes
> Dieter Doepfer
>