> Judging by the amount of threads/posts on muffs, this seems to be a particular problem with the A-124.
> The common cause is that the 14-pin IC marked "4069 usually goes and leads to these issues... it even happened to me.
> The chips are easily obtainable and cheap and also easy to replace.... if yours is not still under warranty.
>
> Good luck, it's a great filter aside from this little quirk.

Great, thank you very much! I've sent off for some 4069 chips, which are certainly cheaper and less hassle than sending this back. :) I can't wait to hear this filter!

Thanks,
Zoë.