Help ...... excesssssssive sssssssssssssssssssss

I assume this problem happens only on vinyl?

If so, phono input impedance too high is a possibility.

I'd go with Doug's suggestion, EXCEPT that you've had the problem with (at least according to your description) so many different cartridges. It could be that something is being overdriven -- like too high a gain setting in your phono preamp.

OR, if it happens with all sources and not just vinyl, it could be due to an impedance mismatch between your preamp and your amp. I've certainly run across that one before! And this particular amp needs to be configured to match your speaker drivers. Both of these issues are mentioned in the notes published on the First Watt website:

"It is well suited to sensitive full-range drivers such as Lowther or Fostex, and allows easy use of parallel loading networks to tailor the driver response.

It has both balanced and single-ended inputs. The input impedance is nominally 80 Kohm, and the output impedance is 80 ohms."

"SIBILANCE" The presence of strongly emphasized s, sh, ch, z, j sounds in speech.

Please keep us posted on the results. Learning experience me.

Good luck.

I suspect the problem is your extremely unusual choice of amp and speakers.

First Watt F1 is a current power amplifier...it will attempt to drive your speakers with a current that is independent of impedance load.

Your speakers only have one driver...it is unlikely that the impedance curve is anywhere near flat ....even it might be an easy or efficient load to drive.

I don't know the impedance characteristics of your speakers but most speakers are such that they tend to be of higher impedance at higher frequencies and usually high around the resonance point of the driver (which for 4 inch is probably some where in the lower mid range or bass).

The end result of this combination is that you will accentuate the speaker response according to the impedance curve...i.e. emphasize the resonance frequency and accentuate the treble (if your speaker behaves as most speakers do) => you will get significant bass and treble response boost and this is why you hear so much sibilance

Current amplifiers are rarely used in audio applications for this very reason....they need to be carefully matched to a speaker with a flat impedance curve.

First off let me say in my humble opinion you have a fantastic system.I don't believe the problem stems from one thing over the next.If you are putting together a system then you have to look at the system as the source of the problem.You have been given a number of great responses of which i would look into trying each one,but do it one at a time and listen for the changes that come about as you go on.Good luck