Best Pre for ATC 100's

Of course, much modern music is highly compressed and unfortunately you will hear that compression as harshness - more so with ATC's than most speakers, which tend to have a more recessed upper midrange due to the use of large 5 or 6 inch drivers in most designs.

If you want solid state then the Benchmark DAC1 or pre version is a good cheap option with ATC. I mention this because you'll need to ensure there is no digital grain in the midrange but without losing nice details - ATC's are similar to good horn speakers in sound and have some "bite" in upper mids. IMHO the Benchmark DAC1 (includes a pre in some verisons) sounds clean and smooth without losing detail and is good value.

If you are using analog or already have a nice clean source then either a tube preamp or some room treatments may indeed help.

Consider your room - 100's need some breathing space as they can easily get to extremely loud spl's - you really need to sit back about 8 to 10 feet to get them sounding best, IMHO. In the case of ATC's 3 inch dome you get very little "beaming" in the mids so the off axis response is nearly the same as the on axis whereas other speakers tend to be increasingly weaker off axis as you go higher in frequency in the upper mids. This is why I suggested room treatments - if you treat reflection points then this will reduce upper mid reflections and a rug or carpet will help too. Remember you hear roughly 50/50 or 60/40 direct/reflected in a room.

The amps in ATC active speakers have rather low input impedance (10K ohms). There are those who believe in maintaining a very high ratio of amp input impedance/preamp output impedance. Perhaps coincidently, or perhaps not, the ACT preamps intended for use with ATC active speakers have uncommonly low output impedance (10 ohms). Many preamps have output impedance in the several hundred ohm range. A pre with ATC-like very low output impedance might be a good choice.

Der has a good point. The idea of not using an overly high input impedance is in order to reduce RF/EM or ground loop noise pickup from the audio connections.

Benchmark DAC1 Pre has a very low output impedance of around 30 ohms. The powerful drive capability of a preamp of this type will be such that it can drive extremely long runs on interconnects without any audible degradation effects due to capacitance. In contrast a preamp of 600 Ohms output impedance or higher may sound dull dynamically and even harsh especially as it becomes overdriven.

It goes without saying you should preferably be using a balanced preamplifier with XLR out but I assume you would not dare power ATC's with anything else.

Second the ATC line of pre-amps.

I used a CA2(the older version) with a pair of the Active 20's and thought it was a great little preamp at the time. Had XLR outputs although it wasn't a truly balanced design, but still sounded great and was reasonably priced.

I don't know what the new versions of these are going for now as prices have increased quite a bit from 7-8 years ago. Tim