[Paul McNeil]

I'm driving my new Maggie 1.7s with a Crown XLS 2500 (770 watts per channel at 4 ohms), and I had loved the sound, until...

...I set the variable gain function on the Crown power amp from near the max (+10dB) back to the center, thinking this might more fully take advantage of the amps full power (not that I needed it). The is Crown driven by Adcom Preamp, GFP-555II (2-10 V output).

Well, now, at the Crown's center gain point, the sound sucks, and turning up the Adcom induces 'blat/bam' sounds from both speakers.

Horrifying, and my initial reaction was that something had broken loose inside the Maggies, but, no, going back to the higher gain function on the Crown, everything is fine again. Bliss...

What is going on?

[Davey]

The premise that you might more fully take advantage of the amps power by reducing the attenuator control is incorrect.

The front panel controls are not calibrated in db, but just a simple 0-10 for reference.
I suspect the attenuator is within the circuit topology such that when you reduced it (and then advanced your preamp level to compensate) you created some internal clipping in the Crown stage(s) prior to the attenuator section.

Leave it at the maximum setting if that works best for you.  That would be the preferable setting for all users of the XLS amps....IMO.

Dave.

[mcgsxr]

I run the gain on my 1500 at about 1pm on the dial.  I used to run it at around 12pm and have tried 2pm.

My Nuforce preamp outputs a max of 4v I think.

[Paul McNeil]

Thanks Dave, for that definitive sounding (I'm an electronics dummy) explanation. And Mark, for your input, though a 1 pm setting gives rise to the problem, on my Crown. Must be the the preamp difference. Maybe my old Adcom is wearing out....

[mcgsxr]

It may simply be that your Adcom pushes more voltage than my Nuforce.

If you have the gains way up, perhaps that gets the volume you want with less output from the pre.  And by turning down the gains you are requiring more of the preamp and that is overloading the Crown input.

Sounds like you can just revert to gains on the Crown at 8-10 and be OK though correct?

[mcgsxr]

It may simply be that your Adcom pushes more voltage than my Nuforce.

If you have the gains way up, perhaps that gets the volume you want with less output from the preamp.  And by turning down the gains you are requiring more of the preamp and that is overloading the Crown input.

Sounds like you can just revert to gains on the Crown at 8-10 and be OK though correct?

[Paul McNeil]

Yes, at 8-10 no problems, sounds great!

[Davey]

There's no reason to run the controls at less than maximum unless you have a gain structure issue (too much voltage gain upstream) elsewhere in your system.
As you found out, you can clip the input circuitry by doing so.

Dave.

[SteveFord]

I'm running them full bore on the wife's MMG system, that worked out the best.