What qualities stand out in really good solid state preamps?

@hilde45 Thanks for the explanation of your gear. You seem to be searching not only for differences, but for value. Your Quicksilver and Pass amps are nice gear. I assume you’ve found the solid state preamps you’ve tried are more neutral than your tube preamp, with tighter bass, a lower noise floor and perhaps more extended highs. Those are just guesses based on my listening experience.

As others have noted, if you haven’t already tried one, the Pass XP-12 should be a good match for your Pass amp. I would expect a pre-owned unit, however, to cost considerably more than an Ayre K-5. 
 

I hope you can audition more preamps and find one that stands out from the others. 

I own an Ayre Acoustics K-5xemp pre-amp and use it in my primary system. I agree with other responses that speak to its virtually inaudible noise level and its exemplary clarity. Having listened to several others, it stands out in those two areas. But as an example of a very neutral preamp, its frequency response is very flat. No emphasis on bass, mid-range or highs. They all come through in a way that makes instruments sound like they’re being played in your room. I listen mostly to acoustic music - classical and jazz. On a well recorded album of acoustic guitar or piano with bass and drums, the sound is lifelike and the imaging is very good. You can spend more, quite a bit more, and get better imaging.

There are a few features that have kept this unit in my system. It has great synergy with my Ayre cd player and Ayre dac. It has two balanced inputs to accommodate those and balanced outputs to my amp. It is said that truly balanced systems are better at rejecting noise. It’s why recording studios and concert venues use balanced equipment and cabling. The K-5 units also have a home theater bypass for those who use their 2-channel systems as part of a home theater setup. The volume control on the K-5 is wonderful, with to me no audible steps as you raise or lower volume, just a smooth progression.

There are also the issues of value and durability. A pre-owned K-5 can be purchased from a reputable dealer or individual at a very attractive price and likely will be noticeably superior to almost anything new at that price. And it can be repaired, if needed, by Ayre - more on that below.

Finally there is the build quality and customer support. Ayre responds to calls and emails. They repair their products for a reasonable charge. And they offer upgrades from time to time that improve their products, again at reasonable cost. The only other manufacturers to which I’ve been exposed that offer comparable service are Bryston, PassLabs and Modwright. I suspect there are others.

I would encourage you to audition the units on your final list, preferably in your home, which is not always easy. The Music Room and several other dealers let you purchase with a return period should you decide you don’t like the unit. That’s the way I prefer to purchase pre-owned. For new gear, if a dealer won’t let me bring it home or return it I wouldn’t do business with them. And with new equipment that hasn’t been burned in, the return right is important.

Good luck!

@hilde45 I'm glad you found my post about my experience with my Ayre K-5emp helpful. I have a few questions for you? Why are you interested in a solid state preamp? What sonic characteristics are most important to you in an audio system? What are the sources, amp and speakers that make up the rest of your system?

I ask these questions because the answers might suggest other preamps I've auditioned that you might find of interest. Also, there are many who prefer a tube pre-amp with a solid state amplifier, including Dan Wright, the founder and owner of Modwright, whom I respect and who produced the tube phono stage that I own.

@hilde45 Ok, since I’m on a roll and correctly assessed the reasons you’re interested in finding a suitable solid state preamp, I will reiterate my recommendation of the Pass Labs XP-12. While it’s their entry level model I found it better than my entry level Ayre K-5emp. It’s a newer design and about double the cost today of what my Ayre cost years ago. But most importantly it is just slightly on the warmer side of neutral, the Pass Labs house sound, and it images better than my Ayre. If you still want a bit of the warmth of tubes, but in a quieter package with more extended highs and tighter bass I think it would be a great fit for your Pass Labs amp, particularly if that amp is your favorite. If your tube Quicksilver amps are your favorite, a more neutral preamp like the Ayre might be better, emphasis on might, but having not listened to your amp/speaker combo I cannot really say. And of course what I found to my liking might not be at all the same as what you like. 
 

So I’m back to encouraging you to audition several in your system before making a final decision. BTW, Moon Audio has a 30-day return policy on new Pass Labs gear. I suspect there are other dealers with the same policy. Return shipping is usually paid by you on a return. 
 

Hope you find what you’re searching for. 

@hilde45 I hope you're able to audition the XP-12. You and I seem to have somewhat similar listening preferences. You mentioned violins as a benchmark and how your tube preamp leaves you wanting more detail and leaves you thinking you're missing some of the top end. I find the same is true when listening to an acoustic guitar with some, not all, tube preamps. And acoustic music, with no amplification and in a great venue, is a great yardstick to use in testing gear. I use a solo acoustic guitar recording, a solo piano recording, both jazz and classical, as well as big bands and symphonic works when I try out gear.

A number of people who posted comments have dissed the concept of neutral. A simple view of neutral is that a device (preamp, amp, dac, speaker, cables, whatever) does nothing to change the recording. It's not complicated. It's why people with high quality gear note that if a recording is poor in quality, or vinyl is poorly pressed, they hear all the defects in the recording. It all gets passed through by their gear. The gear provides a very high level of detail and accuracy to the recording. The frequency response is flat, with no emphasis on any frequency. Audible distortion and noise are virtually non-existent. The device plays back a signal that is true to the recording. To me it's much easier to accomplish this with electronics than it is with speakers or your listening room.

What matters is what sounds best to you, me or any individual. Our listening rooms introduce anomalies, distortion, reflections, etc. Our hearing does the same. So we can start with great gear and still end up with issues. But the concept of neutral is not complicated. And not everyone likes what I've called neutral. There is a large following on this forum of folks who love the "warmer" sound of some tube gear. I respect that and understand why, as I own a tube phono stage and a tube amp, the latter in a secondary system. But that "warmer" sound is typically not neutral, with an emphasis on the midrange.

Everyone should just respect that we each have preferences as to what sounds best. And as others have noted, it is important to consider the compatibility of one piece with another. It's one reason why I think the Pass Labs XP-12 would be a great match for your Pass Labs amp. Pass designs its gear to work together, with preamp output characteristics compatible with their amps' input.

Hope you find the solution you're seeking.

@soix I never said I knew better than anyone else, you did. I never said my statements were objective fact, you did. I made a point of saying everyone has their preferences and prefer different gear. And objective fact is what exactly? Some people on this forum downplay the value of testing equipment using measurement gear. I can understand that, as measurements don’t tell the whole story in my experience. My ears are my reference measuring device. So what is objective fact? In listening to music it’s mostly subjective I think. 
 

You’re right that I don’t know exactly what the original recording sounds like. I wasn’t in the studio or at the venue. But I do know what a piano should sound like. i’ve played one for decades. It’s why I listen to solo piano recordings and solo acoustic guitar recordings, as I know what those instruments sound like quite well, Yes my piano in my room sounds somewhat different from another piano in a different room. But it is the best frame of reference I can have to know if a piece of gear sounds true. The OP uses a violin to evaluate gear for the same reason. Perhaps I should have said that a simplistic view of neutral is that the gear is true  the sound of the instruments. 
 

When I audition gear I use recordings I know well that I find to be true to the sounds of the instruments I know. I can hear a loose/flabby bass, a bloated midrange, a lack of treble extension. It’s similar to what people do every day when they tune their guitar or flute or clarinet. And I compare the gear in my home to what I own. It’s not perfect, but again it’s the best anyone can do I think.

Everything on the forum is opinion and based on individual experiences. You can say I’m arrogant. I can say you’d do better to not to get angry and recognize everyone’s right to post their thoughts and find a respectful way to disagree. I hope you can accept my response in the spirit in which it is offered, as a further explanation of how I characterize neutral. 

@decooney I have only auditioned the XP-12 in my home and can’t speak to the characteristics of the higher end or older Pass models. 
 

i agree with your observation that people sometimes upgrade only to wish they hadn’t sold or given away a piece of gear. Some folks on this forum post of having repurchased a piece they’d had before. 
 

Many of us get upgraditis. I’ve auditioned gear in my home that I thought sounded better only to find I couldn’t justify the additional cost for the incremental improvement. In one instance a dealer loaned me an excellent Luxman amp. I brought it hone and it sounded great until I put on a large symphonic piece and it couldn’t handle the power requirements of the transients and started audibly clipping! The dealer concluded it was likely because of the 86 dB efficiency of my 4 ohm speakers that drop to 3 ohms at some frequencies. It’s just another reason to audition gear in your home with your other equipment. 
 

@audphile1 Kudos on your upgrades. I wish they were within my budget.

Do you think the Pass XP-12 is a good fit for the OP, @hilde45 and his Pass Xa-25?