Universal Audio SOLO/610 by Dean Roddey
The Universal Audio Solo/610 is a standalone mic pre-amp with handle, not the usual rack mounted type. It's about the size of two longish bricks stacked one atop the other, a form factor roughly used by a few other well known mono-preamps or DIs.
'Based on' the original Bill Putnam design that was part of the early UA 610 console, it's anything but modern and clean really, but in a good way in the reviewer's opinion. It has what it needs to get the job done without any extraneous features.
There is also a Solo 110 as well, which is a solid state version of this pre-amp, or there used to be. It appears to now have been dropped in favor of other options.
The 610 has two big knobs of the vintage console sort, the left of which controls the input gain and the right controls the output gain, marked 0 to 10. Generally the suggested method of setting gain is to start with the input gain around 7, lower if clipping is occurring, then bring up the output gain until you are getting the desired levels into the downstream chain.
However, you can get a wide variety of tone variation out of it by playing with the relative levels. Being tube based and not having huge headroom, you can push the the input gain and hear it start to fatten up the sound as it begins to have some subtle distortion, first on peaks and then more and more. There is a clipping light that blinks yellow when clipping is getting close and red when you are into clipping, but that's not always a bad thing with this type of tube-based pre-amp.
Below the knobs are a set of simple single throw switches. First is the Mic/DI switch, then the Low/Hi-Z switch to control the input impedence, followed by the 48v phantom power, an 80Hz engageable high pass, and phase switch. The impedence switch is nominally for switching between mics vs. line level instruments when DI'ing, but can be used for tonal variation in any use case.
On the rear are XML inputs, and a mic/line switch to control whether it outputs a line level signal or passes through a mic level signal, perhaps to feed into some other downstream pre-amp or console pre-amp input. There is also a ground lift switch.
On the front is also a DI input and a passthrough output. The input to the DI is passed right back out to the output, and is typically used to feed both an DI'd signal and an amp signal simultaneously.
In the Studio
The 610 gets a lot of flack around these parts, because of it's supposedly untenably low input overhead, and in some cases because they are contemptuous of the claim that it is the same as the 610 console pre-amps of yore. But I don't find either concern to be a problem. Of course I'm not a metal screamer, or using it to mic snare drums either (not that that might be a bad thing given the nice crunchy distortion that might provide.) I've never run into a situation where it's required anything more than reaching over and bringing down the input gain knob a bit. And of course in some worst case scenario you could use an inline pad.
Those who think that the whole point of digital is to be super-clean and crispy obviously wouldn't like this pre-amp, since it's anything but. Though it can get clean to the point that you wouldn't particularly notice it relative to a plethora of other pre-amps (by cranking the input down and the output up), it can also get quite thick with noticeable harmonic enhancement from the tubes starting to break up. If you are a tube maven of course you could play with various tube replacements to see if you find something you like better. The one I have came with some vintage NOS tubes already in it.
As a bass DI the 610 rocks definitely, though maybe not for super-bright moh-dern type of recording. But for anything from Jazz though country through rock it's a great bass DI, and sounds kind of nice push to the edge of a little breakup. I use it with a Jazz. Use the Low/Hi-Z switch to play with different tones, regardless of whether your bass is active or passive, since you might find something that fits the requirements better.
It also makes a very nice DI for hardware analog synths though you have to be careful of the levels since the synth will put out a line level signal. You can always use a re-amp box to bring the signal down appropriately if necessary. I don't use amp sims myself anymore, but I did back some years ago and it was a very nice way to get a nice guitar signal into the box to apply to a sim.
On vocals be sure to play with the gain structure to get a fatter or thinner sound depending on the characteristics of the singer. For me, keeping it cleaner works better on vocals, but your mileage may vary.
I find the 610 to be an excellent pre-amp for my particular needs, which leans towards more vintagey type material. Though it's a marketing cliche theses days, it really is a good way to offset the overly clean digital capture mechanism and get some old school harmonic distortion into the box (on the way in, not faking it later.) Having had it beside a Great River pre-amp for a good while, I would use the 610 just as often as the Great River, which is considerably more expensive.
Given the quite reasonable price for the 610, compared to most pro level mono pre-amps out there, it has significant bang for the buck. New on the street it runs around $800, as compared to $1150 for the aforementioned Great River. Used they go for around $500 or so, which makes them a great deal.