Available here is a set of all-out, no holds barred upgrades for the Acurus L10 or RL11 preamp that will turn a decent circuit into one that is a true eye-opener. It takes the preamp in the direction it needs to go to finish the design approach, which in stock form, falls shy of necessary features. Both power supply and incircuit updates are implemented to make this the most complete line-level amplification stage I know of. Here's what's done:

Power Supply:

The power supply circuitry is given a new topology that gives superior transient performance and much better matching with the audio circuit. It gets rid of the not so good stock caps and allows much better units to be a more integral part of performance.This mod alone allows the preamp to start to create that edgy realistic sound, and the Acurus cannot sound it's best without it. Power supplies are most certainly important to any circuit and the most often overlooked and even underrated. This same mod is proven with other rebuilds and gets fantastic results each time.

Diode bridge and RC snubbing:

I include softer recovery diodes and RC snubbing with this upgrade. Softer recovery diodes decrease the noise floor a bit and RC snubbing finishes the job. This improves ground for all the circuitry involved and provides benefit to all circuit performance. This is not a minor upgrade.

Circuit:

An incircuit upgrade is done with the front end which has several key features, some of which are not found even in most megapriced gear. Attention was especially paid with this part of the circuit since it is directly responsible for symmetrical balance and sound.

- First, the differential bipolar transistor input stages are changed to mosfets. These mosfets are handmatched to the millivolt level and provide true differential performance. A circuit MUST have this to provide the best symmetry.

- Second, the idle current is increased putting them in that famous "Linear, Class A" mode. The stock version has to run barely turned on at nothing more than a trickle current for DC offset purposes. This mosfet upgrade fixes all that and then some. It has repercussions throughout the circuit.

- Third, active current sourcing is used to bias the mosfets and takes the place of the single stock resistor. All aspects of performance are improved and the result is a real front end the way a front end is supposed to be done. Most manufacturers don't budget for this step because it costs too much and demands special attention since it does not lend itself to mass production. As good as the stock version sounds, this sounds better with solidified imaging, soundstage, and clarity.

Resistors:

Another round of improvement is done with a resistor upgrade. Several different types of resistors are used here, each one selected according to it's location in the circuit. Better performance is achieved and when compared to stock, has a superb natural tone. This upgrade could be said to be equivalent to a cap change.

Additional Circuit Changes:

The rest of the circuit is actually quite good and could be left alone, but I chose to take it a step further and do some additional work effecting the gain-bandwidth performance. This type of work defines the very heart of a circuit and can give an amp it's signature. It is proprietary in nature and nothing I feel the average customer would be much interested in, but I mention it for the sole purpose of disclosure. Needless to say, it will improve the performance or there would be no need to include it. It also illustrates that there are many aspects to circuit performance and that just doing a couple of mods is by no means a complete path to the ultimate sound.

What to expect:

These mods make for an electrically superior preamp and not that far off from the preamp I'd build if I was doing one from scratch. The common complaint most have with this preamp is it's loose bass, compressed midrange, and somewhat harsh highs. These observations do indeed correspond with the stock L10's circuit features. The rebuild will correct these problems so that a very clean and natural, spirited sound with deep, controlled bass, projected midrange and very smooth and silky highs with an open soundstage will be the result. You will notice something is evident at first listening. The Acurus L10/RL11 is truly a remarkable preamp with so much potential bottled up inside that it's just screaming to be fixed. The craftsmanship is impressive too, making it very much worthwhile to upgrade and a pleasure to work on.

Price:

The price on this makeover is only $250 and is probably one of the best, real values in audio. I don't know of a better deal that has so much of an impact.

Some more noteable Customer feedback:

"The Acurus arrived safe & sound. I didn't know what to expect, but hoped for the best. After inspecting the changes and letting it warm up to room temps, I started with the usual PBS FM and heard a lot more 'white noise' than usual in the background. I let it play for a couple of hours and then put a CD on during dinner. WOW!!!!!! I don't really know what you did, but it's a totally different animal. I always asked my wife to give her opinion of things (she's an ex Broadway dancer and actress) and I don't coach her to say anything, one way or another, but she heard a major difference, too. BIG TIME! Anyway, I've had an Acoustic Research SP-11, a Conrad Johnson, a Mark Levinson, Melos, and Luxman systems in the past so I do know a little bit about stereo equipment. The classical music station out here still has a lot of 'white noise'. We'd never been bothered by it before. Obviously, the highs above 10K are effected. We stayed up really late and listened to many Diana Krall CD's. It was like hearing them for the first time."

Additional correspondance during breakin......

"The system was on all day and the local PBS FM, classical station tuned in during dinner. The sound was phenomenal. It's as good as I've ever heard in my home. I tend to think that the recent overall 'improvements' are from the lengthy warm-up and break-in. I don't know all of your upgrade methods or modification techniques, but do know capacitors and power supplies can make major differences. Just finding this inexpensive 'jewel in the rough' on Ebay and getting it 'tweaked' to take its place amongst the heavyweights, is why any of us enjoy this hobby in the first place. When it's done right, the music takes over and all else is forgotten. Thanks again." - Bill H.