InnerSound Line Stage Preamplifier

InnerSound Line Stage Preamplifier

Frank Alles

26 June 2001


Inputs: 6 line level, including tape and video processor loops; one balanced XLR
Outputs: 4 line level (2 fixed level outputs, one variable RCA-type, one XLR balanced) All outputs may be used simultaneously
Frequency Response: -3 dB at 5 Hz and 200 kHz
Noise: Greater than 100 dB below 1-volt reference
Distortion: Less than 0.01% from 10 Hz to 20 kHz
Output Impedance: 50 ohms, non-reactive, balanced or single-ended
Input Impedance: 47 k-ohms, balanced or single-ended
Gain: 20 dB
Maximum Output: 10 volts peak
Crosstalk: Less than 70 dB @ 20 kHz
Power Supply: Regulated with shielded toroidal transformer and 20000 µF of capacitance
Power Consumption: 10 watts
Weight: 14 lbs. (shipping)
Dimensions: 17″ wide, 1 ¾” high, 8 ½” deep
Price: $2995

InnerSound, Inc.
1700 Hwy 16
Whitesburg, GA 30185
Tel: 770.838.1400
Fax: 770.838.0111
Tech Support:

Not Just a Speaker Manufacturer

When audiophiles think of InnerSound, what usually springs to mind is that company’s line of fine hybrid electrostatic loudspeakers. Lately, however, the Georgia-based firm has been gaining recognition for its line of high-quality electronics. I have been most impressed with the excellent performance of the InnerSound ESL amp, as mentioned last year in my joint review of that product with Martin Appel.

Having heard the InnerSound preamp in a friend’s system prior to the arrival of the review unit, I was hoping to duplicate the same musical attributes at another time. As it turned out, I wasn’t to be disappointed, but more about that later.

Physically, the InnerSound preamp is a modern, slim-profile design, available with either a black or silver faceplate that matches the cosmetics of the company’s amplifiers. The vivid blue digital volume display shows settings in 1dB increments, from 00 to 99, large enough to be read from a reasonable distance. The knob that controls the volume also provides precise balance control with LED readout to confirm the settings. Another nice feature that I haven’t seen in other preamps is the ability to set the total system gain to a predetermined maximum, so that the volume cannot be inadvertently set to potentially damaging levels. Audiophiles with teenagers or young children running about will immediately grasp this feature’s significance.

Users can also equalize the volume levels for each respective source, insuring the same apparent volume level at any given numerical setting. All functions are operable via a row of micro-touch electronic switches on the front panel and from the SL-9000 “Home Theater Master” learning remote. The remote can also be programmed to operate your TV, CD player, VCR, DVD, and other sources. Great idea!

An ample array of RCA-type inputs and outputs is provided on the rear panel, including 2 processor loops, as well as one pair of balanced ins/outs via XLR connectors, and a female IEC connector allowing for the use of after-market power cords. All outputs may be operated simultaneously.

Due to the preamp’s narrow profile, the many rear panel jacks are positioned horizontally and fairly close together. Those of you with fat interconnects may find, as I did, that the fit can be very tight. If the connectors on my Full Spectrum Signature interconnects were any wider, I wouldn’t have been able to cram them into the inputs, in which case I’d have had to use less familiar wires to conduct my listening tests. Luckily, with a little tenacity on my part, they just made it.

Additionally, I found the setup instructions a bit difficult to follow. I’d have appreciated a few instructive diagrams to clarify the text. The major area of confusion appeared under the BALANCE heading: “Simultaneously, the number display will show 00, which means zero attenuation (or maximum volume).” Skimming the manual as end-users are wont to do, I erroneously inferred that 99 must then represent maximum attenuation (or minimum volume). Imagine my shock had I set the preamp volume to 99, thinking that I’d set it for 99 dB attenuation, put on a disc and let ’er rip. Yikes! (By contrast, the manual that came with the Home Theater Master learning remote was easy to understand.)

The volume control knob rotates continuously in either direction and has fairly fine detents that correspond to a 1-dB change in volume. InnerSound circumvents the usual channel balance problems and the transient switching noises that sometimes plague conventional volume controls by using the volume control knob to drive an optical-comparitor circuit. The optical circuit operates a micro-processor-controlled electronic gain system, permitting control of the overall level using one hundred, 1-dB steps, thus reducing channel tracking errors to less than 0.1%. Switching transients are eliminated because the microprocessor waits for the musical signal to cross the zero point before going to the next step.

The preamp’s anodized chassis is made of CNC-machined aluminum. Gold-plated printed circuit boards and high-quality components are used throughout. The minimal audio circuitry employs low-noise FETs (field effect transistors), which are claimed to diminish noise, distortion, and crosstalk to vanishingly low levels.


I initially installed the InnerSound line stage in my Plateau equipment rack in place of my custom AHT tube preamp. My source was the Parasound C/BD-2000 transport coupled to the Perpetual Technologies P-1A/P-3A digital gear via a Harmonic Technology silver coaxial digital cable. As previously mentioned, I used Full Spectrum Audio Signature interconnects (good, but out of production) to connect the ModWright PT P-3A to the CD input of the line stage. The RCA outputs of the InnerSound line stage fed my InnerSound active crossover/bass amp, and the Monarchy Audio SE-160 hybrid monoblock amplifiers were used to drive the electrostatic panels of my InnerSound Eros speakers. Normally, I use the Eros with a subwoofer but lacked the right cable connectors (XLR to RCA) to employ the InnerSound’s balanced outputs for that purpose. I suppose I could have used the tape outputs, but that would have necessitated resetting the subwoofer level every time I changed the preamp’s volume setting, so I let it fly sans sub.

For some obscure reason, I couldn’t get the preamp to operate when I first installed it in my reference system. I could switch sources and make balance and gain adjustments via the front panel controls, and the readout showed the gain setting correctly, yet no sound was forthcoming. Later in the evening, for yet another obscure reason, the preamp began working without my having made any further changes. Roger Sanders explained that the preamp’s micro-processor may have failed to boot initially because I may have inadvertently jiggled the AC plug when I originally powered it up. “The usual cure for this,” he said, “is to unplug the preamp for about 30 seconds and then re-power the unit, so that the micro-processor can reboot.” He suggested that a momentary lapse in AC power could have the same effect. While I can’t recall any power line problems, this may have been the cause. At any rate, the preamp has worked fine ever since.

Up and Running!

Right off the bat, it was clear that the InnerSound preamp’s performance is extraordinary: very neutral in its tonal balance, excellent bass, deep and superbly delineated; the mids transparent and detailed, the highs well focused and extended, with no discernible harshness or edginess. Soundstaging is expansive and precise; low-level detailing, superb.

The preamp’s delineation of vocals is in a class by itself; the clarity and articulation this unit preserves is amazing. Even so, I’m not going to tell you I could make out every word on every recording – that would be impossible! – but I can say that I could hear more of the words more clearly than with any other preamp I have used in my system. This is no small feat.

The following is an excerpt from an e-mail I received from Roger Sanders:

“I did the final testing on it [the InnerSound preamp] using double-blind, ABX testing using a short, straight piece of wire as a reference standard. None of the listeners could hear any difference between the preamp and the wire, so I figured we had done our homework well enough!”

Normally, I’d be inclined to attribute such a comment to a designer’s parental bias. However, after using the InnerSound preamp in my own system with my own recordings, my feeling is that the InnerSound folks have done their homework very well indeed. In my experience, if any product has ever sounded completely neutral and transparent, this has got to be the one.

Recently I received a new, high-quality test CD, the Manger CD Sampler, soon to be available from Manger’s US distributor ( The recording encompasses a unique assortment of musical instruments and genres – violin and piano works from Vivaldi and Beethoven, a jazz trio, a couple of vocal cuts from Livingston Taylor, some heavy clanging church bells, and a rambling jazz drumfest from the O-zone Percussion Group. The recording is first-rate, displaying lightning-quick transients, wide dynamic swings, coherent well-balanced sonics and expansive imaging with a superb sense of depth. Using the InnerSound line stage helped to showcase this interesting CD’s superior sound.

One of the best recordings of classical violin that I’ve heard is on track 5, “Winter,” from Vivaldi’s The Four Seasons, performed by the Sonatori De La Gioiosa Marca. The violins’ sound is lively, distinct, and natural, without any sense of hardness, stridency or general distress. At the same time, the energetic and riveting performance held me captive.

The intense chiming and rich harmonic overtones of the church bells on the first cut of the Manger Sampler, Volles Gelaut, were dimensional, weighty, and majestic. Jazz Variants’ percussive joy ride was very convincing. The assorted drum whacks and rolls and cymbal work make for a potent musical mix and verified the preamp’s ability to handle transients and dynamic swings, while at the same time maintaining superior imaging and instrumental localization.

Compared to What?

In this competitive hobby, comparisons are as inevitable as they are essential. I’ve recently had a good cross-section of high-quality preamps in my system, including the Adcom GFP-750, Krell KAV-250p, Rogue Audio 99, and my own custom-built, minimalist tube line stage from American Hybrid Technology (AHT). Of all these fine units, I believe the InnerSound to be the most neutral and transparent.

If memory serves, the InnerSound sounds a bit more musical and coherent than the Krell, while being equal in detail retrieval and all other performance aspects, including transient speed, the Krell’s strong suit. The Adcom unit is very detailed and not really harsh to any significant degree, but the InnerSound seems more relaxed and possibly a little smoother.

As for comparisons to the Rogue and AHT preamps, I would say that these excellent tube units impart a slight softening to the overall presentation, and along with it, a slight smearing or blurring of images, which is mainly perceptible only in direct comparison to the precisely-focused, always-composed InnerSound. Also, the bass of the InnerSound was quite a bit tighter than that of the Rogue and actually quite similar to that of the AHT.

In terms of freedom from the insidious effects of noise, kudos must go to the InnerSound, although the Adcom was also very quiet. I’m not certain if the reason for the apparent improvements in inner detailing or lyric comprehension were due to lower levels of noise, crosstalk, or distortion, but what remains crystal clear is the InnerSound’s delivery of the music. The usual tiny vestiges of interstitial noise were simply not intrinsic to the fabric of the InnerSound’s personality.


Three thousand dollars is a lot of money to spend for a component that some audiophiles consider superfluous since the advent of digital volume control. That said, the InnerSound line stage preamp is a lot of component for the money. Its features and control layout are very well thought out, and the learning remote worked well and was simple to operate. Its clean modern styling should compliment any décor.

If this device has any sonic flaws, they are minor and well concealed. To say it again, this is the most transparent preamp I have had the pleasure to use. Until another preamp does the job appreciably better, I have only praise. It may not be perfect, but I had an unusually difficult time trying to find any area at which to point the critical finger. If pressed very hard, I might admit that the unit’s macro-dynamic envelope may be very slightly compressed when compared to the very best units I’ve auditioned. However, I’m not even entirely certain of that one criticism. The preamp’s unflappable demeanor may just make it appear that way with a few of my recordings. Generally, I am very pleased with the wide range of dynamic gradations the unit provides.

The InnerSound preamp is a solid-state device, yet to my ears it doesn’t sound like solid-state – nor does it sound like tubes. Truth be told, it doesn’t sound like anything. But it sure does let the music play! I have a strong suspicion that many who audition this line stage will find that its unique, user-friendly features and considerable sonic virtues will make it indispensable.

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