Dynamic sounds Associates DSA Pre I preamplifier review

Our beloved industry is offering a rather amazing amount of high-end audio products from all the continents. They are results of the different quests for perfection. There are many approaches and ideas of the high-end audio preamplifier should be designed.

The end result is always affected by the very mindset of the designer behind the preamp and Douglas Hurlburt’s Dynamic sounds Associates DSA Pre I preamplifier is quite a  different performer as you can read on.  


Nothing comes casual with the product designed and manufactured by Douglas Hurlburt, Ph.D. Founder and Principal Designer Dynamic sounds Associates. As you can read below, there are many technical considerations, that were thoroughly contemplated before the Pre I made into the final production. 
Let me refresh Douglas Hurlburt’s most impressive life’s rich carrier and achievements.
As a son of two scientists, Douglas Hurlburt, Ph.D. Founder and Principal Designer of the Dynamic sounds Associates, had pursed a rich and impressive carrier path, that involves RCA Ltd. (Montreal), MIT Lincoln Laboratory, Defense Advanced Projects Agency (DARPA), Department of Defense etc…
Douglas work has included designing integrated circuits, surface acoustic wave (SAW) devices and systems, ultra-wideband spread spectrum communications systems and airborne radar systems, critical systems components for advanced concept communications, radar systems etc. 
With his professional obligations complete, Dr. Hurlburt has been able to focus entirely on his lifelong passion for designing audio components. Over his life, he has designed and built many of his own system components. Finally, in 2004, he went “public” with the introduction of the Phono ONE. Its development came out of a desire to design the finest possible phono preamplifier without regard to the potential cost. Its no-compromise philosophy was transferred to the Phono II in 2012, a unit which weds the sonic performance of its predecessor with unprecedented versatility and ease of operation.


The design of the DSA Pre I linestage presented a number of challenges and considerations that had to be resolved within the context of the basic design principles of DSA. Many people would think that the design of a line stage is easy; after all it only needs to have some selectable inputs and a volume control to meet the basic functionality of a line stage. However, it is those very aspects that seem so simple which turn out to be the most difficult when designing a world class line stage such as the DSA Pre I.
Some of the basic design considerations that were addressed with the:

• How many inputs and of what type—balanced or unbalanced?
• What type of output—balanced or unbalanced– and how many?
• Throughput gain and ability to accommodate different levels of inputs?
• Type of volume control and its relationship to left/right balance?
• Other features that add to overall flexibility and utility of the unit?
• Remote control operation and what functions to be remotely controlled?

There are other considerations that could be added to the above list, but these represent the major ones that went into the design of the DSA Pre I. Each of these brought challenges for the designer and solutions had to be found that were true to the basic principles of DSA, including:

• Maintaining an audio bandwidth that went from a few Hz to several octaves beyond the upper limits of audible sound.
• Extremely high dynamic range over the full bandwidth.
• No loop or global feedback in the design.
• Fully balanced audio input and output capability

To round out the list it was also desired to maintain the same basic chassis dimensions and appearance that DSA introduced with its renowned Phono II. The following sections will discuss each of the design considerations mentioned above and how they were implemented in the DSA Pre I.
1. Number And Type Of Inputs
It was desired to support both unbalanced (RCA) and balanced (XLR) inputs for the Pre- I. The number of each, or having both available for each input is largely a matter of available real estate on the chassis. For the Pre I, this was dictated by the desire to maintain the same chassis dimensions as for the DSA Phono II. High quality RCA and XLR connectors each require a minimum amount of area plus there must be sufficient space for fingers to add and remove cables easily. Since it was also necessary to allow space for the outputs and a power cord with power switch, it was decided to have six (6) inputs for each channel available on the back panel of the Pre I. And, rather than attempt to overly crowd the back panel with an RCA and XLR connector for each input, there are three (3) unbalanced and three (3) balanced inputs for each channel. These are interleaved to maximize the accessibility to each set of inputs. However, knowing that it is sometimes desirable to be able to make a quick connection to an input to test a source, or connect another type of audio device, the Pre I has a seventh input which is located behind the drop down door on the front panel. This input is unbalanced (RCA) only and is selectable from the front panel, but not the remote control.

2. Number And Type Of Outputs
It was decided in the beginning that the main audio output would support both balanced (XLR) and unbalanced (RCA) connections. This is in keeping with the same capability on the DSA Phono II; however, to allow for a wider range of output loading options for the Pre I, a higher bias current driver stage was designed. Like the driver for the Phono II, this driver is fully balanced and operates totally in a Class A mode.

In addition to the main audio output, an output that can be used for recording the audio signal was also desired. Due to space considerations, this output has unbalanced (RCA) connectors only. This output is extracted from the output of the first gain stage which is before the volume control; however, it is affected by the throughput gain selection for the input being used. (See the next section for a discussion of the throughput gain selection.) This output is driven by a Class A source follower instead of a balanced driver and is capacitively coupled. Thus, to maintain the frequency response at the very low end of the audio spectrum, this output should not be loaded with anything less than 10kOhms.
3. Throughput Gain And Different Input Levels
The basic throughput gain of the DSA Pre I is 12dB. In terms of voltage gain this is a factor of four (4) which is adequate for virtually all source material while providing sufficient output voltage to drive all but the most insensitive power amplifiers. However, there may be situations where either the source is a lower than expected voltage, or the power amplifier requires additional voltage drive. To accommodate these instances, there is a toggle switch at each input on the back panel which permits selecting an additional 3dB of throughput gain—making a total gain of 15dB—for that particular input. This same switch also permits the reduction of the gain by 6dB, giving a total gain of 6dB. This is intended to be used primarily with inputs from digital sources where the outputs are typically a standard “line level” that can exceed the output levels from a phono preamp, or other source, by several dB. While the volume control can always be used to reduce or increase the output levels as required, the inclusion of this gain selectable feature was intended to reduce the need to make large volume control adjustments when switching between inputs. The gain selection for each input can be set as required, and when that input is selected the appropriate gain is also chosen. Note that there is no gain selection for the input located on the front panel; this input has a fixed 12dB of throughput gain.
Because these gain changes are implemented in the first input amplifier stage, the record output will be affected by the throughput gain selection. However, this will ensure that the record output level will not vary excessively when switching between inputs with differing input voltages.

4. Volume And Balance Controls
There are many accepted methods for designing volume and balance functions. For the DSA Pre I it was decided that the volume control would be digitally controlled—this to allow for a digital remote control—and that the balance function would be managed by incrementing or decrementing the level of the audio channels. Along with this approach, it was also desired to maintain constant impedance through the volume/balance control, regardless of level. This best supported the goal of very high bandwidths and dynamic range for the Pre-I. Other desires were to minimize the number of actual resistive components in the audio chain as the volume or balance was varied, and to maintain a constant total audio output when the balance between channels was changed. This latter desire immediately defined the minimum step size for the volume control at 0.5dB. With a 0.5dB step the channel balance can be altered in 1dB steps by incrementing one channel by 0.5dB and decrementing the other channel by the same amount. Thus keeping the total audio output unchanged.

The final need to maintain constant impedance and to ensure the necessary precision throughout the volume/balance control range led to the choice of discrete precision “attenuator blocks” based on the use of “T-pad” or “Pi-pad” designs. These designs are well recognized throughout the audio and RF and communities for fixed attenuators, but DSA believe that this is the first time that they have been employed for a volume control application. It was decided to use seven of these blocks in a binary sequence: 0.5dB, 1.0dB, 2dB, 4dB, 8dB, 16dB and 32dB. Various combinations of these blocks permit attenuation from 0dB to 63.5dB in 0.5dB steps, or 127 possible attenuator settings. The attenuator blocks that were designed for the Pre I employ 0.1% precision SMD resistors and each block is accurate to 1% of the step value. Each attenuator block is designed to maintain the same impedance level and they can be cascaded in any combination to achieve the desired attenuation while preserving a constant impedance level throughout. However, for the attenuator blocks to perform as desired they must be either “in” or “out of the audio chain. This requires seven DPDT relays which permit the audio signal to pass through the attenuator block, or through a “bypass” short circuit. Simply short- circuiting the attenuator block is not sufficient to preserve the proper attenuation or the constant impedance. These relays are driven by a pair of 4-bit asynchronous up-down binary counters connected as an 8-bit counter; however, the 8th bit is not used. Matching counter circuits are used for each channel, but with a common “up/down” pulse to maintain synchronization.

It was necessary to use mechanical reed relays for the switching operations for two reasons: a) They have very low resistance, and b) unlike optical relays they are totally linear, even at very low voltage levels. For this application, DSA selected a low power precision DPDT reed relay with very low contact resistance (typically less than 0.1Ohms) and very short duration contact bounce when operating (typically less than 0.5msec). The result is a precision attenuator that meets all of the design goals for both attenuation and balance control, and is virtually silent in operation.
5. Other Features
One feature that is often desired by audiophiles is the ability to invert the phase of the audio signal. The DSA Pre I is a non-inverting amplifier, however, like the DSA Phono II, it permits phase inversion of the audio signal. The inclusion of phase inversion is easily accomplished due to the differential amplifier topology of the Pre I. Also, because not all audiophiles will have a phono preamplifier that has a mono mode (where the two channels are summed) it was decided to also include this feature in the Pre I. The mono mode can be selected with any input regardless of source material.
The Pre I also has a _” headphone jack located on the front panel behind the drop down door. This jack is driven from the same driver stage that is connected to the main outputs on the back panel. However, when the headphone jack is in use, the main output is muted, but all other functionalities of the Pre I remain.
6. Remote Control Functionality
To develop the remote control functionality for the DSA Pre I, Hurlburt turned to his good friend John Chapman of Bent Audio. For many years John has developed remote controls for his line of audio equipment, including attenuators, as well as providing remote controlled stepping motors for those using stepped attenuators. John modified his artfully designed 13-button remote control to address the desired remote functions for the DSA Pre I. These include:

• Selection of all six back panel inputs
• V olume up/down
• Balance left/right
• Mute
• Run
• Phase

John also programs the necessary microcontroller within the Pre I to operate these functions as well as the microcontrollers that decode the digital attenuator bits for the digital level displays. The beauty of using the microcontroller is that, unless it is being used to operate a function, it is “sleeping” and hence adds no interference to the audio signal when not being used.


Let us look at all the wide variety of the DSA Pre I features…. 

• Six inputs on the back panel, selectable by push button or remote control: 3 – XLR balanced inputs- 3 – RCA unbalanced inputs
• Additional auxiliary input (unbalanced RCA) available and selectable on the front panel
• Headphone jack (1/4”) on the front panel which disables main output
• Custom design attenuator employing seven (7) precision attenuator sections:
All digital control of attenuator settings; Attenuator settings in 0.5dB steps from 63.5dB to 0 dB (127 precision steps); Attenuator employs a constant throughput impedance design; Minimal number of precision resistors (0.1%) in audio circuit for any attenuator setting
• Balance control in 1dB increments (0.5dB/channel) that maintains total audio output regardless of balance offset.
• Front panel has controls for stereo/mono mode and non-inverted or inverted total phase.
• Nominal throughput gain of 12dB/channel but additional +3dB or -6dB selectable at input to adapt to different input levels.
• 3-digit digital display showing output level for each channel
• High bias class-A push-pull driver stage for each channel output.
o Output connectors for XLR (balanced) or RCA (unbalanced)
• Separate record output (RCA only) that is independent of volume
• Full remote control capability -Volume, Balance, Mute/Run, Input selection
(6 regular inputs), Phase control (invert/non-invert)
• Appearance fully compatible with DSA Phono II


Dynamic sounds Associates DSA Pre I preamplifier has really proven to be one of the most ink-less active preamplifiers across a wide variety of genres. It was easy to follow the DSA Pre I continuously engaging nature and ability to swiftly handle track by track without any hint of saturation or self-imposed gain signature. Below are few of the albums and songs from my listening notes.

I Robot is certainly Alan Parsons, The Alan Parsons Project’s most iconic album. Inspired by the Isaac Asimov legendary book it offers an amazing sonic scope. The album really expands when the complete system is in sync and of utmost balanced nature. The crucial role is without a doubt performed by the preamplifier. Handling of the system gain is of utmost importance and DSA Pre I expertly performed its role by delivering a splendid rendition of “I Robot” and “Breakdown”. These timeless compositions really demand full control of the sonic territory to expand into the environment. This is especially evident when the listening space allows sound to expand both horizontally and vertically.

Dynamic Sounds Associates rendition of I Robot was really expansive. That was further confirmed with the “News” by Dire Straits from the album Communique. Not your typical audiophile track I know.  “Follow Me Home” has further shown how easily the  Dynamic sounds Associates DSA Pre I preamplifier can establish complex aural presentation.

The Cars – The Cars “Moving in Stereo” is another great example of impressive spatial enforcement, but it doesn’t stop there. Just observe how much pulsating is happening in the lower realms and how well the line stage can conduct the hefty task.

Same goes for the Supertramp’s Crime Of The Century. The  “Rudy” explores the finer details of a complex studio arrangement pushing all the extremes. It’s interesting to observe how components act with this particular track and how much of the Supertramp’s magic will expand. DSA Pre I magnificent ability to not stand in a way of the music fastened the remarkable ”Rudy”’s grip with ease and much-needed authority.

But it’s not all about control with the Dynamic sounds Associates DSA Pre I preamplifier. This preamp could seamlessly mark the fragility and subtleness.

Abandoned Garden might not be the Michael Franks’ top achievement by the critics, but I do tend to disagree. Some of the songs on the Abandoned Garden are as timeless as the very early albums and as subtle as it gets. A brief listening might give an impression of how the album is nothing exemplary sonic wise. Yet, in a well-balanced system, the layers of painstaking compositions are starting to unveil.

Dynamic sounds Associates DSA Pre I preamplifier steeped a bit deeper into the aural realms than expected. Sometimes the audio evaluation closely correlates with the paintings observations. We can at once recognize a particular style or artist’s unique way of expression. But, we’re not seeking out the distorted reality. While similar to the art we can cherish the tone, our new nucleus is quickly shaken by the painting’s power of establishing a vivid and believable illusion.

And this is one of the Dynamic sounds Associates DSA Pre I preamplifier’s major advantages; a palpable and grand believability. I did expect something considerably great based on my experience with the DSA phono preamplifier, but the neutral and spot performance did surprise me quite a lot.

Dynamic sounds Associates DSA Pre I preamplifier focuses on the music and signal purity. While we have many permutations of pureness definition in our industry it shouldn’t be a far fetched goal for any high-end audio preamplifier to ensure the most trait less carrying and amplifying of the fragile signal.

Dynamic sounds Associates DSA Pre I preamplifier is a no brainer in this regard. A highly thought out inner core is capable of serving the music for what it is and not for what it could be.

Classical music surely represents one of the biggest and most complex challenges for any high-end audio component. I cannot stress enough the importance of proper gain propagation and especially with the orchestral recordings the capability of the preamplifier is easily recognized. I’m not an elitist when it comes to classical music, but I do have a strong affection for it. The only problem of yours truly is finding enough time to explore the vast and almost endless universe of compositions and different performances.

“Cello Concerto pour violoncelle: I. Enigme (Très libre et flexible), … Et dans cette nature étrange et symbolique… (Poème XXVII)” from album Dutilleux & Lutoslawski: Cello Concertos by Mstislav Rostropovich, Serge Baudo, Orchestre de Paris will at once demystify any of glorified preamp theoretical features. With “Enigme” the reality strikes hard and unapologetically.

The pure, intrepid rawness of cello and subtle orchestra accompanying is merciless when it comes to the handling of the gain. This song alone can decipher the true capability of the preamplifier. It’s one thing to handle rather well only the high-octane spiritless. There are many preamplifiers both solid-state and tube ones that can deliver the close approximation of needed energy flow. It’s something completely different to seamlessly blend arduousness with the micro-level subtleness. When it comes to this demanded task the list of a stand out preamps shrinks instantly. On both camps; tube and solid-state.

Dynamic Sounds Associates DSA Pre I control of micro and macro dynamic was exemplary. Pre I expertly kept the cello forte energy in very epicenter without losing a much-needed grip and in the same time without a stretch painted the convoluted acoustical atmosphere. That feat alone is never simplistic or something I’ve to stumble upon frequently. For this exceptional ability alone the DSA Pre I is worthy of all the attention!

Although this is a convenient portion of sum ups from listening notes, it should give a clear idea about the Dynamic Sounds Associates DSA Pre I splendid preparedness to serve the music in a most rewarding and satisfying way. 


Over the extended period of Dynamic Sounds Associates DSA Pre I solid-state line preamplifier this unique preamp has proven its track record for offering un-altered sonic performance on a daily basis.  
This is neither typically sounding solid-state nor tube (saturated) preamplifier. In its own way, it combines the very best of both, usually quite opposite words. 
What I like the most about this preamplifier is the absence of push forward sonic imprint. If you’ll ask me what sonic orientation or voicing Dr. Hurlburt took with the DSA Pre I, I simply couldn’t present the exact labeling. I wouldn’t go as far as saying that it possesses the ultimate translucency. No preamp on the market does. But, among the active preamplifiers that I’ve had the luxury to evaluate, this is certainly the most signature-less preamp. 
This was especially evident with the ultra-fast and transparent ubiqaudiolab upcoming First One 600 stereo power amplifier. This unique solid-state amplifier is one of the fastest, most transparent and revealing amplifiers I’ve had the pleasure to try. But, more about The First One in due time. When combined with ubiqaudiolab amp the DSA Pre I found its sonic home harbor and have exhibited all of its virtues. With the selectable gain option, it was easy to find a proper match across the wide variety of system combinations that I’ve tried during the extended testing. 
DSA Pre I carries a utilitarian look with sort of laboratory-like front panel with all the variety of knobs and multiple blue lights. In a positive way, it reflects the research lab instrument panel desk. But like with all of the DSA products there is certain logical practicality that is actually easy to use once its put in practice. 
Like it or not the preamplifier is still the very heart of the high-end audio system. Despite many pursues by the high-end audio companies, very few audio front ends on-board volume/gain handling comes close to the properly designed and executed line preamplifier. 
DSA Pre I is an exemplary product that easily entices audiophile, technocratic and music lover minds. Yes, sometimes all of these three designations are combined in one person :). Anyhow, such labeling only shows how complex yet straightforward preamplifier DSA Pre I is. 
It’s not hard to embrace all of the DSA Pre I qualities. Considering both roles of being a judging reviewer and the listener. One of the tasks of the audio critic is the objective look from the reader’s perspective.  This shouldn’t be a bonus in any review, but a normal way of conduct. Nonetheless, I’m always trying to perform both engagements and tasks most seriously and in a way that the readers benefit the most. 
With the Dynamic sounds Associates DSA Pre I preamplifier it was easy to stay focused with all of the positive attributes. DSA Pre I is feature-packed, easy to use, comes with impressive adjustability and most importantly it poseses the sonic potency that repeatedly glued me to my beloved listening chair. For what it represents I’m more than happy to recognize the Dynamic sounds Associates DSA Pre I preamplifier stand out nature by giving out the 2019 Upper Echelon Product Award. Yes, DSA Pre I is not exactly cheap, but it’s also not over the roof expensive considering its multiplex nature and potent heart. Taking into consideration the ever-rising skyrocket pricing, the DSA Pre I value and the price tag is spot on.  
DSA Pre I is a result of careful and designed by a person with a much broader look and technical know-how. Maybe this is a key advantage and why the DSA Pre I sounds it does. Very, very different and intimately close to the music’ epicenter. 
Matej Isak


– $16,500



Dynamic Sounds Associates
1754 Persimmon Ct.
Naples, Florida 34109
Tel: 386-873-2388