On Controlling Volume…

By Bryan Geyer

The preamplifier has served as a standard link in the audio chain since the dawn of hi-fi. The title doubtless derives from its essential function: To amplify (and equalize, when a phono cartridge input is involved) the incoming low level source signals, and boost them to full line level amplitude prior to driving the power amplifier. The preamp also serves to manage source selection, volume control, and, traditionally, lossy tone controls*. Further, all functions must be achieved consistent with proper source loading, and should provide good output isolation, i.e.: present low Zout relative to the load impedance.

Times change. Your present source signals are likely to already be at full “line level”, and most of them can already drive the power amplifier to full output directly, without further amplification.** Injecting more boost from the preamp’s line level gain stage (generally +8dB to +12dB, sometimes as much as +20dB) will simply force the user to push the volume control down near the 9 o’clock arc, a position where the attenuation taper is cramped, calibration is compromised, and stereo tracking is inherently poor. In this event, you’d do well to entirely bypass the preamplifier’s traditional line level gain.

Although there might be no need to amplify any incoming line level signals, it’s still necessary to provide for source selection and volume management, and to do both in a manner that assures proper source loading and good output isolation. With due care, and by imposing just one reasonable restriction (explained below), that challenge can be entirely satisfied by purely passive means, without resorting to any active circuitry. The consequent solution is normally named a “passive preamp”. It might be more accurate to call such box the main controller.

The main controller is a good place to get fussy. The input selector and the master volume attenuator represent the sole tactile link between your fingers and your auditory perception, so those parts merit top quality. Ditto the requisite input/output connector jacks. The main controller is also the part of your system that you’ll manipulate the most, so it should be prominently placed and readily accessible. Compact size will prove helpful, so consider the advantage implicit with the use of RCA-type in/out jacks. By using RCA jacks you can mount four full stereo channels (L/R inputs x 4 + main L/R outputs = 10 jacks total) on a tidy 2 inch by 6 inch panel (see photo), whereas XLR connectors are too massive for more than two channels. Given normal home environs, the use of XLR connectors here would not confer the slightest noise advantage. That fact is further assured by limiting the permissible output connection cable length to 1 meter maximum, a minor concession that reflects the above noted passive design constraint. This length limit is actually imposed to assure that there’s no significant (-0.3dB) 20kHz rolloff arising from shunt cable capacitance when a passive 10kΩ or 20kΩ log-taper volume attenuator is positioned at its worst case (highest) Zout setting.

A value of 10kΩ to 20kΩ for the master volume attenuator is sufficiently high to provide a Zin that’s fully compatible with any known solid-state source component. The latter typically exhibit a low Zout, on the order of ~ 50-150 Ohms. Conversely, a 10kΩ or 20kΩ load would not be suitable for a vacuum tube source component. The typical cathode-follower output stage of a tube-type source will exhibit a much higher Zout, hence need materially higher load impedance, i.e. ~ 50kΩ. And a passive 50kΩ attenuator would then require active circuitry to provide a tolerable (low) Zout—so forget about using a tube circuit as a source component.

In order to maintain good calibration accuracy, the loading on a 10kΩ or 20kΩ volume attenuator should be on the order of some 5X to 10X the attenuator’s worst case (highest) Zout setting. That Zout is, respectively, 2.5kΩ and 5kΩ. Both values are then fully compatible with the typical input impedance of most solid-state power amplifiers, where Zin is generally ≥ 30kΩ. The potential error is even less when an active external crossover controller is the load, as Zin is then on the order of some 75kΩ to 100kΩ. Check the specified Zin of your own equipment to be sure that it presents a similar value.

There are a great many different commercially available passive preamp designs on the market, at prices ranging from $49.50 to insanity (~ $8k), with a very wide variety of means (some quite bizarre) applied to set the volume level. My personal choice is Goldpoint’s model SA4, as made by Goldpoint Level Controls, of Sunnyvale, CA. Refer http://www.goldpt.com/index.html.

The price (order direct, on-line) for a Goldpoint SA4 is $532 + tax and shipping. That expense may seem steep, given the functional simplicity involved, but the general level of excellence, choice of components, and the craftsmanship applied justifies the maker’s tag. It’s an elegant product. The standard Goldpoint SA4 provides four stereo input channels, utilizing RCA jacks. (There’s also a two channel stereo XLR version if you insist on adhering to those bigger input jacks.) The volume attenuator consists of a premium quality Elma 24 position double-deck switch, with 23 laser-trimmed ±0.5% thin film nichrome low noise resistors per channel.*** See the SA4 product page at http://www.goldpt.com/sa4.html. Also, take the time to read the informative section about stepped attenuators versus conventional volume control potentiometers…https://goldpt.com/compare.html. (It’s way down at the bottom of that page.)

It’s a distinct pleasure to utilize a fully calibrated stepped attenuator to control the output volume. The design accurately exhibits exact incremental gain steps, with closely matched stereo channel tracking and the visual ability to precisely reset a given reference level. Even the very best of the continuously variable rotary controls is crude and sloppy in comparison with this stepped switch.

I recommend Goldpoint’s basic 24 position stepped attenuator, rather than their newer 47 position option. The former is basically a 2dB/step attenuator, with the last 28dB of cut compressed into a tapered 5 step descent as you approach the fully-off position. The net result is 62dB of total attenuation, most of it accessed in gentle -2dB steps progressing from the fully-on position. This design is ideal. In the past 7 years of using my own Goldpoint SA4 (with 24 position attenuator) I have never wished for a control with finer resolution. I find 2dB/step to be quite perfect. The mechanics are equally excellent. The switch mechanism is quiet and reliable, and the rotation is very smooth, optimally damped.

BG (December 3, 2019)

*Tonal adjustments are best accomplished by utilizing a separate external active crossover control unit that directly loads the preamp and feeds the ensuing power amplifiers. Active crossover controls facilitate variable selection of the desired low pass-to-high pass crossover frequency, with adjustable damping and adjustable boost/cut of the independent low/high passbands. This provides a cleaner, more precise, and more logically managed means of altering the tonal nuance of the system than previously possible with traditional tone control filtration.

**Do confirm that you can drive your system to full output directly, without the need for supplementary preamp gain. In most cases this will be true, but exceptions happen; it’s dependent on your power amplifier’s internal voltage gain and on loudspeaker efficiency. Power amplifiers exhibit different internal voltage gains. Most designs range between +23dB and +29dB; refer spec. sheet, see “input sensitivity” (or equivalent term). Power amplifiers with gain = +29dB (e.g.: 1 Vrms input produces 100 Watts output [28.28 Vrms] across an 8Ω load) are inherently capable of reaching their full rated output capability when driven by virtually any modern line level program source. Power amplifiers with internal gain ≤ +24dB fall into an area that I consider marginal for use with a passive preamp when driving low efficiency mini-monitor speakers. Try to stick with amplifiers that provide ≥ +26dB gain.

***If you’re a compulsive DIY perfectionist (me), you might consider buying a naked attenuator (no resistors) switch from Goldpoint that’s made for axial lead resistors, and rig your own attenuator.† That entails some careful work, and some fussy ordering. Why would anyone do this? Well, you might want a different attenuator value. (I wanted a 20kΩ attenuator. Goldpoint’s nearest standard is 25kΩ.) Also, you might want resistors with a ±0.1% tolerance, whereas Goldpoint trims their surface-mounted nichrome resistors to ±0.5%. If you chose to run this DIY route…
(a) Contact Goldpoint for guidance on the discrete resistor values needed for your custom attenuator; they have a programmed “app” for their 24 position model.
(b) Order your resistors on-line from Mouser Electronics. Specify TE Connectivity (brand), 1/4 Watt, axial lead, metal film (low noise), ±0.1% tolerance, with thermal coefficient 15ppm.

†Use Kester “type 44” solder (Sn63/Pb37), 0.025 inch Ø (22 AWG) size, and a small conical soldering tip with good lighting + some magnification. Keep a nearby fan going to disperse the leaded solder fumes. (Do not consider a lead-free solder.) Mouser might need several months to deliver all of the special ±0.1% values that you want, but they’ll keep you informed, and will eventually deliver every value, so don’t compromise. Your reward lies in the knowledge that your DIY calibrated attenuator exhibits exceptional accuracy.

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Meet the Staff

Meet the Staff
John J. Puccio, Editor, Publisher, Reviewer

Understand, I'm just an everyday guy reacting to something I love. And I've been doing it for a very long time, my appreciation for classical music starting with the musical excerpts on the Big Jon and Sparkie radio show in the early Fifties and the purchase of my first recording, The 101 Strings Play the Classics, around 1956. In the late Sixties I began teaching high school English and Film Studies as well as becoming interested in hi-fi, my audio ambitions graduating me from a pair of AR-3 speakers to the Fulton J's recommended by The Stereophile's J. Gordon Holt. In the early Seventies, I began writing for a number of audio magazines, including Audio Excellence, Audio Forum, The Boston Audio Society Speaker, The American Record Guide, and from 1976 until 2008, The $ensible Sound, for which I served as Classical Music Editor.

Today, I'm retired from teaching and use a pair of bi-amped VMPS RM40s loudspeakers for my listening. In addition to writing the Classical Candor blog, I served as the Movie Review Editor for the Web site Movie Metropolis (formerly DVDTown) from 1997-2013. Music and movies. Life couldn't be better.
Karl W. Nehring, Contributing Reviewer

For more than 20 years I was the editor of The $ensible Sound magazine and a regular contributor to its classical review pages. I would not presume to present myself as some sort of expert on music, but I have a deep love for and appreciation of many types of music, "classical" especially, and have listened to thousands of recordings over the years, many of which still line the walls of my listening room (and occasionally spill onto the furniture and floor, much to the chagrin of my long-suffering wife). I have always taken the approach as a reviewer that what I am trying to do is simply to point out to readers that I have come across a recording that I have found of interest, a recording that I think they might appreciate my having pointed out to them. I suppose that sounds a bit simpleminded, but I know I appreciate reading reviews by others that do the same for me -- point out recordings that I think I might enjoy.

For readers who might be wondering about what kind of system I am using to do my listening, I should probably point out that I do a LOT of music listening and employ a variety of means to do so in a variety of environments, as I would imagine many music lovers also do. Starting at the more grandiose end of the scale, the system in which I do my most serious listening comprises an Arcam CDS50 CSD/SACD CD player, Goldpoint SA4 Passive Preamp, Legacy Audio PowerBloc2 amplifier, and a pair of Legacy Audio Focus SE loudspeakers. I also do a lot of listening while driving in my 2016 Acura RDX with its nice-sounding ELS Studio sound system through which I play CDs (the ones I especially like I rip to the Acura's hard drive so that I can listen to them whenever I want) or stream music through the system using my cell phone. For more casual listening at home when I am not in my listening room, I often stream music through the phone into a Vizio soundbar system that has remarkably nice sound for such a diminutive physical presence. And finally, at the least grandiose end of the scale, I have an Ultimate Ears Wonderboom Bluetooth speaker for those occasions where I am somewhere by myself without a sound system but in desperate need of a musical fix. I just can't imagine life without music and I am humbly grateful for the technology that enables us to enjoy it in so many wonderful ways.
Bryan Geyer, Technical Analyst

I initially embraced classical music in 1954 when I mistuned my car radio and heard the Heifetz recording of Mendelssohn's Violin Concerto. That inspired me to board the new "hi-fi" DIY bandwagon. In 1957 I joined one of the pioneer semiconductor makers and spent the next 32 years marketing transistors and microcircuits to military contractors. Home audio DIY projects remained a personal passion until 1989 when we created our own new photography equipment company. I later (2012) revived my interest in two channel audio when we "downsized" our life and determined that mini-monitors + paired subwoofers were a great way to mate fine music with the space constraints of condo living.

Visitors that view my technical papers on this site may wonder why they appear here, rather than on a site that features audio equipment reviews. My reason is that I tried the latter, and prefer to publish for people who actually want to listen to music; not to equipment. My focus is in describing what's technically beneficial to assure that the sound of the system will accurately replicate the source input signal (i. e. exhibit high accuracy) without inordinate cost and complexity. Conversely, most of the audiophiles of today strive to achieve sound that's euphonic, i.e. be personally satisfying. In essence, audiophiles seek sound that's consistent with their desire; the music is simply a test signal.

William (Bill) Heck, Contributing Reviewer

Among my early childhood memories are those of listening to my mother playing records (some even 78 rpm ones!) of both classical music and jazz tunes. I suppose that her love of music was transmitted genetically, and my interest was sustained by years of playing in rock bands – until I realized that this was no way to make a living. The interest in classical music was rekindled in grad school when the university FM station serving as background music for studying happened to play the Brahms First Symphony. As the work came to an end, it struck me forcibly that this was the most beautiful thing I had ever heard, and from that point on, I never looked back. This revelation was to the detriment of my studies, as I subsequently spent way too much time simply listening, but music has remained a significant part of my life. These days, although I still can tell a trumpet from a bassoon and a quarter note from a treble clef, I have to admit that I remain a nonexpert. But I do love music in general and classical music in particular, and I enjoy sharing both information and opinions about it.

The audiophile bug bit about the same time that I returned to that classical music. I’ve gone through plenty of equipment, brands from Audio Research to Yamaha, and the best of it has opened new audio insights. Along the way, I reviewed components, and occasionally recordings, for The $ensible Sound magazine. Recently I’ve rebuilt--I prefer to say reinvigorated--my audio system, with a Sangean FM HD tuner and (for the moment) an ancient Toshiba multi-format disk player serving as a transport, both feeding a NAD C 658 streaming preamp/DAC, which in turn connects to a Legacy Powerbloc2 amplifier driving my trusty Waveform Mach Solo speakers, supplemented by a Hsu Research ULS 15 Mk II subwoofer.

Mission Statement

It is the goal of Classical Candor to promote the enjoyment of classical music. Other forms of music come and go--minuets, waltzes, ragtime, blues, jazz, bebop, country-western, rock-'n'-roll, heavy metal, rap, and the rest--but classical music has been around for hundreds of years and will continue to be around for hundreds more. It's no accident that every major city in the world has one or more symphony orchestras.

When I was young, I heard it said that only intellectuals could appreciate classical music, that it required dedicated concentration to appreciate. Nonsense. I'm no intellectual, and I've always loved classical music. Anyone who's ever seen and enjoyed Disney's Fantasia or a Looney Tunes cartoon playing Rossini's William Tell Overture or Liszt's Hungarian Rhapsody No. 2 can attest to the power and joy of classical music, and that's just about everybody.

So, if Classical Candor can expand one's awareness of classical music and bring more joy to one's life, more power to it. It's done its job. --John J. Puccio

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"Their Master's Voice" by Michael Sowa

"Their Master's Voice" by Michael Sowa