Product Review

Build a Great $99 Dollar Preamplifier from a Kit

December, 1998 -

Upgrade Kit - April, 1999   - Foreplay Update - Critical Review of Capacitor Upgrades, Tube Changes, and Speaker Effects (Lowther vs. NHT) - August, 2000

by Paul Knutson



Electronic Tonalities FOREPLAY Preamplifier Kit

Two 12AU7 Tubes

Dual Mono Volume Controls

Laser-cut Chassis

Size: 4"H x 8"W x 12"D

Weight: 3 Pounds

MSRP: $99 - Wood Base $15



Electronic Tonalities/VALVE, P.O. Box 2786, Poulsbo, Washington 98370; Phone 360-697-1936 (Hours 9-6 Pacific Time, Mon-Fri); Fax 360-697-3348


Lately I’ve been having a ton of fun with audio. Most of the fun I’ve had revolves around building, modifying and tweaking equipment, primarily of the tube persuasion. I’ve always been a do-it-yourself kind of guy, and now finally, armed with just enough knowledge to be dangerous, I’ve applied my DIY tendencies to my audio habit.

This isn’t a true DIY article in that it really doesn’t tell you exactly how to do anything, except maybe how to get in touch with the manufacturer of the product reviewed here and get a kit for yourself. Rather than provide specific instruction, it is meant to encourage readers to try their hand at DIY audio with a relatively simple project. DIY audio is fun, challenging and oh, so rewarding. It is a big rush the first time you fire up a component that you built yourself and have it perform splendidly . . . but that’s when the fun just begins. Once you have built something like this tube preamp, I guarantee that you will soon be overcome by the urge to tweak it and modify it.

Here, I will outline a particularly fun DIY audio project that I’ve been working on. By talking about it, I’ll hopefully provoke some thought, maybe even action, on your part.

Would you like to build a $99 preamp?

No, this isn’t an ad from the classified section of Popular Mechanics, circa 1973 . . . this is for real. Welcome to true, entry-level, hard-core DIY tube audio. Sound interesting? It is.

Over the past fours years or so, a down-to-earth, way smart, innovative, music-loving tube audio dude, reverently nicknamed Doc Bottlehead (aka Dan Schmalle) by his audio buddies, has been publishing a little magazine called Valve. I use the term "magazine" loosely, as the look of this mini-mag is decidedly retro, right down to the photo-copy and staples motif it has going. The magazine looks homebrewed, as do the projects you build after reading it. Let’s just say that Valve is as visually different from Stereophile as Jesse Jackson is politically from Ralph Reed. Valve is a very cool magazine. Despite the low-tech appearance, however, the content is absolutely cutting edge – we’re talking waaaaaaaay out there. The designs these guys come up with are, um, unique. For example, how ‘bout a one-watt, single-ended power amp using an output tube you’ve probably never heard of? Is that wacky enough for you? I thought so.

Doc Bottlehead and his tube audio compadres have come up with a few different DIY kits that they make available to subscribers of Valve, or anyone else for that matter, and who would like to try building their own equipment. The kits are sold under the brand name Electronic Tonalities, which is the kit sales division that was formed by Doc to distribute his products. Doc has a website at and can be reached by e-mail at [email protected].

Electronic Tonalities sells two amplifier kits (both monoblock-based, one using the 6DN7 output tube and one based on the venerable 2A3) and one line-level only preamp kit called the "Foreplay". You’re probably wondering about that name. Well, Doc’s first (and most famous) kit was called the Single Ended eXperimenters’ amp, or S.E.X. amp for short. In its current iteration, the S.E.X. amp kit is a pair of DIY 5-watt monoblock amps, all triode, single-ended, for $399/pr! Hundreds of those babies found their way into the hands of hungry little tube audio DIY’ers who really wanted to build something without breaking the bank.

With that as background, fast forward to 1998 and the release of the "Foreplay" preamp kit. Virtually all of the Electronic Tonalities products are named from the "play-on-sex-words" theme, hence the Foreplay preamp. A line from the advertising copy states that "S.E.X. is always best when preceded by Foreplay". These names will probably prevent the Electronic Tonalities products from becoming too mainstream, but then again, these products aren’t going to be sold on the shelves of your local Electronics Mega Mart anytime soon, so maybe being out of the mainstream is fine with Doc at this point. The whole naming thing is right in line with Doc’s philosophy of not taking the kit business too seriously, although the quality and innovation of the designs are as serious as can be.

How much was that?

The Foreplay preamp kit costs $99. Yep, that’s two digits. It comes complete with all components you will need to have a functioning tube preamp at the end of the project. That’s right around the cost of dinner for two in San Francisco at one of our many fine restaurants, which is a decent way to spend an evening. For about the same cost, the Foreplay strikes me as good entertainment for many years, heck, maybe even a lifetime. I’ll save the dinner money, take the Foreplay and throw a box of macaroni & cheese on the stove, thanks very much.

O.K., $99 is where you start, but if you also want the wood base kit for the preamp (recommended by yours truly), it will set you back another $15. Even then, we’re still talking about a super-duper, you-have-to-be-kidding level of affordability.

Here’s a little good news/kind-of-bad news: The kind-of-bad news is that the passive componentry in the kit is quite basic. Duh. What did you really expect for $99? The good news is that, should you decide to explore other "designer" components by tweaking and modifying what was sent with the kit, you are then doing exactly what Doc hoped you would do. The object of DIY audio is to build something, change it around, have fun and inhale lots of solder fumes while doing so. Don’t get me wrong, you can build the preamp with exactly the parts supplied, and you will be very, very happy. But change an output capacitor here, a resistor there, beef up a few power supply caps, and voila, you have perhaps the ultimate budget preamplifier.

Flawless Instructions = DIY Success

Did I mention that anyone can build this preamp? The step-by-step directions are flawless. Even if you have no idea how to set the clock on your VCR, you will still be able to build the Foreplay. Heck, assuming it isn’t one of the stupid breeds, your dog has an excellent chance of successfully constructing this preamp. Not only is the assembly manual complete, but it also includes lots of safety tips at the beginning, along with post-construction resistance and voltage readings that you reference once your wiring is complete.

How’s it look? Not bad, not bad at all. It is a compact design with all circuitry built on a pre-cut 11" x 7" sheet of brushed aluminum. You have the option of spraying the aluminum with a clear finish for that natural look, or you can be like me and finish it with primer and a couple nice coats of flat black spray paint. I also finished the base with black wood stain and a satin clear urethane – I think it looks absolutely cool. It’s retro and high-tech at the same time.

Features? No, not really, but it does have all you really need for a preamp – volume (individual left/right controls) and input switching (three selectable inputs). Forget the highly sought after remote control – you couch potatoes will have to burn a few calories and walk to the preamp to change volume. Besides, this isn’t a remote control kind of preamp. It’s meant to be hands-on in every respect.

The Foreplay uses the ubiquitous 12AU7 preamp tube – nothing fancy, nothing exotic. While I would rather build a preamp around either of the 12AU7’s cousins, the 6SN7 or the 76, those aren’t the tubes that Doc chose for this design, preferring instead to ensure that the tube was readily available and easy to work with. As part of the tweaking process, I’ve experimented with a bunch of different New Old Stock (NOS) brands/varieties of the 12AU7 (5963, 7316, 5814/A, etc.). The process of experimenting with all these different tubes is called "tube rolling", and it’s a hoot. Imagine being able to "tune" the sound of your system by simply changing tubes in your preamp – a tweaker’s dream for sure. Let’s just say that after lots of listening and switching, I’ve found a few 12AU7 type tubes that really kick tail, but of course I’m not at liberty to disclose those here lest you all go out and corner the market on my favorites.

But how does it sound?

This is where reviewers (I’ve been guilty of it myself) normally break into a blow-by-blow account of the superlative subjective sonic attributes of a piece of gear. To do this, they use multiple references to all their favorite songs that were playing when they had their life-changing aural experience. If you need that type of review right now, please dig out your latest WhatchamaAudio and check out what they have to say about the latest, greatest $3,600 "real world" preamp. I’m not going there.

What I am going to say is that I’ve had a bunch of different preamps, tube and solid state, through my system. To use a tired phrase (but the only one that I can think of right now), if you told me tomorrow that the Foreplay would be the only line-level preamp that I could use from now to eternity, I would not be the least bit upset. It’s that good, folks. They key is that this is an incredibly simple, pure design – short signal paths, point-to-point wiring, compact layout, direct coupling of the amplification stages, etc. If you subscribe to the general theory that simpler is better, you will appreciate the logic and beauty of the Foreplay’s design. Personally, I fall squarely into the "simpler is better" camp – it took me a while to get there, but that’s where I am now. After lots of experimenting, I believe that keeping things simple will almost invariably result in better sound.

Is this the best preamp available? Are you kidding? Is this the most sensible preamp available? Well, you could probably construct an argument to support that. For lots of people, it may very well be. My guess is that many of you, deep down, wish that you could go this direction, but are afraid to tell your audio buddies that you use a preamp that costs less than one meter of their favorite interconnect. I understand where you’re coming from, but hey, take a $99 chance and live on the edge.

Look, this isn’t an article about high-end audio’s ultimate preamp. It’s about the fun of getting your hands dirty and building a preamp that just happens to have a shockingly low price and an equally silly high level of performance. It’s about the satisfaction of DIY audio and listening to something you built yourself. Is this the last preamp I will ever build or own? That’s highly unlikely. In fact, the success of this project will surely lead me to try constructing other designs. To sum up, however, I could not be happier with the Foreplay preamp and how my project turned out. It was, as I’ve said before, lots of fun. Isn’t that what this hobby is supposed to be about?

- Paul Knutson -

Note: Watch future issues of Secrets of Home Theater and High Fidelity for our on-line Tube Preamplfier Project. We will do a series of articles that chronologically document (with photos!) the construction of a transformer-coupled, line-level preamp using a medium-mu triode output tube. This preamp will be a state-of-the-art, very high performance design, yet still be simple to build as you follow along with our project. This is going to be an exciting project for all of you who want to push the envelope in DIY tube audio. Stay tuned!

Upgrade Your $99 Tube Preamp Kit

So, I'm assuming (fingers tightly crossed) that you followed my advice and took your best shot at building the Foreplay preamp. If you did, I'll bet it was a successful project and that you're already grooving to the wonderful sound of tubes -- maybe even as you read this. Heck, there are likely some brave souls out there that have already tinkered around with the parts in the preamp to see what improvements can be rendered by tweaking an already rock-solid circuit design. If so, congratulations! You have the first symptoms of audio DIY disease and it's among the most pleasant of all afflictions.

As pleased as you already are with the sound of the basic Foreplay, you are likely curious about the upgrade kit for the Foreplay, not unexpectedly named Anticipation, that Doc Bottlehead advertises at his website. "If Electronic Tonalities can do this for $99, what would happen with another $75 investment?" you wonder. Well, wonder no more … read on and find out.

What is Anticipation?

Simply put, Anticipation is a major performance upgrade for the Foreplay kit preamp. It goes well beyond the typical tweaking of passive parts into the realm where the operating characteristics of the circuit are changed in a big way. Upgrade BoardsThe cost of Anticipation, in kit form, is $75 and includes everything you need save a couple feet of hook-up wire. You are free to use your wire du jour for this project, but make sure it's small gauge -- I recommend 20-26 gauge solid core wire. Inside Foreplay there are places where many wires meet at common junctions, such as the ground. Installing Anticipation only makes these connections more crowded so don't overdo it with 14-gauge multi-strand or anything silly like that.

The circuit technology behind the Anticipation upgrade is based on something called C4S, which is short for Camille Cascode Constant Current Source. John "Buddha" Camille is the person responsible for the design of the C4S concepts applied to Anticipation. Buddha and Doc Bottlehead are buddies. Between them, they come up with some wickedly effective ways to jointly-implement their ideas.

I'm not going to confuse beginners or insult experts by trying to explain exactly how the Anticipation upgrade and C4S work. That would be folly. To be honest, I don't really understand it myself, but I'm trying darn hard to learn. To summarize, by replacing four fixed-value resistors in the circuit (plate load and cathode loading) with what are known as Active Loads, (which are a variety of resistors, transistors and diodes mounted and soldered onto a mini circuit board), you greatly increase power supply isolation and linearity. The end result is a tube (and preamp, for that matter) that is operating more optimally and happier doing its job.

The obvious goal of the Anticipation upgrade is better circuit performance, and thereby better sound, from your Foreplay preamp. Is it successful? I'm sure you can guess the answer already, but play along for a moment while I talk briefly about the installation of Anticipation, after which I'll move quickly to the punch line.

Installing Anticipation

There's no need to do a step-by-step instruction of how to install Anticipation -- Doc B. does a great job of that as usual with the Anticipation Installation Guide. I'll limit my thoughts to a few basic observations.Installed Boards

If you've already done it, you will agree that building the Foreplay was really very simple. This presumes that you first practiced your soldering and that you also had the patience to followed the clear directions closely.

Installing the Anticipation upgrade was slightly more difficult than building the Foreplay, in my opinion. Remember, I am virtually still a novice (maybe intermediate) so if you are an experienced solder slinger my opinion of difficulty should be taken with a grain of salt. The premise with Anticipation is to challenge the DIY builder just a little more than before as his/her skills develop and interest grows. Bottom line is that with care and patience the Anticipation installation is nothing to worry about.

As a brief aside, Doc and I have exchanged e-mails on the topic of whether to install Anticipation when you initially build the Foreplay, or whether like me you wait and do it at a later time, after you are accustom to the way the basic Foreplay sounds. Installing Anticipation during the initial build is simpler, but my strongest recommendation is that you wait to install it later. Only then will you fully appreciate the improvements. Believe me, it is worth installing later if only for the sheer joy of hearing a true, effective, major circuit upgrade for the first time. You will smile when you hear it, and smiling makes you feel good.

How Does Anticipation Sound?

In terms of whether the Anticipation upgrades the sound of the Foreplay, I guess I've let the cat out of the bag with the final two sentences of the previous paragraph. Yep, it sure does. Oh, so rarely in audio does an upgrade do as advertised, but this is one of those times. Too often an alleged "upgrade" by a major manufacturer will encompass some new hookup wire and a detachable powercord -- welcome to "Mark II" and thank you for the additional $800! Not here, guys and gals … this is the real deal.

For the $75 investment in Anticipation, plus your time and energy, you take the Foreplay preamp to new sonic territory. To my ears, in my system, the Anticipation upgrade resulted in the following improvements:

1. Improved definition and impact in the bass. This was the most noticeable improvement and addressed an area where the basic Foreplay has a slight weakness;

2. A greater sense of space and distinctness of individual instruments within that space;

3. More swing, heft and weight during crescendos of any kind. In all, it was a sense of the power amp delivering more power to the speakers. Obviously the power amp wasn't changed, but it sounded like it;

4. More gain, which I didn't need, but some of you may; and finally,

5. Sharper transients on percussive strikes of any kind.

I am not a huge classical music fan, but there are some emotionally stirring classical works out there that any music fan can appreciate, and until the Anticipation upgrade I wasn't quite satisfied with the way my system did that stuff. I am now. For all other types of music, I must say that I shake my booty and tap my feet just a little more now than ever before. These are excellent barometers if there ever were any.

Final caveat, though you can hear the improvement from Anticipation right away, give the Foreplay about 30-40 hours of use after installing Anticipation to allow it to break in. Save your critical listening until that point. Speaking from experience, you need to give it this much time and you will be glad you did.


The Anticipation upgrade is a winner! It wins by not only being effective for the measly asking price, but it also wins on absolute sonic terms as well, irrespective of price.

I dare you, no, make that double-dare you, to build the Foreplay, add the Anticipation upgrade when appropriate, then take that baby to your next local audio club meeting. Don't tell anyone about it first, just play it. E-mail me and let me know the reactions you get when you finally tell the numerous dumbfounded that 1) you built it yourself, and that 2) it cost less than $200, all in. I need a good chuckle to brighten my day now and then.

Doc Bottlehead and the folks at Electronic Tonalities have been busy as heck over the past number of months -- they've released a parallel feed version of their 2A3 amp kit, a 300B amp kit, an interconnect kit and a host of other goodies and do-dads for the hardcore, and beginner, audio constructor. More products and projects are in the works.

These are pretty exciting times if you are into this sort of stuff, which I most certainly am. Who knows, there may even be other upgrades for the Foreplay available in the future. If so, I'll be in line to get my hands on 'em and tell you all about it. In the meantime, I've got some music to listen to.

Yep, I built it myself (grin).

- Paul Knutson -

Foreplay Update - Crtitical Review of Capacitor Upgrades, Tube Changes, and Speaker Effects (Lowther vs. NHT) - August, 2000

by Tom McDonald

Author Background

Without being an electronics designer, I had no problem building the Foreplay Kit other than burning up my cheap soldering iron. See the Foreplay “Specs” download for more information about my first experiences with this preamp at: I suggest assembling the kit slowly and double checking everything.

My background is in film and video production. While some audiophiles only listen to find perfection, sometimes less than perfection can be useful to me if it creates a new sound signature that enhances the media experience by producing a unique emotional tone. So I am interested in the unique sound signatures of different electronic parts.

What follows are descriptions of the different sound signatures for capacitor and tube substitutions in the Foreplay Preamp which has the Anticipation modification installed. Comments are also made about how two different speakers affected the listening experience.

Listening Material

My test music was the Sade Love Deluxe album's "No Ordinary Love" and "Cherish The Day". Also used was the Bonnie Raitt Luck of the Draw album's "I Can't Make You Love Me". These tunes include female vocals and much bass instrumentation with a soundstage that was probably created artificially by a mixing console.

For acoustic instrument sounds a jazz instrumental was auditioned, "Children's World" by Maceo Parker. It featured saxophone, bass, and drums. I don't know the recording conditions, whether live (in front of an audience) or studio.

Sound Equipment

Sound equipment was an Apple 9600 computer CD player and the Foreplay-Anticipation preamp with shunt pots. The amp was the Doctor B modified Zen SV83 (about 2.25 watts). The Zen's Svetlana SV83 output tubes ($4 each and similar to EL84s which can substitute with some modification) I call “candles” since they look like short little candles rather than like a big output tube.  Check out Svetlana tubes The Zen has an Anticipation upgrade, and I added shunt pot resistors to the volume control pot.

A "shunt pot" is a technique which places a resistor in parallel with the volume pot. This resistor is a higher quality sonic path than an inexpensive volume pot. Since part of the signal goes  through this high quality resistor directly into the preamp, that part of the signal will be higher quality and upgrade the overall sound quality of the preamp. Thus, when using an inexpensive volume pot, some of the sonic noise from the inexpensive volume pot materials is bypassed. Purist designers who concentrate on producing only the simplest circuits that use only the highest quality components probably won’t like this technique, which might be said to confuse the sound path. But the technique is a reasonable low budget modification that should normally provide a little sonic improvement without adding significant noise.

Speakers were 86 dB efficient NHT (Now Hear This) Super Zeros ($230 per pair) pictured in black. A Cambridge Soundworks powered subwoofer was used with the Super Zero speakers since they only go down to about 100 Hz.

The Super Zero speakers include the most excellent North Creek crossover modification kit ($85) found at:

See the Foreplay “Specs” download at: for comment on the crossover kit.

Find Super Zeros at:

Also used were 97 dB efficient British made Lowther speaker drivers type PM2C mounted in bass reflex cabinets constructed by David Dicks ($1,300 combined cost). The driver is pictured (below, right) with the white cone. Lowther drivers are accused of having no bass, but with the David Dicks bass reflex cabinets, they do have bass, though it is rolled off by about 6 dB below 100 Hz. Lowthers are said to be driveable on 2 or 3 watts, but you will need 7 watts or more to hear all the bass that these cabinets are capable of and no more than 30 watts are needed with a good amplifier.

I am told that Lowther drivers have a 10 dB peak in the 2 kHz to 10 kHz frequency range. This peak was great to compensate for older designed tube amps that attenuated high frequencies (due to poor transformers etc.) but not great for most modern designs that lack the problem. A fix for this peak is given later. Also, Lowthers don't have the best soundstage since the high frequencies "beam" in a narrow pattern off the fan shaped inner mounted whizzer cone. So why use them?

I use Lowthers because they display almost any change made in sound equipment due to their special design characteristics. Lowthers have such a large magnet that only 1 millimeter (0.03937 of an inch or about 1/25 of an inch) of driver travel produces a nominal 97dB. Other drivers have a 13mm (1/2”) to 39mm (1 1/2”) driver travel. So clearly Lowther had something else in mind when they decided to use the most powerful magnets in the industry, at 17,000 gauss plus, with only 1mm of travel!

Designed as a single full range driver, Lowthers require no crossover though I would suggest using one (see below). Thus, some Lowther owners use no capacitors or inductors that would otherwise affect sound purity. I experimented by placing an inductor in line with the Lowther driver. The effect was to create a false sense of spaciousness, a spaciousness created by the “sound” of the inductor and not by the source musical signal. I now recognize this fake soundstage characteristic in most commercial speakers that I audition. It isn’t really a bad sound, just a sort of unmistakable sonic signature that makes it sound like the music was created in an acoustic space that had walls and thus has a significant reflective component. It's due in part to phase shift caused by the inductor (or capacitor).

Phase relationships are potentially better preserved with a single driver producing all the sound motion. Lowther drivers do create a soundstage though of lesser size than that of other great speakers.

If a parallel notch filter is added to remove the 2 kHz - 10 kHz frequency peak, then the driver’s sound staging is better, though the sound is then colored by the capacitors, inductors, and resistors used in the filter network. See "The Loud Speaker Design Cookbook 5th edition" page 120 & 121, section 7.70 "Response Shaping Circuitry" for design information on parallel notch circuits. I would like to thank James Carol, speaker designer, from Knoxville, Tennessee for helping me build my first parallel notch filter. Cutting this peak adds needed flattening to the speaker frequency response curve and gives a few inches greater width to the "sweet spot" where the speakers provide center image. For my ears, using some form of filter to cut this peak is necessary for long term Lowther listening enjoyment. With the filter added, I feel like I'm listening to a pair of $2,100-plus purpose built high-end speakers, though I only paid $1,300 for them.

Last, but maybe most importantly, Lowther drivers are "fast". After you've heard a snare drum through the Lowthers, you will be hooked. For probably the first time, you will hear the individual drum stick beats that were slurred by other speakers, though you didn’t realize it. There is an old saying from Formula One racing, "The motor is as fast as the bee's knees." If you want to hear the speed of the bee's knees, then you'll probably have to try Lowther full range cone drivers or a great set of horn speakers. Hearing Lowthers for the first time is a new experience for most people, since they have properties of both cone and horn speakers.

To be fair, this version of a Lowther speaker, with its single driver surrounded by a bass reflex box that gives out its bass 6 dB or so below the level of the the mid and upper frequencies, best plays the music of small jazz groups and individual vocals. Any single driver-based speaker has a limited amount of magnet-to-voice-coil-area in which to transfer the signal's complexity. Rock and orchestra music with their tremendous complexity of signal and significant bass seem to demand more than a single driver can re-create. But for hearing music that emphasizes the tone color and speed of a few individual instruments and/or vocals the Lowthers give a tremendous amount of intimate detail.

Find the David Dicks Lowthers at:

Find Lowther manufacturing at:

Find Lowther America at:

Capacitor Substitutions

The Foreplay Preamp produces beautiful sound with my modified NHT Super Zero speakers. Although this is a budget system, it reproduced the most important sonic elements that can be found in even multi-thousand dollar high-end audio systems. But, on the ruthlessly revealing Lowthers, the stock Foreplay output capacitors sounded dry with a narrowed sound stage. The output capacitors are directly in the sound path, so they are the most important capacitors in the circuit as far as sound quality is concerned.

So, I replaced the stock (green colored) 2.0 µF 200 volt metallized polyester capacitors with Solen (black colored) brand French-made 2.0 µF 400 volt polypropylene capacitors. When buying capacitors, a higher voltage rating than the stock capacitors  is okay, a lower rating is not.

This is an easy modification that anyone can do. Buy two non-polarized capacitors. Desolder the capacitor lead connected to each of the preamp’s RCA output plugs. Desolder only one end of the connected capacitor lead at a time so that you don't forget where the other end is attached! Solder the new capacitor’s lead to the RCA plug for each channel. If you forget where to connect the capacitor, just look at the Foreplay schematic or step-by-step instructions. Due to their flexible lightweight leads, the Hoveland (yellow) capacitors, spoken of later in this article, need a mounting system of heavy double sided tape or a physical mount as shown in the picture. I had allowed them to “hang loose” previously, only to find later that they had broken loose at the RCA plug solder joint.

Please see the pictures of the stock Foreplay (first part of this article, by Paul Knutson), as well as the picture of a Foreplay with Anticipation upgrade and Hoveland yellow capacitors (photo below, right).

Lowther listening showed that, with the Solen caps, the analytical dry nature of the metallized polyester capacitors was gone. The physically larger Solen metallized polypropylene capacitor material gave much greater richness on vocals. Bass depth and volume were vastly improved. Sound stage was also significantly increased in width and depth. Not bad for just changing 1 dollar capacitors to 3 dollar ones.

With a less accurate speaker like the NHT Super Zeros, the dryness condition caused by the stock capacitors hardly showed up at all. I rather liked the "dark" sound of the stock capacitors on the NHTs. By limiting some of the lower power level high frequency information, they gave the sound a mystic quality of "dark black" quietness with music that protruded out of that darkness.

So is it worth the trouble to change to Solen capacitors when using speakers less advanced than the Lowther speakers? Yes, very much so. The NHTs were quite able to give greater satisfaction, including a larger sound stage, from the capacitor change. The Super Zeros just don't reveal the full effect of the component change as do the Lowthers.

Now back to the Solen sound effect. The Solens give midrange and highs with a silky smoothness and detail similar to the most expensive sound systems that I've heard, and they resolve mixing effects better. For example, in much alternative rock, the vocal gets lost as it mixes in with the guitar. But, with the Solens, the vocal separates just enough from the guitar chords that the words become intelligible, yet without losing the creative effect of having the vocals and guitar sonically in the same space. And the Solens gave some nearly free ($) bass, apparently about 6 to 9 dB more power. This  makes sense because the Solen's physically larger capacitor body passes more low frequency power and current.

The sensual beauty of Sade's voice on the album Love Deluxe with the cut "No Ordinary Love" is reproduced excellently with Solens. The bass and female vocal on this particular song is one of the best test audition tracks that I've found for a studio type sound mix. The bass guitar sound at the beginning is hauntingly deep. The vocal is smooth. The rest of the album is also excellent (a rare great album).

The Solens are really inexpensive at about $3 each, yet they give the sense of a $100 upgrade. The swap out of the stock capacitors for the Solen capacitors is probably the most important thing I've ever done for my system short of buying a brand new piece of equipment.

Next, I tried American made Hoveland MusiCap (yellow colored) 2.0 µF 400 volt polypropylene film and conductive foil capacitors at $22 each. This may sound impossible after reading all the positive statements about the Solens, but yes the Hovelands are better and by a great margin. While everyone remarks that treble loses its harshness when a quality capacitor is used, with the Hovelands inserted, the bass immediately improved also. When the electric bass player on Bonnie Raitt's "I Can't Make You Love Me" pulled the string, I could practically see his fingers move. With the Solens inserted, the bass notes seemed to quit early rather than naturally decrease in volume. The feeling received from the Hovelands is that the bass note attack and decay is “rolling” and sustaining so naturally that you think you're hearing a private performance from a live band in your room.

With Marceo Parker's "Children's World", the acoustic decay,  the "roundness" of the instrument such as the bass guitar, and the accuracy of the rhythmic speed, increased as each successively better capacitor was installed. With the Hovelands installed, a Bottlehead forum regular and Dixie Bottlehead principle remarked that the Foreplay-Anticipation would be excellent competition for many commercially available preamps priced at $4,000.

Comparison of the Three Sounds

To compare the three different capacitor sounds, the stock capacitors give the sense of a dramatic live “driving” band playing in front of me in a room with okay acoustics. The Solen capacitors give the sense of a live band playing in front of me in a room with good acoustics with band members playing great quality instruments. The Hoveland capacitors give the tone quality of even better instruments, in a room with nearly perfect acoustics, and the sense that I am fortunate enough to be sitting in exactly the most acoustically perfect position in that room and am experiencing no off-the-wall-reflection based frequency cancellations!

Capacitor Materials

It has been my experience that the material used to build a capacitor affects the sound according to that material’s natural sound dampening characteristics. This was especially noticeable when I took a trip to a famous high-performance speaker manufacturer who used a multi-order crossover network (thus passing the signal through many different capacitors). They used polypropylene capacitors which gave percussion instruments the distinct sonic character as if they were being hit against a plastic pail. High-frequencies seemed to die away as though they were being reflected off a soft plastic wall.

To summarize the capacitors and their “material sounds” that I’ve heard: Physically, much polyester fabric seems scratchy when you run your hand over it, and the sound of polyester capacitors on a highly revealing system can sound harsh or etched, as if the high frequencies are being scratched across cloth. Polypropylene (a plastic material) capacitors give a sound damping somewhat like what can be heard by rapping your knuckles against a polypropylene water pail. Audio Note paper-in-oil capacitors are made of a material that one would think of as a gooey slippery soft combination, and the sound out of these capacitors tends to be distinctly laid back (slower attack envelope, lower slew rate) and softer, yet with a great smooth sense of beauty. Hoveland capacitors use a polypropylene film and conductive foil combination that comes somewhere in between the others in physical properties, and also has arguably the best combination of sound qualities. I would sell shares of may favorite stock to buy them.

Tube Substitution

You will have to install the Solen capacitors, or better, to fully judge the sound signature of different tubes in the preamp stage. When swapping tubes: 1) Turn the preamp off before removing or inserting tubes; 2) Use a thick cloth to cover the tube to avoid being burned; 3) Grasp the tube near its base, then pull the tube out slowly, rocking it only a little to loosen it as needed; and 4) Replace a tube by first  positioning each tube pin in the correct pin hole, and only after your eyes have seen that each pin is pressed into a pin hole, begin pressing straight downward while rocking the tube the minimum necessary (the tube may need no rocking) until the tube bottoms out on the socket.

I swapped the stock Foreplay Sylvania 12AU7A tubes for RCA 5963 NOS (New Old Stock) tubes ($6 each).  My 5963 RCA tube source was Robert Silk of Silk Electronics at (801) 583-6616 in Salt Lake City, Utah. Robert will give you his opinion over the phone, which is quite a useful service to those of us who experiment.

My first sound notes for the 5963 were, "There is a new clarity, more micro and macro dynamics. Where instruments before were mixed in together, they are now separate. Quiet surrounds instruments rather than noise". But as time passed, my notes changed to, "The 5963s cut some of the “air” around instruments, thus the sound is a little darker. They seem to suppress some miscellaneous phase shifting confusion, thus making instrument positions more stable. They seem to eliminate some noise, they sound cleaner, and this cleanup effect also brings out a sense of rhythmic drive".

Ultimately I realized that there had been a loss of detail which made the tube seem cleaner and thus "better" for a while. So it goes when a component change is made, what at first sounds better may later reveal itself as just different or even a worse sound. In this case, both capacitor and tube changes made the little Foreplay Preamp a real joy to listen to.

- Tom McDonald -

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Secrets "Cave"