Shop Talk



JE Labs test bench

From right to left: Genrad W5MT3A Variac, Tektronix 2205 20MHZ dual trace scope, Weller WTCPS soldering station, second shelf - right to left: Heathkit IM21 ACVTVM, Leader LAG27 sine/square wave audio generator, Eico 260 AC/VTVM. Hand held DVMs - Fluke 8060A true RMS, Testmate LCR 195 capacitance/inductance meter and Fluke 75 DMM



SHOPTALK




In retrospect

My first exposure to high fidelity equipment was at The Juilliard School. I entered the pre-college division n the late 70s and the record library/listening room was equipped with at least a dozen Thorens TD150AB, with Shure M7D, Shure phono preamp/headphone amp driving huge Koss headphones as well as a couple of Tandberg reel to reel tape decks for archive tapes while the classrooms had TD124, Shure M3D, Dynaco SCA35 integrated amp driving AR2A speakers. I spent a lot of free time listening to my favorite recordings which was a crucial part of my musical development aside from practicing and attending concerts at Lincoln Center, Carnegie Hall and other venues in the city.

I was an undergraduate by the early 80s had an apartment and some spare change to assemble my first stereo system which consisted of an original AR turntable with a Grado GTE+1 hooked to a NAD 3020 driving DIY speakers with components from Radio Shack. While the school upgraded their vintage equipment to Denon direct drive turntables, CD players, integrated amps and Sennheiser headphones, I removed the jumper wires from the 3020 to drive a Dyna ST35. One day while taking a break from practicing I read an article in Fanfare magazine written by Robert Fulton, "Prerequisites for Capturing the Musical Experience" and his description of directly heated triodes left an indelible impression. My financial status improved in graduate school with a better scholarship grant and concert opportunities that afforded me to purchase used high end gear - conrad johnson PV2Ar preamp, Berning EA230 amp driving Magnepan SMGa speakers. With my DIY nature I purchased most available Merrill mods for the AR turntable, SOTA mat/clamp and a Sumiko FT-3 arm with a Grado Signature 8MX. The Berning EA230 was a 30wpc triode amp using 6JN6 TV triodes driving surplus Scott output transformers and a Williamson derived octal driver tubes (6SN7). On hindsight it was a good sounding amplifier but not the directly heated triodes discussed by Fulton. It was powerful enough to drive Magnepan SMGas in my tiny NY apartment. But as I got to know these speakers it became apparent that despite the lack of cabinet colorations the midrange was veiled and the low sensitivty limited dynamics. As an experiment I bridged my back up Dyna ST70 and another ST70 from a friend to drive the SMGas and the improvement with 70W of EL34 pentode per side was not significant. This system sounded fine playing audiophile recordings but it was not at all satisfying when listening to recordings that have meritorious performance. The SMGa was replaced by Rogers LS3/5a, the cj and Berning were also giving me problems and after one trip to the factory and an expensive repair bill, I unloaded them to cut my losses and reverted to my back up Dyna electronics - PAS/ST70/ST35. I stopped subscribing to Stereophile and TAS after the Walt Bender and Steven Stone articles on "olden goldies" and spent my spare time at the Rodgers and Hammerstein Archives of recorded sound on the top floor of the Lincoln Center Library which has an extensive collection of audio periodicals. This is where I found early tube/DIY publications The Audio Amateur and Audio Update by Audio Dimensions of San Diego, CA which also published Tu-be or not Tu-be.

While my audio buddies where raving about their latest recommended components, I was studying schematics and collecting classic tube equipment from Acro, Dyna, Eico, H-K Citation, Heath, Lafayette, Paragon, Pilot and etc. no Marantz or McIntosh, those were expensive even then. I frequented what was left of Radio Row around Cortlandt street and Canal street for parts and tubes. I must have done every PAS modification published in that era as well as grafting classic input driver/phase inverter circuit onto my ST70 test mule. I kept a Paragon E-1 preamp in stock form as a reference for my PAS hacking experiements because the cascoded 12AX7 front end had a 3 dimensional midrange I never quite achieved until I reverted to using octal based 5691s/6SL7s for phono. By the late 80s I was happy with a much modified PAS preamp powered by a Heathkit tube regulated power supply, a pair of Dyna MKIVs with GSI input boards and EL34s strapped in triode or an upgraded Eico HF87 also strapped in triode driving LS3/5As. The AR/Merrill front end stayed constant since it was not put to shame compared to a Linn LP12 Valhalla Ittok combo. My back-up turntable then was a TD124 which I found for $1 at an antique auction, it had an Ortofon SMG 212 which I foolishly sold for a song and replaced with a Sumiko MMT arm. Deep inside I knew it sounded better than the AR/Merrill but I was in denial since it had no audiophile credibility. I also owned Quad ESL 57s which I found to sound best driven by classic PP EL84 amps I had in my "prized" collection then - Acro 20/20, Dyna ST35, Leak 20 and Pilot SA232, but I gave up the ESLs due to panel reliability and rectifier block issues.

The early 90s was a turning point, I became a customer and friend of Steve at Angela Instruments. Eventually I started working part time in the shop servicing countless classic tube equipment and Audio Note, UK kits. I attended hamfests and radio shows, met Joe Roberts and instantly became a supporter of the then fledgling Sound Practices magazine. 



My first DHT amp was a PP2A3 with a Mullard type input/driver circuit utilizing 6SL7s and 6SN7s, Peerless 16309 OPTs 7W of pure Class A driving Spendor LS3/5a, it didn't go loud but it was so much more transparent than any of my previous efforts. As I go through the mid 90s, I disposed my classic tube amp collection, LS3/5A, AR/Merrill and other vestiges of high-end gear to finance acquisition of Tango and Tamura iron, parts, idler turntables, vintage Altec drivers and wrote a Homebrewer article for SP17. Sadly the presence of Joe Roberts and Sound Practices is no longer to be found in cyberspace. It was an idealistic venture that was destined to remain underground yet had a significant impact on how we view the audio hobby these days.



Tube basics and books

A tutorial or basics chapter in these pages is beyond the scope of my abilities since I developed my skills during pre-internet days almost empirically - through trial and error with the help of reading books, schematics and talking with old timers. A google search will yield websites that will address these concerns. But I recommend to every potential DIYer to acquire a copy of the RCA tube manual and read through the first few pages to get a basic idea of how a vacuum tube operates and read schematics. Another much overlooked book of great basic resource is the Radiotron 3rd edition which contains comprehensive information for anyone who wants to dabble with single ended and push-pull triode amplification as well as preamplifier circuits and power supplies without having to deal with the complex mathematical equations and in-depth discussion of theory found in the 4th edition.

DIY magazines

Since the demise of Sound Practices the only DIY oriented magazine published in the USA is Audio Xpress, occasionally they have articles of interest to Single Ended Triode amp and High Efficiency speaker enthusiasts. Vacuum Tube Valley also went with the tragic loss of Charlie Kittleson. Japanese publications like MJ Audio Technology and Stereo Sound Tube Kingdom quarterly are great. Even without much knowledge of the Japanese language I am able to get ideas by looking at the high quality schematics and illustrations. They are expensive and I only pick up or order an occassional copy at KinokuniyaBookstore in NYC. The Sound Practices Magazine Archive CD is a must have. This is the official CD edition and beware of bootlegs.



DIY Tips

Design Philosophy

As much as possible I do not like making rules for myself since it limits my ability to explore new ideas. However in the projects below you will notice that I do not use negative feedback in my electronics because I have not found a design that employed any form of global negative feedback that sounded good to my ears. Some people swear by cathode followers others swear at it. I take the middle road on this particular topic because I found the addition of a cathode follower at the output of a line stage to be sonically beneficial in some cases but not at the output of my phono stage. My non technical explanation as to why a cathode follower does not sound good at the phono output is because the signal is still below 1 volt and the cathode follower being a 100% regenerative form of local feedback affects the purity of the signal. I only use a cathode follower in this position in severe cases like driving a sound card to transfer LPs to CD-R. For critical listening I do not use it.
With speaker crossovers I also take simpler is better approach and have yet to find a better sounding design than a simple 1st order 6dB/octave with L-pad attenuation to match sensitivity between drivers.

Chassis layout

This is very basic and if you look at the various pictures of preamps and amps in these pages you will notice that I place the power supply as far as possible from the audio circuit in power amps and use a separate chassis for the power supply in preamps. With regular unpotted iron, I orient the core of adjacent iron [chokes, power and filament transformers] so that the laminations "cross" each other. According to the Radiotron Designers' Handbook this prevents magnetic induction. Some people claim that they do not hear improvement in reduced noise or hum nonetheless it is good engineering practice.

Operating points

FAQ: the bulk of inquiry I get regarding amp projects is power transformer substitution especially from newbies. Please note that adapting another power transformer may involve a redesign. I learned the hard way....

I was so impressed with Herb Reichert's Flesh and Blood amp playing in a friend's system that I decided to build a clone. But I did not have the power transformer Herb specified and was disappointed with the sonic result I got from my copy. This is how I discovered the utmost importance of keeping the operating points in creating the sonic signature of an amp since the power transformer and power supply design comprise the heart of a tube circuit.

All the projects listed below use readily available power transformers. Please make sure you follow the circuit diagram and especially if you are a newbie, stick to the power transformer specified in the schematics to insure that you are hearing a JE Labs circuit. If you do not follow my operating points, it is no longer my design.

Signal path

Nowadays I only use paper in oil - Jensen, Sequa, Vitamin Q and Russian K40Y/K42Y - or equivalent capacitors for signal coupling and carbon composition [Allen Bradley or Riken] for plate, cathode and grid loading. I use of cement or wirewound [preferrably non-inductive] resistors for output tube cathode bias. These materials do not have the zippiness inherent in plastic [polypropylene, polystyrene, mylar and etc] type caps or grit I find in metal film/oxide resistors. The cheap Asian OEM carbon film resistors available from Parts Express are good too since Allen Bradleys are hard to find in bulk and Rikens tend to be expensive. Try to buy in reasonaly quantities so that you can match to as close tolerance as possible. It is also worthwhile over rating carbon resistors to make them more stable. Using these type of parts is just second to operating points towards achieving the sound I am searching for.

Cathode bypass

I can justify the use of Black Gate or Cerafine in this position, however if you can no longer find or afford them, Sprague "Atoms" are good replacements at a fraction of the price.

Power supply caps and dropping resistors

Paper in oil 'can type' are ideal but normally not very practical due to chassis space so I use decent electrolytics from Sprague 'Atoms', Cerafine, LCR and even the OEM cans that Angela Instruments and Parts Express sell for reasonable cost. Inductive cement or wirewound resistors are at their best in power supply application because the additional inductance help smoothen AC ripple.

Wire

I use Kimber TCSS bought in bulk because of the high purity copper and insulation which does not melt easily when soldering. In my more deluxe application I even tried Kimber AGSS [silver] but found that 19 gauge 99.99% solid silver covered with teflon tubing to do just as well. I don't practice any religion with wires, cables and interconnects so any good quality insulated conductor of appropriate gauge should do the job. There is nothing wrong with NOS cloth covered wire as long as the conductors are not corroded.

Boutique parts, tube rolling and etc.

I have received numerous emails inquiring about, what is best? The bottom line is, there is no such thing as "the best". A good sounding system is the sum of all its parts working together by reinforcing and negating its own strengths and weaknesses. Using tantalum resistors, silver foil caps, controlled substance wire, power supplies weighing a ton and exotic metal alloy output transformers will not guarantee musical satisfaction, synergy between components in a well designed circuit is the vital issue in assembling a musically rewarding audio system.

My recommended parts are in no way an endorsement of the best they just sound good to my ears, that's why I use them. It would be fair for others to disagree, but why should we indulge in an endless debate if the ultimate goal is to enjoy music?

Same thing with tubes, I've built and experimented with several circuits through the years and you will find in these pages that I favor Art Deco era 5-pin triodes - 227, 27, 56, 37 and 76s; octals - 6SL7/5691 and 6SN7s; and directly heated flea power triodes - 300B down to 71As. These are tubes that were specifically designed for audio amplification. There are slight sonic diffrences between, e.g. - 6SN7s but proclaiming which type is best is an exercise in futility, my preferred driver and preamp tube types are listed in each project, so if you substitute a flavor of the month tube that I did not endorse and disappointed with the sound, you know why....

Once you indulge in DIY you will hear that circuitry and operating points make more of a difference than the latest tweak in fashion. Collect your favorite sounding tubes and build around their virtues.

Have fun and happy listening!

Comments

  1. I saw a mention about the Paragon System-E preamp with the separate P.S. unit. I'm trying to fix that P.S. unit, but can't find schematics ANYWHERE as 250 units were only sold. It sounds great, but not now that there's a P.S. problem. Do you have access to that schematic or can offer any suggestions on my quest? Thank you for your time,
    Mark :)

    ReplyDelete
    Replies
    1. Hi Mark,

      It has been years since I handled the Paragon E but if memory serves me right the PS was a straight forward design using solid state rectifiers in a bridge configuration + computer grade caps down stream decoupled by resistors...very typical 70s-80s design. Sorry I do not have a schematic available but it is quite easy to figure out.

      JE

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