2A3 Firecracker

GOLDEN VOICE 2A3C

Given the unusual times we now live in and the Chinese New Year celebrated just a couple of days ago, I think this is a fitting upload because according to legend, firecrackers are used to chase away evil spirits!😉

About a year ago, I ordered a matched pair of Golden Voice 2A3Cs from AliExpress priced a little below $100, shipped. Within two weeks of receipt, one tube started arcing. I sent the above TV7 test video to the seller.

JE Labs Mono HiFi 2024

Over two decades ago, I ventured into single channel music reproduction to trace the roots of high fidelity. From that whole experience, I developed an aesthetic quest for a certain purity and honesty in sound, which runs parallel with my other hobby of black and white film photography! Sadly, I had to leave that particular mono set up in the attic in 2017.

A Visit to VAS Audio - SPU-G, Miyabi & Ikeda

 

During a recent visit to Steve and Ray at VAS Audio, my attention was caught by an amplifier I built in the early 2000s. This is one of the very few I released into the wild.

SE171A Amp Remastered

My dad would've turned 97 today. To celebrate his birthday, the video clip above features a recording of his favorite violinist, Nathan Milstein, playing Presto from Bach's Sonata No. 1 in G minor for unaccompanied violin. While he was doing post-graduate studies at The Juilliard School in the mid 50s, he was fortunate to have attended concerts of the great violin virtuosos of that era - Jascha Heifetz, David Oistrakh, Nathan Milstein, etc.

He would later recount that Nathan Milstein's performance of the Glazunov violin concerto was the most unforgettable! Even if he never got a chance to add this violin concerto to his repertoire, he conducted the Manila Chamber Orchestra with me playing the Glazunov violin concerto in 1987. The music of the slide clip above is the middle movement from our performance.

Before I bore everyone reminiscing about my dad and our life as musicians, let's get on with the subject at hand. The amp featured in this upload uses a directly heated triode power tube that was introduced around the time my dad was born.

JE Labs Choke-Capacitance Coupled SE2A3 amp

Canon P + Canon 50mm f1.8 LTM 
Foma 100 in Rodinal

Inspired by my plate choke-loaded 76 line stage preamp adventures, I was curious how a similar driver circuit configuration would sound in an SE2A3 amp. So I pulled out my Radiotron Designer's Handbook, 3rd Edition to gain a better understanding of choke-capacitance coupling (aka plate choke loading) vis-à-vis resistance coupling.

Below are highlights of relevant information I gathered.

Bonsai X'mas Tree + Amp

Looking back to 2022

January: Begin the Beguine + A Cousin's Listening Room: Garrard 301, Ortofon RMG309i/SPU Synergy/AB309/SPUmono, JE Labs preamp/amp, Hashimoto transformers & Altec 753C

February: Sony PS1 & Magnavox/Philips NOS TDA1543 mods

March: emails from Ukraine, was Radiotron SE2A3 + Analog LP playback & Film Photography

April: Altec mini 757 =  756B/32C/806/23744 + MC SUT Redux = Hashimoto HM7

May: Snell Type JIII Part 2 + Kutztown Spring Radio Show

June: Fidelity Research FR64fx dead channel fix + Hub City Vinyl

July: SRPP SE2A3 Redux + Factory Records Dover NJ

August: OJAS @ Lisson Gallery NYC

September: Pioneer PL6U Idler Turntable + Realistic 42-2109 phono preamp upgrade

October: Kutztown Fall Radio Show + VAS Audio - SPU-GME MKIII, Supex SD900 MkIV, Stax UA3NL & Tokyo Sound ST900

November: Hifi Show in Manila + Snell Type JIII - Finale

 December: Tube Shields for the Loctal Preamp + Bonsai X'mas Tree & Amp

To celebrate the holiday season I've prepared a short video. Please note that given the dynamic compression and bandwidth limitations imposed on sound quality by YouTube, I upload videos for the visual aspect rather than their sonic merits.😊

Turntable: Garrard 301

Tonearm: SME 3012 

Phono cartridge: Supex SD900 + conical stylus 

MC step up: Altec 4722 

Preamp: JE Labs octal + 76 

Bonsai Amp: 720mW per channel SE 171A, coming soon! 

Speakers: Altec 753C

So watch how the 720 milliwatts per channel Bonsai Amp is pushed to soft clipping by Tchaikovsky's "Pas de Deux" from "Nutcracker" driving the Altec 753Cs. 😉

Thank you to all my readers and supporters!

🎄🎄🎄Wishing everyone happy holidays and a great new year!🎄🎄🎄

SRPP SE2A3 Circuit Redux

Back in the late 90s, I dismissed the hi-mu/low-gm SRPP input/driver because I found that the circuit had a tendency to sound tiring over extended listening. However, my memorable encounter with the Morikawa SE2A3 amp owned by my buddy Jose was haunting. I had to revisit this circuit just to make sure I left no stones unturned. 

Earlier this year, Steve of Angela Instruments shipped me the "shop mule" SRPP SE2A3 amp for a check up. After replacing the leaky coupling caps, the amp was as good as when I delivered it to the shop over two decades ago.  

My hotter operating point = slightly more power compared to Prof. Morikawa's SRPP 2A3 amp.

!!!WARNING!!! 

The voltages in this circuit are potentially lethal! Build at your own risk!

Click here if you'd like to try the SRPP 45 triode circuit.

Use a Hammond 302AX power transformer instead of T1 + T2 A&B

Click here to see the "cleaner" 10kHz square wave from the Morikawa SE2A3 amp

In spite of the 10 kHz square wave spike from the budget Hammond 125ESE output transformers, it was a very refreshing musical reunion with the Angela SRPP 2A3 amp. 

During its residency in the man cave, the amp powered my back up Altec 2-way system above, Altec 755As and Altec 755Cs in Silbatone cabs below. It was totally devoid of the listener fatigue I previously ascribed to the circuit. Even with the brightest and harshest software and/or hardware thrown into the listening chain, I couldn't induce the unpleasant quality which bothered me in the past. 

Then it dawned on me that I started doubting the SRPP's musical abilities when my Altec 2-way project commenced. Sorry SRPP, it wasn't your fault...😟

YMMV!😉

morrison micro 2A3, reimagined + Kasuga Wireless KA6625ST output transformer

Joe Roberts' piece, "I Never Met a 2A3 Amp That I Didn't Like," from Sound Practices Issue 15, is very persuasive. I built jc morrison’s micro 2A3 amp soon after I received the issue via snail mail fresh from the printers in the mid '90s. After rereading the article in ‘07, I got inspired to make a Radiotron SE2A3 variant.

!!!WARNING!!!

The voltages found in the following circuits can be lethal! Build at your own risk!

jc morrison's micro

That '90s morrison micro build used the Angela Universal Power Transformer with a 760 VCT @ 200 mA (very conservatively rated) HT secondary + a GZ37 rectifier for each channel. The thought of my 2A3s broiling way over the plate dissipation was daunting. Even if Chinese 2A3s were only $10 a pop then, my finger tips tingled in anticipation of a fireworks display each time I flipped the toggle switch on. But the sound through Audio Note UK 3K output transformers was delicate yet exuberant, with a touch of mystery! 

Since my Altec 755As in open baffles required more power, or so I thought then, the power and output transformers were expropriated for the classic JE Labs SE300B project. 

Fi "X" by Don Garber
from a Sound Practices ad

 In 2017, I had wanted to build a 6SF5>2A3 amplifier tribute to the Fi "X" in memory of Don Garber 😢 but a busy schedule got in the way. 

During the March 2020 lockdown, I was motivated to review my audio DIY to-do list which led to a long-overdue parts bin inventory. I turned up a 700 VCT @ 150 mA power transformer pulled from a junked Scott 99D mono integrated. This iron is not a stranger since I've used a pair in my PP2A3 mono-blocks in the olden days. I dug up a couple of 6C8G grid capped/octal based twin triodes as well.

6SL7 vs. 6C8G 
transconductance (gm)= 1600 umhos (both)
gain (mu) = 70 vs. 38
plate resistance (Rp) = 22,500 vs. 44,000
max. plate current (each plate) = 2.3mA vs. 3.2mA

Despite the equal transconductance, the 6C8G isn't a drop-in equivalent of the 6SL7. Aside from the different pinout, the mu and Rp are lower. When the triode sections are paralleled, the Rp is closer to a medium mu/gm triode like a 76. 

morrison micro, reimagined

This 2-stage direct coupled circuit is a reimagined morrison micro using a 6C8G front end. The paralleled triode sections draw about 3.4 mA and the 510 ohm cathode bias resistor is bypassed with a 100uf @ 16V cap to maximize input sensitivity. 

Chinese 2A3s typically sell for $100 a pair nowadays

Each 2A3 is AC heated by a Hammond 166M2 (2.5V @ 3A) filament transformer. The operating points are well within the modest specs of the Scott 99D power transformer.

Output Transformers

The fullest potential of an amplifier circuit can't be realized if it's inhibited by a mediocre output transformer.

Hashimoto H203S

Transformer design can be a contentious issue. Audio forums contain at least 30 years' worth of intense arguments amongst gurus with regards to winding techniques and materials - EI laminations, C-core, double C-core, silicon steel, nickel, amorphous or nanocrystalline (aka Finemet). Unfortunately, there have been no definitive conclusions and the debates continue.

James 6123HS

Despite my limited knowledge of electromagnetic induction, I've done lots of serious listening evaluation of various transformers + a bit of basic testing through the years. My ears developed an affinity for the design ethos of Japanese transformer companies like Hashimoto, Nature Sound, Noguchi (now General Transformer, Co. Ltd), Tamura, Tango, etc. I also lament the now-defunct line of James budget and mid-priced output transformers from Taiwan, which sounded akin to their neighbors to the north.

Nature Sound NS70SE

I don't think the skill and expertise is unique to the Japanese. My empirical mind tells me that they just improved upon what they learned from reverse engineering classic American and European audio equipment, analogous to Canon and Nikon copying and innovating upon Leitz and Zeiss cameras and lens blueprints post WWII. 

Tamura F7002 Permalloy

The transformer art is also not lost stateside. Based on my very positive experience with custom-wound nickel plate chokes from Intact Audio's atelier, my hunch is, dave's output transformers are probably wound to similar standards since he's had ample exposure to Nature Sound, Tamura and Tango iron due to his long association with the NY Triode Mafia scene. 

Tango/Hirata NY15S 

Regrettably, I haven't had much luck with budget-priced heavy iron. The ones I've tried usually present my 'pet peeve' tonal curve: boosted upper bass, recessed midrange, a spiked upper midrange to lower treble, followed by a sharp roll off in the top end. To some ears this kind of voicing sounds captivating. But to be honest, it's a musical disaster to mine. 😞  

Budget Output Transformers 
Noguchi PMF-10WS, Edcor GXSE15-16-3.5K, Noguchi PMF-15WS

When I can't afford a top of the line Sumo-sized output transformer, I compromise on full power at the bottom end and settle for a well-designed Bonsai-sized iron with a gradual and smooth roll off beyond the audio band. It's an insurance that my midrange will sound clean due to musically consonant upper harmonics. 

Noguchi (now G-trans.co.jp) Finemet

So far, all the Japanese budget transformers I've tried have not failed me in this regard. Some even exceeded my expectations, like the entry-level Noguchi Finemets above.

Kasuga KA-6625ST

For this project I used the Kasuga Wireless KA-6625ST. This is an entry-level output transformer, which is less than half the size and weight of the Audio Note UK 3K from the 90s. Weighing in at a lean 1.1kg, it can be configured  to reflect a 2.5K, 3.5K or 5K primary Z via the multiple secondary taps. 3K-3.5K has become my de facto load for the 2A3 and 300B, only because my ears prefer it. 

Alas, these transformers aren't available in the USA. But if you happen to be in the vicinity of their Akihabara store, you can pick them up for about $82 apiece.

Kasuga KA6625ST Square Waves
L > R: 100Hz, 1kHz, 10kHz

Although not musically definitive, the square wave pictures presented above indicate good circuit and transformer behavior. Considering that there's no corrective negative feedback loop in this DC SE2A3 amp, it hardly pales (except @100Hz) in comparison to the 100Hz, 1kHz and 10kHz square waves from the classic push-pull EL84 (with negative feedback correction) Dyna ST35 amp, renowned for its fine sonic quality and wide bandwidth ultra-linear output transformers. 

4.34V rms squared/8 ohms = 2.35W

The amp puts out 2.35W at 1 kHz into an 8 ohm load before clipping (lower trace) with an input sensitivity of ~ 1.2 V rms (top trace). If memory serves me right, I measured about 3W per channel from my '90s morrison micro build. About 20% of power was lost due to my cooler operating points. 

Sonic Palate

Connected to my Altec 753Cs in the main system or the Altec 755As in Silbatone cabs in the near field system, the DC SE2A3 amp doesn't have the body, complexity, intense richness, dynamic impact and bandwidth of my Bordeaux-like heavyweight amps which employ lower Z driver circuits + top of the line Japanese OPTs. Instead, it reminds me of the sweet and fruity flavors, earthy spices, color, subtlety and finesse from my White Burgundian Simple 45, which was the main reason I was forever drawn to this archaic method of building amps!

Enjoy the music!🍷

Hi-Fi for the Deck: Rpi3B >TDA1543x4 DAC > Simple Triode SE6V6 amp > EV Sonocaster

Spring and Fall are the best seasons to enjoy food and drinks on our deck. To complement the beautiful atmosphere, I assembled an e-z to set up and dismantle hifi system!

Music Source

This stack consists of a Raspberry Pi 3B loaded with Volumio music player/streamer tethered to a Signstek USB to SPDiF converter which connects to a Muse TDA1543x4 Non-OverSampling DAC.

Volumio offers a wide choice of radio stations streaming MP3 files up to 320 Kbps. The Radio Paradise channel has even started broadcasting FLAC files. 👍

Amplifier

In the late 80s, I built my first amplifier from scratch using transformers from a cosmetically challenged Dyna SCA35. I used this paraphase circuit from the Dynaco Transformer Catalog with a 6SL7 driving a pair of push-pull 6V6s. Musically, I preferred this amp to my then highly modified Dyna ST70 and pair of MKIVs.

with 6F6Gs courtesy of John Piro

Since I always had reservations about the 1626 triode's musical abilities, I converted the JEL Darling Style amp to use triode connected 6V6s. Wow!👍

!!!WARNING!!! 

The voltages in this circuit are potentially lethal! Build at your own risk!

Input sensitivity = 0.3V, no need for a preamp
This amp also does a good job of driving my collection of orthodynamic headphones via adapter.

Triode connected 6V6s mimic directly heated triodes much better! 🎻🎸

Speakers

This pair of Electro-Voice Sonocasters came from the flea market. I guesstimate the sensitivity to be in the mid 90s dB @ 1W @ 1M. Driven by 1.4 triode watts per channel from the SE6V6 amp, I sure won't be annoying the neighbors. 🤣

The 8" drivers are unmarked but look very much like MC-8s - not quite an Altec 755C or Pioneer PIM8L in terms of refinement or realism, but not too shabby either + a lot more rugged!

Happy Listening!🍻

Parallel Single Ended 6SN7 [Headphone] Amp

Ever since I grafted a 6SN7 on the line stage section of my hacked Dyna PAS preamp, I've been hooked on the "octal sound." Could it be the higher heater current draw boiling more electrons and/or larger stature that give it a 3-D quality, richer tonal color, detail, dynamics + more, compared to their 9-pin/noval siblings? 

For these reasons, I've longed to hear how the ubiquitous 6SN7 could sound as a milliwatt amp. The Covid-19 2020 lockdown was a good opportunity to try "off the cuff" experiments. An unbuilt Chinese 6V6 preamp kit I bought at an Amazon closeout languishing in the basement for a couple of years provided a nice pre-punched chassis + power transformer for this project.

Ideally, the 3850 ohm plate resistance of the two triode sections of a 6SN7 connected in parallel should drive a 12K primary Z. I considered getting a pair of Hammond 125BSE output transformers, which have the flexibility of reflecting back a 2.5K, 5K or 10K primary Z but I already had a pair of these 5.5K:4 ohm SE OPTs in my parts bin that I was sure would fit under the chassis.  

!!!WARNING!!! 

The voltages in this project are potentially lethal! Proceed at your own risk!

The circuit is a simple 2-stage cascade - 1 triode section of a 6CG7 functions as the input/driver stage R-C coupled to paralleled 6SN7 triode sections.  

The HT supply output of the 6X5 rectifier feeds a 22uf/450V capacitor, which splits into left and right channel B+ rails via two 5H/50mA chokes filtered by separate 47uf/450V caps, provide clean power to the amp. I rectified the filament supply to run at 6VDC for minimum hum and noise on headphones. 

Square waves at 100Hz, 1 kHz and 10 kHz
Top trace = audio generator
Bottom trace = amplifier output

Due to the primary impedance mismatch previously noted and the bonsai stature of the transformer itself,  these square waves show limited extension at both frequency extremes. Subjectively, this was more apparent via speakers rather than on headphones. I should point out that the absolute lack of ringing is indicative of a competently-wound transformer.

Input sensitivity = 0.9 V RMS 

Output = 2.408 V RMS/ 8 ohm load = 720 milliwatts/channel

Between 16 ohms > 600 ohms, I measured 3.5 --> 4.2V RMS output, which was more than enough power for the most inefficient ortho-dynamic headphones I have in my collection.  

This amp draws the listener to focus on the midrange in which most musical activity transpires. It made the JLH HP amp sound comparatively veiled in the midrange, which shifted the listener's attention to the frequency extremes where the JLH actually does pretty well.

Despite the superior bandwidth of the output transformers fitted to the Darling amp, JEL style, the PSE6SN7 amp displaced it musically! The Darling amp just couldn't keep up with the DHT-like harmoniousness and graceful overload characteristics of the PSE6SN7. 

 

Lush and caramel flavored midrange, nuanced dynamics, silky highs and well-defined bass (within limits) are the virtues of this Lilliputian amp. Perhaps due to the high output impedance and low damping factor, this amp can portray the sophisticated qualities I've experienced from the SE171A, 10/VT25 and Western Electric 205D amplifiers!

TBT '96-'97: JE Labs Project Pics

I'll start the new decade with scanned negatives of my DIY Audio projects from the mid to late 90s. Most of these pictures were taken either with my Pentax K1000 or Leica M3 + Rigid 50mm Summicron, loaded with either Agfa Vista or Kodak Plus X, processed by a local lab. I didn't know how to develop film yet back then. 😉 

ca. '96

My last Dyna PAS hack

This Dyna PAS 2 chassis sports an RCA phono circuit with Ni-Cad batteries for cathode bias. Check out those wonderful (then) anti-high-end paper in oil caps from Jensen, Facon and Icar. Too bad they get leaky after a couple of years.

Yup, that's an octal socket in the line stage for the mighty 6SN7!

Under the hood of the outboard power supply is a choke for the B+ for better filtration. Connection to the main preamp is via an octal plug/socket.

By this time I was already a firm believer in tube rectification. I retained the original PAS transformer for B+ supply duty only and relegated DC filament duty to another power transformer.

JE Labs Stereo "Classic" SE300B with Audio Note UK 2.5K OPTs

A Thorens TD124 + a (then) newly-acquired ($60!) Grace G540L tonearm + Grado 8MZ on my very first laminated plywood plinth project. All these components are still in service.

The original Simple 45

ca. '97

JE Labs Stereo SE2A3 with Tango U808 OPTs

JE Labs Classic SE300B mono-block with Audio Note UK 3K OPT

I briefly owned a pair of AES/Soliloquy 5.2 TQWT speakers. Coming from Spendor LS3/5As, these sounded lean and weren't more efficient either - probably in the high 80s rather than the claimed low 90s.😏

Fortunately, I snagged a pair of Altec 755Cs at a hamfest and quickly whipped out a pair of small open baffles. I was hooked!

The Altec 755Cs in open baffles based on dimensions published by Stereo Sound "Tube Kingdom" Issue No. 3/1996. And yes, I added a Garrard 301 to my system!

I got my Garrard 301 in the early summer of '97 along with the Altec 755Cs. 

This was the block diagram of my system before the end of the millennium as a featured "Home-brewer" in Sound Practices.  I can't believe 20 years went by so quickly!