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.

Kutztown Radio Show - Spring 2021

Most pictures taken with a Sony A7II camera + Chiyoko Super-Rokkor 45mm f2.8 LTM lens

Pavillion 1

Rumor has it that dealer tables were sold out. Just another indication that things are returning to normal.

Pavillion 2

If you're looking for vintage Altec, JBL, RCA, Stephens, Western Electric or '50s to mid '60s classics from Acrosound, Dynaco, Eico, Fisher, Heathkit, Marantz, Scott and etc., they are getting thin on the ground and no bargains are to be found. 

Late 40s to early 50s cutting lathe

This is a fine piece from the monaural era for the serious hifi collector!

Those who are into '70s-'90s components have greater choices.

The main highlight of this season's event was meeting audio enthusiasts from the Philly metro area whom I've only known via Audiokarma and HiFi Haven. I spent most of the time talking shop with them and wasn't able to snap as many pictures as I've done in the past. 

AKG K240 Monitor (left) + K240 "Sextett" (right)
Sony A7II + Schneider-Kreuznach Retina-Xenon 50mm f1.9 DKL

For about a Benjamin, I went home with a pair of AKG K240 Sextett headphones, a TDA1541 chip'd Magnavox CDP, 37s, 76s and 6CG7s, a handful of Jazz CDs + a couple of LPs!

I also found something that's been on my radar for at least 20 years, but it shall remain nameless until...😉

Looking forward to the Fall event!🍻

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.

 2.825 Vrms into 8Ω = 1W of triode power per channel 
I'm not worried about the slight overshoot/ringing, rumor has it, the Sony/Tamradio OPTs have nickel content 
also, the last time I saw a similar square wave was with a pair of Nature Sound NS70SE OPTs.

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!🍻

Marcel Breuer Designed House + Altec 604C + Infinite Baffle

  

This beautiful mid century modern home aka the Snower residence was designed by Bauhaus architect Marcel Breuer and posted by midcenturyhome, whose finely curated photostream I follow on Instagram.

Aside from my interest in mid century modern architecture, the Altec 604C mounted prominently in the living room caught my eye.😄

I've also seen a Fisher 50C preamp (bottom) at FLW's Fallingwater. Unfortunately, interior photography was prohibited there when I last visited. 😞 

The Snower house + hifi installation was already brought to my attention in the comment section of architects, music and hifi  by a blog visitor many years ago. Thank you!

from Dwell.com

More Infinite Baffle Installations

I blogged about this installation before, but this picture offers another perspective of the 2-way horn speaker system installed in Case Study House #9 designed for John Entenza by Charles and Ray Eames and Eero Saarinen.

Scans from How to Build Speaker Enclosures

An office stereo hifi

John Hilliard's home hifi system

Hi-Fi system details

I'm pretty sure all these wall mounted speaker systems were formidable music reproducers! However, ever since soundstaging and imaging took precedence over sound quality, infinite baffle loading fell out of favor. 😔

Lar Retro-resto Shure M65 Phono Preamp

Hamingredient inspired chassis 😉

In the early 2000s, I tried to unload a half dozen or so of my used/test good Telefunken 12AX7s on eBay. The buyer promptly requested for a return claiming that they didn't test well in his TV-7. Was that a sign...? 😉 

So instead of re-listing, I stashed them away. I had forgotten about their existence until they showed up during a 2020 lockdown clean-up spree. 

Shure M65

I met my buddy Lar through Audiomart in the late '80s. He's a trained sound engineer and audio hobbyist who shares my passion for the classic Austin Mini.👍 We hang out and talk shop at ham radio festivals, audio and radio shows. He's firmly committed to tube phono circuits employing active RIAA EQ and posts his projects at Audiokarma and Lenco Heaven.

Shure M65 schematic

The classic Shure M65 "chrome cutie" (as Lar fondly calls them) is one of his favorite platforms for modification. Keen eyes will notice the similarity of this topology to the phono section of the classic Dynaco PAM-1 and PAS-2/3 tube preamps, albeit operated at a lower B+ voltage and with AC heated filaments.

One channel shown

The 0.47uf ceramic disc input coupling caps, C1 and C2 + the 1M shunt resistors, R3 and R4 are discarded. Likewise, the 100k positive feedback resistors (R11 and R12) are eliminated, which I also used to do to my Dyna PAS preamp hacks. IME, this procedure improves transparency. The most significant performance upgrade is Lar's recomputed RIAA EQ capacitor values (see the above schematic) tweaked for flatter response.

I didn't have a Shure M65 but had enough parts to clone one so I could put my rediscovered Tele 12AX7s into good use in the midst of Covid-19 lockdown.

This one chassis configuration sounded fine on first turn on but had an annoying low level hum I couldn't eradicate. 

After trying all possible grounding schemes, I yanked the power transformer out and built an outboard power supply. Problem solved!

My power supply is slightly more sophisticated than the stock M65. The full wave rectified B+ is filtered by a 20H/20mA choke followed by a 47uf/450V cap, which splits to separate left and right channel rails with additional decoupling and filtering. The tube filaments are DC heated. 

1 kHz
stock RIAA EQ

Using the stock RIAA EQ capacitor values, lower frequencies sound bloated with a noticeable treble boost as noted in the Shure M65 literature, which is also visible in the above 1 kHz square wave.

1 kHz
LAR modified RIAA EQ

The 1 kHz square wave is squarer and the phono preamp sounds so much better with Lar's tweaked cap values!

I don't think I was ever able to derive this level of musical satisfaction from any of my past 12AX7 phono efforts using active RIAA EQ. I believe the sonic purity stems from the simplicity of the circuit itself. The Dynaco PAM-1 and PAS-2/3 circuits have an additional cap after the negative feedback RIAA EQ tap + elaborate switching and a balance control in the PAS, all of which can cause veiling. 

In spite of the Shure 5000 ohm output impedance spec, this is still a relatively high output Z device. When connected directly to the 10k ohm input of my Nobsound NS-02g amp, the loss of extension at both frequency extremes was discernible. It sounded best driving a 100k ohm load using low capacitance cables, 3 ft. long, max! 

This phono preamp synergized very well with my favorite magnetic cartridges with conical stylus - Nagaoka MP10, Pickering XV15, Shure M3D and M7D, amongst others. So after a couple of months of enjoying the Lar mod M65, I decided to build it on a nicer (if a bit cramped 😁) cast aluminum box with two pairs of inputs.

Instead of boring you with audiophile adjectives, I'll just say that my RCA passive RIAA EQ octal sounds effortless and airy, while the EAR 834P derived loctal is detailed and dynamic and the Lar retro-resto Shure M65 is sweet and alluring! 

This phono preamp is a most welcome addition to my tools for enjoying LP reproduction. I highly recommend following Lar's phono preamp adventures at Audiokarma! 

Bravo Lar!👏

Snell Type JIII Part 1 - Deconstructed > Re-Foam

 In the late 80s, I could have gotten a Snell Type E or J after unloading my Magnepan SMGas. But I loved the sound of EMI and Decca recordings, for which I give credit to BBC-trained sound engineers, so I invested in a pair of Quad ESL57s and Rogers LS3/5As instead. I was such an Anglophile that I even became a partner in a company that imported Art Audio Amplifiers and Spendor Speakers to the Philippines. Unfortunately, we didn't make money...but that's another story.🤣

 

During a moment of nostalgia, I chanced upon this pair of Snell JIIIs online. I messaged the seller expressing interest. After two weeks of silence, I made a polite follow-up and was surprised to receive a reply that they were still available. According to the seller, he's had several offers from tire-kicking flippers but he chose to sell to me because I sounded like an enthusiast who'd give them a good home.😄

Typical of speakers from this era, the foam surrounds have disintegrated. Other than that, this is a very clean pair with consecutive serial numbers just like when they were sold in high-end audio salons in the late 80s to early 90s.

While waiting for the replacement foam surrounds, I thoroughly cleaned all vestiges of old foam from the cone and speaker frame. This was the most tedious and time consuming step in the re-foaming process but essential for a successful result!

 Meanwhile, I also took advantage of the down time to analyze what makes this speaker system tick. 

Deconstruction

Peter Snell was a very gifted speaker designer. Due to his untimely demise at age 38 in 1984, speaker models that were manufactured during his lifetime have developed a following. Peter Qvortrop of Audio Note UK was a big fan of the 2-way Type E, J and K models and continues their legacy in the Audio Note E, J and K using custom drivers and boutique parts.

The Snell E and J had front mounted reflex ports while the K was a sealed box/acoustic suspension design, which employed a different woofer. A rear firing 3/4" dome tweeter was added to the EII model, while the reflex port was moved to the back of the cabinet in both the EII and JII.

Vifa D26TG-05-006

The EIII, JIII and KII designation denotes the switch from a Tonegen 1" doped silk dome tweeter to the Vifa D26TG-05-006 6 ohm 1" dome pictured above. A tweeter level control was also added on all models. 

According to the Snell Type JIII brochure, the Vifa D26 tweeter handles an octave of upper midrange frequencies from 2.7kHz + another two octaves of harmonic overtones.

Even if the JIII was manufactured posthumously, it retains the cabinet dimensions and proportions of the original model. After many years of experimenting with open baffles, Altec 614 and 618 and  cabinets, I'm a firm believer in the acoustic superiority of Rubenesque front baffles over Victoria's Secret slim waifs.😆 

Was the use of plywood (top, bottom and sides) + chipboard (front baffle and back panel) chosen for acoustic reasons? Regardless, the cabinet is of pretty high quality construction with particular attention placed on rigidity - see the brace from the front baffle to the back panel in the picture below.

Good quality air core inductors, electrolytic and film capacitors or a combination of both + an L-pad for tweeter level adjustment were used in the crossover network.

The high-pass is a straightforward 12 dB/octave 2nd order slope hinged at 2.7kHz, as previously mentioned. On the other unit, there was an additional electrolytic cap in the high-pass section with a higher total capacitance reading. This confirms Snell's claim of matching their units to within +/- 0.2dB based on a reference model in their factory. 

Likewise, the low-pass section is also a 2nd order slope + an EQ/contour network for the Vifa woofer (see the LCR combo highlighted in red above). Explaining how this EQ works is beyond my technical ability. My empirical mind just knows that it "shapes" the woofer's frequency response. A similar, albeit more complex, crossover + EQ can be found in the BBC LS3/5A. 

Since all the capacitors measured close to their indicated values, there was no rationale to change or upgrade. Besides, I want to hear these speakers as close to how they were originally designed.

Vifa 8" M21WN-07-04

AFAIK, the Vifa 8" M21WN-07-04 was the only woofer used in the J, JII and JIII. Based on the 49Hz-20kHz +/- frequency response specified in the JIII brochure, and cross-referenced to my Musical Instrument Frequency Chart, this drive unit/cabinet combo was tasked to cover six and a half octaves of musical information starting from the bass frequencies up to midrange fundamentals. 

Re-Foam

After judiciously sifting through audio sites on the net, I chose the $25/pr. foam surrounds from Simply Speakers because they were recommended by audio hobbyists who exhibited good ears and common sense. Check their re-foaming video for a straightforward and confidence-inspiring tutorial.

 The Vifa M21 voice coil is essentially self-centering. So don't even consider cutting or removing the dust-cap to shim the voice coil. It'll be ruined because the cone + dust cap is one whole piece. 

 

Not bad for a first attempt in replacing foam surrounds, huh? 😉

Since time immemorial, I've been evaluating drivers bare naked (or mounted in a simple baffle) to hear their potential. After 25 years of enjoying Altecs, these drivers sound very different...🤔  

Snell JIII in room RTA (Onyx iPhone app) 
Snell JIII specs

I have to live with this speaker system for a while and play lots of tunes 🎻♫🎶♬🎺and will report back in Part 2!😊

See Part 2 and Part 3