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!👏