Friday, June 18, 2021

Thorens TD124 Tips

 


Cheap and EZ


Neat P58H/Shield MO19


This experiment was inspired by the spring-mounted motor on my Neat P58H.


Realistic MKVIII

Even if the rubber grommets on the MKVIII are still supple and intact, I replaced them with 302 stainless steel compression (1/2" x 0.600") conical springs, Grainger part no. 1NDB4 and heard a significant reduction in noise.


Left = Neat P58H original
Right = 1NDB4

Heck if it works with the Japanese idlers, it should also work with the TD124. So I ordered smaller conical springs from zorotools on eBay for the TD124 and TD124II.


1NCY2 = 5/16" H x 0.48"


Be careful removing/installing the circlips. They can fly across the room, along with expletives.😁


1NCW4 = 1/2" H x 0.48"  

Some may argue that the "springy" motor mount can introduce pitch instability and also, as originally designed, the belt provided ample isolation from motor vibration. The springs are cheap, so let your ears decide.😉

Magnetic vs. Non-magnetic Platter


 TD124 standard platter = heavy iron

Lighter non-magnetic platter
issued with the TD124II
 

I used to believe there was negligible sonic difference between the heavy iron platter from the MKI vs. the MKII's non-magnetic platter. However, in the intervening years, I've come to realize that the heavy iron platter bestows gravitas to the TD124 design!

TD124II + heavy iron platter

I won't go into light vs. heavy plinth.😄


Reference


 For maintenance and restoration information, visit The Analog Dept. Thorens TD124 webpage!👍👏


Saturday, June 5, 2021

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 by JE Labs

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), TamuraTango, 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 correctionDyna 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!🍷



Tuesday, May 18, 2021

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!🍻




Saturday, May 1, 2021

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!🍻




Saturday, April 17, 2021

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. 😔