JE Labs

Friday, April 22, 2022

MC step up transformer redux + Hashimoto HM-7

Altec 756B + 32C + 806 + 23744 = mini 757

The WE756A is the middle child in the Western Electric series of wide range drivers introduced in the late 40s.

I've seen and heard a couple of WE/Altec 728Bs + a dozen or so pairs of 755As, but I've never heard a WE756A and have only seen one in the metal at a radio show many years ago. Although still quite scarce, its Altec 756B brother isn't quite as elusive.

Back: Blonde + Mahogany Altec Melodist 700A
Front L-R : WE728B, Altec 755A/pr. + Altec 756B

The few Altec 756Bs I've encountered all came out of the Altec Melodist 700A. It's a compact bass reflex speaker system loaded with the 756B, supplemented on top by a 3000A horn tweeter via an N3000B crossover. The 700A belonged to the Melodist monaural hifi system line, which Altec targeted at apartment dwellers in big cities of midcentury America.

Subsequently, the 756B was replaced by an 8" Altec 401A and was re-designated as the Melodist 700B. With the introduction of stereo for the mainstream market in 1958, the Altec Melodist line quietly faded into oblivion.

If found in good condition, the Altec Melodist 700A is a fine looking midcentury modern artifact! Unfortunately, the < 1.5 cf ported box doesn't allow the 756B to shine sonically, IMHO. Since it shares similar proportions to its more successful contemporaries like the Acoustic Research AR-1 and the Jensen Duette, the cabinet design may have been dictated by market positioning rather than sound engineering.

My once-in-a-lifetime lucky find 700A above has lived a hard life. The lower front edge of the cabinet was missing while the sweet and airy but very fragile 3000A horn tweeter element had been replaced by a tiny ferrite magnet dome tweeter.😏 A "mod" that has been circulating in the internet, so watch out.

Fortunately, the 756B is very well preserved. If memory serves me right, the WE756A frame is more substantial than the Altec 756B. That’s probably the reason why the back handles were omitted in the Altec. The 756B has an 8 ohm voice coil, while the WE756A is 4 ohms.

J-Rob's Altec 756B at
Capital Audio Fest 2016

Joe Roberts has already done a great job of describing the sonic qualities and proper implementation of the Altec 756B in his (Geekstar) "My big ten inch --Altec 756B" post at the Altec User's Board. He also gave insight on the shifting Asian market for vintage Western Electric and Altec gear. A guaranteed fun and informative read!

Since I don't have Joe's networking skills, I resigned myself to the reality that my Altec 756B will be the main speaker of my monophonic hi-fi set up, just as Altec intended.

Click for a videoclip

Meanwhile, I repurposed (sealed) a Heathkit AS10 (almost 2 cf) cabinet to familiarize myself with the 756B. I listened to it as a wide range driver with and without top end assistance from either a 32A/802/34852 + an XO based on this schematic or 3000H with an L-Pad + 0.5 uf - 1 uf paper in oil cap. The simplest XO I used was a 0.22uf paper in oil cap in series with the + terminal of the 3000H, no L-pad needed. That also sounded good, albeit, with slightly less sparkle.

JE Labs mini 757
inspired by the Western Electric 757A

After extensive listening in wide range mode, I determined that a mono hifi set up will benefit from a wider baffle + the dispersion pattern of the Western Electric-derived 32 horn. So I sketched a slant front ~ 2.5 cf infinite baffle that has a provision for an Altec 32C horn + 802 driver and sent it to John Piro of Hommage Audio.

728B vs. 756B

As expected, the 756B is more extended at the top end than the 728B with almost, but not quite, equal bass extension. However, music through the 728B held my attention appreciably longer without my reaching for a clip-lead to fill in the top octaves with the 32/802 horn/driver for more harmonic overtones above 5 kHz.

RTA = Altec 756B in a ~ 2.5 cf infinite baffle

I confirmed this during one of my shop talks with J-Rob, who also found it more rewarding to listen to 728Bs in wide range mode than to his 756Bs. It makes me wonder if the 756B and its WE756A brother were designed with a middle-child syndrome gene in their sonic DNA.🤔

After many years of collecting Altec 1" compression drivers, I've only landed a single Altec 23744 "light" aluminum diaphragm, which was fitted to an 806 motor that was used in the Altec 9849 monitor speaker.

Things started to crystalize when my friend Dave V. aka Salectric,🙏 sent me his spare .085 mH choke. It was a proprietary part found in the EQ circuit of the Altec 9849 crossover, which is an 8 ohm speaker system. This EQ circuit shapes and boosts the response of the 32/806 horn/driver combo. Incidentally, Dave's "Last PAS" articles written for The Audio Amateur contributed to my 80s Dynaco hacking activities.

RTA = Altec 32C + 806 + 23744

The 4 uf paper in oil capacitor serves as a first order high pass filter hinged around 5 kHz with a gentle 6dB/octave slope, while the variable 8 ohm L-pad shapes and controls upper frequency overtones to taste.

inside the mini 757

John P did a great job of building a very rigid cabinet, which saved me the time and trouble of having to experiment with damping. I just lined the interior panels with Kimpak and I was ready to listen.

RTA = JE Labs mini 757

This project transpired as an opportune moment to assemble all the singleton Altecs from my collection - 756B + 32C + 806 + 23744 - into a formidable monaural hifi speaker system.😊

JE Labs mini 757

My ears hear close to half an octave of bass extension from the mini 757 compared to the 755A in a Silbatone or 618 cabinet. Due to its greater efficiency, it plays louder while dynamics at micro and macro levels are less compressed. The larger cone area of the 756B + wide baffle + 90° horizontal x 60° vertical dispersion of the 32C horn, portray a bigger sense of scale. All of these were achieved without compromising the midrange realism I enjoy from my beloved 755A.

However, the Altec 753C is perceptibly more efficient, offers at least an octave lower of extension with more authority. It also produces higher SPLs.

Alas, we can't defy the physics of sound...

JE Labs monophonic hifi

...so I focused on the aesthetics by spicing it up with a touch of Charles Eames and Dieter Rams! 😉

Saturday, March 19, 2022

Analog LP Playback + Film Photography

Combining my passion for two obsolete technologies

Thorens TD124 MKII with heavy platter + Alfred Bokrand AS309 tonearm
Canon P + Canon 50mm f1.8 LTM
Ultrafine eXtreme 100 in Kodak HC110

Late last year, I acquired the classic AS309 tonearm for my Thorens TD124 MKII from Alfred Bokrand. I really can't hear a difference between the AB309 and AS309, even if I'm forced to split hairs. I'm just happy to own both!

Garrard 301 + Ortofon RMG309 + SME 3012 in JE Labs plinth
Tower 3 (Leica copy) + Leitz Summitar 5cm f2
Ilford FP4+ in Kodak HC110

This was my main turntable for over twenty years. Now the duty is shared with the Thorens TD124 MKII above, and the Garrard 401 below.

Garrard 401 + Alfred Bokrand AB309 tonearm
Bessa R + Canon 50mm f1.8 LTM
Ilford FP4+ in Kodak HC110

A couple of blog readers and Instagram contacts have reached out regarding long delivery times from Alfred Bokrand. All of my transactions with him were done through eBay and on the average, delivery was within two months. I highly recommend that buyers order via eBay since it has a buyer protection guarantee.

Thursday, March 3, 2022

emails from Ukraine, was Radiotron SE2A3

Bach Chaconne
from
Partita No. 2 in D minor for Solo Violin

An important lesson I learned as a classically trained violinist was that music theory evolved from the analysis and study of great masterpieces from Bach to Bartok. Great composers broke theory to reach new heights in musical expression. Just like any artistic pursuit, music continues to evolve through individuals who are not afraid to go against convention for a greater good!

Tube load line simulator
from Trioda.com

On the other hand, audio engineering, for the most part, has always been theory driven. Audio design simulators are significant modern conveniences but don't guarantee musical-sounding circuits even if the metrics look great. Creativity in audio design is when human ears are still the final arbiter, at least in my experience and opinion, which is why my hifi system is a hodgepodge of mostly obsolete technology, some of which date back to almost a century ago.

Last year, a Juilliard-trained pianist turned lawyer visited my man cave and listened to various amps + a couple of speakers I built. On his second visit, he brought his amps for comparison. At the end of that session, he commissioned a pair of Altec 753C speakers, the second pair I built in collaboration with John Piro of Hommage Audio, who crafted the speaker cabinets.

The chosen amp was the Radiotron SE2A3 - a topology from the pre-WWII Radio Designer's Handbook, 3rd edition. This circuit was from an era in which calculators were but a dream and engineers computed complex equations aided by a slide rule.

!!!WARNING!!!

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

Although this pentode-driven circuit sounded fine as is, to my ears, its fullest potential was only realized after I adjusted the plate and screen grid voltages to achieve a 2:1 ratio as suggested by my Ukrainian internet buddy, Sergey Didkovsky in the winter of 2007.

"Try please, to increase the cathode resistor (1,2k-1,5k ohm) and reduce anode resistor (to75k-82k). It will allow to increase Ua up to 150V and to receive Ua:Ug2 = 2:1 ratio. The sound should become more 'interesting and old.' That is especially good for jazz. Still mine 5 cents...use good NOS oil capacitors in G2. I use TCC Visconol. I think oil caps in the grid - adds bass. Reduction of the anode resistor - improves the hi range a little."

Click here for the 2007 Radiotron SE2A3 article

I'm pretty sure the 2:1 ratio wasn't a number crunched by a simulator, it was a figure painstakingly chosen by Sergey's ears because of his love for music!

Sergey, wherever you are, I pray that you and your family are safe. Freedom-loving people around the world are very grateful, yet very sorry that Ukraine is all alone in shielding the free world from the atrocities of a megalomaniacal autocrat!

Friday, February 4, 2022

Sony PS1 + Magnavox/Philips NOS TDA1543 CDP Mod

A revival of interest in CDs is imminent, sparked by Pope Francis' recent visit to a mom and pop record store in Rome.😉

from djmag.com

So before software and hardware prices go through the roof, here are two affordable ways to get maximum pleasure out of CD playback for thrift store/flea market and/or DIY-inclined souls.

Over ten years ago, this early first generation Sony Playstation 1 developed quite a following amongst audiophiles as a CD player because of Art Dudley's favorable write up in Stereophile. The market has probably softened up a bit since then, because I managed to snag two PS1s at '08 prices before the pandemic.

Not all PS1 consoles were created equal - only the machines fitted with the AKM AK4309AVM Sigma-Delta DAC chip have audiophile credibility. Since I've seen some unscrupulous sellers asking $100+ for this obsolete game console, it pays to know two tell-tale features of the desirable PS1:

1. "SCPH-1001" designation

2. A pair of audio output RCA jacks on the back of the console

Don't forget the controller, which I pictured above and below, otherwise there's no way to command the player to play, stop or skip tracks.

Sigma-Delta DAC chips never struck me as unbearably bright, strident or fatiguing. The main reason I reverted back to a multi-bit DAC in the Box in the 90s was because my bitstream'd Philips CD921, and later the sigma-delta Sony DVP NS755V, sounded boring and lifeless. That said, the Sony PS1 is the most exciting sigma-delta chip'd CD player I've heard!

This is a must read: Michael Lavorgna's Sony PS1 Epitaph in Twittering Machines!

However, to my ears, here's a better machine for Digital Sound Processing Redbook CDs. 😉

In my thrift store CD player upload, these TDA1543-equipped twins stood out as very musical sounding machines, meaning, not for audiophiles, but more for people who love music. I actually prefer these Mexican-built non oversampling models over their slightly more upmarket Belgian sibling, the 4 x oversampling CDB610.

These were the entry level Philips CDPs from the late 80s up to the early 90s until they were superseded by inferior-sounding (at least to my ears) bitstream machines like my dreaded Philips CD921.😏 Stock, I'd choose these over the AKM chip'd Sony PS1 for sheer musical pleasure! 👍

I also highly recommend the Sony CDP190 with a TDA1543A + an in-house 4 x oversampling chip and filter. But in the 5 years I've been thrifting CD players, I've only found one, while I've managed to collect duplicates of the CD2000 and CDB492.

Grundig CD8150 analog output section

There is no known service manual or schematic for the Magnavox/Philips CD2000/CDB492, so I searched for other contemporaneous badge engineered Philips CD players. I found the Grundig CD 8150 service manual at HifiEngine.com, which employs a very similar, if not identical, circuit topology. I verified that the machine is indeed non oversampling. In lieu of the SAA7220P oversampling and filter chip, Philips engineered a brick wall filter in the analog output section, which they cleverly marketed as Digital Sound Processing.😊

I wonder if this circuit could have been the inspiration for Ryohei Kusunoki’s non-oversampling articles for MJ in the mid 90s.🤔

My audio buddy Ding R wanted me to improve his CDB492 with a tube output stage, since numerous DIYers have managed to shoehorn a tube analog output stage inside a plastic chassis CD player. But I wasn't keen on making a perilous fire hazard compromise. Besides, I'm also a purist and believe that only a tube-rectified and/or choke-filtered power supply should power tube circuits, nearly impossible to fit inside a CD player chassis.

8-pin DIP sockets, BB OPA2604 op-amps + Mylar capacitors

The inspiration for this simple-to-implement modification dates back to Walter G. Jung's article in the June 1987 issue of Audio. I removed the LM833 op-amps in the signal path of the analog output section, installed 8-pin DIP sockets and listened to check if the FET-input Burr-Brown OPA2604s and Mylar WIMA caps in place of the original electrolytics could improve the CDB492's musical performance.

Magnavox/Philips CDP Teardown by msylvain59

The most laborious part of this modification is gaining access to the underside of the motherboard. Watch msylvain59’s wonderful video above for a detailed teardown of a very similar Philips CD player. Handle the ribbon cables and connectors carefully! Given the age of these components, a crack or tear is enough to render the machine useless.

The motherboard is now ready for upgrades.
Take note of the op-amp orientation; otherwise, the machine may emit
smoke and nasty burnt electronic component odors!

After handling over a dozen 80s era CD players, I have yet to encounter bulging or leaky power supply capacitors. These machines used high quality Japanese-made Nichicon capacitors. In contrast to current audio trends, I don’t endorse across the board capacitor replacement. I'm all for replacing parts judiciously!

Operational amplifiers (more info) or op-amps were developed during the vacuum tube era. Due to the inherent high gain nature of op-amp topology (video), negative feedback is necessary to control gain and/or linearize the circuit. Ever since I started DIY’ing tube circuits, I learned that negative feedback has to be implemented judiciously (or even dispensed with) in pursuit of ultimate sound quality, which also applies to solid-state. Because of this, I don't see the logic behind boutique-priced discrete op-amps. But if that's how you get your audio fix, have fun rolling! ✌️☮

To my ears, the Burr-Brown OPA2604 + WIMAs gave a smoother, cleaner, clearer and less grainy sound. The superior TDA1541 DAC chip in the Magnavox CDB465 with op-amp + output cap upgrade offers better resolution of detail + a marginal improvement in musicality. However, the most musical CD sound I've enjoyed to date is still from the digital stream of a JVC, Magnavox/Philips swing-arm or Sony transport piped into my nosTDA1541tube DAC. But then again, I'm biased! 😆

Ding called after his first listening session with his JE Labs-modified CDB492, "...are you sure that's all you did to this machine?"

Thursday, January 20, 2022

A Cousin's Listening Room

This is a hifi system I built for a cousin who loves music!

The speakers, which I dubbed Altec 753C, is the culmination of my Altec 2-way horn system project.

Western Electric 753 inspired cabinets meticulously handcrafted by John Piro of Hommage Audio

Garrard 301 turntable + Ortofon RMG309i tonearm + Ortofon SPU Synergy for stereo LPs and Alfred Bokrand AB309 + SPU Mono for mono LPs

Turntable plinth by Hommage Audio

The JE Labs preamp line stage is a plate choke loaded 76 while the SE300B mono block amps feature a Komuro-inspired circuit using type 37 input tubes + Intact Audio nickel plate choke loaded 6V6s or 6F6Gs (connected in triode) and Hashimoto H-30-3.5S output transformers.

Preamp and amp woodwork by Hommage Audio.

Hifi cabinet by George Nakashima Woodworkers.

Projects like this keep me busy during the pandemic.😊

Tuesday, January 4, 2022

Begin the Beguine 2022

A well worn 78 rpm shellac disc of a Cole Porter classic recorded in 1938 by Artie Shaw spinning on a Gray Research HF500 turntable + a GE RPX cartridge amplified by my DIY je2a3 mono integrated fitted with a Hashimoto H203S output transformer driving a GE A1-400 speaker in a "vintage DIY" tuned pipe enclosure by Raymond H. Bates from Audio Magazine May 1955.

GE "single stud" RPX + 3 mil sapphire stylus
in a Karmadon slide shell

Cheers to 2022! Hopefully, it will be a much better year for all of us!

Tuesday, December 21, 2021

Happy Holidays 2021

With the blessing of Early Bender of Hifitown.com, I uploaded two articles written in the 1980s for The Absolute Sound by his parents, Walt Bender (1944-2008) and Lennice Werth.

WE/Altec 755A is in Part I

Olden Golden Components Part I

Berning EA230 is in Part II

Olden Golden Components Part II

I've owned quite a few of the components discussed and still listen to a couple. This is a reflection of the articles' profound influence on my pursuit of the audio hobby. Since I believe that they are as relevant then as they are now, I added them to the JE Labs Arkiv.