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!

JE Labs Loctal Preamp

Motivated by Ding's octal version of the 834P, I quickly got my hands dirty punching out and painting a chassis. 

Loctal tubes

The concept of this project was to build a full function stereo preamp utilizing loctal tubes based on the schematics below.

Preamp circuit

!!!WARNING!!! 

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

Power Supply

5AZ4 rectifier = 5Y3 on a loctal base

Line Stage

Zero feedback single gain stage direct coupled to a cathode follower line stage topology featuring the two medium-mu triodes below

The 7AF7 is very similar to the 7N7 and 6SN7
but has slightly less
transconductance and inter-electrode capacitance

7N7 = loctal based 6SN7

Phono

The stock EAR 834P circuit (above) used all high-mu 12AX7s with the second stage capacitor coupled to the cathode follower stage. While preparing this blog entry, I remembered that my dearly departed friend, mono aficionado Brian monofantastico Clark, grafted his own interpretation of an EAR 834P phono stage to his SE 801 mono integrated amplifier. He was an active participant in this discussion of 834P modifications initiated by Thorsten Loesch.

Ding's octal version of the 834P uses all 6SL7s with the second stage direct coupled to the cathode follower stage. Without ever sounding harsh, Ding's octal 834P sounded brighter and had a refreshing airiness in the high frequencies compared to my darker and more midrange oriented RCA derived phono preamp. Even if I never heard an original EAR 834P, I now have a good idea why it was received with great enthusiasm.  

7F7  = 6SL7 on a loctal base

Although the 7B4 and 7B6 are high-mu loctals, they are single triodes. AFAIK, the 7F7 is the only high-mu twin triode available in loctal and was the obvious choice for the 1st and 2nd stages of the 834P circuit given my chassis configuration.

Tube rolling loctal style

I've been tweaking and listening to this preamp for the past 6 months.

During my Dyna PAS hacking days, the 12AU7 always sounded gutsier in line stage and cathode follower applications than the 12AX7 because it had lower Rp and pulled more current. Thus, there was some room to voice the 834P circuit through the cathode follower section.

Warning: 7F8 is NOT plug-in compatible
with the 7N7 and 7AF7

I initially set up the phono section to use the unique 7F8 loctal in the cathode follower position, hoping that the 7F8's greater transconductance will produce a darker and more robust sound. But ultimately, it was the ubiquitous 7N7 (loctal 6SN7) that gave me the tonal balance I wanted, with the 7AF7 as alternate.

With an amplification factor of 48, the 7F8 may not have enough gain as a phono preamp with the RIAA EQ in the negative feedback loop. However, it was too much for a zero feedback single stage line amp.

Typically, I don't split halves of twin triodes for left and right channels. I made an exception in wiring this line stage so that I could exploit the 7AF7 vs. 7N7 comparisons and usage options.

My ears finally chose the 7AF7 as the voltage amplifier for the line stage. The slightly lower transconductance and amplification factor mimics the exotic tonal qualities of its grandad, the 76. Each half of the 7AF7 is direct coupled to half of a 7N7 configured as the cathode follower. This combination is as close as I could get to my 76/6SN7 line stage.

But don't limit yourself to this report, use it as a starting point for your loctal tube rolling adventure. 😉

Which is better?

or

Both are here to stay. 😎

🎅🎅🎅 Happy holidays and merry listening! 🎄🎄🎄

Octal EAR 834P phono preamp

During my visit to NYC earlier this summer, my buddy Ding loaned me his home-brewed octal version of the EAR 834P phono preamp using 3 x 6SL7 octal tubes. Powering the preamp is a General Radio 1201-B tube regulated power supply.

Ding is not into boutique parts. Instead, he used carbon film resistors, mylar coupling capacitors and electrolytic caps gathered from Hamfests and surplus stores. Proper grounding and parts placement ensured a very quiet phono stage.

Traditional tube phono stages like the classic Dyna PAS 3 and Marantz 7 employed active RIAA EQ networks inserted in the negative feedback loop from the final stage to the input stage. In the 834P, Tim de Paravicini used active RIAA EQ with a clever twist - the EQ network is fed from the cathode follower output back to the second stage only. IMO, the benefits of this topology are: a 1st stage unimpeded by negative feedback, low noise and low output impedance.

I've been enjoying this phono stage so much that I'm inspired to build my own version. Good job, Ding!