JE Labs Monaural Playback



Time travelling through the monophonic Hi-Fi era!

One of the fringe benefits of being a freelance musician is travel. I drive close to 20k miles a year and in between rehearsals and concerts I try to make it a point to get to know a new city or town I visit. I particularly enjoy exploring sites that look like it was locked in the 1920s to 1960s timeline. After enjoying Art Deco, streamline and mid 20th century modern architecture, I go to a local diner for a quick bite and then hit the flea markets and thrift stores to hunt for records and vintage equipment. I accumulated several mono LPs and 78s in this manner since I buy records mainly for musical content.

In the past I listened to these treasures using modern stereo cartridges, Stanton 500 or a Grado GTE + 1 equipped with a 78 rpm stylus through a Diego Nardi monophono variable EQ preamp hooked to my main stereo system with the mode switch flicked to mono...nice mellow sound, a bit lacking in dynamics (mostly due to paralleled stereo cartridge coils), very midrange oriented and with 78 rpm discs, accompanied by shellac groove noise. Hi-Fi enthusiasts 60 years ago were already already debating the virtues of triode and pentode output tubes in search for an ideal amp to drive a huge horn loaded speaker using cutting edge driver technology in their quest for better sound.


from "The New High FIdelity Handbook" by Greene and Radcliffe, Crown Publishers, NY, 1956

A typical mid 20th century American high end Hi-Fi set up would consist of a Rek O Kut turntable with a Gray viscous damped transcription arm, a GE RPX triple play cartridge, Fisher 50C preamp and 50A mono amp driving a single Altec 604 duplex speaker with an FM tuner, open reel tape deck and the output from a 20" B&W TV as additional sources. Knowing the capabilities of these classics, there is no doubt in my mind that the sound of this system is formidable. I am aware that there are a few modern day aficionados who maintain that the purest sound can only be achieved from a dedicated mono system.

Some sites to drool over:


My dearly departed friend and inspiration for this project, Brian Clark's mono fantastico! 


Sakuma has maintained cyberspace presence for over 10 years

It is worth noting that stereo evolved from several decades of research and development stemming from monaural sound reproduction. The great recording engineers from the mid 50s who captured the sound cut into the grooves of RCA shaded dog and Mercury living presence as well as other labels like Blue Note, Columbia six eyes and etc., honed their microphone skills in mono.

All these factors inspired me to re-evaluate my approach to monaural playback. Based on my research the starting point is to use a true mono cartridge - single magnet or single coil.

Triple play = 33,45 & 78
GE RPX + GE VRII


Before we proceed to cool gear let's examine the software. During the mono era there were two types of 10" or 12" record formats - LP microgroove and SP coarse groove. In either case the mono signal was etched laterally on both sides of the groove wall. "Hill and dale" Edison discs are notable exceptions. LP = long play (33 or 45 rpm) vinyl and SP = standard play (78 rpm) shellac records that are heavy, brittle, fragile and will break when dropped. Coarse groove SP requires a 3 mil stylus (purists have styli ranging from 2.5 - 4 mil) for proper playback while early mono LPs were cut to playback with a 1 mil. stylus. A .7 mil stylus also works with no danger of damaging the groove but some purists maintain that the smaller profile rides the record groove too low and picks up more noise. I found this to be true only if the record is worn out. It would be safe to presume that any mono LP released after 1967 or thereabouts were cut with narrower grooves and should only be played with a .7 mil stylus.
Aside from the slightly narrower groove width, the reason why stereo LPs can get damaged by using a vintage mono cartridge that does not have vertical compliance is because stereo LPs employ the Westrex 45/45 cutting system wherein the combined stylus motion (horizontal and vertical) is the vector sum and difference of the two stereo channels. Effectively all horizontal stylus motion conveys the L+R sum signal and vertical stylus motion carries the L-R difference signal.

Guide to GE VR stylus replacement


The American GE variable reluctance cartridge was considered state of the art when first introduced in the late 40s. Variable reluctance is a moving iron principle that still exists in modern form in Grado cartridges. A lot of GEs were sold to professional studios and domestic users, thus used samples are still easy to find and affordable. The triple play feature is very convenient to use - flip the red button to switch from an LP to a 78 stylus. "Clip on" replacement styli are still available from dealers at eBay; I use .7mil or 1mil spherical tip for mono LPs and a 3 mil tip for 78 rpm. Cantilever suspension is via rubber blocks (almost rigid) which are not prone to decay but can fall off. Since there is practically no vertical compliance I do not use it for stereo LPs. NOS GE styli are scarce and I use generic replacements.




After hearing the GE l could not go back to a mono strapped Grado or Stanton. But be prepared for needle talk due to high tracking force and lack of vertical compliance. The GE VR cartridge mounted on a viscous damped tonearm has great sonic synergy with the sensuous feel of a cueing lever at your finger tips. The earlier RPX on this tonearm track LPs between 4-5 grams and 6 - 8 grams VTF for 78s; take a gram off in both cases for the later VRII.

GE RPX + Denon DL102


The Denon DL102 is a high output (step-up device not required) moving coil type true monophonic cartridge that can play all types of microgroove format including stereo since it has vertical compliance but no signal sensitivity since it only has one armature. Superb technical information on the DL102 was uploaded by Murray Allen to dispel all the lost in translation issues found in internet forums. A must read! This cartridge was introduced in 1961 for broadcast applications and reissued in 1996 to cater to monaural aficionados. It is a fine cartridge with the familiar DL103 sonics, better tracking ability (3 grams VTF minimum) than the GE VR/RPX but edged slightly in the midrange where the GE posesses an SPU like warmth and transparency.The DL102SD model is for SP/78 rpm shellac playback.

For best performance these 10-13 gram cartridges (DL102 and GEs) require a high mass tonearm like an SME 3012, vintage Ortofon or Rek O Kut, FR64/66, Audio Technica ATP12T, Lenco L-70 or my favorite viscous damped arm.

SPU Mono

For those with Dom Perignon budget yet classic taste Ortofon offers the SPU (Stereo Pick Up) mono which has the motor armatures connected in series and rotated 45 degrees to minimize vertical sensitivity. Even if the SPU mono has vertical compliance it is not stereo compatible because the stylus is 1 mil. The single coil CG25di and CG65di are direct descendants of the 1948 Fonofilm mono cartridge. These mono cartridges are expensive and remain in production mainly due to interest in Japan.

Rek O Kut B12H + Velvet Touch
viscous damped tonearm + GE VR


The RIAA EQ curve was established as the standard EQ for stereo and microgroove record cutting in 1955. Prior to that various EQ curves were used in cutting mono LPs and 78s that was why I built the Nardi monophono circuit from SP 16. This is a good design concept and uses my favorite tubes however I was not too sure about the split EQ time constants which may not be tracking each other accurately for a given curve. The direct coupled cathode follower also made it sound dark and a bit lifeless. I also found myself spending too much time fiddling with EQ rather than listening to music. Initially I was scouting eBay for a Fisher 50C but due to collector interest this unit is priced out of reach for mere mortals. I ruled out the McIntosh C8 and Scott 121 because they use negative feedback EQ. In my audio journey I try as hard as possible not to set design rules but so far any preamp or amp circuit that I encountered employing negative feedback always chokes the sound.

JEL mono preamp with variable phono EQ


After going through my collection of vintage preamp schematics I built a monophonic preamp with passive EQ networks taken from the RCA SV1 preamp which is very similar to my stereo preamp that was based on the phono circuit found at the back of an RCA tube manual. I wanted a period correct project and did away with Ni-mH battery biasing.




As shown in the schematic the standard RIAA/New Orthophonic, AES, Columbia LP and Old 78 passive EQ networks are inserted between the two triode halves of a 6SL7 and selected by mounting them on a 6 position double pole rotary switch. The "Old 78" EQ setting sounds and looks in the scope like it averages various American 78 EQ curves used from the late 30s until the mid 50s with a mild scratch filter that reduces shellac groove noise but still preserves enough top end to 10khz. This might not be compatible with European 78 pressings and do not have any to confirm. I have been enjoying American 78s from RCA, Columbia, Capitol and Decca using this EQ curve.

Even if one uses a vintage tube preamp equipped with a comprehensive EQ selection it is almost impossible to determine exactly what EQ curve was used prior to RIAA standardization, thus the existence of tone controls in vintage units for the user to season to taste. One can get carried away with dialing various EQ curves before playing a record but I would rather live with my four EQ settings sans tone controls and enjoy!


The preamp can be built as a standalone mono preamp with this line stage circuit using a 250k log taper potentiometer for volume control. Cheap carbon track CTS or 250k Alps Blue Velvet will do the job.


Separate chassis CLC power supply with B+ 300-330V @ ~ 10ma. with DC rectified filaments connected via umbilical cord for lowest noise.


JEL mono amps
SE2A3 + SE410
Warm glow of an SE10 amp


Altec 605B Duplex in a folding open baffle
mono = single speaker

The use of a single speaker was a revelation! Monaural playback is not as simple as flicking the mode switch to mono and hoping for a precise phantom center image. Listening through a pair of stereo spaced speakers introduces phase incoherence that leads to loss of detail and compression of dynamics. There is a wealth of musical information imbedded in the microgrooves of a mono LP. Even the limited bandwidth electrically recorded 78 coarse groove format has information that we have not heard for several years due to improper playback. Pure unadulterated sound - the aural equivalent of B&W images captured by Henri Cartier-Bresson and other fine photographers of that era - with detail, warmth and dynamics to satisfy modern day audiophile requirements. No need to psyche oneself to the illusion of being transported to Carnegie Hall because there is no soundstage to worry about. I now understand why some die-hard mono enthusiasts from the 50s initially claimed stereo was a conspiracy to sell more amps and speakers. The standard achieved at the height of monaural high-fidelity era was great!


Have fun and happy listening!

Comments

  1. MONO Lives-On with me!!!! I have had FANTASTIC RESULTS that literally brought TEARS OF JOY to my eyes and FULL-CONTENTMENT to my EARS...

    I have NEVER had as much fun and contentment as an AudioMan with ANY So-Called stereo rig I have donstructed or owed...

    ReplyDelete
    Replies
    1. I am sure there are other mono enthusiasts out there...thanks for visiting and happy listening!

      Delete
  2. Thanks and compliments for sharing all this information! I'm a diy electronics 'newby' and a not native English speaker/reader.

    In your description and scheme' s I can't see wich tubes you used because I' m not sure if Diego Nari' s or the RCA scheme is used as an example for your design. I Think it imgihgt be the RCA schem ,without the second 12ay7 ?

    ReplyDelete
    Replies
    1. Thanks for the kind words. I used a 6SL7 as indicated in the schematic which is derived from the RCA SV1. Happy listening!

      JE

      Delete
  3. Your piece was wonderfully written. And, I get it. Right now I'm not in a good position to take on a mono project, but your article has "bit me with the bug". I'll be thinking about this. And you've motivated me to retain the single JBL 15 inch woofer and potato masher horn to put into a mono setup. Thanks for that new perspective - otherwise they'd be headed for ebay. Sorry my signature says "Dad/Mark" - I usually use it to post to my kids blog, hence the odd signature - all the best...

    ReplyDelete
    Replies
    1. Thank you very much! I am glad you found useful information from this post.

      Happy 'mono' listening!

      JE

      Delete

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