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!
Susumu Sakuma (1943-2018) owner of Concorde Restaurant and avid DIYer has been a monaural hifi advocate since the 90s. Watch more Sakuma Videos.
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 possesses 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.
SE2A3 + SE10 mono amplifiers |
Warm glow of a thoriated filament |
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!
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...
ReplyDeleteI have NEVER had as much fun and contentment as an AudioMan with ANY So-Called stereo rig I have donstructed or owed...
I am sure there are other mono enthusiasts out there...thanks for visiting and happy listening!
DeleteThanks and compliments for sharing all this information! I'm a diy electronics 'newby' and a not native English speaker/reader.
ReplyDeleteIn 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 ?
Thanks for the kind words. I used a 6SL7 as indicated in the schematic which is derived from the RCA SV1. Happy listening!
DeleteJE
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...
ReplyDeleteThank you very much! I am glad you found useful information from this post.
DeleteHappy 'mono' listening!
JE
As always a very interesting post!
ReplyDeleteI'm using a lot the old GE VRX. Enough to get another changer with it! (a Webster 126B and Garrard 88/4). Listening lots of jazz mostly of my records are mono LPs and 78s. Ny now I'm using mostly the RCA preamp, but I believe the VRX can give even more. I'll try this, I'm sure it's marvelous.
What do you think about the classic GE preamp circuit with 6SC7?
Best,
Martin
Hi Martin,
DeleteThe GE phono circuit is in my "to-do" list, just haven't found the time to build it. If you build it soon, please let me know how it sounds.
Thanks!
JE
I'm just starting to make it. Just not yet sure about to put a 6J5 after 6SC7.
DeleteAs far as I know the GE preamp was just half of the circuit because it was mainly to adapt with a radio receiver with tone control. The equalization would be another circuit. And as far as I can understand the complete circuit would be very near what you put here, with several options. I believe it's worth to take a look. I don't like cathode follower too, so this basic circuit can be interesting.
I pretend to use this on a PP circuit using 6B4G, attibuted to Jack Rosemberg as a gift to Einstein (1949). I don't know if this is true, but the amplifier is very good. The original preamp is fine for old records, but the LPs doen't like it very much! :)
DeleteI made GE preamp and I got great results! Easy to construct indeed. I made it with RIAA, EAS, Columbia, Decca and 78rpm. After it the 6SN7 to give a little more gain. I don't have equipment to measure distortion, etc, but by listening I believe it's as good as the RCA,
ReplyDelete