Playback of mono records

Listening to mono records is fashionable again. An unprecedented range of “mono cartridges” and special phono equalizers is suddenly available again. For the music lover, the question is whether he needs all this, and if so, what does he actually need? What kind of “sound” can one get out of such old mono records at all?

In the beginning there is the desire to listen to a certain piece of music. If vinyl is the preferred medium and the recording is old enough, it may be a mono record. You can often find mono pressings of older stereo recordings that were available alongside stereo copies. This has to do, among other things, with the fact that the true mono pickups, which only allow horizontal movements of the needle, would immediately destroy a stereo LP when played!

Mono recordings (until about 1960) are not only available on mono LPs but also as so-called electronic stereo editions (“Breitklang” etc…, e.g. on Decca “Eclipse” or DGG “Heliodor”), which are a kind of pseudo-stereophony and usually sound horrible for today’s listening habits. Different frequencies (i.e. pitches) were mixed differently on the two stereo channels. In such a case, it is therefore advisable to look for a true mono LP of the recording.

Then there are mono LPs of stereo recordings (until about 1970, depending on the country and record producer). If the stereo output is rarely sufficient or the recording was released in stereo only on tape, for example, then even then you can’t get around the mono LP or only for a lot of money.

But how can you recognize mono records? In principle it’s quite simple – it doesn’t say stereo on it!

And how does mono sound now?

Basically, the term monophony means that only one channel is transmitted. When playing back through a stereo system, this means that the music comes, or at least should come, from the center of the two speakers.
Apart from the lack of spatial width, the quality of the reproduction can be brought to a level that makes you forget about the transmission through a stereo system when enjoying music. With high-quality mono cassettes, as with stereo reproduction, a certain ambient sound of the recording room is presented as reverberation, which can give a satisfying spatial impression in combination with the depth staggering.

Due to the lack of acoustic width, depth staggering is the essential design element in mono recordings, so that soloists often stand more clearly in front of the accompaniment/orchestra than one is used to in stereo recordings. Due to the fact that sound sources are spatially closer together in mono than in stereo, the mixing of instrument harmonics and other conditions for masking sounds (and distortion) results in a different, mono-specific sound characteristic. Apart from spatiality, perfectly reproduced mono discs also have a different sound than the corresponding stereo output.

However, monophonic playback through a stereo system also has advantages. Excitation of the room in the bass range at two different points is acoustically more favorable in terms of room modes (adding wave superpositions) than a single speaker. The virtual mono loudspeaker in the center also cannot psychoacoustically act as a phantom sound source, since it has no enclosure on which reflections could occur. So it is by no means the case that a separate mono system has to be used for mono playback. The variant with two loudspeakers is rather a listening-philosophical concept of the modern age.

Real mono pickups or rather quasimono?

The stereo record contains a ninety degree offset stereo channel in each groove flank. The scanning is thus done in a combination of lateral and deep writing (left/right/top/bottom), the mono record contains only one channel encoded purely by lateral writing, i.e. left/right deflection of the needle. The mono groove is therefore a push-pull arrangement. Similar to the signal being protected from interference etc. by balanced amplifier sections and signal connections, a true mono cartridge can also play new mono records with little ambient noise, even less than when played back with a stereo system. Whereas stereo records, when worn, exhibit problems primarily in the high-frequency range, wear on mono records tends to manifest itself in a diffuse loss of quality across the entire frequency spectrum.

True mono cartridges mechanically allow only side-to-side scanning and are therefore not suitable for playing stereo records. They would be destroyed in the process. The groove of monophonic records before the introduction of the microgroove in 1948 until about 1970 is wider than the stereo groove, so that the diamond of the mono cartridge has a radius of curvature of 25 µm, while the stereo version has a radius of curvature of only 12 to 18 µm. This inevitably means that a stereo system runs deeper in the mono groove on the one hand, and on the other hand, its ability to write deeply means that it also samples significantly more noise! On a mono LP, there is no information in the deep writing. True mono cartridges don’t do well with wavy records because they can’t sample in that plane, which highlights the often heavier pressing weight and flatness of 50s records.

Between real mono and stereo pickups there are (today) many wrongly designed hermaphrodite mono systems with too small 17µm needle, stereo systems with only one electrical channel (mechanically designed for side writing) and 25µm needle and all kinds of nonsensical combinations. Often it is not even clear from the manufacturer’s / dealer’s descriptions what it actually is. Some classic systems that have been on the market for a long time have mono stereo cartridges that can be interchanged with the same weight, size, etc. without major adjustment work on the tonearm. Since true mono systems have a completely different design and mechanically destroy stereo records, they require at least a separate tonearm, at least if mono records are not to be played exclusively.
Again, in a nutshell: A real mono cartridge for micro grooves (=M33/45) has only one channel, scans only horizontally (=side writing) and a circular needle (=ball) with a rounding radius of 25µm.

The PE 7000 pickup system

This report is about the revival of an old, genuine mono side-scan pickup from PE (= Perpetuum-Ebner). It is a so called reversible system with a normal needle N78 for shellac records and on the other side with a micro groove needle M33/45 for real mono LPs and singles.
This pickup system is NOT a conventional piezo system (= ceramic or crystal), but a real dynamic pickup, i.e. a so-called high-speed transducer. Due to its construction with an internal magnet and a moving iron plate, this pickup is actually an MI (= moving iron). Not to be confused with MM (= moving magnet) where the magnet moves.
However, the electrical characteristics of MI and MM are absolutely comparable. With both types, an equalization (CCIR, AES, LP, RIAA etc.) suitable for the disk medium must be “switched on” in the preamplifier, just as with today’s modern MMs and MIs. In contrast to this, piezo systems, which are so-called amplitude converters and therefore do not require equalization.

Already at that time on the so-called cutting foils of the Microgroove / micro groove record cutting machines qualitatively more or better was written by scratching on it, than the best crystal systems at that time got down again. And this should change with the new magnetic systems: the 78 shellac records, for example, could only process a frequency range of about 80 to a maximum of 7,000 Hz, the then new 33 vinyl record (mono from 1949 and then stereo from 1958) could store from the beginning in about 40 to 18 Khz.

1956 – It was possible to switch the system from N to M. N stood for NORMAL = shellac at 78 rpm and M stood for “microgroove” vinyl mono LP at 33 1/3 rpm.
Switching is done by turning the switch knob at the front of the tone arm by 180°. It is advisable to set the changeover switch to the middle position when the unit is at a standstill, so that the two sapphires are protected.

System exchange
The system snaps springily into the mounting bracket and can be removed from the tone head without tools.

To remove the system, pull the system body forward by the switch button and remove it downward from the mounting bracket. Proceed in the same way when inserting the system. First insert the system body at an angle to the rear so that the rear system axis comes to rest in the hole in the bearing plate. The system is locked in place by pressing lightly on the switch button in the direction of the longitudinal slot.

Installation of the system in the tone head
The system can be installed in any tonearm with 1/2″ standard dimensions. To install the system, remove the system body from the mounting bracket as described above and fasten it in the tone head with the two screws. The two soldering lugs on the mounting bracket are then connected to the contact sleeves by the two connecting strands 10. After installing the system in the sound head, check the tonearm support weight (e.g. using a small spring balance). If the manufacturer of the turntable does not give any other information, set the tonearm support weight to 8-10 g.

Replacing the armature
The armature can be easily removed from the system body with a fingernail and replaced with a new armature. Make sure that the needle carrier 9 faces forward during this procedure and is not touched when it is pressed in. So only apply pressure to the red or green plastic surfaces! Subsequent adjustment is not necessary.

Technical data

  • Principle: four pole magnetic system
  • Mounting: suitable for USA standard tonearm head
  • Switching N-M: by axial rotation of the system by 180° by means of a toggle knob on the head of the system
  • Capsule weight: 25g
  • minimum tonearm weight: 4g
  • Pickup needle roundness: 55-60µ for 78 rpm | 23-27µ for 45 and 33 1/3 rpm
  • reset force: 3g/100µ
  • Frequency range: 20Hz – 30kHz -3db
  • DC resistance: 1500 0hm
  • Inductance: 350 mHy
  • Impedance at 1000 Hz: 3500 0hm
  • Output voltage: Normal 6 mV/cm sec -l | Micro …. 8 mV/cm sec -1
  • Most favorable terminating resistor: 100 kOhm parallel 500 pF

For full scale of the record at 1000 Hz the fast:

  • 33 1/3 rpm approx. 11 cm/sec i.e. 88 mV
  • 45 rpm approx. 11 cm/sec i.e. 88 mV
  • 78 rpm approx. 16 cm/sec i.e. 95 mV
  • Necessary bass equalization according to DIN 4533
  • CCIR cutting characteristic: U 100 Hz 13 db = 1 :4.5 | U 1000 Hz : U 50 Hz 17 db – 1 :7

Remarkable details
The PE 7000 Duplo magnet system has the highest output voltage of all Duplo magnet systems, so that equalization and amplification can be obtained by cheap means. The output useful voltage of the micro and normal sapphire is the same when playing normal playing records and long playing records. This prevents the equalization amplifiers from being overdriven when playing normal-playing records, and the physiological volume control operates at a constant useful level.

As a result of the system’s closed magnetic field, no magnetic pull occurs even with an iron platter. Thus, a change in tonearm weight due to magnetic pull does not occur. The magnetic air gap is completely encapsulated so that neither iron filings nor dust particles can settle there during operation. The exact magnetic symmetry allows the use of low restoring forces, so that a distortion-free sound pickup is guaranteed up to a minimum sound arm weight of 4g.

The resonance at the upper transmission range, which is physically caused by the elasticity of the sound grooves as well as the mass of the vibrating armature, is higher than even that of known dynamic studio pickup systems due to the low reduced vibrating masses. This unavoidable resonance is so high that it is above the music frequencies recorded on the record.

Since the resonances are well outside the audible range, there is no need to artificially damp them. Additional damping material increases the dynamic restoring force at higher frequencies and would thus increase the stress and wear on the sound grooves. This would quickly destroy the recordings of the high frequency parts of the music, which to a large extent make up the quality of the record.

Revival of NOS anchors/needle inserts for the PE-7000 [ LAZARUS ]

PE 7000 | 33/45 mono diamond

PE 7000 | 78 shellac

Today’s market doesn’t offer much in the way of N78 (sapphire green) and M33/45 (sapphire or diamond red) styli … Unfortunately, most of the ones you can still get somewhere are no longer usable. The reason for this is the condition of the damping rubber, which was completely hardened/brittle and swollen on all specimens found. This hinders or blocks the movement of the needle carrier and does not provide any damping or restoring forces. So the so-called anchor or needle insert is not usable, although all components, except for the rubber, are completely in order. How can a revival of these needle inserts look like ? After a longer look, only a disassembly of the needle carrier came into question. To do this, the small locking cross pin must be pushed out and pulled off. Then the needle carrier together with the longitudinal axis and the iron plate can be moved downwards. Thus freed and with more air and play, the old rubber can now be carefully cleaned out with suitable solvent.When the unit is cleaned, it goes to the most important part of the operation, namely the insertion of a new rubber. After a long period of testing, a pressure insertion using a medical syringe and a suitable hose attachment has proven to be very effective. After that, the needle carrier must be meticulously centered horizontally and left at rest until the rubber has “hardened”. This is followed by the reinstallation of the small cross pin and an adjustment of the lateral angle (= VTA) of the scanning needle and, of course, a listening and scanning test.

Revived needle inserts according to the Lazarus principle are available again today and amaze with excellent mono reproduction on the legendary Perpetuum-Ebner PE-7000.