Announcement
Introduction
Quality
of broadcasts in the UK
Specification
Board
only version
Trough Line identification
Reviews
One Thing Audio
One Thing Audio
MPX1 / MPX2
Announcement
IntroductionJan 2007: MPX2 STAND-ALONE DECODER
Later than expected (for which apologies all round!) our MPX2 stand-alone decoder makes its long-awaited appearance.
A few 'tweaks' have taken place (better resistors, polypropylane caps etc), but the spec. remains substancially the same, so no-one owning our original decoder need feel 'left behind'. For reasons of international compatability, the MPX2 uses an external AC power adaptor (12V), and its new 'slimline' appearance should make it easier to accommodate on those cluttered shelves! The MPX2 is supplied with a 2 YEAR GUARANTEE and costs just GBP £169.37.
The MPX1 / MPX2 stereo decoder has been developed to partner any FM tuner which does not have its own integral decoder, or in cases where a decoder is fitted but deemed poor by modem standards. Although the decoder is a solid-state device, great care has been taken to ensure that the tuner's audio 'signature' is not lost in the stereo processing. Noise and distortion figures are the lowest achievable with current techniques.
The decoder is also available as a ready-assembled p/c board with integral power supply for mounting inside a tuner (eg. QUAD FM2) NOTE: With valve tuners, internal temperatures in excess of 40 degrees C may degrade stereo separation.
The MPX1 / MPX2 decoder needs no adjustments on the part of the user to get it up and running. It has been carefully designed to work first time, without adjustment, providing a suitable composite signal is available from the tuner.
Quality of broadcasts in the UK
Since the late '90s Ron Best has been a tireless compaigner in the UK for the retention of the Frequency Modulation Broadcasting System on the basis of its superior quality over DAB. He is considered a Dinosaur by the Broadcasting authority although evidently not yet ready for extinction. Here are some of his thoughts on the matter:
The following is reproduced from the MPX1's instruction manual dated August, 1997:
Quality of broadcasts in the UKCurrent transmission practices have resulted in a 'swing' of broadcasting quality that sometimes beggars belief. This ranges from the breathtakingly superb to the excruciatingly awful. At best, with dynamic processing avoided or at least kept to a minimum, a 'live' broadcast can be very good indeed, if variable. Our own opinion, for what it is worth, is that the best of modern transmissions are the best ever heard. We do not believe there was ever a 'golden age of broadcasting' and suspect that fond memories rather than demonstrable proof form the core of this myth. (If you have both, it is possible to form a more balanced view!) This is not to diminish the inspiration and artistry, sometimes bordering on genius, of some pioneering BBC engineers, who worked with much cruder tools. There is less excuse for them to get it wrong these days, yet they frequently do! This is sometimes due to carelessness or incompetence, or plain bad judgment. What is more depressing is when it is "got wrong" as a matter of policy!
This makes it impossible for any self-respecting audiophile to enjoy musical broadcasts during the daytime when 'Optimod' is in full swing. However, this is sonic bliss compared to what lies in wait for one further up the band: on most pop stations a combination of over-modulation and dynamic squashing can produce a muddled cacophony that, at the very least, mocks the high standards achieved by broadcasting authorities over the years. But ... it may be argued that anyone owning a top-notch FM tuner playing through a high resolution system is NOT
likely to subject it to these sonic horrors except in error or in a wild scurry to the next station along the dial.Is there any future for FM broadcasting in the UK?
Few facts are available and much speculation! The broadcast authorities would nave us believe NOT. Investment in digital broadcasting has been substantial, and there is no turning back. If the system meets its specification in full, for those who have the need it should be possible to select a wide variety of distant stations with negligible distortion and background noise. Certainly there should be real gains for listeners in poor reception areas, but other 'gains' may be less tangible. Most committed Radiophiles complain more bitterly about transmission practices and quality rather than inherent limitations of analogue broadcasting or FM receivers. We quote the words of a former BBC engineer: "Cherish your well designed and proven analogue tuner. It may be years before you hear anything as good.' (The same may be claimed for NICAM, another story of past excellence and unexplored potential in the wake of digital broadcasting).
There is also the intriguing 'conspiracy' theory. This alleges that engineers, sworn to silence, have been told to progressively limit and degrade analogue broadcast quality whilst at the same time giving every possible advantage to its digital counterpart as and when it in phased in. Thus the perceived 'sound improvement' will quickly spread amongst the general public making the digital option more desirable and bringing closer the day when the FM waveband will fall silent. Tut tut ... how absurd.
So what will happen when those transmitters are finally switched off? Is it really the scrap heap for all those hi-spec analogue tuners that have given so much pleasure over the years? Well, we probably have ten years' grace anyway; this has been accepted privately, if not publicly, as a realistic hypothesis. But long before that there will be a glut of digital-to-RF converters. The real threat to analogue tuners, relegating them to museum pieces, is more likely to come when the asking price for a digital-to-RF converter is many times that of a cheap'n'cheerful digital tuner. But. ..perhaps by then there will be few of our generation around to care. GOOD LISTENING! Steam radio still has a lot to offer.
Postscript, March 2001
At the time the above was written, very few people, including ourselves, had listened to a digital transmission. In the late 1970s Angus Mackenzie was of the opinion that very few FM tuners then marketed were good enough to do justice to the excellence of the BBC's transmissions. He also believed that a good live FM broadcast was better than any sound from an alternative 'hi-fi' source - ie, tapes and LPs. Mackenzie can be credited, due to the accuracy and professionalism of his reviews and lab tests, with forcing manufacturers to design FM tuners not only with higher specifications, but ultimately allowing them to occupy their rightful place as a genuine piece of hi-fi. The improvement in domestic tape recorder technology convinced most music lovers (remembering the days of hissy tape recordings with high distortion and restricted bandwidth) that paradise was within reach.
Digital mastering of tapes in the studio, and digital links in the transmission chain virtually eliminated noise and distortion, and the 'state of play' in the late eighties and nineties was such that, at least with live broadcasts of major concerts in the evening, it was difficult to know, or foresee, what the BBC could possibly do to improve matters.
Enter DAB
Suspecting that most commentators on the new technology were little more than casual knob-twirlers (most of whom, we were convinced, never listened seriously to radio anyway) , we took great pains to compare the two systems in a balanced and scientific manner. Two identical, hi-quality analogue tape recorders were brought into commission, simply in order to 'capture' live broadcasts and replay them to listeners who were completely in ignorance of the recording source. Tuners by Leak, Quad and NAD were used at various times to represent the FM ability; tuners by Cambridge Audio & Panasonic were sworn into service to represent DAB.
Listeners were, in turn, played the identical piece of music in FM and digital format. They were not told which broadcast system they had listened to - simply requested to say which sound they preferred. 11 out of 12 listeners chose the FM as the 'superior' and far preferable sound. Ironically, many believed the better sound was the digital sound. When asked why they assumed the better sound was digital, most responded with endearing logic: 'Well, it's supposed to be better, isn't it?' Thus, the vast majority chose the FM sound but thought it was digital!! Perhaps after having this rammed down their throats by broadcasting authorities for half a decade, it's not surprising they made this curious mistake.
Digital live broadcasts, or tapes of live broadcasts, have to date been most disappointing. The sound is 'forward', bright and thin. Dynamic compression in classical music is present - and can be heard distinctly on both FM and DAB. There is an objectionable 'strangled' quality to the BAB and very little sense of space. Voices are either too forward or too loud -but beware of trying to compensate. by adjusting the volume, for just the change of a microphone will call for another adjustment.
The 'realism' one takes for granted in a studio discussion on FM is virtually non-existent on DAB. Not only is the sound definitely NOT CD quality, it barely qualifies for the epithet 'hi-fi'.
Will it get better? This is unlikely due to the data selection inherent in the system.
As the rest of the world is sticking with FM (or made digital broadcasting available only as an 'optional' service for those who feel they need the sheer quantity of stations) it seems the UK alone will have imposed upon it a system of inferior audio quality by an Authority whose name was once synonymous with quality. A depressing state of affairs.
Stereo Demodulator MPX1 / MPX2
Noise (CCIR) 76db Total Harmonic Distortion (<500mV p-p input stereo) 0.08% (800mV p-p input stereo) 0.1% (1000mV p-p input stereo) 0.3% Frequency response 3Hz- 14kH
-1dbStereo Trigger Level (Standard Version) 300mV Input Impedance 50K Output Impedance 100 ohms Recommended Load Impedance (min) 10 K Output level Relative to input setting. Average: 1.6V Channel Seperation 40db De-amphasis 50µ Mains 240V/110 V
50/60HzDimensions Board only MPX1 (Height, inc feet) 35mm (Width) 63mm (depth) 120mm Dimensions Stand alone version MPX2 (Height, max) 60mm (Width) 105mm (depth) 227mm
OT MPX1 stereo decoder now available, with simple-to-follow fitting instructions, for Quad FM2. The decoder is self-powered, so no need to worry about providing a separate power supply. The decoder will fit into the rear space previously occupied by Quad's original 1961 decoder, and gold-plated phono sockets are provided for mounting onto the back plate of the tuner if desired. If your FM2 sounds moderately good (but perhaps a bit 'lifeless') through its original decoder, you'll be pleasantly surprised - as have many purchasers to date - just how marvellous it sounds through a modern decoder! (Note: it is assumed that the tuner has no serious fault condition or has had its alignment tampered with).
Leak Trough Line 2 (maroon front panel)
Leak Trough Line 3 (original, silver front panel)
Leak Trough Line 3 (later type, silver front panel)
Leak Trough Line Stereo (silver front panel)
Leak Trough Line 2 (maroon front panel)
Your tuner conforms to one of the above. Ignoring Leak’s original Trough Line 1 (circa 1955), the Trough Line 2 (1960) was the first ‘hi-tech’ design anticipating stereo broadcasting, and was nothing short of a technological breakthrough (as reviews of the day will confirm).
Trough Line 3 (original) was no more than a Trough Line 2 with a silver front! It was considered that the maroon front plate was a bit old fashioned for the first year of the ‘swinging 60s’, as it was subsequently known.
Leak Trough Line 3 (later type, silver front panel)
Trough Line 3 (later type) had no visual characteristics to identify it, but as the Multiplex system of broadcasting had now been signed up to, both for Europe and America, it was now desirable to incorporate a number of modifications which would benefit the performance in conjunction with the decoder which Leak was developing. These included a number of circuit or component modifications, but specifically a lower distortion discriminator.
Trough Line Stereo was essentially the above (later Trough Line 3) but utilising an ECC88 in place of ECC84 as the first RF valve. (Note: the two valves are not interchangeable without modification to the valve base, but in our experience there is little measurable difference in performance between the two valves). Additionally, a cathode-follower output without de-emphasis was provided to give a low impedance drive to any future decoder.
From the foregoing it is clear that we are talking, not of one Trough Line, but 3! (Or 4 if you include the original design of 1955: although this is truly innovative and represents the flagship from which all the Trough Lines metamorphosed, its selectivity/sensitivity is poor compared to the later Trough Line 2).
When we service and align a Trough Line tuner, if it isn't already a Trough Line Stereo or the later Trough Line 3, it gets modified so that it IS! However, the first RF valve (ECC84) remains for reasons stated above.
Sit back and enjoy: Trough Lines never sounded better!
