Lexicon PCM96 A Reverb Masterclass? - Audio Media

More documents

Recommendations

Info

POWER FACT AND FICTION, PART 2 More Pulling of Fluff from Fact… Last month we tried the subjective approach. This month, ANDREW GRAEME puts some theories to the test and more myths to rest with a more technical approach. Last month, David Helping took a very subjective look at the various products that claim to clean or somehow alter studio power supplies, and their effects on the final sound. He told us that he will not ‘go into engineer geekiness’, so I thought I would. The issues raised in the first article were voltage regulation, balanced power, power conditioners, and esoteric power cables. I decided to actually see, or rather hear, what exactly is going on when people claim to have vastly improved audio, as the result of some change in the power is delivered. Testing, One, Two… To do this, I had to first create a poor mains supply. The voltage had to vary by 10%, radio frequency interference (RFI) and switching noise had to be carried on the mains supply, and connection to earth (ground) had to be less than absolute. I then compared the effects of adding esoteric screened power cable, power conditioners, and the effects of RFI under both these and normal conditions. I also created a poor earth by rigging up a 20m length of wire with a 10Ω resistor at the end, connecting to the studio earth. This simulated the typical situation one finds in older buildings, where lengths of old wiring are often linked to ageing junction boxes with less than perfect connections. I found that this acted as a splendid antenna for signals coming from flat screens and energy saving light bulbs, and also led to a marked increase in clicks and pops from switches and outside relays from air > 48 AUDIO MEDIA OCTOBER 2008
conditioning and heating plant. No connections were made with other pieces of equipment, so as to prevent any RFI entering from any other source than the mains cable or the earth wire. A significant transmitter of unwanted RF that is sometimes used in a studio is the compact fluorescent lamp (known to its friends as the energy saving light bulb). By wrapping an open ended cable around the lamp, I could get up to half a volt of RFI, but only 2mV in a power cable that connected to the mains but not earthed. I got no RFI in the mains cable at all when the cable was properly earthed. Lighting dimmers can also cause problems, and if your studio is near unsuppressed dimmers, such as in a block of flats, the RFI they cause can bleed into the mains. To test the levels of RFI carried in the mains, I set up 16 stage dimmers, each cutting the phase to its own 500W PAR lamp at exactly 50%. The result was less than expected at about 20mV when not earthed. With a poor earth, this increased to between 50mV and 100mV, depending on equipment used, and the effects of the dimmers could be clearly heard. I also tested the effects of multiple flat screens and CRT monitors, but these did not produce any mains-born RFI that I could measure, except when using the poor earth and then, the mains cable had to be lying right next to the source of interference, just to get 1mV of interference. The studio analogue mixing desk with its large PSUs showed no sign of mains-born RFI, and I could not test it with the poor earth or with earth lifted, as this would mean unplugging several hundred cables, just to isolate the effects of the mains interference. The <strong>Lexicon</strong> 960L did not seem to mind whether it had a good earth, a poor earth, or no earth at all – it remained serenely quiet at all times. Other than that, nearly every other piece of equipment increased its noise floor significantly, when the poor earth was used. This varied from piece to piece, and there seemed to be a tendency for the digital stuff to suffer most. Adding a power conditioner to the above tests had no effect on any units that were properly earthed. When the poor earth was used, some improvement could be measured in most units that were of an earthed design. This was far from massive, but the effect was there. The earth-free designs varied, with one unit, a small desk-top mixer that used the dreaded wall-wart, having slightly more thyristor buzz from the dimmers when the power conditioner was used. Off Balance Again and again, the topic of balanced power is brought up and often hailed as the one thing you can do to your studio that will improve signal to noise ratios more than any other. Subjective statements are sometimes added, like, “After installing balanced power, we got clearer highs and better defined lows.” Sometimes, almost magical properties are ascribed to it. Let’s see what balanced power is – and what it is not. Balanced power is created by installing a simple 1:1 separation transformer, the difference being that, instead of ground or earth being linked to the neutral wire, it is linked to a central tap that has 115 volts difference (i.e., half the mains voltage) from either of the two live ‘legs.’ The idea of this arrangement is the same as for POWER FACT & FICTION balanced lines for microphones or line feeds, that it rejects interference from outside and causes less induction in neighbouring cables, as the opposing voltages cancel one another out. All power supplies in Europe are either single phase AC and about 230 volts, or they are threephase, each phase being out of step with the other phases to provide a voltage of about 400 volts AC. All studio equipment is single phase. European law on mains supplies is complex and has to take into account such things as current and application, so as to make such uses as electric cattle fencing and high voltage industrial DC motors possible. But as far as studios, commercial or domestic, are concerned, any voltage above 50 volts is deemed to be a mains supply and must adhere to the strict laws governing their installation. Because each leg of a balanced supply is independent of the other, should the chassis become live as the result of a fault, the fuse to that leg may be triggered, but the chassis will now have a potential of 115 volts to both ground and any neutral wires not within the system. For this reason, both sides of the balance have to be fused at the wall socket or within the equipment, and the fuses have to be linked, so that, if one side is tripped, the other side is switched off as well. An alternative is to use a power relay or contactor that switches off the entire system. In the EU and in the US, balanced power may only be installed by a qualified electrician. A DIY installation of balanced power is definitely dangerous to both people and equipment. Laying Out The Ground Rules It sometimes happens that one sees the uninformed disconnecting the earth or ground wire in an attempt to interrupt a mains hum loop. In a word – don’t! The law requires all equipment to be either earthed, or to be of an earth-free design and, in a commercial environment, lifting the earth is a breech of health and safety laws in every European country. Also, nearly all audio equipment has circuitry that suppresses interference by bleeding HF to earth via the chassis. If the earth is lifted by disconnecting the green and yellow earth wire (or even using a dedicated earth-lift switch) under the right circumstances, this circuitry acts as a voltage divider and part of the mains supply is sent to the now earth-free, disconnected chassis. People have died, sometimes live on stage, because some idiot decided it would be a good idea to lift an earth to get rid of a mains hum loop. Disconnect the screen on the offending audio lead instead! Contacting Planet Earth I am often asked, “How do I know if the earth for electrical supply is OK” The simplest test is to take a multimeter and measure the resistance between the earth lead on any electrical socket and a metal structural part of your building. This should read zero Ω. You may of course get something like 0.001Ω, but if you get the same value by holding the leads to the multimeter together, then recalibrate your meter (or just make allowance for that value) and test again. If you get any value other than zero, call an electrician and get it fixed. Rather like modern cars, accessing the metal > AUDIO MEDIA OCTOBER 2008 >
Page 1: AUDIO-FOR-VIDEO • BROADCAST • I
Page 5 and 6: RUSHES 64 aUDIo tEchnIca IEM M3 REV
Page 7 and 8: from £11,270 www.smartav.net from
Page 9 and 10: ecording news streaming news @ www.
Page 11 and 12: AUDIO TECHNOLOGY PARTNERS FOR POST
Page 13 and 14: plug system 6000 into your DAW Powe
Page 16 and 17: geo focus: Madrid’s Classic & New
Page 18 and 19: what’s up UK whatsupuk@audiomedia
Page 20 and 21: IBC ‘08 Show Report Going Dutch I
Page 22 and 23: GEFELL UM 930 Large Diaphragm Dual
Page 24 and 25: The latest update of Cubase introdu
Page 26 and 27: ADK CUSTOM SHOP HAMBURG II-AU & VIE
Page 28 and 29: Jason Ouzts owns and operates TreeF
Page 30 and 31: LEXICON PCM96 Digital Reverb The re
Page 32 and 33: Plug Me Into Lexicon! Lexicon is ve
Page 34: Lexicon | PCM 96 > To begin with, o
Page 37 and 38: And The Winners Are… Described va
Page 39 and 40: Conch Award Sponsors 2008 Audio Med
Page 41 and 42: Compact flash is swiftly becoming t
Page 43 and 44: Sound Devices| 788T > additional me
Page 45 and 46: Lexicon Reinvents Reverb PCM96 Ster
Page 47: was, but given the development with
Page 51 and 52: New PD Series Location Recorders Au
Page 53 and 54: COMPROMISE IS NOT A VIRTUE APx525 a
Page 56 and 57: video guide A Sound Pro’s Guide T
Page 59 and 60: TOURING • INSTALLATION • THEATR
Page 61 and 62: www.audiomedia.com Stadius Wins Got
Page 63 and 64: There were four major digital conso
Page 65 and 66: AMSR 10|08 By using the supplied ra
Page 68 and 69: 10|08 AMSR > nasties that present t
Page 70 and 71: 10|08 AMSR To be any good at kickbo
Page 72 and 73: AUDIO MEDIA CLASSIFIED Angela Brown
Page 74 and 75: AUCTION The UK’s leading Pro Audi
Page 76: Colourless. Clean. Transparent. Smo

Lexicon PCM96 A Reverb Masterclass? - Audio Media

Create successful ePaper yourself

Delete template?

Save as template?