4stringslow

[quote name='bassman7755' timestamp='1470115749' post='3103298'] If the amplitude of the light is solely controlled by the source signal than that is not AM since AM is where a carrier frequency is modulated by the source signal and then the carrier is filtered out by the receiver. Yes you could consider consider the frequency of the light itself as the carrier but then air molecules are also in a constant state of vibration at room tempurature in the absence of any sound so taking that absolutely literal approach you could also argue that all acoustic sound transmission is AM. For me the acid test would be - If there is no light transmitted at a zero signal level then that would not qualify as AM. [/quote] Nope - changing the carrier frequency would be FM. It's quite simple really. The light is the carrier - it must be, it's the only thing to travel along the cable. The brightness (amplitude) of the light is varied (modulated) according to the varying voltage from the pickup. That's AM, by definition. The level of light transmitted at a zero signal level is irrelevant and depends on the bias applied to the Tx device. The important thing is the variation in brightness, which conveys the information, not the actual brightness. Any applied bias at the TX is simply removed at the Rx end.

In theory perhaps but I'm not aware of any device that could convert the tiny amount of power from a passive pickup into a suitable light source. Another approach might be to use a composite copper/fibre cable and supply power from the Rx end, but really, what's the point?

That'll teach you Funny how even apparently simple things can become quite complex as you zoom in on the detail. As the old saying goes 'the devil is in the detail'

Sorry, but I disagree. Yes, the voltage and amps can vary between the input and the output but the point that they BOTH vary such that when you multiply the input volt/amps and the output volt/amps you'll find the power is much the same. I say much the same because no device is 100% efficient so power out will always be less than power in, with the 'lost' power heating things up. Think about your 130 amp welder with its 13A fused plug. Max input power is 230V x 13A = 2990W. This is the maximum amount of power available to the sharp end of the welder, so if you select a 130A arc then the maximum voltage across that arc will be 2990 / 130 = 23V (again, in practice some power is 'lost' inside the welder as heat because nothing is 100% efficient). This is generally why mains powered arc welders don't electrocute you - because the output voltage is quite low. Watts are watts, there are no 'reduced amperage' watts. If the amps are reduced, so are the watts, unless the voltage is increased to compensate. It's basic thermodynamics - you can't get more power (watts) out than you put in.

Is that 2500W rating peak or rms? Watts is a measure of power and while you're quite right that volts and amps can be varied between input and output, depending on the circuitry inside the box, I don't think you can have more power out than goes in. What you can do is measure that power in different ways and marketing people love to use peak power ratings because it gives them a nice big figure for the spec sheet So if the Crown amp max input is 600W that means 2.6A at 230V (ignoring any AC power factor). If you raise the output voltage using a transformer then the output current will drop because the power MUST remain the same (actually the output power will be somewhat less because the transformer will not be 100% efficient, but that's a detail). The point is that you cannot get MORE power out than the power input. If you could then you wouldn't have an amp you'd have a power source and have solved the worlds energy problems!

[quote name='gapiro' timestamp='1470066429' post='3103022'] I'd be interested to know how tight you can have the cable in terms of bends. I would have thought the (presumably glass) optic carrier would be susceptible to breaking at a kink/bend in the cable? [/quote] Good question. In the YouTube interview I mentioned above, the designer said they used plastic cable. This makes perfect sense because the cable lengths are so short that multi-mode issues are pretty much irrelevant and plastic cables are relatively thick (large c/s area) which means it's very easy to launch light into the fiber at the Tx end and receive it at the Rx end. The 'proper' high speed glass optical fibres used in datacomms are really small (to eliminate multi-path distortion - hence 'single mode' as opposed to 'multi-mode') and consequently it's a precision job to correctly terminate them, which means higher cost. The other big advantage of plastic optical fibre is that it's very robust and highly resistant to bending and stretching, so I don't think that looping such a cable through a guitar strap would be a problem.

[quote name='gapiro' timestamp='1470066128' post='3103020'] Just because they are using the brightness (ie amplitude) to control the signal - doesn't make it AM. AM uses the input to control the output level of a carrier wave - Ie as per the bottom one here They are saying they can just use the modulating signal as the signal transmitted. [/quote] I don't understand your point. The modulating signal is the electrical output of the guitar, which cannot be directly sent down an optical fibre. You have a light source and an electrical audio signal. How are you going to use that light source to carry the information in the electrical audio system? The easiest method is to convert the signal voltage into light intensity. No signal voltage = no light, peak signal voltage = peak light brightness . . . and all signal voltages in between. The receiver just does the opposite thing to convert light intensity into voltage and voila, there's the audio signal back again. But it is very definitely amplitude modulation. There are other techniques that don't require ADCs and DACs but they require switching the light source on/off and so could be regarded as a 'digital' transmission system (e.g. Pulse FM or PFM - check it out in wikipedia). Given that they clearly state its a purely analogue system then I'm betting they use AM.

[quote name='Woodinblack' timestamp='1470044074' post='3102820'] Obviously they can't hear them but you know guitarists, if it wasn't present on the original strat or LP it is crazy new technology to be hunted down and killed. Having spent more than a few hours talking about analogue vs digital effects, why spending 100s on boutique effects is better etc.. It's very much in the realm of, as you hinted at, £1000 speaker cables. Voodoo is strong here. When people won't even use active instruments as the sound of passive guitars are so much better, who is going to buy an optical lead? The only reason I can see it selling is because it's expensive. [/quote] Agreed. The voodoo is probably the biggest issue Edit: as for the tone issues (ie frequency response), this chap is not at all convinced: http://youtu.be/YljQyirf1RM

[quote name='Woodinblack' timestamp='1470008233' post='3102691'] Not in the traditional sense, and no more than in that sense a piece of copper is a carrier. Traditionaly if you are speaking of a carrier of a signal you would be refering to another signal that is modified such as FM or AM. [/quote] I disagree. In an optical fibre system, light is precisely the 'carrier' of the signal in exactly the same way that a radio wave is the signal carrier in a wireless system. And yes, because the signal is conveyed by a carrier, some form of modulation of that carrier is required in order to superimpose the wanted signal onto the carrier. There are various ways of doing this but in the analogue domain it's usually AM or FM. [quote name='Woodinblack' timestamp='1470008233' post='3102691'] Well, if it is analogue, and it isn't by FM/AM, then it has to be by intensity, which would be the same as down a copper cable. However, doing it that way makes it as prone to noise on the cable as copper would, possibly more so as light is more sensitive. [/quote] But 'intensity' really means amplitude so you are actually referring to AM. This is what I would expect - the amplitude of the analogue audio signal controls the brightness of the optical source, thereby 'modulating' the carrier light wave by 'amplitude', i.e the voltage of the audio signal controls the brightness of the light. This is the very definition of AM. [quote name='Woodinblack' timestamp='1470008233' post='3102691'] It would seem an odd way of doing things, and the only reason I could see you would do it that way is that guitarists are neophobes, so would magically be able to hear a carrier wave and thus dismiss it. [/quote] Not odd at all. It's a very simple and well-proven method. What I'm surprised about is why their literature states it is NOT AM or FM. I'd also be interested to read their claimed patent because transmission of analogue audio signals (and analogue video for that matter) over optical cable using AM has plenty of prior art, so I'd guess that any patent will cover some specific aspects of the packaging or application rather than the fundamental technology. As for guitarists being able to magically hear a carrier wave, I know what you're getting at but how many guitarists dismiss wireless links because they can hear the carrier wave? . They can't of course, because the radio carriers are millions times higher than any audio frequency and even the most 'golden eared' audiophile would be hard pressed to convince me that they can hear a light source, which has a frequency of millions times higher than even a radio carrier! Edit: here's an interview with the two behind Iconic Sound and if you listen carefully to the designer of the system it is stated that the system is purely analogue and works on the principle of 'light brightness' - I.e. AM. http://youtu.be/cQWsECxpBDM

[quote name='EBS_freak' timestamp='1470003807' post='3102675'] Psst. http://www.iconicsound.com [/quote] Hmm. [i]This signal is not digitised in any way, and is not on any kind of carrier.[/i] So light is not classed as a carrier then, unlike every other optical fibre system? [i]The optical audio signal is analogue therefore there is NO conversion time or delay. This is NOT a digital device, or an FM/AM transmission.[/i] Not digital, fair enough, so how is the audio signal conveyed by light if not by AM or FM modulation? Never mind guitar leads, they should be selling into the Hifi marketplace Still, undoubtedly a good solution for electrical isolation but at £120 how many musicians would actually buy one? Edit: the Harmony Central review emphasises the effect that long copper cables can have on instrument pickups because of impedance and capacitance issues, which is fair enough, but doesn't mention active instruments that already have powered drivers that completely buffer the instrument cable from the pickups. Or indeed a wireless link that effectively does the same thing, I.e isolates the pickup from a long length of cable.

Is the 'average expected functional life' of the cable actually stated anywhere? Otherwise 'lifetime warranty' could be cynically interpreted as meaning it is guaranteed to work for as long as it does and that is its 'lifetime'.

Not so much reinventing the wheel as adding too many unnecessary bells and whistles. Did they actually do any market research among musicians to find out who would actually buy one?

The SRM450s have a 'low cut' switch that filters out frequencies below about 75Hz, so take the main desk feed to the subs, use the sub's 'feed thru' output to connect to the SRM450s and set the 'low cut' switch to on. Saves wasting a couple of AUX outputs that can be used for stage monitors.

Disappointing to read all these derogatory comments from a bunch of supposed musicians. Not liking something is one thing, but rubbishing other artists' works? Hmm.

It wasn't my sort of thing but I'm glad it was done. It would be a boring world if boundaries were not pushed. Heck, without a bit of boundary pushing most of Bowie's catalogue would not exist in the first place!

[quote name='obbm' timestamp='1469805059' post='3101221'] Assuming that the cable is of adequate rating, the lowest rated item in the lead is the IEC connector. Most IEC connectors are rated at 10A so a 10A fuse is perfect. [/quote] True, but ratings are, of course, deliberately conservative and 10A fuses are not commonplace in the UK. 13A fuses in a short IEC mains lead are acceptable according to IET codes of practice and BS1363. [i]"Where manufacturer’s flex is less than 2m in length, has a csa of 0.75mm2 and is fitted with a non-rewirable plug, it may be rated at 10A and be fused to 13A, in accordance with BS1363 Table 2 note C." IET Code of Practice.[/i] http://www.pat-testing-training.net/articles/fuse-ratings.php Anyone using lower rated fuses and keeping all their IEC leads in one large box to be pulled out as needed would be wise to carry plenty of spare fuses

Strictly speaking, kettle lead fuses are there to protect the lead not the device they are plugged into. Indeed, USA and European versions don't even have a fuse. Thus, it is the responsibility of the amp, or whatever, manufacturer to include the appropriate fuse in their product because they should assume that the kettle lead itself is unfused. So, for most** UK kettle leads it's ok to use a 13A fuse. This also means there's no need to worry about pairing a specific lead to a specific device. There's no harm in using a lower rated fuse if you wish but there's really no need and you risk eventually getting leads mixed up and blowing a low-rated fuse if the lead is used in a high power device. ** this assumes the cable itself is rated for 13A. If the lead has been made with a lower rated cable then the fuse should be adjusted accordingly, but the principle remains the same - the fuse is to protect the lead, not the appliance.

[quote name='ivansc' timestamp='1469653659' post='3100151'] What I make of it is that James Jamerson is dead & therefore not around to contradict anything she or anyone else says. And of course you can bet your life that with his history of drtug and alcohol abuse, you would ahve to take a fair bit of what he "remembered" with a pinch of salt. As far as I am aware Carole didnt start working for Motown until they opened a "branch" in California, which at least gives us a bit of a temporal context.... "Shrouded in mystery" is the phrase that comes to mind. [/quote] I've no particular insight to this controversy, but Kaye was hugely prolific and already widely acknowledged as a great session player so why would she feel the need to boost an already established and solid reputation by falsely claiming some songs she didn't play on? There are many possible answers to that of course, either way, so I guess we'll never actually know. Shrouded in mystery is probably right, but mysteries generally require an open mind.

No speaker protection circuitry in the amp then, or were you bluffing?

[quote name='RockfordStone' timestamp='1469718864' post='3100624'] not even that, my DSLR exports high quality raw files at 35mb each my dad bought a pc with a 10gb hard drive and zip drive as selling points, my phone by comparison comes with 16gb as standard... oh how times have changed [/quote] Oops - I was thinking jpegs. But you're right, times have massively changed as far as storage is concerned. I've just bought a USB memory stick for my key ring - 64GB for less than a tenner!

Zip drives were something of a revolution given that they stored 100MB when launched compared to the 3.5 inch 1.44MB 'floppy' disks of the day. They connected to the PC parallel port as well (pre-usb days!). I used to back up PCs onto Zip disks in the early 90s. They were later updated to 250MB but died a natural death when external hard drives and memory sticks became available with higher capacities. A 100MB Zip disk would only store about 10 pictures from a decent DSLR these days!

I agree that hearing people chatting on the dance floor would suggest the volume is a bit low. As for squeaking shoes . . . Noise nuisance wasn't a problem at the wedding I attended as the marquee was in the middle of a field on a large farm, so the band could have turned up to 11 with no neighbour problems, but they were admirably restrained and got it just right.

Perhaps part of the problem for a wedding band is the eclectic nature of the audience. Some will be enthusiastic about getting up to dance while others will be more interested in chatting to all those far-flung relations they haven't seen for years. Plus, who wants to go away from a wedding with their ears ringing or have to wear earplugs? I was at a wedding last weekend (guest, not playing) and the band got the volume thing spot on. It was a large marquee with half the sides folded up because it was pretty warm but their volume was plenty for the dance floor at one end of the marquee while at the other end guests could still have a conversation without having to shout at each other. I guess a marquee might be easier in this respect than an enclosed room or hall, but even so there is a happy medium.

I don't know that derivation for cover, but word meanings can change over time, eg gay, sick, etc. Just one of those things I guess.

But what damage could a limiter power trip do that a genuine power cut couldn't?