Kevin Wood

Newbie Wammer
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    55
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26 Excellent

About Kevin Wood

  • Rank
    Junior Wammer

Wigwam Info

  • Turn Table
    SL1210 Mk 2
  • Tone Arm & Cartridge
    Benz ACE L
  • SUT / Phono Stage
    Partridge / VSPS
  • Digital Source 1
    SBT
  • DAC
    Homebrew
  • Pre-Amp
    Homebrew
  • Power Amp/s
    Quad 405
  • My Speakers
    Eminent LFT-8b
  • Trade Status
    I am not in the Hi-Fi trade
  1. RFI/EMI and LED bulbs

    Given that the lights in most UK homes will already be on dedicated lighting circuits, so separate from the ring main to which the Hi-Fi is connected, I can't see how this could help. In addition, interference to a DAB radio is most likely by radiation of interference from the mains cables feeding the lights into the antenna, not conduction through the mains wiring. A lot of the cheaper lights have filtering components omitted so they generate significant EMI. Ironically, some of the really cheap LED lights just have a capacitive dropper from the mains, so generate very little interference. I think the best advice is to buy "known" branded products and take them back if you find they cause interference. At least then there's a chance the retailers will decide the cheap non-compliant rubbish is too much hassle to stock.
  2. Measurements v Listening Tests

    Comparing measurement with listening is like comparing Apples with Oranges. We make measurements to determine if the equipment is doing its job accurately and to determine what effects the room is having on the performance of the equipment. If we want to know how a system sounds, surely we listen to it instead? We might infer certain things about the sound from the measurements - we might predict it sounding rather boomy if there's a large peak in the bassresponse caused by a room mode. Equally, we might expect it to sound rather bright if there's a peak in the upper midrange. Measurements simply aren't there to provide a description of how a system sounds although they can often provide clues to why a system doesn't satisfy, and therefore to help us find solutions.
  3. turntable for 22 tr old daughter advice please

    Yes, and the lesser Technics direct drive turntables can be had for much more reasonable money than the 1200 / 1210. They are reliable and sound great. I've just renovated an old SL-3300 and have it in my system at the moment. Very nice.
  4. DIY remote controls

    I have a kit similar to those which I've never got round to using. I'll see if I can dig it out of the junk box.
  5. Do you trust magazine reviews

    Indeed. the Quad specifications tell you exactly what will happen into a whole range of impedances if you care to read them. The problem, if there was one with the Quad, and I'm perfectly happy with my 405-1, is that speaker manufacturers of the time were not equally honest about the impedances they presented! Like measurements or loathe them, it's not as if a purely subjective review will tell you anything useful about how it'll drive your speakers (or anything else, for that matter). If the Amstrad review had told me, for example, that it had 50mV of hiss on the output, I could have decided if that would be a problem given the sensitivity of my speakers. Maybe it was not a subjective issue for the reviewer because his were insensitive. .. or perhaps a glowing review was purchased with advertising revenue. Either way, they aren't much use to me so I've given up reading them.
  6. Amp humming, solutions please.

    Yep, I think your solution would be to try a DC blocker in the supply to the amp if possible or to find a better replacement switched mode PSU. I must admit, I'm slightly puzzled by the fact that such a small switched mode PSU is causing enough DC on the mains to cause trouble in this instance. I've only normally noticed it caused by larger appliances such as washing machine motor controllers which often use half-wave drive to the motor for slow tumbling and full-wave for the spin cycle. I guess the PSU probably has a half wave rectifier at the input.
  7. Amp humming, solutions please.

    No, the core of a toroidal transformer is buried under the layers of winding and insulation material. If you tried to apply a clamp to it you would most likely damage these and destroy the transformer. Toroidal transformers tend to be more susceptible to DC on the mains too.
  8. Amp humming, solutions please.

    Actually, toroids designed for 50Hz mains use still have a stack of laminations as a core, not ferrite, which is only useful at switched-mode frequencies in the tens of kilohertz up, but your comment still stands.
  9. The eternal CD player

    This is something I've always "been meaning" to have a go at too. Seems a better investment than yet another short lived cheap knock-off KSS240 laser module for my CD player.
  10. Quadraphonic LPs - Is there anyone else playing them?

    Yes, I've never seen anything like them before, which I why I picked them up. I guess they're probably just an elaborate way of mixing a 4 channel source back to stereo in reality, but somebody must have bought the idea!
  11. Quadraphonic LPs - Is there anyone else playing them?

    Here you go, some pictures: .. and, in a welcome flashback to the days when published specs meant something in Hi-Fi, I've confirmed that each element is indeed 8 ohms!
  12. Quadraphonic LPs - Is there anyone else playing them?

    I picked up a pair of JVC 5844 "Quadrophonic Headphones" at a vintage shop recently - just because I thought they were an interesting curiosity and they were pretty cheap. They are basically 70's style closed back "over ear" headphones but with a front and rear driver in each side and a pair of 1/4" stereo jacks to feed front and rear. I can't believe you'd get any real Quadrophonic image from them, but they were an interesting find. I'll have to bring them to Scalford some time to try them out on the intended source material!
  13. Yep, that doesn't surprise me. I didn't mean to imply that the amplifier I cited in my example would be typical, or even sensible. It's an example to show that the conditions under which specifications were determined are important.
  14. I think we have to remember why we make measurements. It's not to satisfy the subjectivist as to how a system will sound. It's to satisfy an engineer that he has done a decent job. Most engineers would argue that an amplifier should take its input signal and increase the voltage and lower the impedance such that the output signal can drive a loudspeaker whilst adding as little noise or distortion as possible, over a frequency range consistent with human hearing, say 20Hz to 20KHz or better. Walker's "wire with gain". Measurements provide an indication of how well an engineer has met that goal, so, during the process of developing a product they are vital. Engineers can't simply form a subjective opinion of how "good" an amplifier is, as only measurements can direct them to any aspects of their design that need improvement. As to the test signals used, with conventional measuring equipment, it was only possible to measure distortion using sine wave test signals. In theory, one could probably measure distortion while playing real music with modern digital processing but that is less useful in practice because the distortion products from a single or a couple of sine waves at discrete frequencies tell the designer much more about the way in which the amplifier is distorting, and therefore impart clues as to what deficiencies in the design may need improvement, than the mess that would result when using music as a test signal. Measurements in this context are all about validating and improving the design. How measurements are made is indeed important. I am sure you could build an amplifier that exhibits sub-0.1% distortion at 30 Watts output but 10% distortion at 100mW output. With some speakers such as my 83dB/W sensitivity examples, such an amplifier might be acceptable at normal listening levels. Feeding very efficient horns, it certainly wouldn't. Those horn speakers might sound lovely when fed with a SET amplifier that produces laughable distortion at full output, but relatively little at sub-Watt output levels. The load an amplifier is presented with might affect how it measures, particularly if it sends it into current limiting, and the designer can't anticipate and design for every impedance that might be presented by a speaker. Also, unless we make measurements ourselves, the "side of the box" measurements published for any piece of kit will normally only tell the part of the story that will sell the product, as they will be a product of the marketing department not the engineer. They might not be measuring at the signal levels, or into the loads, that we will present to the amplifier in actual use. Psychoacoustic tests have given us loose targets such as the frequency range of human hearing and the rule of thumb that 0.1% distortion or less is a good target to make it inaudible. This doesn't give us a complete picture of the human hearing's sensitivities, of course, but it's good enough to enable pleasing reproduction of music. There may be aspects that we are not aware of but personally I doubt that there's anything in psychoacoustics that could suddenly provide a breakthrough in Hi-Fi design that leads to massive leap forward in subjective sound quality. Then again, I'm not an expert in that field.
  15. Watts - Quantity v Quality

    The Quad 405 was rugged because the current limiting strategy ensured that Safe Operating Area of the output devices was respected regardless of the load. Shortly after that, another meaningless measurement, maximum peak output current, started to get quoted in reviews and I suspect a lot of amplifier designers deleted the current limiting to get a good measurement and to hell with the SOA. Now audiophiles get nervous of such "unnecessary" circuits in the "signal path" despite the fact that they don't do anything until a harmful overload occurs.