Kevin Wood

Newbie Wammer
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    45
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About Kevin Wood

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. 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!
  2. 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!
  3. 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.
  4. 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.
  5. 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.
  6. Watts - Quantity v Quality

    Surely all doubling (the clipping) power into half the impedance proves is that someone's sold you a bigger power supply than you needed! The power supply is naturally going to sag a little with much increased load, so one would expect the power to drop off a little from the "ideal amplifier" expectation. It would be quite an effort to design an amplifier that didn't exhibit some drop from double power, and probably a fruitless one in terms of end result. Since it would be bad practice to be operating an amplifier anywhere near clipping in actual listening, I fail to see what relevance it has. Now, if we were to consider testing an amplifier operating at a realistic level of perhaps 6-10db below full output into 8 Ohms, then halve the impedance to 4 Ohms and check it again, that might tell us something more interesting about its output impedance and if it's likely to run into current limiting when delivering normal programme material into a speaker with an impedance dip. The other thing to consider is that, even if the speaker has a "dip" somewhere in its response, how much of the programme material will result in power in that band of frequencies? If a speaker is 12 Ohms everywhere except for in a small section of the audio band where it dips to 4 Ohms, it's unlikely that the amplifier will be pushing much power into that area, so the overall current requirements probably won't trouble even a relatively feeble amplifier. What is needed is an indicator on the amplifier that flags up whenever something (clipping, current limiting, etc) has caused its output to deviate from the "wire with gain" relationship to its input. In the pragmatic world of amplifiers for professional use such things are available, of course, but not so in Hi-Fi.
  7. Quadies Unite!

    I'd say either power amplifier will offer adequate power. The 405 is not the quietest amplifier in standard form and I wonder if, with those sensitive speakers, you'll hear some background noise. I've no experience of the 303 but on paper it looks quieter relative to its' full output and that reference is also lower in the first place, of course. Since you'll not need the extra power of the 405 and the 303 is perhaps a better aesthetic match to the 33, that might be the one to go for? Tape inputs with "H" (high level) selected would probably be best for a modern source. You might still need to apply some attenuation as the 33 dates from a time when line levels were much lower.
  8. Is every system a compromise?

    The thing is, it's only with acoustic music that there's any concept of "live". We can familiarise ourselves with what an acoustic guitar sounds like at close quarters, or a string quartet at the other side of the room, or a classical concert in a hall, and make some judgement as to whether we are reproducing it accurately. Listen to a rock band live, for example, and you're listening to how the guy who did the sound check liked it. Often that just means everything turned up to 11 to try and compete with the drum kit! Listen to it recorded and you're listening to how the mastering engineer liked it to sound. The two are completely different starting points, so we shouldn't expect the latter to reproduce the former. I'm always stuck by how bright and piercing a cymbal crash sounds when listening to a pub band, for example. If it sounded that bright on recordings played back on my system I'd hate it, but it seems right when the music is live. What matters is that the illusion is pleasing. I find that neutrality and low distortion does it for me, with all types of music. I've found more coloured systems pleasing on acoustic music but they fall apart on something more complex like rock, perhaps because there are more components to intermodulate with each other. Then again, that's exactly what I'd expect to happen, given that I'm an electronics engineer, and expectations play a big part too!
  9. Less than 3 ohm load... help please

    Sounds like it's doing the job, then. Regarding possible issues, I'd expect it to shut down if there are any thermal issues. I suppose you might run into current limiting if the load is too sever and you turn it up. That will probably manifest itself as distortion or a muddled sound. The fact that they publish specs for 4 ohms probably means it's designed to drive reasonably low impedances and, of course, in an active system, the power is shared between all the channels so I doubt you'll be pushing it too much.
  10. Less than 3 ohm load... help please

    I'd say it's normal for the DC resistance of a drive unit to be less than its nominal impedance, so your measurements are plausible. If driving a bare driver it's not going to dip below its DC resistance in impedance terms but it is, as you say, quite an awkward load. The amplifier you quote does give specs into 4 ohms, but it delivers slightly less power than into 8 ohms, which does suggest to me that it isn't that happy driving low impedance loads. If it were me, I'd use that amp to drive the drivers in series rather than parallel, as it would still deliver plenty of power into 12 ohms, I should think. As always, YMMV, as it's difficult to get a complete picture from the specs in a manual that are often more marketing oriented than technical. I hope this helps.
  11. Not only the music itself but the way it's mastered. There's no point in listening to a lot of recent recordings on a competent system as there's nothing there to work with.
  12. Armstrong A20 / A220 any owners here?

    Lovely job!
  13. I think, with streaming, you have to differentiate between streaming your own CDs from a local server onto which you have ripped them and listening to music from online streaming services such as tidal. I do a lot of the former, and, since you can verify the accuracy of the rips using the accuraterip database, then store the data losslessly encoded using FLAC, you are listening to the same data that you get by playing the CD, and therefore there is no reason for the sound quality to be inferior. It's also much more convenient. The latter normally involves losslessly compressed music, which can compromise sound quality, but, on the flip side, it can be a great way to explore new music without purchasing physical media. I still play vinyl as I enjoy perusing 2nd hand record shops for material, I also buy a lot of CDs still, but they get as far as my PC, where they are ripped, stored on a server and streamed. I very seldom play a physical CD any more. Some will say the ritual of putting the cd in the player is important, or that having fingertip access to your whole collection on a server causes you to chop and change too much and not listen to an album, or even a track, in its entirety any more. I don't personally find this to be the case.
  14. DSD upsampling- worth it?

    I may be misunderstanding what's meant by "DSD upsampling" but this sounds very much like what delta-sigma DAC chips do internally anyway. Namely, take PCM encoded multibit samples and turn them into a single bit pulse stream before using an analogue filter to recover the audio signal. ..or is it simply that it supports playback of DSD files and SACDs?
  15. Do I still need a valve preamp?

    Does your Lyngdorf device have a digital input? Just thinking that there is no real need to go to analogue only to go back digital in the Lyngdorf. Presumably the Lyngdorf device can work as a preamp too (i.e. it has a volume control, which is all you really need with digital sources)?