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Kevin Wood

Wammer
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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

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  1. Kevin Wood

    Can I determine wattage from a schematic?

    Yep, square instead of square root. Also, 28 volts at the secondary will give DC rails closer to 35 volts under load, so your capacitors could be quite conservatively rated at 63V. That would give you around 75W into 8 Ohms in theory for a split rail - a few less in practice as the output stage won't quite swing rail to rail.
  2. Kevin Wood

    Can I determine wattage from a schematic?

    As a fast and dirty way to identify power output (assuming solid state): Try an identify the topology of the DC power supply. It'll typically either have a centre-grounded split rail supply or a single rail, and you can tell this from the arrangement of the reservoir capacitors. Single rail: Single reservoir capacitor or bank of capacitors in parallel. One side connected to ground (usually negative but not always). Large coupling capacitor in series with speaker output Split Rail: Double reservoir capacitors or two banks of parallelled capacitors Negative of one capacitor to ground, positive of the other one. No spekaker coupling capacitors. Once you've determined that, have a look at the voltage rating of those capacitors and reduce by perhaps 10% (or measure the voltage, if it's safe to power up). Halve this value if it's a single rail amplifier. This will tell you the approximate peak voltage available at the output at the onset of clipping. Multiply this by 0.707 to get the RMS voltage. Square this and then divide by the speaker impedance (e.g. 8 for 8 ohms) to get the maximum theoretical power output. In practice, you'll get a little less than this, and it'll depend on the topology of the amplifier circuit, but you'll be in the right ballpark. For valve amplifiers, probably the best way is to look at the plate dissipation of the valves and the class they are operating in, whether push pull or signle ended and then look at power outputs available from a similarly specified amplifier. Size and weight of the transformers can be a cue in either case, but not 100% reliable, as some can be significantly oversized while other manufacturers scrimp badly on these parts. Photos, schematics, etc. would give us a better idea but the above with hopefully be useful.
  3. The Weller W61 might also be worth looking at if the "soldering station" style are too spendy. They are a little more cumbersome but with a small tip they'll be fine for all but the most intricate work and have plenty of power for large speaker / power supply connections. I used a predecessor of that iron as my only one before I srtarted "collecting" TCPs. Temperature control means that the tip never gets too hot, and this in turn means they last much better than the tips on cheaper irons where the temperature can run away when idling. Bits, thermostats and elements are readily available and not too expensive too.
  4. I have an Iroda solderpro gas soldering iron. It's excellent for jobs where a mains iron would be a pain, such as in the footwell of a car or behind a speaker. I wouldn't have one as a main soldering iron for electronics but it's certainly a handy thing to have in the toolbox. As said, temperature control can be an issue. It's completely manual by altering the gas valve on the side. With light use you'll find them getting too hot, solder a heavy joint and they run out of heat unless you remember to crank the wick up! I think once you're into decent temperature controlled soldering irons such as the Weller, genuine Hakko and Metcal people will have their preferences but they're all "good enough" for serious hobbyist construction. It's the bottom end of the market you need to avoid. Some of this end of the market likes to emulate the temperature controlled stations, but you'll find that they aren't properly closed-loop controlled, they've just stuck a pot on it to control the heat input. ..and a good point about bit availability. You'll probably find yourself wanting to use smaller bits on solid state stuff, something bigger on valve construction and larger again for soldering big capacitors, speaker terminals, transformers, etc. so a selection is handy. If such bits aren't readily available, you're probably looking at an iron that isn't up to the job.
  5. Yep, Metcal or, if the budget doesn't quite run to that, a Weller TCP. Plenty second hand on Ebay or at audio jumbles and you can still get the parts, bits and so on. Also, keep the tip in good condition by cleaning it regularly on a wet sponge or, I find, a quick wipe with a wet cloth while it's hot.
  6. Kevin Wood

    Polishing swirls/scratches from turntable lid

    I've done well in the past with car bodywork stuff, starting out with fine grade wet and dry used with a little soapy water to get really deep scratches out and moving up to T-cut style polishes (Farecla G3 in my case) then a finishing polish such as Autoglym super resin. I tend to do it little by little by hand keeping a careful eye on the results. I've taken covers from seriously knackered / previously used as a storage bin to presentable enough for the living room using this technique.
  7. Kevin Wood

    Dual capacitor confusion

    I suppose it might have been cheaper to make the 2 capacitors in one can. Often, power supplies would have C-L-C filtering after a valve rectifier, so splitting a large capacitance in two allowed a choke to be put between them.
  8. Kevin Wood

    What companies, out of Business, did you LOVE???

    Yep, very much this. Even now, nothing seems to have appeared that can touch (no pun intended!) what their devices were capable of.
  9. Kevin Wood

    What did YOU use to connect in 1980

    I think I'm still using the cables I had in the 80's. Tandy used to sell nice interconnects with sturdy gold plated phono connectors that were a bit more robust and less prone to failure than the "red and white" leads that came in the box. When they had a sale on I bought a load of them. I'm still using most of them today.
  10. Kevin Wood

    Buying a Balanced Mains Power Supply

    Amen to that.
  11. Kevin Wood

    Efficent speakers for Chord TT2?

    Indeed, and the other thing that concerns me is that the DAC output stage might have been compromised as a line output stage by making it capable of driving a speaker (albeit poorly). I think I'd rather have a DAC with a quality line output and choose a separate amplifier to suit the requirements of either my speaker or headphones. The signal doesn't know or care how many boxes it has passed through, after all. Talk of simplifying signal paths, and so on, is just marketing jargon.
  12. Kevin Wood

    Mains shield earthing?

    Yes, and I wouldn't mind betting the output waveform will be distorted as a result of the saturation. Then again, most mains supplies have quite a bit of distortion due to exactly this type of device being prevalent. Conventional power supplies as found in most Hi-Fi gear only draw current on the peaks of the mains supply, so you could reason that the mains is incredibly distorted by the time it passes through the rectifier. Luckily, subsequent stages of smoothing and, perhaps, regulation should render the equipment immune to this.
  13. Kevin Wood

    Mains shield earthing?

    Yes, this is true, of course. It would only be an issue if noise from the isolation transformer was a concern.
  14. Kevin Wood

    Mains shield earthing?

    If it's making transformers hum it's probably DC on the mains. I'm guessing the laser printer probably uses phase angle control to drive the heater in the fuser, and perhaps it doesn't draw equal current on positive and negative peaks of the supply. A DC blocker is probably all you need to combat this. There don't seem to be many commercially available but they are simple to build: http://sound.whsites.net/articles/xfmr-dc.htm
  15. Kevin Wood

    Class A amplification & Valve rectification musings

    Yep, it's power dissipation that reduces as output power increases. Draw from the supply should remain exactly the same.