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Miles Prower

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  1. Perhaps he could use a Gate Controlled Switch instead. Those can turn off, unlike a SCR.
  2. I wouldn't put an ammeter on a very low output impedance amplifier if its offset voltage wasn't zero. The only current limiter is the fuse. (the fuse in your meter) I wouldn't either. That's not what I believe he's telling us. It would seem he wants one lead of the ammeter to be connected to the output, with the other lead being connected to the speaker. That way, the resistance of the voice coil will protect the meter. Of course, too much DC will burn out the voice coil. An ammeter is cheaper than decent speakers. ::) He should have specified the use of a 10 Ohm dummy load to make that DC offset adjustment. In any case, it's far better to put a voltmeter in parallel and measure DC offset directly. An old 741 opamp is slew-rate limited above 9kHz. Modern (for the last 20 years) opamps at 100kHz. An old 741 opamp doesn't have much gain at and above 20kHz where high gain is needed for high negative feedback, modern opamps have plenty. That's why I wanted to see if the 741 used in that project was an "enhanced" version. Upon Googling it up, the specs hadn't changed a bit. Same rise time, same 0.5V/uS slew rate, etc. (Although I like 'em for use in voltage regulators, comparators, undemanding audio applications (audio stage of longwave comm receiver, where you don't want much more than 3.0KHz anyway.) They're dirt cheap, and easy to get, easy to use. What do you think about the thermal runaway issue with this amplifier? The use of darlingtons makes it worse. I have seen Darlingtons that incorporate on-chip thermal run-away protection. If these don't, then I'd guess it's only a matter of time till the finals blow. I could see one or the other latching to the rail. That could bring a 10W resistor to red heat in seconds. That would take out the finals, and the speakers. :'( (I believe he's had this problem already. He includes a fuse in series with the speakers. This, too, is a no-no from an audio quality perspective.) Regardless, I wouldn't use them anyway from an audio performance stand point. I'd also like to see a couple of resistors between the Darlintons and the output. The Sziklai Pair topology does include these. I'd have to see some test results on this design. If that thing is hi-fi, I'd have to hear it to believe it. (Then, again, I'm not necessarily the one to ask about that anyway.)
  3. I think the author makes an error when he says to put a current meter on the output and adjust the trimpot for zero current reading. I think the adjustment is to reduce offset voltage at the output to zero so there isn't a DC voltage on the speaker. The instruction is ambiguous at best. He could mean to connect the ammeter in series with the speaker, then adjust for as low a current as possible. Regardless of whether you adjust for minimum DC voltage across the load, or minimum DC through the load, I would prefer to make that adjustment into a dummy load, not the speakers. I also see a half fast attempt to implement a Sziklai pair. As for the output stage, Doug Self referred to it: "...Darlington configuration, the latter implying an integrated device with driver, output, etc in one ill-conceived package." The Darlington package might be good for voltage regulators, or a quick and dirty solution where you aren't particularly concerned with fidelity. Otherwise, avoid. Same goes for the 741 (I checked to see if the MC1741 specified here might be an enhanced version. It's not.) I won't say anything until someone carefully listens to the amp. Definitely. "I am very contented with this amplifier. It gives a very good sound quality. Have fun with it!" Who knows? May be it does. I've seen similar claims made for some of the strangest designs from those who should know what they're talking about.
  4. In the mathematical sense, C is completely arbitrary. Use it to turn the general solution of a differential equation (of which there are an infinite number) into a particular solution that depends upon initial conditions. In the electrical sense, since you're dealing with time varying signals, C is a signal that does not vary with time. IOWs: a superimposed DC voltage.
  5. You can use this handy little tester to check for shorted out coils on an iron core xfmr. Simply close the momentary contact switch, release and see if the neon light flashes. If it does, then you don't have any shorted coils. If it doesn't flash, then you likely have a shorted coil that's loading down the inductive flyback (or not enough inductance if it's a very small unit). As for open coils, simply use any continuity tester. Another thing is simply physical inspection. Remove the covers (if any) then look and sniff. If you see discolored laminations, or evidence of melted insulation, or detect a burnt odor, then your unit has likely been overheated. Even if the coils didn't short, the unit should be discarded, as its core characteristics have likely been altered by overheating, and it probably won't last much longer anyway. If all seems well, then test with the mains, and a light bulb in series. Once again, look, listen and sniff. Loud humming, crackling, wisps of smoke, smells like something burning, brightly lit bulb: something's not right.
  6. One question: why? It'd be a helluvalot easier to write a graphical program to put the chronometer right on the screen. The PC, itself, already has time and date information, which can be accessed via library functions. The FOX Toolkit already has a seven segment display widget. It really wouldn't be much of a C++ programming job at all.
  7. diyaudio.com There's a site that'll keep me busy for awhile.
  8. All car amplifiers are rated in Whats where the amp is clipping badly to make the numbers much higher. I caught that in the original post, and figured the whole thing was a joke site. I went through all 26 pages on that, looking for the punch line before realizing that it wasn't a satire. Although it is still a joke, but not that way. Our 10W mini-amp project is much worse. [...] The project's text says to use a 9V battery and does't mention a recommended load. I saw that too, and wondered just what kind of battery that could possibly be. ;D That's mainly why I avoid ICs for audio projects: can't trust the specs. ::) I'm sure the local rude boy crew won't mind - you don't need a good quality amplfier to play hip-hop at full blast in your car with the windows down. Grin Often these idiots have the volume way too high and you can hear the speakers clipping as they strain to produce the booming bass. I did say that it would be good for applications not requiring fidelity ;D ;D Where does Texas Instruments get their supply of chutzpah anyway? ::)
  9. Take a LQQK at those specs. 10% THD?! It takes some set of brass cojones to call this "high fidelity". That thing might be good for a PA system or, perhaps, an AM modulator for a ham rig (for those who still haven't made the move to SSB -- how many of those are left anyway?) where fidelity isn't a consideration. Other than that: FUGGEDABOUDIT!. A simple single-ended VT design sounds better.
  10. The power input on a tube radio is usually a multi voltage input transformer. And a transformer is an inductor so yes the frequency matters. I am just not sure how much! Take a LQQK at the general transformer equation: VN= 4fSB where: VN: Volts/Turns ratio f: Frequency (Hz) S: Core X-section area (sq. m.) B: Flux Density (Wb/m2) Now: B= VN/(4fS) so: B ~ VN/f Since B is porportional to the reciprocal of frequency, you can go to a higher frequency while keeping the V/N ratio the same. This will mean that the xfmr is operating at a slightly lower flux density, which won't do any harm, other than to somewhat compromise the efficiency due to increased core losses. Going lower in frequency is the killer. In most xfmr designs, the core's already operating close to its saturation flux density so as to make the core and the core losses as small as possible. Operating a 60Hz xfmr at 50Hz could very well lead to core saturation if the voltage isn't porportionally reduced. I noticed an extra fuse included with this radio In a ziploc bag. On the head of the fuse it reads "T630mA/250V" Is this fuse just a replacement fuse for the 220V setting? Or did he include the 110V fuse i need in the ziploc bag? The only thing a voltage rating means concerning fuses is that the fuse is guaranteed not to arc over once it blows if operated at or below the voltage rating. A 250V fuse on a 120V main will work just fine. A 110V fuse on a 240V main could possibly arc after it blows.
  11. It had nearly double the bytes of your schematic but looked like nearly 4 times the pixels. I counted 12 steps on the ramps of your opamp symbols but 19 steps on mine. I count 12 as well. Looks like the only alternative is to re-draw the whole thing. Oh well... My previous post got deleted somehow... Mine too, I guess the mods don't like it when you make fun of IE.
  12. Can you convert an original bit-map to a GIF? That's exactly what I did. I made both the *.jpg and the *.gif from the same original: a *.bmp image I made a long time ago, when I still used Windows. It looks like you converted the JPG to a GIF. I didn't. I really can't explain this since I'm having no trouble seeing either form *.jpg or *.gif on my system with either Firefox or Mozilla. In each case, a right click + "View Image" brings it up with perfect clarity. I've tried several image viewers on my system, and all three versions, *.bmp, *.jpg, and *.gif all look the same. I never ran into this sort of problem before. Have you tried clicking on the file itself and opening it in a different image viewer? Could the problem be screen res? According to the X Server, I'm running at 1024 X 768.
  13. Haha! Yep, and hopefully those idiots will listen. They'll be lucky to be able to hear anything, let alone listen. :o Every time I hear one of those damn things, I imagine the owner spending the rest of his life going: "What'ja say? What'ja say? What'ja say?" Then I feel better. ;D
  14. May be it's a screen resolution difference? It still looks good here. Anyway, here's a *.gif. Let's see if that works better.
  15. Just like I stated: lots of possible implementations. ;D
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