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"Gareth Magennis" <sound.service@btconnect.com>: Jul 26 07:50PM +0100 "Gareth Magennis" wrote in message news:TP7tx.48715$m04.7988@fx43.am4...       "Cursitor Doom" wrote in message news:mp2lbl$9no$2@dont-email.me...   Hi all,   I have an Audiolab 8000 amplifier I picked up at a boot sale and would like to establish what it's capable of, since subjectively the power output seems a bit on the low side when driving recommended speaker loads. Anyway, ideally I'd like to use an 8 ohm 100W power resistor as a dummy load for each channel and then measure the p-p voltage output across it on a scope with the amp turned right up. Trouble is, I don't have such a resistor and was wondering if there's any suitable substitute? I recall someone somewhere using a car headlamp bulb but I doubt they come as 8 ohm units so some sort of elaborate series/parallel combo of lamps would be necessary to get that value. Has anyone a better idea? cheers, CD.         Here's another idea: Get a reel of this - http://uk.farnell.com/pro-power/ecw0-80/wire-0-8mm-copper-enamelled-125m/dp/1230984   By my calculations it will have a resistance of 4.25 ohms. (117m of the 125m length gets you 4 ohms) Although it is only rated at 0.8A, I reckon you could extend that massively by unravelling it all and laying it in a large container of water. You could even have a flow of water through the container to keep the temperature down.   It would be interesting to find out what power rating this could actually tolerate.   Or is this a really stupid idea?! (For some reason this amuses me)       Gareth.               Just to extend that idea a little further:   You could probably put a wood former into the chuck of an electric drill, and quickly and easily make a long coil using this enamelled copper wire. You could then partition the coil into several smaller ones without cutting the wire, and suspend them vertically in a container of water.   Quick back of a fag packet calculations: Suppose you made a long coil 10cm diameter. You would then suspend 0.5m lengths vertically in the container, so the windings are spaced 5mm apart on average. This gives 100 turns at 31.4cm per turn giving 31.4 meters of wire per coil.   So you would need 4 of these series coils from the 117m of wire required to get a 4 ohm load.     Now, how many Watts could this contraption handle?       Gareth.

Trevor Wilson <trevor@SPAMBLOCKrageaudio.com.au>: Jul 27 06:56AM +1000 On 26/07/2015 10:55 PM, Cursitor Doom wrote: > ohm units so some sort of elaborate series/parallel combo of lamps would > be necessary to get that value. Has anyone a better idea? > cheers, CD.   **Lamps are a really bad idea. Don't do it. Incandescent lamps exhibit a HIGHLY variable resistance, depending on how much current is flowing.   Just buy four of these of these:   http://www.newark.com/vishay-dale/rh0504r000fe02/wirewound-resistor-4-ohm-50w-1/dp/41K9167   Dump them in a bucket of water, or bolt them to a chunk of aluminium and place a small fan on the aluminium.   -- Trevor Wilson www.rageaudio.com.au   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

Phil Allison <pallison49@gmail.com>: Jul 26 04:43PM -0700 Cursitor Doom wrote:   > load for each channel and then measure the p-p voltage output across it > on a scope with the amp turned right up. Trouble is, I don't have such a > resistor and was wondering if there's any suitable substitute?     ** 10 watt rated resistors will handle 100 watts if submerged in a container of water.     .... Phil

jurb6006@gmail.com: Jul 26 06:54PM -0700 >"Just buy four of these of these:   >http://www.newark.com/vishay-dale/rh0504r000fe02/wirewound-resistor-4-ohm-50w-1>/dp/41K9167 "   Why do those Vishays look so much like Dales ?

Trevor Wilson <trevor@SPAMBLOCKrageaudio.com.au>: Jul 27 12:26PM +1000 >> "Just buy four of these of these:   >> http://www.newark.com/vishay-dale/rh0504r000fe02/wirewound-resistor-4-ohm-50w-1>/dp/41K9167 "   > Why do those Vishays look so much like Dales ?   **Success breeds imitation. That's my take. You probably should ask Vishay (who owns Dale). It would seem that Dale originated the aluminium clad resistor (I may be wrong though) and others have copied the design. Engineers don't have to worry about supply, since there are several suppliers of essentially identical parts.   -- Trevor Wilson www.rageaudio.com.au   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

Jeff Liebermann <jeffl@cruzio.com>: Jul 26 08:18PM -0700 On Mon, 27 Jul 2015 06:56:53 +1000, Trevor Wilson   >Just buy four of these of these: >http://www.newark.com/vishay-dale/rh0504r000fe02/wirewound-resistor-4-ohm-50w-1/dp/41K9167   The RH variety is inductive. For non-inductive, you want the NH series, which Newark and Digikey do not seem to carry. Mouser has it at: <http://www.mouser.com/Search/Refine.aspx?Keyword=NH0504R000FE02> for twice the price.   >Dump them in a bucket of water, or bolt them to a chunk of aluminium and >place a small fan on the aluminium.   An aluminum heat sink will keep my coffee warm. All the water does is raise the humidity in the lab and create a huge mess when I tip over the bucket. I'll take the aluminum heat sink, but without the fan, which makes too much noise.   -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

Cursitor Doom <curd@notformail.com>: Jul 27 12:50PM On Sun, 26 Jul 2015 20:18:28 -0700, Jeff Liebermann wrote:   > The RH variety is inductive. For non-inductive, you want the NH series, > which Newark and Digikey do not seem to carry.   Is that inductiveness seriously likely to be a problem at audio frequencies?

"Ralph Mowery" <rmowery28146@earthlink.net>: Jul 27 12:21PM -0400 "Cursitor Doom" <curd@notformail.com> wrote in message news:mp59en$khn$3@dont-email.me... >> which Newark and Digikey do not seem to carry.   > Is that inductiveness seriously likely to be a problem at audio > frequencies?   I just did a quick check with a 10 ohm 60 watt wire wound resistor and a couple of other low value resistors. Used a 100 MHz scope, function generator and Fluke 87 meter.   From low audio up to 20,000 Hz and a sine wave with the 10 ohm WW there did not appear to be any noticable difference. When I switched to a square wave I noticed a large spike on the leading and trailing edges, especially as I went higher up in frequency. I did not see the spike with the resistor removed from the test leads.   From this rough test, I would say that if using sine waves you could get a close to true test, but if music or other odd ball waveforms then you would want the noninductive types.

N_Cook <diverse@tcp.co.uk>: Jul 27 11:52AM +0100 PA and PREA work separately and as normal but low output at normal signal input and control levels. I don't think I've come across this situation before. The ground or common to all the "level set" pots on all the channels is missing presumably. You can only get normal throughput with the pots set in range 95% to 100% of each of their tracks, jumping from very low to max in a couple of mm of movement and all such pots would not have failed at the same time. So inside we go.

N_Cook <diverse@tcp.co.uk>: Jul 27 03:52PM +0100 Made 2007 Although the pmp1000 uses 4580 opamps like the 1280, not the same in the prea area. The wipers of the level pots there are at ground, "low" and "high" via Rs/Cs to opamp inputs. The 1000 has stereo pots, the pairs of low-side, wipers or high-side are not connected together, but similarly close connected to opamp inputs. Without a SM this will be a pain. Next thing is check +/-rails for the opamps.

N_Cook <diverse@tcp.co.uk>: Jul 27 02:07PM +0100 Luckily I'm not directly involved with the installation of these, its subcontractor's problem , just interested bystander, in what would be done in the electrical world to cure this problem. A batch of local houses as part ofa marine flood protection scheme have had sumps and pumps installed,one per house, about 2KW motors surprisingly. One of the residents tested one setup , with buckets of water to trigger the pump. It cut out at the mini "consumer unit" installed utility side of the normal consumer unit. All the others are likely to do the same. I assume it is large inductor , current inrush problem, like the notorious spin-cycle of washing machines. Inductive unbalancing the RCD or short duration over-current of the MCB. In my sort of electronics world, for torroidal transformers an NTC thermistor would be included to avoid down-rating RCD or uprating MCB. What would they do in the electrical world, anything like NTC thermistors?

M Philbrook <jamie_ka1lpa@charter.net>: Jul 26 01:36PM -0400 In article <eca56518-7629-4947-b234-d9e3ea2c7e28@googlegroups.com>, petereasthope@gmail.com says...   > Can anyone explain how a computer serial port is disabled and enabled? Many Web pages cover the software topics but I've found nothing explaining how a BIOS disables a port. Is is done by clearing any interrupt assignment to the port? Is the power to the UART shut off? Other ways? Probably more than one technique has been used but not a large number.   > Can anyone cite a Web page which answers this?   > Thanks, ... Peter E.   if Bios has control of it, it simply flips a bit in a device manager chip on the board..   From that point, the OS does not see that serial port. Which also means, there is no IRQ assigned to it or port addresses etc.. in otherwords, no resources assigned to it.   USB serial ports are a different story..   Jamie

Peter Easthope <petereasthope@gmail.com>: Jul 26 11:09AM -0700 On Sunday, July 26, 2015 at 10:32:05 AM UTC-7, M Philbrook wrote: > if Bios has control of it, it simply flips a bit > in a device manager chip on the board.   OK, that would be in evidence when the Bios interface allows disabling.   > From that point, the OS does not see that serial port.   There must be a customary way for the OS to read the state of the bit. Otherwise communication software would have to allow for obscure hardware variations. Can software flip the bit? Ie. can a port can be enabled and disabled when the system is running?   > USB serial ports are a different story.   Fortunately I'm only interested in RS-232 style serial ports, for now at least.   Thanks! ... Peter E.

Johann Klammer <klammerj@NOSPAM.a1.net>: Jul 27 03:04PM +0200 On 07/26/2015 08:09 PM, Peter Easthope wrote: > to allow for obscure hardware variations. Can software > flip the bit? Ie. can a port can be enabled and disabled > when the system is running?   Depends what you mean by software. The ancient vt1211 superi/o chip does its configuration via port writes. You may need to be in kernel context to be allowed to do that(or ioperm()). You may have to browse datasheets, to find out if others are similar or if there's a de-facto standard. Having a look at intels LPC bus specs may be necessary, too. (they're available online)

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