Discussion in 'DIY' started by EchoWars, Nov 16, 2010.
Iirc, it's a 212.
I want to be able to measure watts per channel and wondered if someone could list out what I needed to complete this task. Ranges of amplifiers are 250 to 550 wpc @ 4 ohms
I have a fluke 192 2 channel scope to start.
Thanks for any suggestions.
you will first need dummy loads to handle that. probably 2 x 8 ohms 250w or greater in parallel. Then a signal source.. easy to find and download from the web that runs on your pc or phone. then your scope. The scope you have has a high enough range so you can connect directly. You will be able to see the clipping on the scope but probably more accurate to measure Vrms on the voltmeter just before clipping. Remember that clipping voltage is peak.. and you measure power as Vrms^2/R where Vrms= Vpeak/Sqroot(2)
Thanks, that's what I been rigging up. How much past the resistor spec wattage can they be driven? 10% 20%
that should be fine for a short time.
Back to the head magnifier - seems like a great thing to have, but I'm surprised there wasn't more discussion or recommendations on specific models. Are they not that useful or is there a better solution?
Reading glasses of various distances and powers from Dollar Store type outlets.
I use these type of glasses for close up work, they're a great ( and cheap ) solution. My first pair allowed me to see each individual solder joint of a 40 pin IC on a Technics board and solder them all fine.
For those that still wear glasses: Cabelas has clip on magnifiers in their fly fishing section. These are flipup type, and, as I recall, they come in +1.0 to +4.0 diopters with .5 steps. They may not have them all, at they same time, you may have to special order the size(s) you want. I think I have 1.5 and 2.5, somewhere .
So is the Hakko FX888D still decent even if looking like a Fisher Price toy? I need to replace my old station.
Doing watts/channel correctly/accurately is more difficult than many appreciate, and more difficult as the power goes up. Watts will be a squared function of power supply voltage, so small changes there translate into larger changes on the output. That means you need to control the line voltage accurately, so you need a Variac and an AC meter on the line. In perfect world you'd have an automatic Variac, but those are harder to come by. Next, you need to know the distortion level, so you need a THD analyzer, since most power specs are for a specific THD. You should have non-inductive resistors, but in particular avoid the green import double layer "non-inductive" power resistors, as they have a surprisingly bad effect on high frequency distortion. Be sure to measure the output voltage at the amp terminals, not the load terminals, as there will be some wire drop.
Went ahead and ordered the FX888D. I needed one and it's better than what I have now and wasn't that much money with spare tips.
Good information and a lot of tools to choose.
That really depends on the dissipation of the resistors. As the resistors get hotter, their resistance changes, sometimes dramatically. I have used several ceramic resistors soldered in parallel with heavy gauge solid wire (14-10 gauge) in a physical circle and then submerged in a gallon can filled with oil and banana jacks on the top. .Now I just have a pair of huge open wire Ohmite flat wire wound sir cooled resistors (about 12 inches long by 2 inch diameter). Both work great. A true RMS meter in parallel with a 'scope and a calculator for E squared / R and you will be good to go!
Have a Fluke 12. Picked up 2 Tek 475s for 40. Ayoue knockoff of a 436. A solder sucker with 2 extra tips. Side cutters. Some cheap DMMs. Use a 12X slide loupe for checking out PCBs. Now at work have a USB magnifier/camera (20), thinking about that at home for real close pics. Just have to get a roll of Kester leaded solder. It's a start. Using minigrabbers with belden 600V test lead wire to make test leads. Never use the leads that came with the meters. Don't need to go boom on live AC circuits, non isolated controllers. Float the meters and scopes from the line. Superviking welcome to AK. Love the speaker load idea, lotts of watts to cool. Trying to do this on no budget.
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