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.
Thanks for this detailed list/information! I appreciate it.
May I ask (I have watched a few vids on this...) when using an oscilloscope and one is testing a new audio device (unknown about its state of condition) do you use the isolation transformer and plug both the audio device and the oscilloscope into it Or do you plug the audio device into the Isolation Transformer and use the house hold wall outlet for the Scope?
One video says equipment goes to the IT and the Scope to the wall (earth ground). And the other guys 12voltxxxx on YT I think he says put both into the IT?!
Then, on an older IT there is an older guy showing how the manufacturer bonded the Transformer and this would be bad when testing old radios as you probably know (just learning here lol!) he said that would make the radio's chassis live if you got the polarity wrong when plugging in the radio.
But for me as I am new to this IT safety thing, I wanted to make sure I isolate properly because I am sure I am going to poke around some day and touch the wrong polarity!
In any case, may I ask if you can recommend a great IT with at least two plugins or more please...I am building my gear for a future repair/hobby shop!
Thank you very much for the above information - big help for sure!!!
Stereos are isolated from both the line and earth ground when plugged into the wall. so you can hook your scope probe ground to its chassis. the stereo uses the chassis as its ground. you can hook a stereo chassis up to earth ground if you wish. if using the scope ground you are now earth grounding the stereo chassis. You isolate a scope when hooking it up to something that is not isolated from the line. In doubt always use a differential probe that can handle the line V. A isolation transformer will isolate the scope ground from earth ground.
Sometimes you get a bit of a tingle when you touch some stereos, that it its leakage currents which can be measured as shown in some kenwood service manuals.
You can check isolation by using a DMM to measure ohms from chassis ground to each AC plug pin.
When you check for isolation with the DMM what would a person see if it was not grounded? I did get a small tickle when I had this one apart while turning up the volume just a tad...or at least I thought I was getting a small shock as the volume shaft touched the face-place because with the knobs off it rested on there. Mind you all pieces of the face-plate were separated from the frame!
Hopefully mega ohms. leakage currents should be in uA ranges.
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