How Do I Test My Crossover Recap Prior to Re-Installing Them?

[tlarwa]

I'll be soldering new caps onto my Forte II crossovers tomorrow, and would like to test them prior to resinstalltion to make sure everything is right. I have a meter, I'm just not sure what I should measure that will tell me they check out properly. Any help?

Tom

[mustang guy]

If you have a multitester, look for the symbol below. The readings should match the rating on the side of the capacitor. Readings are in microfarads, which looks like uF.

[Budman]

i'm sure bob crites would help you out

[tlarwa]

And where do I measure across? On the board itself, I assume? Measuring across the cap won't tell me anything except the value of the cap. I want to make sure my solder joints are good and I didn't damage the board in any way. Oh, and you don't have to take it down to the simplest level for me ... I have a degree on mechanical engineering. I'm just not that experienced with the practical side of working on electronics. I'm learning though! Thanks for the help.

Tom

[mustang guy]

And where do I measure across? On the board itself, I assume? Measuring across the cap won't tell me anything except the value of the cap. I want to make sure my solder joints are good and I didn't damage the board in any way. Oh, and you don't have to take it down to the simplest level for me ... I have a degree on mechanical engineering. I'm just not that experienced with the practical side of working on electronics. I'm learning though! Thanks for the help.

Tom

Sorry, I wasn't aware of your credentials. There are special ESR meters which operate at extremely low voltage than can test caps in circuit, but the best way is to simply inspect your solder joints. The meter I use is this: http://www.ebay.com/itm/AnaTek-Blue-ESR-Low-Ohms-Meter-Fully-Assembed-/181171317882?pt=LH_DefaultDomain_0&hash=item2a2ea6ec7a. Here's a picture used for showing good solder technique

[tlarwa]

I wasn't trying to flaunt a degree or anything, in fact, I'm what you'd call a "non-practicing" engineer! But I have had my share of electrical engineering classes in the past, so I know the difference between an ohm, volt and amp! It's one thing to be able to read a schematic and quite another to be able to build something from it. I appreciate the pics ... I'm a decent solder-er, but I haven't done much work on circuit boards. I'll just take my time and do the best i can!

[djk]

.

[mustang guy]

HAHA

[tlarwa]

Exactly why I don't even think about doing any work on my Fisher 400 receiver ... I'm not getting anywhere near tube equipment.

[WMcD]

I wouldn't bother. But you could test the electrical input to the drivers over a range of frequencies and see how the roll off works.

I haven't done it except with automated equipment a long time ago. But these are my thoughts

Your meter will have to work down well below one volt on AC but that is common today with DVMs.

You will need a signal generator. That can be accomplished with this: http://www.nch.com.au/tonegen/index.html . The free version is good. I used an earlier version years ago and tried the download at the office today. Always fun.

You'll see that the main menu works for the musical notes but also gives Hz. The musical scale is logarithmic, with 13 half notes in each octave (doubling). You'll be using a spreadsheet to display but this works okay because on a linear x-axis, you'll get a logarithmic scale of freq if plotted by equal points.

Hook the output of your computer, headphone out is good, and drive your amp. Hook the amp to the crossover input. All drivers must be attached to the crossover.

You'll have to keep the voltage output of the amp low. The tweeter is most delicate but 0.282 or less should be okay and 0.089 volts easier on the ear. Use 0.089 volts and you should set this before hooking up to the crossover input.

Then you will test the woofer from about 30 up to 2500 Hz and record the voltage for each note up to about 2500 Hz.

Then test the mid from about 400 Hz up to 10,000 Hz.

Then test the tweeter from 3000 up to 15000 Hz.

Now: using the spread sheet.

Put freq in column A.

Put the raw voltage reading in B, C, D with cells according to the freq. You'll have to convert each to dB in E, F, G column using 20 log (measured voltage / 0.089)

Then graph E, F, G versus freq.

You should get some nice curves showing the input to each driver.

The woofer input will be somewhat above the mid and tweeter and start roll off at 700 Hz.

The midrange crossover is just a high pass filter, not bandpass IIRC. It should roll up to near max at about 700 Hz.

The tweeter is a high pass and should roll up to near max at 6000 Hz.

It is a lot of work but in theory should give some good results.

Note that we are actually plotting the frequency response of each section of the crossover and not the frequency response of the speaker.

WMcD