Schematics to Crossover -- my first, need help - diyAudio
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Old 15th July 2013, 04:24 AM   #1
drtebi is offline drtebi  United States
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Default Schematics to Crossover -- my first, need help

Hello,

I am new here, please be easy on me

I have to admit I am a complete newbie to making my own electronics. I however have some basic soldering knowledge, made some of my own cables and similar easy stuff like that; I am also a woodworker and work with metal...

Anyway, I have a pair of T+A A3D speakers, which are digital-active, and their active section is beyond reasonable repair. I have decided to convert them to passive speakers, which was once also available, as can be seen in this brochure:
http://tebert.com/dump/diyaudio/TA-P...tedEdition.pdf

T+A was kind enough to send me the schematics for building the necessary crossover. Here it is:
Click the image to open in full size.
I also have a PDF version, if that's easier to read:
http://tebert.com/dump/diyaudio/Schaltplan_P3.pdf

OK, and now I am completely clue-less as to what parts I need, how to arrange them etc. I basically need a complete-beginners course, and I hope some of you could provide me with some good links to start off.

Google is my friend, but I believe people here can be better friends--saving me some time to try to hunt down some well explaining tutorials for the beginnner.

After looking at a few online tutorials I noticed that most of them have only one "-" and one "+" connection, while my T+A schematics have two separate ones? This is what confuses me the most at the moment... while I try to decipher the other symbols.

There are two woofers, a midrange and a tweeter, so shouldn't there only be one +- connection to the crossover?

Again, I am completely clueless at the moment, and just some good pointers to tutorials would greatly be appreciated.

Thank you,
DrTebi
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Old 15th July 2013, 04:57 PM   #2
DougL is offline DougL  United States
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The First thing I would do is assign a number to each node.
The schematic basically is a graphical way to tell what components are tied together.
There is only one + and one -. Simply consider them one node.
For example, the schematic for the midrange shows the 82 uF cap, the 1.8 mH coil and the 10 uF cap (With the wrong Symbol) are connected.

Hopefully, someone will have the link to a basics tutorial.

Its not rocket science.

Hang in there and you will get it.

Doug
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Old 15th July 2013, 06:45 PM   #3
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You have to make a complete list to order.
Various other list of materials (like solder for electronics).

List of components (a pair) needed for the crossover:
Inductors
L1 = 5.6 mH
L2 = 5.8 mH
L3 = 1.8 mH (mid)
L4 = 2.8 mH (mid)
L5 = 0.25 mH (tweeter)

Capacitors
C1 = 150 uF (35V/min)
C2 = 82 uF (32V/min) (mid)
C3 = 10 uF (MKT) (mid)
C4 = 12 uF (MKP) (tweeter)
C5 = 10 uF (MKP) (tweeter)

Resistors
R1 = 3R9, 10W n.i. (mid)
R2 = 3R9, 10W n.i. (tweeter)
R3 = 10R, 5W n.i. (tweeter)

Some basic links:
PE 101
NODAL ANALYSIS 101
Parts Express - DIY Speaker Crossover Assemb VIDEO 101
A complete LIST OF MATERIALS example by Troels for his speakers for the complete kit.
Crossovers 101
How to Rebuild Speaker Crossovers 101
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Old 16th July 2013, 07:44 AM   #4
drtebi is offline drtebi  United States
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Quote:
Originally Posted by Inductor View Post
You have to make a complete list to order.
Various other list of materials (like solder for electronics).

List of components (a pair) needed for the crossover: [...]
Thank you so much, that really helped me a lot! At least now I know what I will need to get.

I also went to the library today and got a few books... there was nothing specific on crossovers, but a couple of DIY loudspeaker books and I also got a "basic electronics" book.

A question that comes to mind which may not be in the books:

When I start shopping for these parts, how would I be able to tell whether e.g. one capacitor is better than another? I am sure there will be options...

Thanks again,
DrTebi
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Old 16th July 2013, 08:16 AM   #5
tinitus is offline tinitus  Europe
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Old 16th July 2013, 04:59 PM   #6
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Passive is better in this case, that it was already sorted out (crossover layout). Active would need reverse engineering for different from original amp sections and attenuation slopes.
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Old 16th July 2013, 06:09 PM   #7
jReave is online now jReave  Canada
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A couple of other pointers if you can't find the exact values:

Capacitors in parallel add their values.
Resistors in series add their values.
Inductors are more troublesome. You should try to get very close values.

For your purposes, PE's npe caps should suit fine: Non-polarized Electrolytic Capacitors in the Speaker Components Department at Parts Express | 293, although you can go more expensive than that if you want to.

For the larger value inductors, you may want to go with iron core. Air core for the smaller ones will be good.

Also, all inductors also have resistance but unfortunately your schematic isn't showing these. You should probably try to keep these as low as your budget will allow, ie, .2 or .3 or .4 ohms if you can.
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Old 17th July 2013, 06:15 AM   #8
drtebi is offline drtebi  United States
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Thank you... slowly but certainly I am understanding this a bit better.

I still have a couple of things I am uncertain about--what is the difference between a lower priced and a higher priced capacitor/resistor? Will it have a great impact on sound quality?

Also, I wonder why the T+A layout I posted above does have two times a + and - connection. Should these actually all go to one + and - terminal in the final install? Or are there supposed to be two binding posts that are bridged or something like that? That's what confuses me the most, as all crossover examples/tutorials I have seen only have one + and - connection.
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Old 17th July 2013, 06:36 PM   #9
jReave is online now jReave  Canada
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Well there are pages and pages of debates written as to the sonic merits and differences of different capacitors. As a general rule, if you want to spend more money on better caps, do it on those that are in series for the tweeter and mid. Don't worry about the parallel caps. So, from the list in post #3, those will be C2, C3 and C4. But cap costs should be kept relative to the costs of the drivers. No sense spending big money on components if the drivers only costs a few bucks.

Dayton or Solen caps listed here should be fine I think for those series caps if you want to go that way. Metalized Polypropylene Capacitors in the Speaker Components Department at Parts Express | 294

For resistors, the Daytons here should again be fine. Audio Grade / Non-inductive Resistors in the Speaker Components Department at Parts Express | 301

I find the catalog pages helpful when I'm selecting inductors.
For air core - http://www.parts-express.com/catalog...log-Pg-162.pdf
For iron core - http://www.parts-express.com/catalog...log-Pg-164.pdf
For these, I think you're looking for the lowest dc resistance (dcr) that you can afford. These things can get kind of expensive.

As for the wiring, don't worry that the diagram separates the 2 xo's. Simply connect both positive ends to the positive terminal and both negatives to the negative terminal. Or to a common pos and neg on the xo board which can be easier.
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Old 18th July 2013, 07:13 AM   #10
drtebi is offline drtebi  United States
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Thanks again, I am now putting my order together.

A 5.8mH inductor seems to be rare, would I still play safe by using a 5.6mH one instead?

It was also mentioned in this thread that capacitors in parallel add their values and resistors in series do as well--is that relevant for my order? E.g. do I need to re-calculate the uF values? Or... does this mean if I cannot find a certain value, I can split it into two with half the value?

Regarding the Resistors: I see
3.9 R 10W (2x)
10R 5W (1x)

So are these 3.9 Ohm, 10 Watts and 10 Ohm 5 Watt resistors? I cannot find the exact values... should I try to find one that is as close as possible in Ohm, or/and Watts? Or rather use several in series to get the exact values?

Last edited by drtebi; 18th July 2013 at 07:42 AM.
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