I need some pretty basic crossover help (Modula MT)

[JonW]

I’m just about ready to tackle the Modula MT’s. My first real speaker project. The part that has me most concerned is the crossover. I’m looking at the circuit diagram as well a people’s photos. There are a few things I don’t understand (OK, many things). Using those white plastic Radio Shack terminals looks to make the whole crossover a little neater,. Some questions I have:

-Where do you wire in the binding posts? Is one post the “In -“ and one the “In +” in the bottom photos? On the circuit diagram, the ends seem to be just a few lines. I’m not sure what that means. Although one of the ends is labeled with “Generator 1.”

-Does one binding post color (red or black) usually correspond to + or -?

-The + and - will be marked on the drivers, correct?

-I can use those white plastic terminals to go between:
> the binding post and crossover board 1
>crossover board 1 and 2
>each crossover board and each driver
right?

I’m not sure what I’m doing here. It will be my very first circuit experience. Thanks.

-Jon






The tweeter section:



The woofer section:

[chasw98]

Jon:

>>-Where do you wire in the binding posts? Is one post the “In -“ and one the “In +” >>in the bottom photos? On the circuit diagram, the ends seem to be just a few lines. >>I’m not sure what that means. Although one of the ends is labeled with “Generator >>1.”

The square with the circle inside labeled "generator" is the AC signal source to drive the crossovers which pass the signal to the drivers. Normally the generator would be your stereo amplifier. The downward pointing triangle underneath it represents ground or common. Ground or common is associated with the black binding post on the amp and the black post on the speaker. That would be the "-" minus in the diagrams. The line coming out of the top of the generator symbol represents the "+" side of the signal or the red binding post on both the speaker and the amplifier feeding the speaker.

>>-The + and - will be marked on the drivers, correct?
Yes, some indication of + and - will be located on the drivers. Usually right next to the tabs that the connectors go on. Sometimes there will only be a + sign.

>>-I can use those white plastic terminals to go between:
>> the binding post and crossover board 1
>>crossover board 1 and 2
>>each crossover board and each driver
>>right?
Yes, you can use those white plastic terminals. There are a lot of terminals out there in the world that are useful. The white terminals are convenient because they require no soldering or preparation of the wire with a connector.

You will notice at point "0" in the diagram another "earth ground or common" symbol. One thing to realize about all circuits is that they are big circles. The signal leaves the amplifier via the + terminal and then feeds a load, the crossover and drivers, and then returns back to the amplifier through the ground or - terminal. I believe that Radio Shack sells a book about basic electronic circuits. I have been told it is quite useful for basic understanding of electrical circuits such as "Whats a capacitor, Whats a resistor, etc.". Next time you are near one see if it is available. It is light reading and just might give you a kick start to put this thing together. While you are at it, you might want to pick up a digital volmeter or DMM. If you can, buy one that will measure capacitance and/or frequency along with AC & DC voltage and resistance. It can come in very handy for checking your work before hooking it up to your more expensive equipment. You are not so much looking for accuracy in the DMM as the basic ability to measure and check resistance to make sure things are not shorted. If you find you get into circuit building then start looking into tektronix or fluke equipment.

Chuck

[JonW]

Hey Chuck,

Thanks very much for the detailed explanation!

Let’s see if I have this right: The generator is the amp. The +/red post will follow above the generator, toward intersection 1. And the -/black post will go the other way, it’s a ground. Near intersection 0 is also a ground. Are these two grounds the same? In other words, will the -/black cable go from intersection 0 to the amp? And the +/red cable go from the amp to intersection 1? Although if that were the case I’d think that both of these ends would be connected in the diagram, but they’re not.

Thanks for recommending a basic book at Radio Shack. I could probably use that. If I were to buy a DMM/DVM, how might I want to use that to test things? I was thinking about building the crossover, hooking up the drivers, connecting the amp, play some music, and just seeing if any sound is produced. There is probably a better way to go about things, I’d think,

[JonMarsh]

Thanks Chuck for posting for JonW.

The grounds are in common. Note that LspCAD doesn't use junction dots to show connections where wires meet, so anywhere you see wires touching, there's a connection. Such as where L2, L4, C10, C11, and R8 connect in what is node 6 (the single number sitting on the wire by itself). Nodal naming is done with schematics prepared for simulation, which of course is what is happening with LspCAD, to predict the total response.

The Modula MT and Natalie P have an unusual quasi-series topology that doesn't lend itself to the neat little two board setup (one Low pass for woofer, one high pass for tweeter) that conventional parallel crossovers have. So, sometime I should make a recommended layout picture for you guys, but I'll have to build another set to do that- my daughter won't give me her's back to take apart and document.

~Jon

[JonW]

Jon-

Thanks for the further education. If the two grounds really are the same, that makes a little more sense to me. I still should probably get a basic book and learn these things. The electronics aspect of this project is both what gives me pause and makes me really want to try this out.

Might I want to get a DMM/DVM for testing the crossovers? And if so, what am I trying to determine?

I enjoyed building my sub more than I expected. I'm gradually building up my woodowrking skills. So it's on to real speakers now.

[WillyD]

I don't know which tweeter you are using, but note that the last two xover pics (mine) are of the Seas tweeter version (not that the xover is that different..)

And I got those white terminals at radio shack. They came in a big strip but I cut/snapped them into smaller segments.

And as others have explained, the IN- and IN+ correspond to the binding posts/incoming signal for the speaker itself. It was just easier for me to set it up like that.

[JonW]

Thanks Willy. And thanks for posting your photos.

Ah, OK, yours is the Seas version. I was not able to follow the diagram to your photo, but I was using the RS28A diagram. Makes more sense now. Not sure I can follow it 100%, but it’s better using the correct diagram.

I’m going to use the RS28A tweeter. Never having heard any of the tweeter options in person… Idunno. I’m kind of biasing this project toward Dan’s version because of the very nicely labeled photo he provided, above. That will help me make it through my first crossover.

[chasw98]

[QUOTE=JonW]Hey Chuck,

Thanks very much for the detailed explanation!

Let’s see if I have this right: The generator is the amp. The +/red post will follow above the generator, toward intersection 1.

>> Correct

And the -/black post will go the other way, it’s a ground. Near intersection 0 is also a ground. Are these two grounds the same? In other words, will the -/black cable go from intersection 0 to the amp?

>> Yes, wherever you see the symbol for ground or common, the points are equal, i.e. the same wire as if they were connected together.


And the +/red cable go from the amp to intersection 1? Although if that were the case I’d think that both of these ends would be connected in the diagram, but they’re not.

>>Yes, the line leaving the top of the generator is the + signal, seperate from the ground symbol below the generator. The + side of the generator will attach to C1, C10, C7, and the RS180 woofer.

Thanks for recommending a basic book at Radio Shack. I could probably use that. If I were to buy a DMM/DVM, how might I want to use that to test things?

>>With the DMM you can check the value of resistors in ohms to see if they are close to what the schematic says it should be. You can also use the DMM to check continuity to make sure that all your connections are good and solid (no intermittents). And most of all you can use the DMM to make sure that you haven't inadvertently miswired your circuit and created a short circuit to the amplifier that might blow it up when you turn it on to see if there is sound coming out of your project.

I was thinking about building the crossover, hooking up the drivers, connecting the amp, play some music, and just seeing if any sound is produced. There is probably a better way to go about things, I’d think

>>You would want to use the DMM to make sure that you have a safe circuit to hook you're amp to before risking your amp.

Now, Jon, you are a professor at a University, correct? Does this university have an engineering dept.? If they do, you should be able to get some basic info out of that department to get you going. BTW, what are you a professor of? I'm just curious. I am quite happy to help you in any way I can with this, but at some point a picture is worth a thousand words. If I lived near you I could explain this in a matter of hours very clearly and succinctly by using the schematic shown and by showing you with a DMM exactly what you are looking at. If you were to print out the schematic and walk into an EE lab, any first year student would be able to explain the basics of the schematic drawing to you in about 10 minutes. Please don't take this the wrong way, but I think we will reach a point shortly where it will be hard to explain further without being able to point at the drawing and talk back and forth. If you want to PM me, I will give you a link to a program that will let you view my screen here at home and I can get your phone number, call you at a pre arranged time and get you going so that you don't make mistakes or feel overwhelmed by the circuit. I really don't want to here that you hooked up your new crossover and a little wisp of magic smoke came from your amp and then "SILENCE"! PM me. :T

[WillyD]

Thanks Willy. And thanks for posting your photos.

Ah, OK, yours is the Seas version. I was not able to follow the diagram to your photo, but I was using the RS28A diagram. Makes more sense now. Not sure I can follow it 100%, but it’s better using the correct diagram.

I’m going to use the RS28A tweeter. Never having heard any of the tweeter options in person… Idunno. I’m kind of biasing this project toward Dan’s version because of the very nicely labeled photo he provided, above. That will help me make it through my first crossover.

Hah, yeah, I thought that might confuse you some. :T

And from everything I have heard, either tweeter is good for the money. I think those that have heard both might actually prefer the RS28A...but the differences are not major (not that I know of).

And what I did to test the crossover first (since it was my first time) was to wire it up (just twisted the wires together) and made the proper connections to the drivers and listened to a bit of music on low volume. Everything sounded fine minus the lack of bass due to no cabinet, so I knew I was on the right track.

[JonW]

OK, this is all great- thanks. I think, at this point, I only have 2 more questions that I can think of.

First, I understand what you're saying here:

>>With the DMM you can check the value of resistors in ohms to see if they are close to what the schematic says it should be. You can also use the DMM to check continuity to make sure that all your connections are good and solid (no intermittents).

Basically, put the DMM eelctrodes on either side of, say, a resistor and make sure you see the correct value. Also use it to make sure all soldered connections are OK. But how to measure the whole crossover? After you check the individual connections, it would be good to make sur the whole thing is OK. What are you looking for there?

Second question: Are there any particular DMM's or DVM's you'd recommend buying?

Now, Jon, you are a professor at a University, correct? Does this university have an engineering dept.? If they do, you should be able to get some basic info out of that department to get you going. BTW, what are you a professor of? I'm just curious. I am quite happy to help you in any way I can with this, but at some point a picture is worth a thousand words. If I lived near you I could explain this in a matter of hours very clearly and succinctly by using the schematic shown and by showing you with a DMM exactly what you are looking at. If you were to print out the schematic and walk into an EE lab, any first year student would be able to explain the basics of the schematic drawing to you in about 10 minutes. Please don't take this the wrong way, but I think we will reach a point shortly where it will be hard to explain further without being able to point at the drawing and talk back and forth. If you want to PM me, I will give you a link to a program that will let you view my screen here at home and I can get your phone number, call you at a pre arranged time and get you going so that you don't make mistakes or feel overwhelmed by the circuit. I really don't want to here that you hooked up your new crossover and a little wisp of magic smoke came from your amp and then "SILENCE"! PM me. :T

How did you guess that I'm not an electrical engineering professor?!?! :P It's chemistry. And I obviously have zero experience with electronics. Umm, it just never came up, I guess. But having both the crossover circuit diagrams and the photos side by side is a tremendous help. It also helps quite a lot if I use the correct diagram, like I was not for Willy's crossover photos.

I appreciate all the help. :T I _think_ I'm OK at this point. The only remaining questions I can think of are the two I just asked. It all seems to be pretty logical. I just need some experience doing it. Probably once the first crossover is made and works, I'll be OK with it all.

[JonW]

Hah, yeah, I thought that might confuse you some. :T

And from everything I have heard, either tweeter is good for the money. I think those that have heard both might actually prefer the RS28A...but the differences are not major (not that I know of).

And what I did to test the crossover first (since it was my first time) was to wire it up (just twisted the wires together) and made the proper connections to the drivers and listened to a bit of music on low volume. Everything sounded fine minus the lack of bass due to no cabinet, so I knew I was on the right track.

Yup, _much_ better with the proper diagram. I like Chuck's idea of testing the crossover with a DMM prior to risking the amp. But it seems to have worked AOK for you. Once Iget my first crossover build and working, all should be well. I'll just do it really carefully.

[WillyD]

Yup, _much_ better with the proper diagram. I like Chuck's idea of testing the crossover with a DMM prior to risking the amp. But it seems to have worked AOK for you. Once Iget my first crossover build and working, all should be well. I'll just do it really carefully.

Aye. Just double check your connections (or triple check) and you will probably be just fine. :T