Dayton CX150-8 Coaxial Project

[Wolf]

Crossover boards are almost done and ready to install. Here is the final schematic, with the tweeter & mid padded down to the tune of about 4-5dB BSC.

I'm trying to figure out why the 5th wire is there on the tweeter board, Bill. It almost looks as though you series wired the caps, and tapped something in the middle of them. If you are using a cap-charge biasing circuit, then I get it, and the caps should be twice the value of what's specified in the schematic. Remember that paralleling adds capacitances, and series reduces.

Later,
Wolf

[4thtry]

Bill where did the 15 watt resistors come from?

Sorry for the delay in response. Have not logged on for a while. These old 15 watt units were purchased from Madi-----ound, 1991 or so. They landed in my junk box after I re-vamped the crossovers on my Symmetrical Isobarik project. I played the prototype speaker for about 30 minutes at roughly 85dB 1 meter and these resistors do not even get warm. The two 10 ohm resistors that I have paralleled for R4, however, get warm to the touch.

[4thtry]

I'm trying to figure out why the 5th wire is there on the tweeter board, Bill. It almost looks as though you series wired the caps, and tapped something in the middle of them. If you are using a cap-charge biasing circuit, then I get it, and the caps should be twice the value of what's specified in the schematic. Remember that paralleling adds capacitances, and series reduces.

Later,
Wolf

You have a very sharp eye. I was wondering if anyone would notice that extra wire! You are exactly right! I split the tweeter cap out in series, and then doubled the value, so that I could charge couple the circuit at 18VDC. This wire will run down to a small 4/40 machine screw mounted next to the banana plugs. The charge coupling stays on the capacitor for weeks, so there is no need for an internal battery to maintain the voltage. I'll just check the voltage now and then and re-charge it as necessary. As I understand it, this is a static charge, and this charge will hold its value for a very long time when using high quality poly caps. I've tried this with PE's NPE caps and have discovered that the charge disappears within a few hours. But not so with good quality PP caps.

Question: Is static charge coupling, with no battery on the PCB, allowed for the competition? I plan to charge the cap up to 18VDC before leaving home for Ft Wayne. It should still be at about 17VDC when I get home. If this is not allowed, I can simply short out the cap before playing them.

[Wolf]

If no power is applied, should be fine! I didn't know it would float for poly caps, but knew the NPEs or polarized versions needed batteries.

Wolf

[wogg]

Tangent: What does that 18V cap charge bias do for you in this application? Google sent me to a whole lot of unrelated circuits, mostly bootstraps for amplifiers and what not.

[Wolf]

It's mainly for capacitor biasing, and allows the result of operation to never cross 0. 'Capacitor biasing' or 'charge coupled audio capacitors' is really what you need to research. Back in the day, JBL used it on all of their larger electrolytics via a 1Mohm resistor and a 9VDC battery.

Later,
Wolf

[ugly woofer]

What difference do you hear with the cap charged?

[PWR RYD]

What difference do you hear with the cap charged?

+1

I understand there might be a tiny bit of hysteresis with a film cap around the zero crossing point at very high frequencies. But is that even audible at AF? I can almost see the point of it with NP electrolytic caps.

[4thtry]

Here are a couple threads discussing this technique in more detail. Sorry that I cannot be of more help on this.

http://techtalk.parts-express.com/forum/speaker-project-gallery/1306683-monkey-coffin-build-the-vintages

toggle down to posts 25 to 50 in the above thread

Also:

http://techtalk.parts-express.com/forum/tech-talk-forum/66498-charge-coupled-crossovers

I have been flipping back and forth between charge coupled and non-charge coupled for a few days now to see if I can hear a difference. I also have the charge coupled circuit installed on a pair of the original Esoteric tweeters in my "Dual Exhaust" speakers and have been doing some comparisons on that system as well. All my tests have been done using a 9 volt battery to charge up a pair of smallish PP caps through a pair of 500K resistors. I have not, as yet, compared charged and non-charged NPE capacitors.

Here is the problem. It takes a few minutes to switch back & forth because it takes a certain amount of time to charge and discharge the capacitors. I have to get up, walk behind the speaker, then either short out or charge up the caps, then go back to my listening chair. This process takes at least 5 minutes to complete each time. So, do I hear a difference? Maybe. Maybe not. I need a faster switching mechanism, as the difference appears to be quite small. Perhaps a 3 position DPDT switch next to my listening chair with wires running back to the crossover would help!!

[xmax]

How would the caps hold a charge with a choke and voice coil connecting them to "ground"?

[Wolf]

Because the position where the charge is kept is between 2 caps and it doesn't see ground.
Wolf

[xmax]

Lol.

[xmax]

You have a very sharp eye. I was wondering if anyone would notice that extra wire! You are exactly right! I split the tweeter cap out in series, and then doubled the value, so that I could charge couple the circuit at 18VDC. This wire will run down to a small 4/40 machine screw mounted next to the banana plugs. The charge coupling stays on the capacitor for weeks, so there is no need for an internal battery to maintain the voltage. I'll just check the voltage now and then and re-charge it as necessary. As I understand it, this is a static charge, and this charge will hold its value for a very long time when using high quality poly caps. I've tried this with PE's NPE caps and have discovered that the charge disappears within a few hours. But not so with good quality PP caps.

Question: Is static charge coupling, with no battery on the PCB, allowed for the competition? I plan to charge the cap up to 18VDC before leaving home for Ft Wayne. It should still be at about 17VDC when I get home. If this is not allowed, I can simply short out the cap before playing them.

Look at it this way, the 2 caps are 2 batteries in series, the chokes and voice coil (and on the woofer leg) are bulbs in series in a flash light. The caps will be drained instantly.

[Wolf]

No- they won't, they are not like batteries, and this is not DC.
Wolf

[wogg]

The fist cap in the series charges up to the 18VDC. There is no path to ground for the discharge, but Kirchhoff's Voltage Law muct be satisfied, the next cap will charge to -18V to compensate and net the DC voltage back to 0. When you solve the circuit with the battery in place across the first cap, the two caps are effectively in parallel with only the low coil resistance between them.