Cerwin Vega V30X speaker cabinet

[johnhoef]

Hi, all,
Wondering of anyone here can help me understand the workings of these Cerwin Vega V30X speakers? No simple crossover. There is a relay in there that is energized by the input signal with a 1000mfd cap across the relay coil to keep it engaged. Of course no schematic available, so I drew one from observation, and posted here. So, as I see it, the tweeter is connected directly to the output of the presence control. After a moment of signal input, the relay engages and creates a network of series/parallel resistors in series with the tweeter, while also enhancing the input to the relay coil. I have no idea what is trying to be accomplished here. Any ideas?

[Helmholtz]

Input capacitor(s) together with the inductor constitute a high-pass filter. Presence pot varies corner frequency and slope. The arrangement witrh the relay is a protection circuit supposed to open the direct connection to the tweeter if high frequency signal level exceeds a certain level.

[J M Fahey]

Not sure your schematic is 100% correct, but in general I see it as a Tweeter protection circuit.

For general purpose the tweeter has a "weak" crossover, only 4uF/8uF capacitors (adjustable with the Presence potntiometer ), because the inductor is fed from a relatively low impedance, sound must be sweeter, everybodyīs happy.

Once heavy handed "DJ Joe" or inexperienced High School "Jimmy Soundman" smash it with overdriven distorted squarewave Audio, 1000uF capacitor charges, relay is activated and stops bypassing the 45 ohm attenuation resistor , now you have some 10/12dB attenuation, the inductor attenuates more than before, since its own impedance remains the same, but id fed from a 45 ohm higher impedance. I guess the tweeter is 8 ohm.

To avoid an annoying up-down-up-down attenuation effect, the relatively long time constant plus the addition of the 520 ohm alternative path to straight feed the rectifier turn it into some kind of passive Schmitt trigger ("once turned on, it stays on easily" and viceversa) mask the effect.

So the tweeter stays alive lon ger, hopefully until the end of the party.

Or at least until everybody is so drunk/stoned they wonīt notice.

[johnhoef]

Thanks, guys, for your thoughts. Indeed, I neglected to read the writing on the crossover panel "self resetting overload protection". So, JM, looks like you are right on in circuit explanation. Thanks. My next question is what are the input capacitor values? It is near impossible to read off the caps themselves, and they are both bad. JM, you suggestion of 8 and 4 are correct? Is the 4 in series with the presence control?

[TomCarlos]

Do you have the crossover? If so, take a look at the components or take a photo and post. I looked for a schematic (on the web) and I don't think you'll find one.

[johnhoef]

[TomCarlos]

Looks like someone hacked up the crossover!! I don't know why the leads to the cap would have been cut. And just my first impression, the connections look bad. But we will assume your diagram is correct!!!

Can you lift the yellow cap to see what is underneath? Also, you identified the 1000uf. Do we assume that is the blue cap?

[johnhoef]

TomCarlos, This crossover is hardly hacked! It was I that "hacked" it. I would prefer to call it "cut out" the two defective capacitors. They need replacement. As you can see in the photo, the writing on the caps is not readable, thus, my request for their values. If anyone knows the value of these two capacitors, please help. Thanks.

[nevetslab]

TomCarlos, This crossover is hardly hacked! It was I that "hacked" it. I would prefer to call it "cut out" the two defective capacitors. They need replacement. As you can see in the photo, the writing on the caps is not readable, thus, my request for their values. If anyone knows the value of these two capacitors, please help. Thanks.

[ATTACH=CONFIG]53132[/ATTACH]

The Yellow cap is 1.5uF/200V Mylar (or metallized Mylar). The print on the white cap is out of focus, so you might try again to get the best lighting on it that might yield the faded text. I gather you don't have a capacitance meter or bridge. Film caps in a crossover aren't known for outright failure. BTW, where did you get the 4uF values in your schematic?

[J M Fahey]

Same here.
I described them as 4/8 because you always have the 4uF one connected and the parallel 4uF (which adds up to 8uF ) is graduallynconnected/disconnected by the presence pot.

I clearly read 1.5uF on the top one and seem to read 1.8uF on the bottom one.

Why do you think those caps are defective?

Being film type and 200V rated (even 63 V would have been enough, go figure) I can hardly imagine any way to damage them.

Please redraw your crossover with proper values and connections.

Agree that the 1000uF (or whatever until we actually see its label) cap is the blue one, we can see itīs īpolarized.

It would be interestingb to read the relay labels, mainly its *coil* (not contact) rating.
Should be in the range 5 - 12 - 24V DC

[johnhoef]

Juan, thanks for your continued help. I wrote in 4 and 4 just as a guess, as 8mfd would be a typical value for a tweeter crossover. Indeed, the yellow cap would be either a 1.5 or 15. So a good guess is 1.5. The decimal point on the cap is barely readable. The white one is impossible to read. it's x.5, and my guess would be 6.5??? This gives us a total of 8. The caps are definitely defective. I cut them out, and temporarily connected in an 8, and the tweeter came back to life. Indeed, the blue cap is 1000....easily read. This cap is not in question, although, being an electrolytic, I may as well replace it also, considering this circuit is very old. I have no idea of the relay's ratings. The markings on the relay are totally unreadable! So, here's a photo of the white cap through a magnifier:

[J M Fahey]

Donīt you have a capacitance reader?

Many multimeters have a simple one built-in.

Not Lab quality but 10% error is very acceptable here.

Solder a couple pigtails to each cap and measure.

[johnhoef]

Juan, Indeed, measured the caps - both bad!! I took another look at the unit as I suspected I made an error in the schematic, but no, the schematic is correct. Upon initial use of this crossover, the inductor is switched out of the circuit. In overload condition, the 45 ohm resistor and the inductor are brought into the circuit. I find this peculiar. Would we not want the inductor in the circuit in either condition? I updated the schematic to show the two capacitor value guesses:

[Helmholtz]

Juan, Indeed, measured the caps - both bad!! I took another look at the unit as I suspected I made an error in the schematic, but no, the schematic is correct. Upon initial use of this crossover, the inductor is switched out of the circuit. In overload condition, the 45 ohm resistor and the inductor are brought into the circuit. I find this peculiar. Would we not want the inductor in the circuit in either condition? I updated the schematic to show the two capacitor value guesses:[ATTACH=CONFIG]53135[/ATTACH]

The 45 Ohm resistor and choke are not out of circuit in normal operation. Their series combination is wired to ground and is one "leg" (the shunt part) of the high pass crossover. It is actually a second order LCR filter. The choke shunts lower frequencies to ground, the series resistor adjusts the Q/damping and "equalizes" the tweeter level to the woofer's for a smooth transition.

[johnhoef]

Helmholtz, Indeed, the 45 resistor and choke ARE out of the circuit in normal mode. Look at the connections to the relay contacts. The 45 resistor is shorted in normal mode. Anyway, what I am after in this thread is for someone that has experience with these speakers to tell me what the value of that larger capacitor is...the one I labeled 6.5mfd (a guess). Or if anyone here can tell me what you think it should be? Thanks for everyone's help here.