Electro-voice EV-4A Crossover components

[jsengxx]

Hi all,

I need some help here in order to rebuild my crossover with new caps and resistors.

I bought a pair of Electro-Voice EV-4A speakers and I need to recap it but I have my doughts about the components I have to buy.

Components specs that I can read from the caps:
1 x 4.5uf 40V NP
1 x 13uf 40V NP

The resistors I have really no idea.

I have incluided pics.

Could someone help me figure out what components to use for this recap?

Thanks

 

[jsengxx]

For the caps I was thinking of:

- Clarity cap ESA 4.5uf 250V and

- Clarity cap ESA 1.0uf + Clarity cap ESA 12.0uf to make it total 13.0uf like the original

Please help with the 2 resistors and what kind of wattage......

Thanks in advance.

 

[jsengxx]

I have measured the resistance with the resistors in place at the board and 1 gives me 7.3ohm the other 6.0ohm. They have both the same color strips so if this is the correct way to measure them (resistors still in place at the crossover board), I can assume that they are out of specs.

The big question now is:

What resistors to use and wattage to replace the old ones?

Thanks

 

[Rick Owen]

Conversion Calculator Resistor Color Code

The resistor color code calculator makes it easy to identify and select resistance and tolerance values for 4, 5, and 6 band through hole resistors.

www.digikey.com

 

[jsengxx]

Conversion Calculator Resistor Color Code

The resistor color code calculator makes it easy to identify and select resistance and tolerance values for 4, 5, and 6 band through hole resistors.

www.digikey.com

I have looked at it and it gives me 40ohm but what my confusion is is that on another thread about the EV FOUR they used a 5.6ohm 10W resistor but from the color code it should be 47ohm on that speaker crossover (Yellow / violet / black). If I measure it with a multimeter it gave me 7.3 and 6.0ohm

 

[Rick Owen]

need a better photo of the color bands on the resistors, and no, you should remove them from the circuit to test them.

 

[jsengxx]

Better pic of resistor

 

[jsengxx]

need a better photo of the color bands on the resistors, and no, you should remove them from the circuit to test them.

 

[Stuart Pedaso]

First band looks kinda' orange in the pic above. Though this one shows a more yellow appearance.



From the traced out schematic, they load the shunt portion of the voltage divider making up tweeter and mid level controls.
[ EDIT -- updated resistors in schematic to 10Ω per revelations in subsequent posts below ]

As suggested above, disconnect at least one lead of the resistor to measure it out of circuit. Replacing [ Edit -- 10Ω ] resistors with something much smaller will reduce output of mid and tweeter.

 

[Rick Owen]

First band looks kinda' orange in the pic above. Though this one shows a more yellow appearance.

View attachment 3212299

From the traced out schematic, they load the shunt portion of the voltage divider making up tweeter and mid level controls.
View attachment 3212301
As suggested above, disconnect at least one lead of the resistor to measure it out of circuit. Replacing 40Ω resistors with something much smaller will reduce output of mid and tweeter.

Is the first band on that resistor yellow or orange?
Hard to tell with the flash/photo.

 

[jsengxx]

Is the first band on that resistor yellow or orange?
Hard to tell with the flash/photo.

It is more orange or brown

 

[jsengxx]

First band looks kinda' orange in the pic above. Though this one shows a more yellow appearance.

View attachment 3212299

From the traced out schematic, they load the shunt portion of the voltage divider making up tweeter and mid level controls.
View attachment 3212301
As suggested above, disconnect at least one lead of the resistor to measure it out of circuit. Replacing 40Ω resistors with something much smaller will reduce output of mid and tweeter.

Thanks for the scematic.

I have taken out the resistor and it measures 11.7Ohm so way of from the 40Ohm. At this point I really don´t know what resistor to swap it with...

 

[jsengxx]

picture without flash

 

[malden]

@jsengxx , before you close up the cabinets, can you post some photos of the drivers front and rear?

 

[EarlK]

What you have there are 2 old-style, adhoc, variable LPads ( using a potentiometer and a fixed "stopper-resistor" ) > which works "good-enough" for balance adjustments >> within a restricted range.

FWIW, Altec used a 20R to 25R in that same "stopper" position that goes to ground ( for their nominal 12 ohm drivers of the 50s + 60's ) >> before they started using bona-fide variable LPads.

You should also determine the value of those 2 pots ( for future replacement consideration ).

Are those 3 drivers 8 ohms or 16 ohms ?? ( disconnect them and then measure each individual DCR ).

 

[jsengxx]

picture without flash

@jsengxx , before you close up the cabinets, can you post some photos of the drivers front and rear?

 

[jsengxx]

What you have there are 2 old-style, adhoc, variable LPads ( using a potentiometer and a fixed "stopper-resistor" ) > that works "good-enough" within a restricted adjustment range.

FWIW, Altec used a 20R to 25R in that same "stopper" position that goes to ground ( for their nominal 12 ohm drivers of the 50s + 60's ) >> before they started using bona-fide variable LPads.

You should also determine the value of those 2 pots ( for future replacement consideration ).

Are those 3 drivers 8 ohms or 16 ohms ?? ( disconnect them and then measure each individual DCR ).

8ohm drivers

 

[EarlK]

What resistance do you measure ( for each pot. ) when measuring between the pot's terminal that's connected to the capacitor and then the center terminal ( that has either the green or yellow lead-out wire attached to it ?? )
- ( measure with the drivers disconnected, plus the "stopper-resistors" disconnected from ground ).
- Also measure from the center tab of each pot to the outer terminal that was connected to the load//stopper resistor.
- Guesstimate the amount of wiper rotation that brought the components into balance with each-other.

This will help determine if those adhoc pads were meant to provide an 8 ohm load ( or something else higher or lower ) for the included caps + coils.

If 8 ohms >> I'd simply replace with a low wattage 8 ohm Lpad.
- If the speculated load turns out to be higher >> add the appropriate valued resistor, inline ( in-series ) with terminal 3 of your new Lpad.
- If the speculated load is lower than 8 ohms >> you're sort of stuck with this antiquated topology.

 

[jsengxx]

I have taken the other resistor out too and this measures 11.2Ohm so I think the color is brown / black / black making this a 10 Ohm resistor. The color for me is more orange (making it a 30ohm ris) but I don´t think the resistor could loose almost 20Ohm in 60 years? It works the opposite way, resistors will increase over time.

 

[Stuart Pedaso]

I have taken the other resistor out too and this measures 11.2Ohm so I think the color is brown / black / black making this a 10 Ohm resistor. The color for me is more orange (making it a 30ohm ris) but I don´t think the resistor could loose almost 20Ohm in 60 years? It works the opposite way, resistors will increase over time.

Results that consistent does suggest they have light brown first bands. They may actually still be in spec (±10%) if your meter's lead resistance can account for 0.2Ω.

I've updated the schematic in post #9 to reflect this more likely resistor value.