Best value capacitor with 2405H

[David Ketley]

What value capacitor in series do you recommend for the 2405H Im using a JBL 2446 crossed over at 1600 Hz?

Dave

[Champster]

In some places you say you're going 4 way active. Are you running your 2446 and 2405 with a passive cover?

[4343]

Factory XO's mostly had 1.0uF or 1.5uF in the series side, plus inductor and padding and damping resistors, and usually an L-pad.

For passive I like to just use a pair of 2.0uF or 3.0uF in series (1.0-1.5uF effective) so that I can tie a 2-3M ohm resistor to the center point, which is fed by a 9V battery. Bias sounds better...

Really it does depend on whether you are running them off their own amp or not. With active you just need a DC blocker cap. 1.5uF is too high for active XO, you need to be an octave lower so the rolloff does not interfere with your active slopes. Start with 3.0uF (or a pair of 6.0uF in series).

I have also driven my 2405's with a small chip amp, usually Class T, and simply fed the amp full range and let the passive XO filter out the lows. Works pretty good as a way to eliminate the L-Pad.

[David Ketley]

Mike that's really helpful. I've tried them with the pre out from my JBL 2446 into a 70 watt/ channel Musical Fidelity amp with a 2.5uf capacitor and they sound fine. What sort of attenuation does the capacitor give compared to a dedicated active crossover?
The Marchand is a 3 way active crossover so its only the JBL 2405s that require something simple.

Thanks

Dave

[Mannermusic]

Factory XO's mostly had 1.0uF or 1.5uF in the series side, plus inductor and padding and damping resistors, and usually an L-pad.

For passive I like to just use a pair of 2.0uF or 3.0uF in series (1.0-1.5uF effective) so that I can tie a 2-3M ohm resistor to the center point, which is fed by a 9V battery. Bias sounds better...

Really it does depend on whether you are running them off their own amp or not. With active you just need a DC blocker cap. 1.5uF is too high for active XO, you need to be an octave lower so the rolloff does not interfere with your active slopes. Start with 3.0uF (or a pair of 6.0uF in series).

I have also driven my 2405's with a small chip amp, usually Class T, and simply fed the amp full range and let the passive XO filter out the lows. Works pretty good as a way to eliminate the L-Pad.

Question re last paragraph: I already have a number of smallish amps both solid state and tube I could use for this experiment. If I understand what you are saying, you are doing a parallel tap at the output of your preamp and feeding the signal to the input of an additional power amp and the output of that amp to the input of the UHF passive circuit? Seems most any amp would do the trick? Anything special re connectors, etc.? Schematic? Also Mike

[Allanvh5150]

Drive the small amp straight from the passive crossover. You will need to pad it down of course.

Allan.

[Mannermusic]

Drive the small amp straight from the passive crossover. You will need to pad it down of course.

Allan.

OK - thanks Allan. Your last sentence says it all - that's what had me scratching my head. Could smoke the whole deal. I'd say, pad it WAY down as you begin the experiment. Little surprised it isn't problematic in some manner or another - noise, impedance, whatever. Will be interested to hear how it sounds. Thanks again!

[Allanvh5150]

Impedance won't be a problem as you are driving a high impedance source with a low impedance one.

Allan.

[Mannermusic]

Impedance won't be a problem as you are driving a high impedance source with a low impedance one.

Allan.

OK! Appreciate. Mike

[Allanvh5150]

This is actually how Greg Timbers say to do it.

Allan.

[Mannermusic]

This is actually how Greg Timbers say to do it.

Allan.

Yes, I remember the post back a-ways. An extremely clever idea (who-da-thunk-it!). And, anyone who has heard a ring radiator on a separate amp - I ran a tri amp for some time - will never be satisfied with a passive driven ring radiator again (a lame substitute at best). Maybe this exchange will encourage folks to wire it up and give it a try. Mike

[Allanvh5150]

It works fine. I am using the idea in some cabinets I am building at the moment.

Allan.

[audiomagnate]

Drive the small amp straight from the passive crossover. You will need to pad it down of course.

Allan.

Wait a minute. Are you saying you hook up a pair of multi-way JBL speakers normally, but yank the leads going to to 2405's and pad that already amplified and filtered signal back down to line level and then feed it to a second amp, the output of which is connected directly to the 2405's? My head is spinning.

[hjames]

I don't think he meant feed it from another amp, I think he meant feed it from the preamp with a high-pass to avoid any potential Amp thump.

But make up your own mind - the original post by Greg Timbers talking about the 4345s can be found here:

http://www.audioheritage.org/vbulletin/showthread.php?10490-The-JBL-4345-Club&p=110075&highlight=#post110075

I think the relevant part is this: (no edits by me - text is intact)

The ring radiator hates passive networks. A major improvement in the upper range would be to drive the 2405 from its own little amp. You only need 3 or 4 v rms. The 2405 does 110 dB for 2.83v. It is padded way down in the system. There is little real power at those frequencies anyway. You only need to know the voltage output of the amp, power is irrelevant. The 2405 is about 12 ohms and won't draw much current. I would use some little chip amp with a 2ond or 3rd order low level highpass in front of it. Take off the passive network to the ring and just feed it straight. Make sure the amp doesn't make a DC thump on turn on or turn off. That will fatigue the diaphragm. The amp will also have to have really low noise characteristics as any hiss will be really loud directly into the ring. I used to use an old Marantz 1030 integrated amp to run my rings. I could separate out the power amp section and the tweeters always sounded really good.

[Allanvh5150]

No. Disconnect the 2405 from the passive crossover, run that through a pad into another small amplifier and then drive the 2405. Simple.

Allan.

[David Ketley]

In my original set up I was using a Heil PS5a Air Motion Tweeters the output was only 96Db. I ran the pre out from my amp Musical Fidelity KW 500, this has a dedicated separate pre amp output, to another small power amp to bring the output up to the JBL 2446 111Db horn mounted. The JBL 2304H is 105 Db so I will keep this configuration so I can boost the output up to the 2446.

The 2.5 Uf capacitor is on the power output of the small power amp driving the JBL 2304H.

All my power amps have their own volume controls.

As an amateur I welcome any better ways of doing this.

Dave

[Don C]

I don't think he meant feed it from another amp, I think he meant feed it from the preamp with a high-pass to avoid any potential Amp thump.


This. Two power amps in seires would be a big mis-interpretation of the instructions. The padding is to minimise the noise because of the high efficiency. You would never want to double the noise by adding an un-necesary amp stage.