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PA 4ohm linkage


la bam
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Hi all, not sure where to put this as theres no real PA section, so this seemed closest.

I've just bought a second hand pa. 2 tops and 2 subs.

The cabs are 4 ohm each, but have 2 connections on each cab (a + and -). Well in truth they have 4 - 2 speakons and 2 of those old 3 pin connectors.

Question - if I was to link these (top to sub etc) are they designed to stay at 4ohm load, or do they drop to 2?

Also, the tops work fine on usual 2fc speakons, but the subs only work on the 3 pin. Could it be the subs are powered using the 4fc speakons? (or whatever variant it is).

If it helps it's an old model, a hk linear L24 and L30.

Any help appreciated.

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Are these powered? I assume not, as powered don't specify impedance. If that's the case you can't link the tops and subs, you have to separately power them, using an electronic crossover to send the lows to the subs amp, the rest to the tops amp. Also, be aware the the way you see 99 out of 100 bands set up their PA, with the mains above the subs. is incorrect. The mains should be pole mounted to the front left and front right, the subs placed together, preferably next to a wall to one side.  

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Thanks bill.

These have an IN and OUT on them though?

I remember years ago, I had some cerwin Vega subs that were similar.

I've no idea on whether or not the subs or tops have a built in crossover like some cabs do. Theres no info on them. I know they're probably 20 years old and from a time when HK Audio (Harmon Kardon) and Hughes & Kettner where the same company in the same building.

I've been out of the passive pa game for a while. I agree powering the tops and subs separately with a crossover and 2 amps is probably the way to go unless I can find any info.

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It sounds like the old Peavey system we used to have in an old band. Passive subs with a crossover, linked to passive tops. 4Ohm each side, total load 2Ohm with everything plugged in.

When you say 3-pin connectors, do you mean XLRs? These are not power connectors, neither are speakons. If they were powered there would most likely be a female IEC connector. Some pictures might help.

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11 minutes ago, la bam said:

I remember having a peavey UL system linked like this.

No, the 3 pin look like xlrs but are also the same cables you find on old bass cabs and amps, like older trace elliot's.

I'll try and get some photos, thanks.

Maybe post a pic of the connections at the back of the speakers & subs?

 

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They're all parallel, no crossover. If the speakons don't work you may not have the right connection on the cable plug. Those are four pole. According to the diagram 2+2- are connected to the driver, 1+1- are pass through, so you can use a four conductor cable to send both the low and high frequency signals from a breakout panel on the amp rack to the subs and then just a two conductor cable from there to the mains.

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Thanks Bill, someone in an hk group, suggested the tops are connected +1 and -1 and the subs +2 and -2.

I've just tried 4 core cable (had one lying around) and it works fine into the top from the amp, then works fine from the top into the sub via the link, but not the amp direct to the sub.

 

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21 hours ago, Bill Fitzmaurice said:

 Also, be aware the the way you see 99 out of 100 bands set up their PA, with the mains above the subs. is incorrect. The mains should be pole mounted to the front left and front right, the subs placed together, preferably next to a wall to one side.  

This comment got me interested in why subs shouldn't go under tops, and I found this SOS article on sub placement.

https://www.soundonsound.com/techniques/bass-place

 

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I would recommend you contact John Hornby Skewes who are UK distributor for HK, and get a copy of the documentation for the cabs in question - I have recent experience of using their(HK) active PA cabs, and the correct wiring scheme is somewhat counterintuitive and doesn't fall in line with standard convention or the labelling on the plate amps.

Edited by SubsonicSimpleton
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Yes, it took some working out.

However, I think weve worked it out now.

Tops run on +1 -1.

Link is +1 -1 +2 -2.

Subs are +2 -2.

My only thing left to work out is how to power them now.

Do I use:

1. x4 amps (1 for each cab) will it be ok running one channel at 4ohm?

2. x2 amps capable of running down to 2 ohm (1 for x2tops and 1 for x2 subs).

3. Are there any other ways? Could I use x2 amps put power them daisy chained? Ie 1 top and sub per amp, but one one channel.

4. Any other ideas?

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Whilst I am sure someone will either correct me, or better still a diagram, here's my 10 penneth. As PA Amps are usually 2 channel, ie: Left and Right You can use 2 amps that will run down to 4 Ohms on each channel and connect them up as below using a Crossover to split the frequencies.

I Amp to power the tops, (Left and Right) and 1 amp to power the Subs, (Left and Right). It doesn't matter that the subs should be placed together, this is just to explain the linking up.

So you would come out of your mixer, Left and Right, into an electronic crossover, and then Lows to one amp and Subs,  highs to a second amp and Tops.

Edit: Found a diagram I did a while ago which hopefully will explain.

PA Basic Diagram.pdf

Edited by BassBunny
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11 minutes ago, BassBunny said:

Whilst I am sure someone will either correct me, or better still a diagram, here's my 10 penneth. As PA Amps are usually 2 channel, ie: Left and Right You can use 2 amps that will run down to 4 Ohms on each channel and connect them up as below using a Crossover to split the frequencies.

I Amp to power the tops, (Left and Right) and 1 amp to power the Subs, (Left and Right). It doesn't matter that the subs should be placed together, this is just to explain the linking up.

So you would come out of your mixer, Left and Right, into an electronic crossover, and then Lows to one amp and Subs,  highs to a second amp and Tops.

Edit: Found a diagram I did a while ago which hopefully will explain.

PA Basic Diagram.pdf 5.22 kB · 0 downloads

Yes, that's what I was thinking.

Just weird that they build in the links to connect the tops to the subs but that then makes this system 2 ohm per side per one input from the amp which is unusable for any amp (combined 1ohm).

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1 hour ago, la bam said:

Yes, that's what I was thinking.

Just weird that they build in the links to connect the tops to the subs but that then makes this system 2 ohm per side per one input from the amp which is unusable for any amp (combined 1ohm).

It might be that the "links" are there so you can use more than one sub/top per side. We had an HK sysyem that had 3 subs/mids and 1 top per side.

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