Bridging an H&H m900 (400w/ch@4ohm) to run two 16ohm H&H Bass Bins in parallel? - diyAudio
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Old 15th February 2005, 12:59 PM   #1
Ovation is offline Ovation  United Kingdom
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Default Bridging an H&H m900 (400w/ch@4ohm) to run two 16ohm H&H Bass Bins in parallel?

Hi All,
Whilst this isn't strictly DIY audio, you guys were mega helpful a couple of months back when I revamped our Disco speakers - I though I'd see if you can help again.

I've just bought an old H&H m900 amplifier which I believe is rated at 400W/channel @ 4ohms - AND that it is somehow bridgeable internally. I've also bought two Bass Bins made also by H&H which are rated at 300W @ 16ohms. and a Behringer CX2310 - 2 way X-over
http://www.behringer.com/CX2310/index.cfm?lang=ENG

I believe what I want to do is as follows, but I'd appreciate all the advice you can throw at me:

The amp currently struggles to drive the bins (so I am told - I've not tried myself as I've only just ordered some XLRs to connect to it!!) - 16ohm loading on a 4ohm amp. From what I have read, If I bridge my amp it will be theoretically a mono block of 4x the output power (minus lots of inefficiencies) which should be driving a load which is double the usual load it supports. Hence, I think it will end up as a mono block that can drive my two 16ohm bins in parallell (8ohms) at more than 600w which is the max rating of the combined speakers.

BUT - How do it do it??
I think I can choose whether to use the mono Sub output or the Stereo Bass output on the crossover - If I use the stereo output I have connectors to go into both inputs of my - now mono, bridged - amp. If I use the mono output do I have to split it to feed both sides?

Then - Does anyone know how to bridge this particular amp, and which pins do what on the back of it after it's bridged? (From the diagram on the back and a little bit that I've read, there is some kind of internal connection for bridging).

The ultimate goal it to use my original speakers to run the High/Mid sound in Stereo using a different amp, along with the Bass Bins to pump out the power hungry bass in Mono through the m900.

Here's a slightly crappy rendition of the 'bridging' part of the diagram on my Amp:
Click the image to open in full size.
Where I've written 'Bridge' there is what looks lik a diagram of a button or switch, but this does not exist on the outside of the chassis.

Any help you can all offer will be much appreciated .

Many Thanks
Jonathan
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Old 15th February 2005, 03:29 PM   #2
Ovation is offline Ovation  United Kingdom
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-- By the way:
I'll try and photograph that actualy functional diagram on the back of the amp - That way you might be able to see more than my diagram.

I realize my post above is full of too many words :-

I think I can reduce the question to one line......

o How does bridging an amplifier affect it's rated wattage and load ?

Cheers
Jonathan
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Old 15th February 2005, 03:53 PM   #3
mcp is offline mcp  United States
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Hello Jonathan

To get your amp working, switch over to Bridge Position internally first. Use Mono Sub from Output of Crossover. Input into CH1. CH2 input should be tied to signal ground (if there is a 1/4" TRS, it is internally grounded if no jacks are inserted).

Speakers (+) terminals to CH1 RED OUT
Speakers (-) terminals to CH2 RED OUT

Do not use any of the Black Terminals (-ve Return) at the back of the amplifier otherwise you will be shorting the amp.

In Mono-Bridge, you will be getting 800W into 8 ohms, enough for 2 parallelled 16 ohms of 300W each.

Regards
Attached Images
File Type: gif bridge.gif (2.6 KB, 153 views)
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Old 16th February 2005, 09:14 AM   #4
Ovation is offline Ovation  United Kingdom
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Hey - Thanks mcp !!!

That's just what I wanted to know.... Did you know that off the top of your head, or are you familiar with this amp? ( I managed to get the user manual last night and what you told me EXACTLY matches!!)

The only thing I'm still not sure of, is what to do with the second input:

So I've got a 'balanced' mono XLR output from my crossover, but I've tied -ve and GND together so it's now unbalanced. This means that I have +ve and GND to connect to my amp.

The amp has XLR inputs, so I think I have two choices:


Connect +ve from the source to +ve on Channel 1 of the Amp AND Connect GND from source to +ve on Channel 2 of the Amp.


OR


Connect +ve and GND from the source to +ve and GND on Channel 1 of the AMP AND Short all three pins on the Channel 2 Input so that +ve is connected to earth.


Sorry if this is a dumb question, but this concept is very new to me.

Thanks
Jonathan
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Old 16th February 2005, 02:19 PM   #5
mcp is offline mcp  United States
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I've never owned a HH amp before but the majority of pro amps work along the same lines.

In pro environments, you should be running balanced lines whenever possible. Since the HH amp has XLR Inputs (I am assuming they are Balanced), run Balanced from crossover to amp at CH 1 input.

Often, by switching over to bridge internally, it also grounds the input of the second channel. You will need to verify this in the manual. If so, you won't need to do anything about the second XLR input. But as a precaution, I would plug in an empty XLR connector so that others don't accidentally plug in a signal cable. For this "Dummy" plug, I would also take the extra effort to short all the 3 pins internally.

Most important, the speaker wires are never connected to any one of the Black Binding Post Terminals. It is always the 2 RED ones that are used in Mono-Bridge Mode. Once connected properly, you will get nice bass with your setup.

Regards
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Old 17th February 2005, 11:36 PM   #6
Ovation is offline Ovation  United Kingdom
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Default Amp Good - Speakers Bad??

Okay, well I've done all that was suggested for my amp - So, the output of my mixer goes to the Behringer crossover - the high and mid are connected to my Lyonforge amp and work well, and the mono Sub output is connected to Channel 1 on my H&H Amp.

+ve to Pin 2 of XLR input and -ve/GND to pins 1&3
Channel 2 In has all three pins shorted.

I have made an adaptor so that I use Pin 2 (+ve) of Channel 1 as the +ve for my speaker, and Pin 2 of Channel 2 (+ve) as the -ve input for my speakers.

If I send High Frequency through this configuration into my High/Mid speakers it works , but when the Bass Bins are involved it seems to be a different story :-(

I've looked inside the bins and they actually contain the following cones:

H&H Model: 1200E
Rating: 150W
Ohms: 16

They have Monster sized voice coils on them and weight several kilos (they're only 12" at a guess).
Basically, unless they are being hit by heavy and loud Bass they just seem to 'rattle' - They sound pretty horrendous really.
What seems more strange is that I'm driving 2 bins in parallell which means the load on the Amp should be 8ohms (I assume the total power should still be 300W) - but I have to turn the Amp up at least half way, and that's with a heavy bass line playing. If the AMP is capable of 800W output at 8ohms, then I don't really want to turn it too high!

I'm no expert when it comes to voice coils and impedence but I always thought that a Speaker would read short on a Multimeter.
I've got a reasonably good (and calibrated) Tektronix DVM, and I tried measuring the resistance of the voice coils - For some reason they both read around eleven ohms.

So I'm a bit lost - Either the AMP just can't drive these things, or they're damaged / faulty (burnt out coils? But surely not in such huge speakers).
It is normal for Bassbins to sound totally rubbish until you start driving extremely loud bass through them (i.e. at least loud enough to *really* annoy the neighbours)?

These bass bins are about 60cm wide by 70cm high and bout 50cm deep (purely at a guess). They have an interesting design which somebody may be able to comment on:

The front of the cone faces the back of the cabinet. Imagine that the dimensions of the cabinet are just an empty box. Then get a sealed cavity completely full with foam in the shape of Toblerone chocolate and install the cone into this, then leave it for the rear of the cone to face the front, with about 10cm between the front of the cone and the rear of the cabinet.
All this is vertically central, and there is free movement of air all around the front and the rear of the cabinet.
(basically I don't understand why the cone housing is sealed.)

Hopefuly this builds up some kind of impression of these boxes.

Please can anyone suggest what I might need to test or change to improve this.

Many Thanks
Jonathan

(If you need answers to questions in order to help me just ask and I'll try my best to answer).
I have the service manual for this Amp if anyone's interested.
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