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Bridged mono for sub amp?  

post #1 of 20
Thread Starter 
I built a box for my 12 in. Dayton 1200 Titanic subwoofer. It is powered by my old but capable Adcom GFA 545II. It does a great job but the subwoofer can handle a lot more power than this amp can deliver. The 12 in. Titanic has a nominal impedance of 4 ohms. The Adcom can pump out about 200 watts into 4 ohms, but the sub can handle 500 watts. I learned one way of getting more power from an amp is to bridge the output by connecting both channels to output as one channel mono or bridged mono as it is called. My manual says nothing about how to do this.
How does one setup an amp for bridge mono? A link to a diagram showing how the
two channels should connected would be a great help too. Thanks for any advice, suggestions, and tips.
post #2 of 20
Bridging is pretty simple, from what I understand. All you have to do is drive the inputs with opposite-polarity signals. In other words, one channel has the (-) signal going to the RCA’s tip, and the (+) to the sleeve. Then you connect the speaker to the two positive posts.

Basically, if an amp is designed to be bridged, it will be set up to accomplish the signal inversion with a switch, and directions in the manual or on the chassis for speaker connections. If not, proceed at your own risk and don't come looking for me if it goes up in smoke. You’ll have to make your own cable to accomplish the signal reversal for the second channel.

Frankly, I’m surprised the 545 isn’t set up for bridging. My 555 is.

Regards,
Wayne A. Pflughaupt
post #3 of 20
Another thing you may run into if the amp is bridgeable is trouble with the 4 ohm speaker.

Not many consumer grade amps like to run bridged mono into 4 ohm loads since this is like running the amp stereo with 2 ohm speakers.
post #4 of 20
Thread Starter 
Thanks Wayne and whoaru99 for your replies. I decided not to hook it up bridged mono. I agree with Wayne that it could be risky since the amp does not have a bridged mono switch on it (probably for a reason). That reason might have been hit upon by whoaru99 in his reply that this amp is probably not designed for this task sinceit would be like driving a 2 ohm stereo load with the 4 ohm speaker connected to bridge mono. Until I can find a good high end subwoofer power amp, I will continue running my Adcom from one channel. 200 watts rms into 4 ohms will be ok for most movies, except perhaps War of the Wars with it's very demanding LFE. If anyone has a suggestion for one, please let me know. It must be a separate amp not designed to be mounted on the subwoofer. Those I have seen have smallish transformers and power supply filter caps ranging 10K to 15K uF, yuck. If money were no option I would go for the Gallo sub amp but it is expensive. Pro power amps
are another option but I don't want to mess around with balanced line inputs coming from
my unbalanced subwoofer line out (I have the Pioneer VSX-1015TX). Anyway, thanks again for your help and I am open to other options in sub amps.

Star Hawk
post #5 of 20
I used to run (4) Adcom 555mkII's for my subwoofer system. They are great stereo amps and have great bass respose for mains and centers.They do have a problem with content below 25hz. Mine would clip often during bass intense scenes.

You may want to concider a pro amp (QSC).
post #6 of 20
the 545 cannot be bridged.
post #7 of 20
Quote:
Originally Posted by Star Hawk
Thanks Wayne and whoaru99 for your replies. I decided not to hook it up bridged mono. I agree with Wayne that it could be risky since the amp does not have a bridged mono switch on it (probably for a reason). That reason might have been hit upon by whoaru99 in his reply that this amp is probably not designed for this task sinceit would be like driving a 2 ohm stereo load with the 4 ohm speaker connected to bridge mono. Until I can find a good high end subwoofer power amp, I will continue running my Adcom from one channel. 200 watts rms into 4 ohms will be ok for most movies, except perhaps War of the Wars with it's very demanding LFE. If anyone has a suggestion for one, please let me know. It must be a separate amp not designed to be mounted on the subwoofer. Those I have seen have smallish transformers and power supply filter caps ranging 10K to 15K uF, yuck. If money were no option I would go for the Gallo sub amp but it is expensive. Pro power amps
are another option but I don't want to mess around with balanced line inputs coming from
my unbalanced subwoofer line out (I have the Pioneer VSX-1015TX). Anyway, thanks again for your help and I am open to other options in sub amps.

Star Hawk
i am running the 545 as well driving one 15" atlas on each channel in IB config. I've never had it clip at my normal listening volume

http://www.cyberfrogs.net/photo/inde...diaroom&page=3

even with WOTW at -10 from reference, you dont mention if the box is sealed or ported?
post #8 of 20
Great point! I run a sealed system.Not only is it sealed but I use a Marchand BASSIS to extend the low frequency response. I need pro amp juice.

An IB or ported may not have the demands that I put on them.

I could run one QSC 1450 for all four Tumults in an IB config.Even that would be over kill.
post #9 of 20
Thread Starter 
Quote:
Originally Posted by need4speed
i am running the 545 as well driving one 15" atlas on each channel in IB config. I've never had it clip
even with WOTW at reference, you dont mention if the box is sealed or ported?
The subwoofer enclosure is 3.2 cu ft and sealed. I did not measure the f3 due to lack of equipment, but according to the specs and plans for the enclosure for this small internal volume, partially filled with fiberfil stuffing, it should be ~25 HZ. The 545 is a good amp and even drives a 4 ohm nominal Z driver like the 12" Titanic without clipping. But I have not tested it yet with the recent War of the Worlds release. If I do view the movie I will probably use my Pio amp -10 db subwoofer out attenuator just to be on the safe side.
post #10 of 20
Thread Starter 
Quote:
Originally Posted by kgveteran
I used to run (4) Adcom 555mkII's for my subwoofer system. They are great stereo amps and have great bass respose for mains and centers.They do have a problem with content below 25hz. Mine would clip often during bass intense scenes.

You may want to concider a pro amp (QSC).
Thanks for the suggestion. Others have mentioned the QSCs too. Sounds like it will be worth taking a look at them.
post #11 of 20
Thread Starter 
Quote:
Originally Posted by kgveteran
Great point! I run a sealed system.Not only is it sealed but I use a Marchand BASSIS to extend the low frequency response. I need pro amp juice.

An IB or ported may not have the demands that I put on them.

I could run one QSC 1450 for all four Tumults in an IB config.Even that would be over kill.
What interconnects did you use to go from your HT receiver (or discrete HT preamp) to your QSC 1450. The specs I just reviewed only listed balanced line inputs:
"Barrier strip, XLR and 1/4" balanced inputs plus Speakon and binding post outputs provide easy connections." Unless your HT receiver has a balanced subwoofer line out, did you make or buy special interconnects? What about impedance matching?
I wanted to avoid this, unless there is an easy way around it.
post #12 of 20
To feed a balanced input with an unbalancedsource, connect the hot to XLR pin 2, and the sheild(ground) to XLR pin 1.
There is no need to worry about impedance matching. The input impedance on that amp is 20K...it bridges the source.
post #13 of 20
Thread Starter 
Quote:
Originally Posted by Targus
To feed a balanced input with an unbalancedsource, connect the hot to XLR pin 2, and the sheild(ground) to XLR pin 1.
There is no need to worry about impedance matching. The input impedance on that amp is 20K...it bridges the source.
It sounds simple enough. Another question for you. Would it be better to buy a balanced line cable and cut off the XLR connector at one end and solder an RCA plug hot lead to the corresponding pin 2 wire and the shield to the corresponding pin 1 wire? Or take a length of unbalance cable, cut off the RCA plug at one end and solder an XLR connector (male, right?) pin 2 to the hot lead and the pin 1 to the shield. Does it make any difference which way?
post #14 of 20
Quote:
Does it make any difference which way?
Go with whatever is cheaper, it won't matter either way.
post #15 of 20
I have a 15" titanic sealed (~3.5cuft) and I run it off a QSC 850 bridged mono=830Watts. I bought the amp at Guitar Center and they had a cheap (8 bucks) cable for converting the XLR to plain old rca. Works great. I just use a home made coaxial cable with rca's on both ends (canare cable and connectors) and use the adapter cable (about 8 inches long) to connect to the rca at one end and plug the XLR into the amp input. On my qsc there is a switch on the back for bridging and you use the gain for channel one but it uses the power from both. No soldering involved and the sub is seriously impressive.
post #16 of 20
Thread Starter 
Quote:
Originally Posted by Targus
Go with whatever is cheaper, it won't matter either way.
Great! Now I need to decide which QSC to buy. Thanks.
post #17 of 20
Thread Starter 
Quote:
Originally Posted by bonedoc2be
I have a 15" titanic sealed (~3.5cuft) and I run it off a QSC 850 bridged mono=830Watts. I bought the amp at Guitar Center and they had a cheap (8 bucks) cable for converting the XLR to plain old rca. Works great. I just use a home made coaxial cable with rca's on both ends (canare cable and connectors) and use the adapter cable (about 8 inches long) to connect to the rca at one end and plug the XLR into the amp input. On my qsc there is a switch on the back for bridging and you use the gain for channel one but it uses the power from both. No soldering involved and the sub is seriously impressive.
I am definitely going to order a QSC. I was looking at the RMX1450 but for $100
less I can still get all the power I'll need from the model you have, the RMX850. And I am back full circle 'cause I bought my 12" Titanic at Parts Express. I was not impressed by their subwoofer amps and so I had the idea of trying my old Adcom 545 amp which works ok but may wimp out on real powerful deep bass LFE. So all the time the amp I really need is right under my nose. I will check out PE's pro cables at the same time to see if they have something like yours. Thanks for your very helpful suggestions. :cool:
post #18 of 20
There seem to be quite a few guys running cheaper pro amps such as Behringer (sp?) Samson, Blue Ice, and others. I can't vouch for any of these, but quite a few people claim success for sub duty at a lower price than Crown, QSC, etc.
post #19 of 20
Id say go with as much power as you can. If you can swing the extra 100 for a QSC 1450 I'd go that route just incase you decide you want to upgrade in the future. Or maybe a Behringer EP2500, it's around the same price as a QSC RMX 850.

As far as the quality of any I can't say as I use a Kiega 1000w plate amp with my Tumult. If I could do it all over again I'd go with a pro amp with ATLEAST 1400-1500 watts. The only issue is all but the Crown K1 or K2 use fans so you may have some noise from it. It bothers some folks.
post #20 of 20
Fan noise stinks! I did a fan mod which helped, but nothing beats no fans at all.

They all may be going in the basement soon! :D
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