jstanton8 Posted October 14, 2002 Share Posted October 14, 2002 To anyone knowledgable about amplifier bridging: I've got a pro amp I'm planning on using to drive an unpowered subwoofer with. The subwoofer I get will depend on whether or not I can easily bridge this thing and run one big subwoofer off it or alternately have to run two smaller units. The amp is rated at 250 watts/channel (8 ohms), 325 watts (4 ohms), and has no "bridged mode", per sec. What do I have to do to bridge this thing? Is is as simple as connecting both A & B output terminals of the amp to a single pair of subwoofer terminals? Or do I need some sort of external bridging "device"? Thanks Quote Link to comment Share on other sites More sharing options...
JohnA Posted October 14, 2002 Share Posted October 14, 2002 We need more information to tell if briging is safe for the amp. The final word on that is the manufacturer. The way it's done is to make/use a Y-adapter and reverse the polarity of one channel (+ to - and - to + on one channel). Plug your adapter into the normal inputs of the amp and connect the speaker leads to the + terminals only for each channel. There has to be some internal design features to allow this without damage. I *think* a common ground for the speaker terminals and chassis is one requirement. Large heat sinks are another one. The briged amp behaves like it is driving 1/2 the impedance it actually sees, so your power increases accordingly. Caution: experiment at your own risk. John Quote Link to comment Share on other sites More sharing options...
lynnm Posted October 14, 2002 Share Posted October 14, 2002 Bridging an amp typically requires that the amp be designed to permit the 2 channels of a stereo amp to be combined into a single channel configuration. Not all amps are designed this way , ( most are not) , and even when they are designed for bridging stereophonic reproduction will require the use of 2 amps - one bridged amp per channel. Generally this will be a very expensive route - If for no other reason most amps designed for bridging are rather expensive to start with. This option then might be useful if one already has a bridgeable amp and is willing to spend the money for another matching unit. In most cases amps that are designed to be bridgeable are more than sufficiently powerful to drive Klipsch speakers to very high SPLs. Quote Link to comment Share on other sites More sharing options...
jstanton8 Posted October 14, 2002 Author Share Posted October 14, 2002 I got this pro amp on e-bay and it came without a manual. The guy I bought it from listed it as "700 watts bridged" but I did not see any indication on the back of the amp that it is capable of running bridged, much less any switch for bridging. It is a very hefty amp (over 40 lbs.)and has a monster fan in it & two 16 sq. inch air intakes (4"x4") on the front panel. I presume it has adequate heat sinks based on the weight of the amp & its fan cooling system. (One interesting thing I noticed is that when the amplifier power is turned OFF the speakers attached to it keep playing for about 20-30 seconds! Never seen that before. In any case, when I get home tonight I will take a real good look at the back panel and see if I can glean any other info from it. Like I said, the guy I bought it from advertised it as "bridgeable", maybe I can get ahold of him and see what he based that on... Later, Quote Link to comment Share on other sites More sharing options...
jstanton8 Posted October 14, 2002 Author Share Posted October 14, 2002 Hey Lynn: I didn't mention it, but ths pro amp won't be running Klipsches (my Yamaha DSP-A1 is handling all 7 of those quite nicely, thank you...). I'm bought it with the intent of running either a couple of SVS subs (unpowered) or an 18" or 15" JBL theater-type subwoofer(s)(also unpowered), which will eat up from 600 to 1200 watts each. Hence my question about bridging this pro amp to a "supposed" 700 watts. Those JBLs will need ALL those watts... PS Kenrat, if you're out there, I might take that JBL 4648A-8 off your hands if I can figure out how to bridge this thing... Later, Quote Link to comment Share on other sites More sharing options...
j-malotky Posted October 14, 2002 Share Posted October 14, 2002 All the bridge(able) amps I have every owned, mostly McIntosh and NAD, have had a switch on the back switching it into bridged mode. I think John A is on the money, you will need to contact the MFG if there is no switch, because the speaker will look like 1/2 the impedance to a bridged amp. Most bridged amps can not drive 4 ohm or less speakers. If you get too low, you can damage an amp. The sampson I got with my SVSs can be put in bridged mode, but is recomended to run in parellel, spliting the single input into each 500 watt side directly connected to each SVS Ultra. If your running several subs, you may want to run a Y cable into each channel, driving each sub separately on its own channel. JM Quote Link to comment Share on other sites More sharing options...
kenratboy Posted October 14, 2002 Share Posted October 14, 2002 It's me!!! I am not sure about selling it, but first, where do you live? Shipping could be as much as $200. The thing weights 150 pounds and MUST be shipped on a pallet. NOT cheap. Did you get my e-mail? Here it is: Hey! Well, the bad news is that JBL sold these things for $220 SHIPPED, but they are usually about $1000. What happened is that the cinema industry collapsed and JBL liquidated these things for below cost (after shipping, they made about $100 off of them, VERY BAD for JBL.) They sold out in the first few days and I was one of the lucky ones that got one. They offered a 4638 (all on JBL's web site, not for sale, just info as a normal product) also, but that sold out in a few days. If you have some money to spend and you are interested in the pro audio approach, I would have to recommend one of the JBL cinema single or dual 18" subs (http://www.jblpro.com/pages/cinema/lfsub.htm#4641), they will go an octave lower and, well, would kick more ***. If you are not interested in that, go for some SVS action! To be perfectly honest, the JBL's (NOT the 18" models) I have have a flaw for my (subwoofer) application. They are NOT subwoofers, they are the LF section of large main channels in a movie theater and are meant to be crossed over at ~40-60 Hz. and have subwoofers take over from their. They will NOT give you any real bass below 30 Hz. From the 30's and above, they will loosen studs and shake the hell out of doors, pictures, windows, or anything else! This is GREAT+ is you listen to "live" music and "played" music. For movies and electronic music (like what I listen to...), these are not the best choice and SVS would kill the JBL's in the 10-30Hz. range. However, even with my deep bass techno, these subs will shake the house and give the full effect. Basically, they have unlimited output above 30Hz. The woofers (2 of em') cost $350 EACH and even with my $150 Parts Express amp, sound like a fine musical instrument. So depending on what you listen to, either big speakers like the JBL or the SVS's might work best. If you want some more detailed info on the JBL's, drop by www.audioheritage.com I am active on that forum and although there is far less traffic there, the people on the site are so freaking smart, it scares me! If you have any more questions, ask them here or better yet, e-mail me (at the address you used before), as I check that account about 10 times a day! If anything, spend some time on Audio Heritage and they will tell you so much stuff, you will cry from data overload. I am on Audio Heritage too, so shoot on over!!! Quote Link to comment Share on other sites More sharing options...
jstanton8 Posted October 16, 2002 Author Share Posted October 16, 2002 John A, Lynn M, & JMalotky: Evidently the amp in question IS bridgeable. I took a real close look at the back of the amp and found something I had not seen previously. The two positive ( +, red terminals) have a line drawn between them labeled "MONO" and are secondarily labeled plus & minus. However, there is still no bridging switch. Also, the inputs have another label associated with them, a "0" on one set and an infinity symbol on the other set (if this is of any help). So, in light of the above, do you think it can run bridged simply by hooking the sub's terminals to the amp's two positive posts and not have to worry about the y-adapter-switching-polarity routine? The amp was made by "Sound Code Systems" in Garden Grove, CA. I can not find hide nor hair of them on the Internet, so I can't ask them a whole lot as to how they recommend running bridged. Since I don't particularly want to fry anything, any further advice will be more than welcome... One other thing. Below the amp's inputs it says "8 OHM/275 WATTS, 4 OHM/350 WATTS, 2 OHM/!!NO!! What does this mean practically, other than the amp does not like looking at a 2 ohm load? Kenrat: For some reason or another I didn't get your e-mail, no telling why. I had already gathered from some of your previous posts that the 4648-A is not a true sub, however I was interested in it anyway for music for the exact reasons you stated...sounds like with enough wattage they would be able to keep up with my K-horns, which is precisely what I am looking for. Low end support. I need it for the type of music I generally listen to (The Who, Rush, AC/DC, Leslie West..you get the picture...) But that's OK, I found a place called Acoustic Visions who will build custom made subs for a mere pittance. For 500 bucks they said they'd make me a 141 Liter (5 cu. ft.) sub which they claim will blow away anything in that price range. Their curves look good, too. Maybe one of those 18' JBL THX theater subs would be good also, IF I can find a used one for 500 or so (maybe not so easy to do). Then there's SVS, of course...the CS series can be had for about that much also. Decisions, decisions...all I know is I need some serious low-end support for my K-horns. They & the KSW-15 already shake the house we're in, but we're moving into a larger house soon & I'm looking to have the capability of causing some actual structural damage. To my way of thinking, if I cannot duplicate live concert dB levels with ease, the system's of no use to me. I shall check out the audio heritage site as you suggested, see you there... Thanks, J. Stanton Quote Link to comment Share on other sites More sharing options...
jnorv Posted October 16, 2002 Share Posted October 16, 2002 The best primer on bridging amps is probably Levinson's amplifier manuels. Try http://www.madrigal.com/i/manuals/No33456OM.pdf A decent amp wil double output from 8 to 4 ohms. A great amp will double to 2 ohms. Only the big Krell will double to .5 ohm. Jim N Quote Link to comment Share on other sites More sharing options...
lynnm Posted October 16, 2002 Share Posted October 16, 2002 jstanton8 I could find only one reference to your amp: http://www.stillmusic.com/equip_link.html The guy invites people to contact him re his equipment. Maybe he could give you some info. Quote Link to comment Share on other sites More sharing options...
k2dx Posted October 16, 2002 Share Posted October 16, 2002 Have you looked inside the amp for a switch labeled 'mono' or 'bridge'? The connection for the speaker would be the two positive terminals. The bridge mode will split the input signal (from usually the left input)to the two channels, OUT OF PHASE. Just using a 'y' connector on the inputs is not the way to accomplish bridging. You can use a 'y' input with seperate subs connected to each output however. Quote Link to comment Share on other sites More sharing options...
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