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Author Topic: How to bridge a 2 channel amp for sub ? Paul Vollmers Expert Film Handler Posts: 161 From: Sister Lakes, MI, USA Registered: Jul 2001 posted 01-30-2012 07:46 PM                     I have a Smart TA425 2channel amp that I want to Bridge for a subwoofer. The info page in the paper manual says it is 250 watts per channel at 8 ohms, and 650 watts at bridged mono at 8 ohms. The manual does not explain how this is done. How do I wire this to power a subwoofer?  |  IP: Logged Markus Ito Film Handler Posts: 27 From: San Diego, CA, USA Registered: Apr 2011 posted 01-30-2012 11:37 PM                     There is usually a set of dip switches on the back of the amp that set bridged mono mode. What this does is use the two amplifiers inside the amp to amplify the signal in different directions; one goes negative, the other goes positive. Channel 1 does the positive side, and channel 2 does the negative side (depends on the amp). Once you have the amp set in bridged mono, you will need to connect the positive and negative speaker wires to the two positive(red) posts on the rear of the amp. They are usually marked indicating which one will become positive and negative when operating in bridged mono. Hope that helps. Markus  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 01-31-2012 12:31 AM                     Is this like a "push-pull" circuit then when you bridge the amps like this?  |  IP: Logged Sean Weitzel Jedi Master Film Handler Posts: 619 From: Vacaville, CA (1790 miles west of Rockwall) Registered: Dec 1999 posted 01-31-2012 12:34 AM                     Echoing what Markus said. In car audio amplifiers, there's no need for dip switches or jumpers. Just connect the positive lead to positive channel 1 and the negative lead to negative channel 2.  |  IP: Logged Ian Parfrey Phenomenal Film Handler Posts: 1049 From: Imbil Australia 26 deg 27' 42.66" S 152 deg 42' 23.40" E Registered: Feb 2009 posted 01-31-2012 03:10 AM                     Page 4 - 2nd bottom paragraph. "Bridged mono output is easily achieved feeding the two inputs of the dual channel amplifier with a balanced audio source. Both of the front panel gain controls are used to set the level. Make sure both of the controls are in approximately the same position."  |  IP: Logged Paul Vollmers Expert Film Handler Posts: 161 From: Sister Lakes, MI, USA Registered: Jul 2001 posted 01-31-2012 06:16 AM                     Okay, here's where I'm confused.... From the Dolby CP65 SW out ...two wires normally go to the channel one, red (+) and one black (-) to the input side of the Amp. two wires one red (+) from the output and one Black (-)from the out put to the subwoofer + and - red and black etc. So what is changed from that wiring pattern to Bridge the amp? Two wires input...two wires output to subwoofer??  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 01-31-2012 07:52 AM                     You will need to get a small balancing transformer and connect the unbalanced output of the cp65 sub to the txmr input and the + output to the hot input of the left input and the - output of the txmr to the hot input of the left input and the speaker load is across the two hot terminials  |  IP: Logged Paul Vollmers Expert Film Handler Posts: 161 From: Sister Lakes, MI, USA Registered: Jul 2001 posted 01-31-2012 01:55 PM                     Gordon, Thank you for your reply. What is a txmr , and where would I find such a thing??  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 01-31-2012 02:10 PM                     txmr is short for transformer Jensen is one of the best makes you probably want a 10k to 10k one mouser and newark will sell other broadcast grade ones Hammond mfg also make them  |  IP: Logged Paul Vollmers Expert Film Handler Posts: 161 From: Sister Lakes, MI, USA Registered: Jul 2001 posted 01-31-2012 05:25 PM                     Man.........I'm still in the dark on this transformer......have no clue what this is about, and how it works.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 01-31-2012 07:42 PM                     The output of the 65 is unbalanced ie a hot signal (+) and earth a balanced signal is a + and a - signal not referenced to earth to bridge the amp effectively one needs to send a + going signal into on channel and a negative going signal into the other so that the signal measured between the two + speaker terminals will be double that of just one channel driven effectively a larger voltage swing So one need to drive that arrangement with a differential signal one way is a transformer because as you notice neither lead of the output side is connected to ground it is floating It also is important that on the speaker and booth monitor that there is no connection to ground on the output lines The other way is to use a inverting op amp  |  IP: Logged David Buckley Jedi Master Film Handler Posts: 525 From: Oxford, N. Canterbury, New Zealand Registered: Aug 2004 posted 02-01-2012 04:21 PM                        Heres what should be a workable solution. It uses a RDL ST-DA3 Line Level Distribution Amplifier 1 1x3. Avaliable from Amazon and myriad other places, do a google for it. You'll need to get a 12vdc wall wart power supply for it. Connect it up like this: Greens are shields of cables. Note one hot of each amplifier input goes to a +, and the other one to a -. The transformer suggestion above is a reasonable solution, but many small transformers will not handle line level at 20Hz without saturating, so I'd prefer something electronic. This device claims flat from 10Hz to 100KHz, so even if you're running Bag Ends down to 7Hz there should be much LF drop, and no loss or distortion at all down to 10Hz. Disclaimer: this should work, but my advice is worth (and liable to the tune of) exactly the price paid.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-01-2012 04:58 PM                     http://www.rdlnet.com/product.php?page=159 Radio Design Labs - Bridging Input Transformer [How to buy this product] [ECO PASSIVE – The RDL product is passive with no provision to connect an external power source. ] Used to add transformer isolation to any line‑level RDL product input Frequency response: 20 Hz to 20 kHz (+/‑ 0.5 dB) THD: < 0.05% (1 kHz) 10 kΩ input bridges any audio line Balanced input and output Connections on Detachable Terminal Blocks  |  IP: Logged Rick Raskin Phenomenal Film Handler Posts: 1100 From: Manassas Virginia Registered: Jan 2003 posted 02-01-2012 05:34 PM                     quote: Monte L Fullmer Is this like a "push-pull" circuit then when you bridge the amps like this? Strictly speaking, not really. To be brief, push pull amps typically are biased Class B (or AB) so that each half amplifies either the positive or negative portion of the sine wave input signal. The amplified outputs are usually combined at the output transformer.  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 02-02-2012 08:12 AM                     Not really "push-pull". Transistor stereo amps (ie no output transformer) have one of the output terminals grounded and the other one's voltage swings between some positive voltage and some negative voltage. The voltage depends on the amplifier's output power (as does the current capacity of the output semiconductors). For "bridge mono" two amp channels are fed the exact same signal, but one is inverted. One channel's not-grounded output terminal will be at positive-to-ground voltage and the other channel will be at the same voltage but negative-to-ground. The speaker is connected from one channel output "live" wire to the other channel channel output "live" wire, the grounded terminals are not used. This effectively doubles the output voltage and quadruples the output power. That rarely actually happens, the power supplies and output stages in most amplifiers will not put out 4X the single channel power in bridge mono, but it's definitely more than a single channel. There are output impedance limits as well: an amp that can with a 2 ohm minimum load impedance in single channel mode will have a 4 ohm minimum in bridge mono for example.  |  IP: Logged

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