AVS Forum banner
Status
Not open for further replies.
1 - 5 of 5 Posts

·
Registered
Joined
·
109 Posts
Discussion Starter · #1 ·
I need to compute the input impedance of a pair of amplifiers when operating in bridged mode - (Marantz MA500s) which each have an input impedance of 30K ohms, The reason is that I am adding a Vandersteen W2Q subwoofer to my system and the crossover must be set to match the amplifiers imput impedance or I run the risk of blowing the subs internal amplifier. Can someone help me with a formula please as this is a bit over my head? Thanks.

Paul (aka 1SrCitizen) :)
 

·
Registered
Joined
·
240 Posts
pmonroe,


In a stereo amplifier when the two channels are bridged, generally the input impedance isn't affected. The two amplifier sections basically operate out of phase resulting in a doubling of the output voltage that can be developed across a single load.

This (in theory) results in four times the output power. The unused input is usually left open. The result is no change in the input impedance.


I thought the Marantz amp you have was a mono block? I guess they must have some provision for you to use two of them in the bridged mode. If they are somehow splitting the input line and inverting one input, then certainly your input impedance will drop in half, but I'm afraid I don't quite understand how they are using a monoblock in bridge mode, unless maybe this monoblock is like the Bryston 7BST and is a true bi-monaural design with two power supplies (two power transformers, two rectifiers, independent capacitors, etc) for the one mono channel. It can be operated in both a series or parallel mode allowing for the use of very low impedance loads. The series voltage mode connects the two mono channels in a bridged type configuration giving you a large combined voltage swing for loads of 3 - 8 ohms or you can operate in the parallel current mode for driving loads of 1 - 3 ohms.

If this is the case, then your input impedance wouldn't change.


Perhaps someone else can comment....


brucek
 

·
Registered
Joined
·
109 Posts
Discussion Starter · #3 ·
Thanks Bruce. Ok, maybe its not too complicated after all, even though I still am not sure whether the impedance remains the same or drops in half. Yes the Marantz MA500 is a monoblock. Two are bridged in the following manner: They each have a preamp imput and a preamp output. The preamp imput is fed to unit #1 and its preamp output is fed th the imput of unit #2. A jumper wire is then connected across the negative speaker terminals of each unit. Lastly the speaker is then connected across the positive terminals of the two units. So, does the impedance remain 30K ohms or does it drop in half to 15K ohms? Thanks again.

Paul
 

·
Registered
Joined
·
240 Posts
Well, it would seem they are routing the input to the monoblock internally through an inverter and providing this an an output to second monoblock for use in bridging.

Since no switches are used to incorportate bridging mode, then this inverter is in the circuit all the time whether it is used or not, so it would indicate that your input impedance would not be affected and would stay at 30K.


brucek
 
1 - 5 of 5 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Status
Not open for further replies.
Top